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MICHAEL SHORT: So, before we
begin today's bit on dose,

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00:00:25,470 --> 00:00:27,180
dosimetry, and
background radiation,

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00:00:27,180 --> 00:00:28,770
I promised you guys
a story about how

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00:00:28,770 --> 00:00:32,409
to use 22.01 to get out of
Apartheid, South Africa.

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00:00:32,409 --> 00:00:35,910
So, I got told this story when
my cousin was about to get

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married because he needed a
diamond and he was going to go

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00:00:39,480 --> 00:00:42,430
buy one and his dad said, don't.

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00:00:42,430 --> 00:00:46,870
So back in the 70s, when
my uncle and his family

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00:00:46,870 --> 00:00:48,460
were living in
South Africa, anyone

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00:00:48,460 --> 00:00:51,190
who wasn't Dutch white,
so that would be blacks,

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00:00:51,190 --> 00:00:54,010
Jews, including
us, anyone else was

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00:00:54,010 --> 00:00:57,252
considered second-class citizens
by the Apartheid Government.

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00:00:57,252 --> 00:00:59,710
And you were allowed to leave,
because they didn't want you

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00:00:59,710 --> 00:01:01,570
there, but you had to
surrender all of your funds

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00:01:01,570 --> 00:01:03,220
to the government
in order to leave,

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00:01:03,220 --> 00:01:05,880
which gives me everything
you have and then

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00:01:05,880 --> 00:01:07,630
you can leave the
country penniless is not

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00:01:07,630 --> 00:01:09,280
a winning proposition.

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00:01:09,280 --> 00:01:13,270
So, my uncle and his brother
devised a pretty brilliant idea

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00:01:13,270 --> 00:01:16,660
to get their funds out of
South Africa unnoticed.

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00:01:16,660 --> 00:01:19,450
They were both dentists
or radiologists

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00:01:19,450 --> 00:01:22,750
or some sort of medical doctor
that requires x-ray reading.

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00:01:22,750 --> 00:01:26,015
So, one of them gave the
other one all of his money,

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00:01:26,015 --> 00:01:28,390
then reported bank statements
to the Apartheid Government

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00:01:28,390 --> 00:01:30,670
and said, I'm pretty
much penniless.

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00:01:30,670 --> 00:01:32,173
My practice went broke.

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00:01:32,173 --> 00:01:33,340
I want to leave the country.

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00:01:33,340 --> 00:01:35,050
And they said, OK,
get out of here.

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00:01:35,050 --> 00:01:37,180
So he went to the
US, established

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00:01:37,180 --> 00:01:40,180
a dental or radiological or
some other sort of practice,

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00:01:40,180 --> 00:01:44,140
I forget which one, and
started requesting his brother,

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00:01:44,140 --> 00:01:46,510
back in South Africa, to
send him x-rays to read

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00:01:46,510 --> 00:01:48,760
to help boost his business.

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00:01:48,760 --> 00:01:51,910
Because that was their actual
business, it was pretty legit.

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00:01:51,910 --> 00:01:54,640
So then my uncle would
send him packets of x-rays

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00:01:54,640 --> 00:01:57,220
to interpret and send back.

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00:01:57,220 --> 00:01:59,950
Except that there would
be 10 x-rays on the front

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00:01:59,950 --> 00:02:02,110
and 10 on the bottom,
and the middle 80

46
00:02:02,110 --> 00:02:03,130
would be hollowed out.

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00:02:03,130 --> 00:02:04,930
AUDIENCE: Oh!

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00:02:04,930 --> 00:02:07,120
MICHAEL SHORT: Now that
would have ordinarily have

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00:02:07,120 --> 00:02:10,690
tripped off alarms because
any change in density

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00:02:10,690 --> 00:02:13,090
would trigger a change
in x-ray contrast.

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00:02:13,090 --> 00:02:15,670
Because these packages were
being inspected by x-ray,

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00:02:15,670 --> 00:02:17,968
and if it looked like
these x-rays were hollow

53
00:02:17,968 --> 00:02:19,510
and you were smuggling
something out,

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00:02:19,510 --> 00:02:22,080
they'd be caught
and confiscated.

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00:02:22,080 --> 00:02:25,740
So what sort of materials
are valuable that you

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00:02:25,740 --> 00:02:28,620
find in South Africa,
that are pretty

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00:02:28,620 --> 00:02:34,128
similar in x-ray contrast to
other light media like film?

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00:02:34,128 --> 00:02:34,920
AUDIENCE: Diamonds.

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00:02:34,920 --> 00:02:36,910
MICHAEL SHORT: Diamonds.

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00:02:36,910 --> 00:02:39,940
So the remaining brother
went and converted

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00:02:39,940 --> 00:02:42,550
all of his life savings into
diamonds, which is something

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00:02:42,550 --> 00:02:45,040
that you can do in South
Africa because this

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is where diamonds come from.

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00:02:47,000 --> 00:02:49,660
He then slowly, over a
period of months or years,

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00:02:49,660 --> 00:02:52,840
sent packets of hollow
x-rays full of diamonds

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00:02:52,840 --> 00:02:56,200
to his brother in the
states, knowing full well

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00:02:56,200 --> 00:03:00,580
that the mass attenuation
coefficients of soft tissue

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00:03:00,580 --> 00:03:04,430
and carbon are pretty similar
and so are their densities.

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So their total
attenuation coefficients

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00:03:06,700 --> 00:03:08,950
are pretty similar, to.

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00:03:08,950 --> 00:03:11,770
Let's pull those up
so we can check it.

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00:03:11,770 --> 00:03:13,536
Carbon graphite.

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00:03:13,536 --> 00:03:17,420
I'm going to add a new tab
and bring up soft tissue

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00:03:17,420 --> 00:03:19,210
and we can compare them.

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00:03:19,210 --> 00:03:22,850
Let's see, what's
the most similar--

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00:03:22,850 --> 00:03:25,025
so long as you can see
it-- thing to film?

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What should we call film here?

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00:03:31,140 --> 00:03:32,468
X-ray film?

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AUDIENCE: I don't even know
what X-ray film [INAUDIBLE]

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MICHAEL SHORT:
Photographic emulsion.

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How about that?

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AUDIENCE: Kodak.

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MICHAEL SHORT: Is
there something Kodak?

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00:03:39,586 --> 00:03:41,620
OK.

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Kodak, standard nuclear.

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I don't think that sounds right.

87
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Let's go with
polyethylene and plastic.

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00:03:49,610 --> 00:03:52,220
Carbon, plastic.

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00:03:52,220 --> 00:03:53,765
Carbon, plastic.

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00:03:53,765 --> 00:03:55,160
AUDIENCE: [LAUGHTER]

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00:03:55,160 --> 00:03:57,590
MICHAEL SHORT: Carbon, plastic.

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00:03:57,590 --> 00:03:59,840
Basically identical.

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So this is a way they were
able to smuggle wealth out

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00:04:02,480 --> 00:04:04,980
of the country without
x-ray contrast tripping off

95
00:04:04,980 --> 00:04:05,480
the guards.

96
00:04:05,480 --> 00:04:06,980
And once all of
the slave savings

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00:04:06,980 --> 00:04:08,948
had been converted
into diamonds,

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00:04:08,948 --> 00:04:11,240
he then went to the government
and said, I'm penniless.

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My practice went broke.

100
00:04:12,387 --> 00:04:13,470
I want to get out of here.

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And they said, good riddance.

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AUDIENCE: [INAUDIBLE]

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MICHAEL SHORT: Yeah.

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00:04:16,610 --> 00:04:18,140
So they were able to
restart their life

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in the states with
all of the money

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00:04:19,598 --> 00:04:21,015
that they had had
in South Africa.

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And when my cousin wanted
to get married and said,

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00:04:23,098 --> 00:04:25,440
I'm thinking of buying a
diamond, my uncle just said oh,

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00:04:25,440 --> 00:04:25,940
don't.

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00:04:25,940 --> 00:04:27,398
He's like, what,
don't get married?

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00:04:27,398 --> 00:04:28,910
He said, no, don't
buy a diamond.

112
00:04:28,910 --> 00:04:30,743
Here, let me take you
to the diamond drawer.

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AUDIENCE: [LAUGHTER]

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00:04:31,887 --> 00:04:32,720
MICHAEL SHORT: Yeah.

115
00:04:32,720 --> 00:04:34,670
Because there was some leftover.

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00:04:34,670 --> 00:04:37,250
So he said, pick out
an extra diamond.

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00:04:37,250 --> 00:04:40,370
And that's the story of my
cousin's engagement ring,

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00:04:40,370 --> 00:04:42,620
as well as why part of my
family's here in the States.

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00:04:42,620 --> 00:04:45,260
AUDIENCE: [INAUDIBLE] That's
like a very cool diamond story.

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00:04:45,260 --> 00:04:49,200
MICHAEL SHORT: Yeah, very,
very nuclear diamond story.

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00:04:49,200 --> 00:04:51,510
Diamonds aren't forever, as
the finish have shown us,

122
00:04:51,510 --> 00:04:55,550
but they can get you out
of repressive regimes.

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00:04:55,550 --> 00:05:00,032
OK, back to the dose stuff.

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00:05:00,032 --> 00:05:01,740
So today, and for the
rest of the course,

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00:05:01,740 --> 00:05:04,950
we get into biological and
chemical effects of radiation.

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00:05:04,950 --> 00:05:06,475
As soon as this pops up.

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00:05:06,475 --> 00:05:08,100
And so in the first
slide is everything

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00:05:08,100 --> 00:05:11,220
you need to know
about dose and units.

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00:05:11,220 --> 00:05:13,230
Don't worry, it's
not up there yet.

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00:05:13,230 --> 00:05:15,330
I know that different
units of dose

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are a common point of confusion.

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So I wanted to put
everything on one slide

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00:05:18,950 --> 00:05:21,520
so you can refer back to
it like a cheat sheet.

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So, you've probably heard
of the roentgen before.

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You've definitely seen
the roentgen as a unit

136
00:05:26,760 --> 00:05:30,810
because you've all looked in
those pen or pocket dosimeter

137
00:05:30,810 --> 00:05:32,820
that you actually had
at the nuclear reactor,

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00:05:32,820 --> 00:05:35,970
when you guys took a tour of
it and controlled the control

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00:05:35,970 --> 00:05:36,810
rods.

140
00:05:36,810 --> 00:05:39,810
The roentgen is not really a
unit that we use much anymore

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00:05:39,810 --> 00:05:43,470
for very careful
calculations because you

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00:05:43,470 --> 00:05:46,080
have to do some tissue
equivalency stuff

143
00:05:46,080 --> 00:05:49,830
in order to go from
ionizations in air, which

144
00:05:49,830 --> 00:05:51,285
is what it actually
measures, it's

145
00:05:51,285 --> 00:05:55,500
the amount of charge
dissipated or built up in air,

146
00:05:55,500 --> 00:05:58,320
to some damage to soft tissue.

147
00:05:58,320 --> 00:06:00,360
And the way you actually
calculate roentgens

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00:06:00,360 --> 00:06:03,510
from first principles, linking
the physics and the biology

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00:06:03,510 --> 00:06:06,540
part, is remember
this equation here?

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00:06:06,540 --> 00:06:09,360
Stopping power, which
is some energy transfer,

151
00:06:09,360 --> 00:06:12,270
divided by the energy
required to make an ion.

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00:06:12,270 --> 00:06:15,510
Each one of those will give
one electron unit of charge

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00:06:15,510 --> 00:06:18,040
towards [INAUDIBLE] coulombs.

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00:06:18,040 --> 00:06:20,400
And so this is the direct
link between the physics

155
00:06:20,400 --> 00:06:22,740
and the chemistry/biology
in this course.

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00:06:22,740 --> 00:06:25,363
It's not something that's
done that carefully in any

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00:06:25,363 --> 00:06:27,780
of the readings, which is why
I'm going to harp on it here

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00:06:27,780 --> 00:06:29,070
in lecture.

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00:06:29,070 --> 00:06:31,560
These two parts of the course
are often taught differently.

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00:06:31,560 --> 00:06:33,420
And they're actually
totally related

161
00:06:33,420 --> 00:06:36,130
and everything's all the
same, which is kind of nice.

162
00:06:36,130 --> 00:06:39,260
You don't have to just relearn
a whole new lingo and field.

163
00:06:39,260 --> 00:06:41,060
Then there is the
SI units of dose.

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00:06:41,060 --> 00:06:43,557
The ones that, when you do
calculations in the homework

165
00:06:43,557 --> 00:06:45,140
and the rest of your
life, I recommend

166
00:06:45,140 --> 00:06:48,410
that you use whenever
possible because they're

167
00:06:48,410 --> 00:06:52,100
in units that we're familiar
with, in standard units.

168
00:06:52,100 --> 00:06:54,370
The one where you start
with all along is the gray.

169
00:06:54,370 --> 00:06:59,240
A gray is the simple measure
of absorbed energy in joules

170
00:06:59,240 --> 00:07:01,850
per kilogram of whatever.

171
00:07:01,850 --> 00:07:05,130
And so calculating it is
fairly straightforward, too.

172
00:07:05,130 --> 00:07:08,420
For example, if you want to know
what sort of dose you would get

173
00:07:08,420 --> 00:07:11,690
in gray from
absorbing gamma rays,

174
00:07:11,690 --> 00:07:14,827
you can use this old
equation from the first third

175
00:07:14,827 --> 00:07:15,410
of the course.

176
00:07:20,660 --> 00:07:25,210
And if you integrate
this from, let's say,

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00:07:25,210 --> 00:07:28,000
over the range of
whatever object or person

178
00:07:28,000 --> 00:07:29,830
you happen to be
irradiating, you'll

179
00:07:29,830 --> 00:07:32,440
get some fractional
difference in intensity.

180
00:07:32,440 --> 00:07:35,440
That, multiplied by the original
intensity of gammas, which

181
00:07:35,440 --> 00:07:38,710
could be given in maybe
gamma rays per centimeter

182
00:07:38,710 --> 00:07:42,010
squared per second,
maybe times time

183
00:07:42,010 --> 00:07:44,590
to get total number of gammas
per centimeter squared.

184
00:07:48,740 --> 00:07:53,420
All that multiplied by
the energy of each gamma,

185
00:07:53,420 --> 00:07:58,670
divided by the mass of whatever
is doing the absorbing,

186
00:07:58,670 --> 00:08:01,140
equals your dose in gray.

187
00:08:01,140 --> 00:08:03,840
So you can use all the old
stuff from the previous parts

188
00:08:03,840 --> 00:08:07,355
of the course directly to
calculate dose in gray.

189
00:08:07,355 --> 00:08:09,480
And this is the starting
point for any calculation.

190
00:08:09,480 --> 00:08:11,910
If you don't know what
tissue was exposed,

191
00:08:11,910 --> 00:08:15,390
what type of radiation provides
what biological effectiveness,

192
00:08:15,390 --> 00:08:16,230
it doesn't matter.

193
00:08:16,230 --> 00:08:19,130
You just start here.

194
00:08:19,130 --> 00:08:20,720
Then the other unit
you may have seen

195
00:08:20,720 --> 00:08:22,820
is a unit, not of
energy absorption,

196
00:08:22,820 --> 00:08:25,430
but of increased risk
for something going

197
00:08:25,430 --> 00:08:27,470
wrong in the biological sense.

198
00:08:27,470 --> 00:08:29,030
It's called the sievert.

199
00:08:29,030 --> 00:08:33,039
For simple things like whole
body dose from gamma rays,

200
00:08:33,039 --> 00:08:35,900
sieverts equals
gray, because sievert

201
00:08:35,900 --> 00:08:39,500
is multiplied by this quality
factor, or this effectiveness

202
00:08:39,500 --> 00:08:40,549
factor.

203
00:08:40,549 --> 00:08:42,870
That Q factor is actually
a couple of factors.

204
00:08:42,870 --> 00:08:47,770
There's a Q for
the type of tissue

205
00:08:47,770 --> 00:08:49,610
and there's a Q for
the type of radiation.

206
00:08:53,780 --> 00:08:55,730
And the total quality
factor for whatever

207
00:08:55,730 --> 00:08:59,388
you're trying to calculate
is just the multiplication

208
00:08:59,388 --> 00:08:59,930
of these two.

209
00:09:07,835 --> 00:09:09,460
And so it's fairly
easy, if you're ever

210
00:09:09,460 --> 00:09:13,240
dealing with whole body gamma
dose, gray equals sieverts.

211
00:09:13,240 --> 00:09:16,180
If you're dealing with pretty
much anything different, gray

212
00:09:16,180 --> 00:09:17,290
does not equal sieverts.

213
00:09:17,290 --> 00:09:19,480
There'll be just some
factor to add in,

214
00:09:19,480 --> 00:09:21,280
which can be looked
up from a lookup table

215
00:09:21,280 --> 00:09:23,860
but, as I've told you before,
I don't like that explanation,

216
00:09:23,860 --> 00:09:25,120
look it up on a table.

217
00:09:25,120 --> 00:09:27,850
We're going to explore why the
lookup tables are constructed

218
00:09:27,850 --> 00:09:30,400
the way they are.

219
00:09:30,400 --> 00:09:32,770
And then there's the
CGS units, the ones

220
00:09:32,770 --> 00:09:35,950
that are based in
centimeter-gram-second, instead

221
00:09:35,950 --> 00:09:39,150
of kilogram-meter-second.

222
00:09:39,150 --> 00:09:41,420
The rad is a simple measure.

223
00:09:41,420 --> 00:09:44,085
It's, let's say, 100
rad is just 1 gray.

224
00:09:44,085 --> 00:09:45,460
Where the rad
actually comes from

225
00:09:45,460 --> 00:09:50,560
is, it's defined as 100 ergs
absorbed energy per gram,

226
00:09:50,560 --> 00:09:53,410
where an erg is 10
to the minus 7 joules

227
00:09:53,410 --> 00:09:56,843
and a gram is 10 to
the minus 3 kilograms.

228
00:09:56,843 --> 00:09:58,510
And so, you can do
the mental math there

229
00:09:58,510 --> 00:10:01,000
to make sure these all work out.

230
00:10:01,000 --> 00:10:04,120
And then a REM, a
roentgen equivalent man,

231
00:10:04,120 --> 00:10:06,850
is just a hundredth
of a sievert.

232
00:10:06,850 --> 00:10:08,950
So there's historical
basis for this.

233
00:10:08,950 --> 00:10:11,380
Back in the day, more
folks used CGS units.

234
00:10:11,380 --> 00:10:13,660
There's been a push
to SI units, which

235
00:10:13,660 --> 00:10:16,225
I happen to like because
everything works out

236
00:10:16,225 --> 00:10:18,100
and you don't have to
remember things like 10

237
00:10:18,100 --> 00:10:21,530
to the minus 7 joules
or whatever like that.

238
00:10:21,530 --> 00:10:24,130
So I'd say, when in doubt,
for equal comparisons

239
00:10:24,130 --> 00:10:26,740
always use the SI
units and always

240
00:10:26,740 --> 00:10:28,330
start with the
gray because that's

241
00:10:28,330 --> 00:10:31,420
something where you can take a
physical calculation of energy

242
00:10:31,420 --> 00:10:35,860
per kilogram and go into
some increased cancer risk

243
00:10:35,860 --> 00:10:38,630
by using the dose
quality factors.

244
00:10:38,630 --> 00:10:41,620
So let's take a look
at how these appear.

245
00:10:41,620 --> 00:10:43,930
First of all, gammas,
x-rays, electrons,

246
00:10:43,930 --> 00:10:46,630
positrons of any LET.

247
00:10:46,630 --> 00:10:49,870
LET, as I mentioned before,
is linear energy transfer.

248
00:10:58,267 --> 00:10:59,850
And to put this
mathematically, you've

249
00:10:59,850 --> 00:11:06,020
actually seen this before, which
would be some change in energy

250
00:11:06,020 --> 00:11:09,850
over some change in distance.

251
00:11:09,850 --> 00:11:11,660
It's the stopping power.

252
00:11:11,660 --> 00:11:14,660
It's not like the stopping
power, it's the stopping power.

253
00:11:14,660 --> 00:11:17,660
So with the formulas you got in
the second half of this class,

254
00:11:17,660 --> 00:11:20,600
you can calculate
linear energy transfer.

255
00:11:20,600 --> 00:11:25,670
Now, why are these things given
in, let's say, discrete tables,

256
00:11:25,670 --> 00:11:30,380
or now what's currently
recommended is these functions?

257
00:11:30,380 --> 00:11:31,510
Does anyone have any idea?

258
00:11:38,480 --> 00:11:40,100
How many of your
Core Seven friends

259
00:11:40,100 --> 00:11:44,380
know the formula for stopping
power, or could parse it even,

260
00:11:44,380 --> 00:11:45,840
or understand it?

261
00:11:45,840 --> 00:11:48,090
You don't have to,
not everybody has to.

262
00:11:48,090 --> 00:11:52,470
So, for the rest of us, there
are simpler empirical relations

263
00:11:52,470 --> 00:11:55,350
or relations that get the
numbers right that aren't

264
00:11:55,350 --> 00:11:58,110
necessarily based on physics.

265
00:11:58,110 --> 00:11:59,760
So a simple lookup
table, for those

266
00:11:59,760 --> 00:12:02,895
who don't have time to take
22.01 or something beyond,

267
00:12:02,895 --> 00:12:04,020
is the easiest thing to do.

268
00:12:04,020 --> 00:12:05,310
And in most cases it works.

269
00:12:05,310 --> 00:12:08,310
It's not exact, but it's
probably close enough.

270
00:12:08,310 --> 00:12:11,790
Given uncertainties in
the amount of radiation

271
00:12:11,790 --> 00:12:15,420
that one could absorb or the
weight of a certain organ

272
00:12:15,420 --> 00:12:18,600
or the energy of
some x-ray tube,

273
00:12:18,600 --> 00:12:22,548
I think these empirical things
are pretty much good enough.

274
00:12:22,548 --> 00:12:24,090
And what this tells
you is that there

275
00:12:24,090 --> 00:12:27,450
is some effectiveness of
different types of radiation

276
00:12:27,450 --> 00:12:29,580
and different
energies of radiation

277
00:12:29,580 --> 00:12:34,140
at imparting energy to the
parts of cells and organs

278
00:12:34,140 --> 00:12:36,050
that cause damage.

279
00:12:36,050 --> 00:12:38,540
To say that in a little
smaller sentence,

280
00:12:38,540 --> 00:12:41,210
different energies of radiation
can have different effects

281
00:12:41,210 --> 00:12:46,020
biologically, and these tissue
factors account for that.

282
00:12:46,020 --> 00:12:46,800
It's also a table.

283
00:12:46,800 --> 00:12:48,508
I want you to keep in
mind because you're

284
00:12:48,508 --> 00:12:50,780
going to have to do a
calculation about it.

285
00:12:50,780 --> 00:12:54,230
The principle elements in
soft tissue in unit density,

286
00:12:54,230 --> 00:12:56,300
otherwise known
as number density,

287
00:12:56,300 --> 00:12:57,830
which you've seen before.

288
00:12:57,830 --> 00:13:01,040
If you want to calculate the
dose using a stopping power

289
00:13:01,040 --> 00:13:04,970
formula to a human, you have to
know what this human is made of

290
00:13:04,970 --> 00:13:06,710
and this is a pretty
good assumption.

291
00:13:06,710 --> 00:13:09,417
And this is something you'll
be doing on homework number 8,

292
00:13:09,417 --> 00:13:11,000
is finding the dose
that you're giving

293
00:13:11,000 --> 00:13:14,116
to each other in a
particular situation.

294
00:13:14,116 --> 00:13:15,980
If anyone's seen the
particular situation,

295
00:13:15,980 --> 00:13:18,500
check OCW for last
year's course and you'll

296
00:13:18,500 --> 00:13:20,930
see what that situation will be.

297
00:13:20,930 --> 00:13:25,670
Has everyone gotten your whole
body counts at the EHS Office?

298
00:13:25,670 --> 00:13:27,890
If anyone hasn't, do
them in the next week

299
00:13:27,890 --> 00:13:31,130
because you'll need that
data for the homework.

300
00:13:31,130 --> 00:13:33,020
You'll also need this table.

301
00:13:33,020 --> 00:13:36,770
Because if you think about
it, if you want to say, well,

302
00:13:36,770 --> 00:13:41,000
what's the damage by
electrons to soft tissue?

303
00:13:41,000 --> 00:13:43,430
And you want to calculate
this from scratch.

304
00:13:43,430 --> 00:13:45,750
You have these four
number densities,

305
00:13:45,750 --> 00:13:47,470
so we'll keep those in account.

306
00:13:47,470 --> 00:13:50,990
And let's put up the
formula for ionization

307
00:13:50,990 --> 00:13:52,010
stopping power again.

308
00:13:54,560 --> 00:13:57,980
Comes out with 4
pi, k not squared,

309
00:13:57,980 --> 00:14:01,450
little z squared, big
Z, number density,

310
00:14:01,450 --> 00:14:07,840
e to the fourth, over
MeV squared, log.

311
00:14:07,840 --> 00:14:09,600
Let's see, what
goes on top again?

312
00:14:12,830 --> 00:14:18,100
Oh, yeah, 2MeV squared, over
the mean ionization energy.

313
00:14:18,100 --> 00:14:19,940
The nonrelativistic form.

314
00:14:19,940 --> 00:14:21,830
Which of these
terms vary depending

315
00:14:21,830 --> 00:14:26,850
on the atom that an electron
or whatever would strike?

316
00:14:26,850 --> 00:14:30,380
Let's circle them,
there's a couple.

317
00:14:30,380 --> 00:14:31,520
AUDIENCE: Big Z.

318
00:14:31,520 --> 00:14:34,370
MICHAEL SHORT: Big Z, what
the electron's hitting.

319
00:14:34,370 --> 00:14:35,480
N, the number density.

320
00:14:44,066 --> 00:14:45,510
AUDIENCE: Ionization potential.

321
00:14:45,510 --> 00:14:48,703
MICHAEL SHORT: Yes, the
mean ionization potential.

322
00:14:48,703 --> 00:14:50,370
So these three terms
are the only things

323
00:14:50,370 --> 00:14:52,440
that change when
you're doing a stopping

324
00:14:52,440 --> 00:14:54,910
power to dose calculation.

325
00:14:54,910 --> 00:15:01,760
So if you want to get the
total dose in gray to a human,

326
00:15:01,760 --> 00:15:08,325
you have to sum over these
four different isotopes.

327
00:15:08,325 --> 00:15:08,950
Actually, wait.

328
00:15:08,950 --> 00:15:12,580
Let me put all the other junk
in front to make it quicker.

329
00:15:12,580 --> 00:15:16,625
So the 4 pi k0 squared
little z squared

330
00:15:16,625 --> 00:15:22,180
e to the fourth
over MeV squared is

331
00:15:22,180 --> 00:15:31,710
just a constant, times the
sum over all your isotopes

332
00:15:31,710 --> 00:15:37,560
of zi, the number
density of isotope i,

333
00:15:37,560 --> 00:15:43,250
which inside there has the
element fraction of that,

334
00:15:43,250 --> 00:15:48,600
times the log of 2 MeV squared
over the mean ionization

335
00:15:48,600 --> 00:15:52,446
potential of isotope i.

336
00:15:52,446 --> 00:15:55,378
And in this case, notice
there's no isotopes given.

337
00:15:55,378 --> 00:15:56,670
They're just given as elements.

338
00:15:56,670 --> 00:15:59,630
Why do we do that?

339
00:15:59,630 --> 00:16:02,900
Why don't we care for humans?

340
00:16:02,900 --> 00:16:06,830
How many isotopes of hydrogen
tend to exist in you?

341
00:16:06,830 --> 00:16:10,657
One, pretty much one, to
about five significant digits.

342
00:16:10,657 --> 00:16:11,990
You all have a little deuterium.

343
00:16:11,990 --> 00:16:14,960
Something like 1 in every 20,000
atoms of hydrogen is deuterium.

344
00:16:14,960 --> 00:16:16,760
But it's not a lot.

345
00:16:16,760 --> 00:16:18,140
I think it's even
less than that.

346
00:16:18,140 --> 00:16:20,840
Carbon is just carbon-12,
except for the tiny amount

347
00:16:20,840 --> 00:16:23,630
of carbon-14 you use
for radio carbon dating.

348
00:16:23,630 --> 00:16:27,530
Oxygen, it's oxygen--
think what, 16?

349
00:16:27,530 --> 00:16:29,510
Nitrogen is nitrogen-14.

350
00:16:29,510 --> 00:16:31,580
So as long as you know
what isotopes to use,

351
00:16:31,580 --> 00:16:35,630
you'll know what
z's, what i bars.

352
00:16:35,630 --> 00:16:37,380
And the number
density is given here.

353
00:16:37,380 --> 00:16:39,310
So this right here is
how you calculate dose

354
00:16:39,310 --> 00:16:42,800
in gray to a human
over some distance.

355
00:16:42,800 --> 00:16:46,830
Then all you'd have to do is
integrate that over your--

356
00:16:50,360 --> 00:16:52,160
let's say thickness
of the human,

357
00:16:52,160 --> 00:16:53,750
whatever that happens to be.

358
00:16:53,750 --> 00:16:56,955
And you get the total amount
of dose imparted to them.

359
00:16:56,955 --> 00:16:59,080
So a lot of questions came
up in last year's class.

360
00:16:59,080 --> 00:17:00,980
How do we actually do
these calculations?

361
00:17:00,980 --> 00:17:02,868
Well, this is how right here.

362
00:17:02,868 --> 00:17:04,910
First, separate out
everything that's a constant.

363
00:17:04,910 --> 00:17:06,950
Because you only have
to calculate it once,

364
00:17:06,950 --> 00:17:09,140
as I hope problem set 7
and 6 taught you guys,

365
00:17:09,140 --> 00:17:11,300
is separate out
whatever you can first,

366
00:17:11,300 --> 00:17:12,770
and don't repeat yourself.

367
00:17:12,770 --> 00:17:14,540
Then sum over all
the things that

368
00:17:14,540 --> 00:17:16,520
are unique to each isotope.

369
00:17:16,520 --> 00:17:19,730
And inside this number
density is the fraction

370
00:17:19,730 --> 00:17:21,349
of that isotope in every human.

371
00:17:21,349 --> 00:17:22,700
So it's all built in.

372
00:17:22,700 --> 00:17:24,983
So these calculations
aren't that bad.

373
00:17:24,983 --> 00:17:26,650
Since you know how
to do stopping power,

374
00:17:26,650 --> 00:17:28,600
you can take out
2/3 of the terms.

375
00:17:28,600 --> 00:17:31,630
I don't know why
I still have this.

376
00:17:31,630 --> 00:17:33,760
It's not terrible.

377
00:17:33,760 --> 00:17:35,800
Can anyone not see
through how to do this?

378
00:17:35,800 --> 00:17:37,182
Or yeah, have a question?

379
00:17:37,182 --> 00:17:39,140
AUDIENCE: Where do we
find the ionization term?

380
00:17:39,140 --> 00:17:41,560
MICHAEL SHORT: The mean
ionization potential

381
00:17:41,560 --> 00:17:45,940
can be usually approximated
as about 10 electron volts

382
00:17:45,940 --> 00:17:48,610
times z.

383
00:17:48,610 --> 00:17:51,790
Except for the very light
isotopes like hydrogen,

384
00:17:51,790 --> 00:17:55,870
it's somewhere
between 10 and 19 eV.

385
00:17:55,870 --> 00:17:58,000
I would say one, you
can just look them up.

386
00:17:58,000 --> 00:18:00,370
Or two, you can use
this empirical relation

387
00:18:00,370 --> 00:18:03,230
to get a good approximation.

388
00:18:03,230 --> 00:18:06,910
And empiricism definitely enters
into the biological world,

389
00:18:06,910 --> 00:18:08,590
because uncertainties abound.

390
00:18:08,590 --> 00:18:11,890
And it's not always worth
being ultra crazy exact,

391
00:18:11,890 --> 00:18:15,280
although it can't hurt.

392
00:18:15,280 --> 00:18:18,220
Any other questions on
how to actually carry out

393
00:18:18,220 --> 00:18:20,250
a dose calculation
using stopping power?

394
00:18:22,900 --> 00:18:25,020
Hopefully it's pretty
straightforward.

395
00:18:25,020 --> 00:18:27,900
Guess we'll find
out on the homework.

396
00:18:27,900 --> 00:18:31,740
The other quality
factors to mention--

397
00:18:31,740 --> 00:18:34,300
there are some different ideas
about these quality factors.

398
00:18:34,300 --> 00:18:37,780
Notice the scales
are fairly coarse.

399
00:18:37,780 --> 00:18:40,780
So again, there's a lot
of uncertainty or slop

400
00:18:40,780 --> 00:18:42,200
in these values.

401
00:18:42,200 --> 00:18:45,340
But notice that for, let's
say, X-rays, gammas, betas

402
00:18:45,340 --> 00:18:49,900
of all energies and charges,
the quality factor is 1.

403
00:18:49,900 --> 00:18:51,130
Why do you think that is?

404
00:18:56,550 --> 00:18:59,640
Let's go for the case
of X-rays or gammas.

405
00:18:59,640 --> 00:19:02,340
What tends to be the
attenuation coefficient

406
00:19:02,340 --> 00:19:07,460
of any photon in soft tissue
of considerable energy?

407
00:19:07,460 --> 00:19:08,990
Pretty low.

408
00:19:08,990 --> 00:19:11,120
And the amount of energy
that can be transferred

409
00:19:11,120 --> 00:19:14,510
by those photons is
variable, anywhere

410
00:19:14,510 --> 00:19:16,490
from pretty low to pretty high.

411
00:19:16,490 --> 00:19:18,650
And so the resulting
electron cascade

412
00:19:18,650 --> 00:19:20,780
isn't going to be that damaging.

413
00:19:20,780 --> 00:19:22,940
And it might not even
be that localized.

414
00:19:22,940 --> 00:19:25,910
So let's say if you really
want to know how much damage

415
00:19:25,910 --> 00:19:28,070
is it going to go do to
the DNA of a cell, where

416
00:19:28,070 --> 00:19:31,730
it could mutate and cause
cancer, not that much.

417
00:19:31,730 --> 00:19:33,650
Most of the gammas
pass through you,

418
00:19:33,650 --> 00:19:35,600
and the ones that
do get absorbed

419
00:19:35,600 --> 00:19:38,900
can have rather long
energy deposition tracks.

420
00:19:38,900 --> 00:19:43,650
Neutrons, however, interact
nuclear stopping power.

421
00:19:43,650 --> 00:19:47,360
Or let's say they just interact
with the nuclei of you,

422
00:19:47,360 --> 00:19:49,100
or whatever they're irradiating.

423
00:19:49,100 --> 00:19:50,690
And so when you
knock out a nucleus,

424
00:19:50,690 --> 00:19:52,520
it can then slam
into other atoms,

425
00:19:52,520 --> 00:19:56,210
causing a huge and dense
cascade of ionization.

426
00:19:56,210 --> 00:20:00,470
If that cascade happens to be
near the nucleus of a cell,

427
00:20:00,470 --> 00:20:03,140
you better believe it's going
to cause a lot of damage.

428
00:20:03,140 --> 00:20:06,260
And that's why these
more energetic neutrons

429
00:20:06,260 --> 00:20:08,870
have a much higher quality
factor, because they're

430
00:20:08,870 --> 00:20:11,870
much better at causing
damage until you

431
00:20:11,870 --> 00:20:14,260
reach some sort of threshold.

432
00:20:14,260 --> 00:20:16,420
Why do you think it goes
down at higher energies?

433
00:20:20,830 --> 00:20:21,370
Yeah.

434
00:20:21,370 --> 00:20:22,890
AUDIENCE: Well, because
there's less of a probability

435
00:20:22,890 --> 00:20:25,240
that it would actually
interact with [INAUDIBLE]..

436
00:20:27,860 --> 00:20:29,150
MICHAEL SHORT: Absolutely.

437
00:20:29,150 --> 00:20:33,290
Right around 2 MeV or 1
MeV, these cross sections

438
00:20:33,290 --> 00:20:35,040
tend to go down.

439
00:20:35,040 --> 00:20:38,730
If we look at the cross-section
for neutrons in anything--

440
00:20:38,730 --> 00:20:42,780
let's look at
hydrogen. [INAUDIBLE]

441
00:20:42,780 --> 00:20:45,800
still got to do the screen
cloning thing again.

442
00:20:45,800 --> 00:20:46,400
Bear with me.

443
00:20:50,650 --> 00:20:52,780
Let's look at any old cross
section for, let's say,

444
00:20:52,780 --> 00:20:54,613
neutron scattering in,
I don't know, oxygen.

445
00:20:54,613 --> 00:20:58,080
We've looked at
hydrogen enough already.

446
00:20:58,080 --> 00:20:58,580
Cool.

447
00:20:58,580 --> 00:20:59,510
You can see that.

448
00:21:09,310 --> 00:21:11,350
Oxygen-16.

449
00:21:11,350 --> 00:21:15,280
We have incident neutrons,
elastic scattering,

450
00:21:15,280 --> 00:21:16,210
the bouncing off.

451
00:21:16,210 --> 00:21:18,790
Let's look at the form
of this cross-section.

452
00:21:18,790 --> 00:21:24,010
Right around 1 MeV,
things start to dip.

453
00:21:24,010 --> 00:21:26,910
And so yeah, the probability
of any sort of interaction

454
00:21:26,910 --> 00:21:28,150
is going to go down.

455
00:21:28,150 --> 00:21:31,930
In addition, the
atom that struck

456
00:21:31,930 --> 00:21:34,670
has a much higher energy,
and therefore a higher range.

457
00:21:34,670 --> 00:21:36,430
So chances are,
even if the neutron

458
00:21:36,430 --> 00:21:39,310
strikes an atom
near the nucleus,

459
00:21:39,310 --> 00:21:42,010
it will have a higher range
and can travel farther before

460
00:21:42,010 --> 00:21:46,570
that secondary cascade ends up
depositing most of its damage

461
00:21:46,570 --> 00:21:48,150
at a lower energy.

462
00:21:48,150 --> 00:21:52,060
So if you remember for the
stopping power for ionization

463
00:21:52,060 --> 00:21:56,280
or nuclear stopping power,
they both look the same.

464
00:21:56,280 --> 00:21:58,030
So I'm not going
to label which one.

465
00:21:58,030 --> 00:22:00,100
It's fairly low
at high energies,

466
00:22:00,100 --> 00:22:03,280
peaks at a rather low
energy, and then comes down.

467
00:22:03,280 --> 00:22:07,120
So it's at the end of the
range of whatever particle,

468
00:22:07,120 --> 00:22:10,480
whether it be the neutron
or the atoms that it struck,

469
00:22:10,480 --> 00:22:12,040
that it does the most damage.

470
00:22:12,040 --> 00:22:14,830
So you can kind of think
like all forms of radiation--

471
00:22:14,830 --> 00:22:15,940
except for photons--

472
00:22:15,940 --> 00:22:17,860
as armor-piercing bullets.

473
00:22:17,860 --> 00:22:20,470
They don't do damage
right where they enter.

474
00:22:20,470 --> 00:22:23,627
They do damage right where
they stop and explode.

475
00:22:23,627 --> 00:22:25,210
In the case of
armor-piercing bullets,

476
00:22:25,210 --> 00:22:26,800
it's a literal explosion.

477
00:22:26,800 --> 00:22:31,450
In the case of neutrons,
electrons, protons, heavy ions,

478
00:22:31,450 --> 00:22:33,910
it's at the end of their range
they have the most stopping

479
00:22:33,910 --> 00:22:34,410
power.

480
00:22:34,410 --> 00:22:36,910
And that's where the dense
cascade's going to be.

481
00:22:36,910 --> 00:22:39,250
So chances are,
again, if a neutron

482
00:22:39,250 --> 00:22:43,270
happens to interact with
the nucleus of a cell--

483
00:22:43,270 --> 00:22:47,020
that's the simplest
cell I can draw--

484
00:22:47,020 --> 00:22:49,390
if a neutron comes in
and strikes another atom,

485
00:22:49,390 --> 00:22:56,318
it may move far away before
its armor-piercing explosion.

486
00:22:56,318 --> 00:22:57,360
Let's see the other ones.

487
00:22:57,360 --> 00:23:01,530
For protons, depending
on which book you go to,

488
00:23:01,530 --> 00:23:03,250
you get a different
effectiveness.

489
00:23:03,250 --> 00:23:07,440
It's higher than that of gammas
and X-rays and electrons,

490
00:23:07,440 --> 00:23:10,050
because you get a big
cascade at the end.

491
00:23:10,050 --> 00:23:13,380
And alpha particles,
really, really, damaging.

492
00:23:13,380 --> 00:23:15,300
And energy is like
even a few MeV,

493
00:23:15,300 --> 00:23:16,710
they have a very short range.

494
00:23:16,710 --> 00:23:19,350
They tend to deposit
a ton of energy.

495
00:23:19,350 --> 00:23:22,170
And that's why they have
a huge effectiveness.

496
00:23:22,170 --> 00:23:24,210
This is also why
alphas are the--

497
00:23:24,210 --> 00:23:25,710
that's the one
cookie you don't want

498
00:23:25,710 --> 00:23:29,040
to eat, if you guys remember
this, the four cookies problem.

499
00:23:29,040 --> 00:23:31,080
Never eat the alpha.

500
00:23:31,080 --> 00:23:32,940
It's not going to get
in through your skin,

501
00:23:32,940 --> 00:23:34,470
but if it gets
into your body and

502
00:23:34,470 --> 00:23:38,190
incorporated into the
material directly surrounding

503
00:23:38,190 --> 00:23:41,350
your nucleus, that's how
things go really bad.

504
00:23:41,350 --> 00:23:44,070
That's why smoking's so bad.

505
00:23:44,070 --> 00:23:46,350
Did anyone end up
getting into a smoke shop

506
00:23:46,350 --> 00:23:48,670
to do that measurement?

507
00:23:48,670 --> 00:23:50,670
I did check the one by
my house, and they just

508
00:23:50,670 --> 00:23:53,260
put up a sign that
said no one under 21.

509
00:23:53,260 --> 00:23:55,500
So you guys are
right about that.

510
00:23:55,500 --> 00:23:57,210
Weird law.

511
00:23:57,210 --> 00:23:58,890
Whatever.

512
00:23:58,890 --> 00:24:01,170
Now let's look at the
tissue weighting factors.

513
00:24:01,170 --> 00:24:04,320
We've talked about the
factors for different types

514
00:24:04,320 --> 00:24:05,370
of radiation.

515
00:24:05,370 --> 00:24:08,250
It also matters what
tissue it enters.

516
00:24:08,250 --> 00:24:10,620
So for things like
skin or bone surface,

517
00:24:10,620 --> 00:24:13,047
you think of these tissues
as not that critical.

518
00:24:13,047 --> 00:24:14,880
If you get a scratch
and you lose some skin,

519
00:24:14,880 --> 00:24:16,690
it's not that bad for the body.

520
00:24:16,690 --> 00:24:19,170
Same thing if a little
bone chip flakes off.

521
00:24:19,170 --> 00:24:21,660
You might get shin splints,
but it's not so bad.

522
00:24:21,660 --> 00:24:23,570
Not for the same reason.

523
00:24:23,570 --> 00:24:27,290
These tissues aren't
dividing very fast.

524
00:24:27,290 --> 00:24:29,660
The surface of your
bone, the hard part,

525
00:24:29,660 --> 00:24:31,610
is basically standing still.

526
00:24:31,610 --> 00:24:34,790
It's just calcified minerals
with some osteocytes trapped

527
00:24:34,790 --> 00:24:35,690
in there.

528
00:24:35,690 --> 00:24:37,310
Not much happens.

529
00:24:37,310 --> 00:24:42,350
What's happening in these
tissues constantly--

530
00:24:42,350 --> 00:24:46,333
gonads, bone marrow,
colon, lung, stomach?

531
00:24:46,333 --> 00:24:47,500
AUDIENCE: [INAUDIBLE] cells.

532
00:24:47,500 --> 00:24:48,292
MICHAEL SHORT: Yep.

533
00:24:48,292 --> 00:24:51,710
This is where stem cells and
fat-- rapidly dividing cells--

534
00:24:51,710 --> 00:24:53,640
tend to be found.

535
00:24:53,640 --> 00:24:56,240
So there's been some theories
and some papers saying

536
00:24:56,240 --> 00:24:59,210
whatever cancer you're going to
get, you probably already got

537
00:24:59,210 --> 00:25:01,460
it in the first
few years of life,

538
00:25:01,460 --> 00:25:06,580
when you're just a big
rolling sack of stem cells.

539
00:25:06,580 --> 00:25:09,400
This is part of why
occupational hazards for infants

540
00:25:09,400 --> 00:25:11,680
and pregnant women are much,
much lower, because they

541
00:25:11,680 --> 00:25:14,660
are giant sacks of
stationary stem cells.

542
00:25:14,660 --> 00:25:16,660
And you don't want to
irradiate something that's

543
00:25:16,660 --> 00:25:18,830
dividing really, really fast.

544
00:25:18,830 --> 00:25:21,480
And so the older
you are, the more OK

545
00:25:21,480 --> 00:25:23,230
it is to get more and
more radiation dose,

546
00:25:23,230 --> 00:25:26,230
because a lot of these effects
take a long time to manifest.

547
00:25:26,230 --> 00:25:28,330
Because they all start
with a single cell.

548
00:25:28,330 --> 00:25:30,460
And it takes a long time
for that single cell

549
00:25:30,460 --> 00:25:33,970
to exponentially grow and
divide over a longtime scale

550
00:25:33,970 --> 00:25:36,870
into a mass that be
considered a tumor.

551
00:25:36,870 --> 00:25:39,300
So it's a little
worrying to think, OK,

552
00:25:39,300 --> 00:25:42,352
probably most of the cancer
I'll get I got when I was five.

553
00:25:42,352 --> 00:25:44,310
But then again, it means,
don't worry about it.

554
00:25:44,310 --> 00:25:47,008
What can you do?

555
00:25:47,008 --> 00:25:47,550
There's what?

556
00:25:47,550 --> 00:25:48,383
AUDIENCE: It's free.

557
00:25:48,383 --> 00:25:50,460
MICHAEL SHORT: Yeah, it's free.

558
00:25:50,460 --> 00:25:51,810
It's done.

559
00:25:51,810 --> 00:25:53,650
Not all of it.

560
00:25:53,650 --> 00:25:55,800
You can still limit your
dose, because well, one,

561
00:25:55,800 --> 00:25:59,070
any acute radiation exposure
will have short term health

562
00:25:59,070 --> 00:25:59,910
effects.

563
00:25:59,910 --> 00:26:03,260
And two, your cells
are still dividing.

564
00:26:03,260 --> 00:26:07,320
As we had a seminar speaker
say, a biological organism

565
00:26:07,320 --> 00:26:09,750
at static equilibrium
is not very interesting.

566
00:26:09,750 --> 00:26:11,300
It's dead.

567
00:26:11,300 --> 00:26:13,070
It's not dividing anymore.

568
00:26:13,070 --> 00:26:14,930
So your cells are
still dividing.

569
00:26:14,930 --> 00:26:17,180
It still means you should
minimize radiation exposure.

570
00:26:17,180 --> 00:26:19,730
But a lot of what
happened already happened.

571
00:26:19,730 --> 00:26:22,340
And if you can see
here, the pattern

572
00:26:22,340 --> 00:26:24,890
is the more rapidly
the cells are dividing,

573
00:26:24,890 --> 00:26:29,420
the more it has this
tissue quality factor.

574
00:26:29,420 --> 00:26:31,820
Because the more
quickly these effects

575
00:26:31,820 --> 00:26:34,640
would manifest themselves,
and the more quickly the cells

576
00:26:34,640 --> 00:26:38,360
may divide with that mutation
before these cellular repair

577
00:26:38,360 --> 00:26:42,025
mechanisms fix that
mutation before a division.

578
00:26:42,025 --> 00:26:43,400
We'll get into a
lot of that when

579
00:26:43,400 --> 00:26:47,890
we talk about biological
effects, probably next week.

580
00:26:47,890 --> 00:26:50,340
So now, how do you do
a calculation of dose

581
00:26:50,340 --> 00:26:51,750
in Sieverts?

582
00:26:51,750 --> 00:26:56,890
First you can take the dose in
gray, like we have over here,

583
00:26:56,890 --> 00:26:59,680
multiply by these radiation
weighting factors,

584
00:26:59,680 --> 00:27:01,810
and you get a total
amount of dose

585
00:27:01,810 --> 00:27:04,880
to that tissue,
where that tissue may

586
00:27:04,880 --> 00:27:08,270
be a certain organ, a part
of your muscle, whole body

587
00:27:08,270 --> 00:27:12,340
if it was a broad blast of
radiation from a bomb far away

588
00:27:12,340 --> 00:27:13,730
or something like that.

589
00:27:13,730 --> 00:27:18,480
And you get these
single doses to tissue,

590
00:27:18,480 --> 00:27:21,570
where each of these
radiation equivalent factors

591
00:27:21,570 --> 00:27:24,810
can be equated to this
average quality factor, where

592
00:27:24,810 --> 00:27:28,140
you integrate the quality
factor as a function of length

593
00:27:28,140 --> 00:27:30,780
times the dose at that length.

594
00:27:30,780 --> 00:27:33,030
This is where the stopping
power formula comes in,

595
00:27:33,030 --> 00:27:37,110
is you'll have a stopping
power as the energy decreases,

596
00:27:37,110 --> 00:27:39,300
as the particle moves
through the material.

597
00:27:39,300 --> 00:27:41,400
And its stopping
power will change.

598
00:27:41,400 --> 00:27:44,910
So then you have to integrate
that stopping power times

599
00:27:44,910 --> 00:27:49,530
some constants and stuff over
that distance times the quality

600
00:27:49,530 --> 00:27:54,410
at that distance to get the
simple weighting factor.

601
00:27:54,410 --> 00:27:57,890
You then take these
weighting factors,

602
00:27:57,890 --> 00:28:00,850
plug them into your
dose to tissue,

603
00:28:00,850 --> 00:28:04,430
and sum up all the exposures
to different tissues.

604
00:28:04,430 --> 00:28:07,420
So each tissue will have
its own dose in Sieverts.

605
00:28:07,420 --> 00:28:09,790
It'll have its own
tissue weighting factor.

606
00:28:09,790 --> 00:28:12,220
You sum up all the
tissues exposed,

607
00:28:12,220 --> 00:28:15,220
and you get the total effective
dose to the whole body.

608
00:28:15,220 --> 00:28:17,950
This means that some
organs incur dose

609
00:28:17,950 --> 00:28:21,910
faster than others for the
same radiation exposure.

610
00:28:21,910 --> 00:28:25,647
So the whole body dose
should sum up to 1.

611
00:28:25,647 --> 00:28:27,730
And I believe-- I remember
doing this calculation,

612
00:28:27,730 --> 00:28:29,790
but it may be worth your
while to just try it.

613
00:28:29,790 --> 00:28:31,350
These numbers
should sum up to 1,

614
00:28:31,350 --> 00:28:33,900
because all of these
individual organs

615
00:28:33,900 --> 00:28:36,897
plus the remainder
of your body should

616
00:28:36,897 --> 00:28:37,980
constitute the whole body.

617
00:28:41,543 --> 00:28:42,960
And so this is,
in a nutshell, how

618
00:28:42,960 --> 00:28:45,670
you do these dose calculations.

619
00:28:45,670 --> 00:28:49,030
So let's take an example
from the actual reading.

620
00:28:49,030 --> 00:28:53,642
Let's say a worker gets 14
milligray of uniform whole body

621
00:28:53,642 --> 00:28:55,350
dose-- this would just
be from background

622
00:28:55,350 --> 00:28:58,860
radiation, cosmic
rays, food, whatever--

623
00:28:58,860 --> 00:29:01,680
plus a targeted
dose of 8 milligray

624
00:29:01,680 --> 00:29:07,250
to the lung from alphas,
plus 180 millgray from betas

625
00:29:07,250 --> 00:29:08,458
in the thyroid.

626
00:29:08,458 --> 00:29:10,750
Anyone know why they chose
alphas in the lung and betas

627
00:29:10,750 --> 00:29:13,540
in the thyroid?

628
00:29:13,540 --> 00:29:16,312
What's the most likely
sources of those?

629
00:29:16,312 --> 00:29:17,590
AUDIENCE: Iodine and nicotine.

630
00:29:17,590 --> 00:29:19,760
MICHAEL SHORT: Iodine
and let's say smoking.

631
00:29:19,760 --> 00:29:20,660
Yeah.

632
00:29:20,660 --> 00:29:22,630
Yeah, exactly.

633
00:29:22,630 --> 00:29:25,533
As we saw, a lot of the
radon daughter products

634
00:29:25,533 --> 00:29:26,950
tend to be alpha
emitters, and you

635
00:29:26,950 --> 00:29:28,690
tend to inhale those
through the lungs.

636
00:29:28,690 --> 00:29:33,340
And iodine is a beta decay with
about an eight day half life,

637
00:29:33,340 --> 00:29:35,800
and that gets preferentially
absorbed in the thyroid.

638
00:29:35,800 --> 00:29:38,260
So this is a pretty
realistic scenario.

639
00:29:38,260 --> 00:29:43,410
And we'd say, how much effective
dose did this person get?

640
00:29:43,410 --> 00:29:45,240
To do this calculation,
you first-- well,

641
00:29:45,240 --> 00:29:47,010
let's go through those steps.

642
00:29:47,010 --> 00:29:51,860
You look at the dose to each
tissue times the effectiveness

643
00:29:51,860 --> 00:29:53,410
for that type of radiation.

644
00:29:53,410 --> 00:29:56,550
So the dose got 8
milligray of alphas.

645
00:29:56,550 --> 00:29:59,780
So you multiply by 20
for that quality factor.

646
00:29:59,780 --> 00:30:02,420
And the lung gets
160 millisieverts.

647
00:30:02,420 --> 00:30:05,240
You do the multiplication for
the thyroid, the multiplication

648
00:30:05,240 --> 00:30:06,560
for the whole body.

649
00:30:06,560 --> 00:30:10,760
And then you do a summation
of these single tissue doses

650
00:30:10,760 --> 00:30:15,237
here, here, and here, times
the tissue weighting factors,

651
00:30:15,237 --> 00:30:16,820
which you then look
up from that table

652
00:30:16,820 --> 00:30:20,180
or calculate from the cell
division rate here, here,

653
00:30:20,180 --> 00:30:21,260
and here.

654
00:30:21,260 --> 00:30:24,390
And you get a total dose
of 42 millisieverts.

655
00:30:24,390 --> 00:30:26,360
So I want to point
something out to you guys.

656
00:30:26,360 --> 00:30:29,570
His thyroid got
180 millisieverts.

657
00:30:29,570 --> 00:30:32,210
He got 42 millisieverts.

658
00:30:32,210 --> 00:30:33,900
Interesting.

659
00:30:33,900 --> 00:30:36,090
Sounds a little
counterintuitive.

660
00:30:36,090 --> 00:30:38,760
But in this case, these
doses for each tissue

661
00:30:38,760 --> 00:30:41,290
are calculated for that tissue.

662
00:30:41,290 --> 00:30:45,930
So if you have a probability
of organ failure or mutation,

663
00:30:45,930 --> 00:30:48,120
you can now then know
how much increased

664
00:30:48,120 --> 00:30:50,160
risk he may have
of thyroid cancer

665
00:30:50,160 --> 00:30:56,223
specifically, or sum it up to
an equivalent whole body risk.

666
00:30:56,223 --> 00:30:57,640
And it just so
happens you're only

667
00:30:57,640 --> 00:31:00,887
allowed about 50
millisieverts of exposure.

668
00:31:00,887 --> 00:31:02,470
So he'd only be
allowed another eight.

669
00:31:02,470 --> 00:31:04,600
But we'll get into
limits and what

670
00:31:04,600 --> 00:31:06,460
this ICRU whatever
whatever means.

671
00:31:06,460 --> 00:31:07,960
I'll actually show
you the document.

672
00:31:07,960 --> 00:31:09,760
It's also posted online.

673
00:31:09,760 --> 00:31:12,620
This International
Committee on Radiation

674
00:31:12,620 --> 00:31:15,250
U. I forget what the U is.

675
00:31:15,250 --> 00:31:17,350
But this is the
whole document that

676
00:31:17,350 --> 00:31:19,810
has the basis for these
recommendations, the numbers,

677
00:31:19,810 --> 00:31:21,010
and the reasons.

678
00:31:21,010 --> 00:31:24,250
And that's all online for
you guys to check through.

679
00:31:24,250 --> 00:31:28,158
So anyone have any questions
on a example dose calculation?

680
00:31:31,086 --> 00:31:32,070
Cool.

681
00:31:32,070 --> 00:31:34,153
Let's look at some of the
ways that you'd actually

682
00:31:34,153 --> 00:31:35,620
measure dose.

683
00:31:35,620 --> 00:31:37,620
One of them we looked at
the first day of class,

684
00:31:37,620 --> 00:31:39,570
the old Chadwick experiment.

685
00:31:39,570 --> 00:31:43,140
Send radiation through
a fixed amount of area

686
00:31:43,140 --> 00:31:44,350
so you know the flux.

687
00:31:44,350 --> 00:31:47,520
If you know the total
amount of gammas

688
00:31:47,520 --> 00:31:50,350
is produced by this X-ray
tube, you know the area,

689
00:31:50,350 --> 00:31:51,600
then you know the solid angle.

690
00:31:51,600 --> 00:31:52,920
You know the flux.

691
00:31:52,920 --> 00:31:55,890
Then you have just a free air
chamber with a high voltage

692
00:31:55,890 --> 00:31:58,750
to suck up those ions
before they recombine.

693
00:31:58,750 --> 00:32:03,400
And that's how you can calculate
things like dose in roentgens.

694
00:32:03,400 --> 00:32:05,470
You also have pocket
versions of these things,

695
00:32:05,470 --> 00:32:08,230
sealed tubes with
two electrically

696
00:32:08,230 --> 00:32:11,320
insulated electrodes.

697
00:32:11,320 --> 00:32:17,230
And that cannot discharge unless
ions in the gas allow them to.

698
00:32:17,230 --> 00:32:20,230
And this is the basis behind
these civil defense air wall

699
00:32:20,230 --> 00:32:22,940
chambers, one of which I
happen to have right here.

700
00:32:22,940 --> 00:32:24,730
So I want to pass
this around and let

701
00:32:24,730 --> 00:32:26,158
you guys take a look at it.

702
00:32:26,158 --> 00:32:27,700
Like the ones you
saw in the reactor,

703
00:32:27,700 --> 00:32:30,520
you can look through
and see a little needle

704
00:32:30,520 --> 00:32:32,680
that will tell you the--

705
00:32:32,680 --> 00:32:34,780
not dose, but the
amount of ionization

706
00:32:34,780 --> 00:32:37,000
this thing has
received in roentgens,

707
00:32:37,000 --> 00:32:41,140
which can then be equated
with some calculations

708
00:32:41,140 --> 00:32:43,060
to dose in soft tissue.

709
00:32:43,060 --> 00:32:45,670
And also there's the base for
the civil defense dosimeter.

710
00:32:45,670 --> 00:32:47,920
I want to tell you
guys how it works.

711
00:32:47,920 --> 00:32:49,890
It's a battery.

712
00:32:49,890 --> 00:32:50,633
That's it.

713
00:32:50,633 --> 00:32:52,050
If you open that
thing up, there's

714
00:32:52,050 --> 00:32:56,460
a couple of big T cells in
there and a voltage divider.

715
00:32:56,460 --> 00:32:58,640
And you just turn the knob--

716
00:32:58,640 --> 00:33:00,390
which sounds complicated,
all you're doing

717
00:33:00,390 --> 00:33:02,280
is turning a potentiometer--

718
00:33:02,280 --> 00:33:07,590
to decide at what voltage this
wire end inside of the tube

719
00:33:07,590 --> 00:33:08,460
will be.

720
00:33:08,460 --> 00:33:10,680
And that voltage deflects
the wire a little bit

721
00:33:10,680 --> 00:33:13,710
by just coulombic
attraction or repulsion,

722
00:33:13,710 --> 00:33:16,020
bends it, and
gives you the dose.

723
00:33:16,020 --> 00:33:17,520
And it stays there.

724
00:33:17,520 --> 00:33:20,970
Nothing can get in or out
of that sealed chamber,

725
00:33:20,970 --> 00:33:23,830
except penetrating radiation.

726
00:33:23,830 --> 00:33:26,880
When gammas or
neutrons get through,

727
00:33:26,880 --> 00:33:29,190
they can cause
ionizations in the gas.

728
00:33:29,190 --> 00:33:32,010
Those gas ions can move
to these electrodes,

729
00:33:32,010 --> 00:33:36,630
partially neutralizing them,
making the needle tilt a little

730
00:33:36,630 --> 00:33:38,760
farther and a little farther.

731
00:33:38,760 --> 00:33:41,760
So the interesting thing is when
that needle read 0 roentgens,

732
00:33:41,760 --> 00:33:43,480
it's fully charged.

733
00:33:43,480 --> 00:33:47,610
And as the detector discharges
from radiation interactions,

734
00:33:47,610 --> 00:33:49,920
the needle moves higher
on the roentgens scale.

735
00:33:49,920 --> 00:33:51,420
Because you can
paint whatever scale

736
00:33:51,420 --> 00:33:53,647
you want on it, as long
as the physics works out.

737
00:33:53,647 --> 00:33:55,980
So it's kind of neat to think
that the charge is highest

738
00:33:55,980 --> 00:33:57,820
when the dose is lowest.

739
00:33:57,820 --> 00:33:59,920
Because all the
charge is doing is

740
00:33:59,920 --> 00:34:02,390
deflecting that little needle.

741
00:34:02,390 --> 00:34:04,930
Quite simple design,
and quite robust.

742
00:34:04,930 --> 00:34:07,790
These things were
designed by civil defense

743
00:34:07,790 --> 00:34:10,800
in case the Cold War
became a hot war,

744
00:34:10,800 --> 00:34:13,380
and they'd have to last
for a very long time.

745
00:34:13,380 --> 00:34:16,010
So having had this one
for about 10 years,

746
00:34:16,010 --> 00:34:19,730
I can tell you I've not
yet filled the meter, which

747
00:34:19,730 --> 00:34:21,300
is probably a good thing.

748
00:34:21,300 --> 00:34:24,710
And I took that on flights
across the world and hiking

749
00:34:24,710 --> 00:34:28,280
in Nepal, where the background
dose was considerably higher.

750
00:34:28,280 --> 00:34:31,580
And the needle moved like half
a roentgen for the entire three

751
00:34:31,580 --> 00:34:33,969
weeks up at elevation
and plane rides.

752
00:34:33,969 --> 00:34:37,300
And I got more dose on the plane
ride than I did on the hike.

753
00:34:37,300 --> 00:34:40,522
Interesting fun fact.

754
00:34:40,522 --> 00:34:42,480
That's pretty much exactly
what you should see.

755
00:34:42,480 --> 00:34:43,907
And so Alex tells
me these things

756
00:34:43,907 --> 00:34:46,449
are starting to get kind of rare
on eBay, and that's a shame.

757
00:34:46,449 --> 00:34:48,940
Because this is the best
possible teaching dosimeter

758
00:34:48,940 --> 00:34:49,929
there is.

759
00:34:49,929 --> 00:34:52,420
If you understand 8.02 and
a little bit of radiation,

760
00:34:52,420 --> 00:34:55,475
you know how these work and
can predict what the dose is

761
00:34:55,475 --> 00:34:56,350
actually going to be.

762
00:34:59,170 --> 00:35:02,660
Now, how do you do things
like detect neutrons?

763
00:35:02,660 --> 00:35:06,230
If you want to detect neutrons,
you want a good moderator.

764
00:35:06,230 --> 00:35:09,590
Because well moderated neutrons
deposit all their energy

765
00:35:09,590 --> 00:35:12,830
in the detector instead of
bouncing off, transferring

766
00:35:12,830 --> 00:35:14,360
a little energy, and leaving.

767
00:35:14,360 --> 00:35:18,200
If you want to know how many and
what energy neutrons you have,

768
00:35:18,200 --> 00:35:21,440
you can fill a similar chamber
that's got a high voltage.

769
00:35:21,440 --> 00:35:23,240
It's got a wire on the inside.

770
00:35:23,240 --> 00:35:27,050
But instead of air or
some other gas in there,

771
00:35:27,050 --> 00:35:30,410
you can fill it with things
like ethylene or propylene

772
00:35:30,410 --> 00:35:35,150
or some sort of very hydrogenous
hydrocarbon gas, something

773
00:35:35,150 --> 00:35:38,180
full of hydrogen to act
as a good moderator.

774
00:35:38,180 --> 00:35:41,340
That hydrogen ion
then becomes a proton,

775
00:35:41,340 --> 00:35:44,180
which then damages
a lot of other ions,

776
00:35:44,180 --> 00:35:46,730
causing an ionization
cascade, and leading

777
00:35:46,730 --> 00:35:50,285
to some current pulse, just
like any other detector.

778
00:35:50,285 --> 00:35:52,160
There's going to be some
movement of current,

779
00:35:52,160 --> 00:35:55,770
which is picked up as damage.

780
00:35:55,770 --> 00:36:00,355
You might then ask also, why
is that alpha source there?

781
00:36:00,355 --> 00:36:01,230
Anyone have any idea?

782
00:36:08,000 --> 00:36:10,710
That's your calibration source.

783
00:36:10,710 --> 00:36:15,780
So as the gas in this chamber
is attacked by neutrons,

784
00:36:15,780 --> 00:36:18,900
you will be blasting
some of the hydrogen

785
00:36:18,900 --> 00:36:21,450
atoms out of the
ethylene or propylene

786
00:36:21,450 --> 00:36:23,040
or whatever gas you have.

787
00:36:23,040 --> 00:36:26,520
The gas will change in
effectiveness over time.

788
00:36:26,520 --> 00:36:29,550
The energy of the alpha
particles will not.

789
00:36:29,550 --> 00:36:33,450
So that is your absolutely
fixed energy calibration source.

790
00:36:33,450 --> 00:36:35,160
So you know exactly--

791
00:36:35,160 --> 00:36:39,600
if, let's say, 3.72 MeV
alphas make a current pulse

792
00:36:39,600 --> 00:36:42,900
of a certain height,
then you can equate that

793
00:36:42,900 --> 00:36:47,610
to a 3.72 MeV neutron that
would strike a hydrogen atom.

794
00:36:47,610 --> 00:36:49,330
And because the gas
degrades over time,

795
00:36:49,330 --> 00:36:52,180
you have to recalibrate
with that built-in alpha.

796
00:36:52,180 --> 00:36:53,980
And any sort of shutter--

797
00:36:53,980 --> 00:36:56,530
like a little piece of
foil-- will block the alpha

798
00:36:56,530 --> 00:36:59,540
so that you can use it
as a neutron detector.

799
00:36:59,540 --> 00:37:01,760
Quite clever design,
in my opinion.

800
00:37:01,760 --> 00:37:06,245
It accounts for the degradation
of the gas and the detector.

801
00:37:06,245 --> 00:37:07,870
Anyone seen one of
these things before?

802
00:37:11,830 --> 00:37:14,770
Then there's the Geiger counter,
which is an ionization counter

803
00:37:14,770 --> 00:37:17,260
run in avalanche mode.

804
00:37:17,260 --> 00:37:20,260
You can use these free
air ionization chambers

805
00:37:20,260 --> 00:37:24,370
or other counters as an energy
proportional counter, where

806
00:37:24,370 --> 00:37:28,000
a higher energy particle will
impart a bigger ionization

807
00:37:28,000 --> 00:37:29,050
cascade.

808
00:37:29,050 --> 00:37:31,780
And you can then use that
to get energy resolution.

809
00:37:31,780 --> 00:37:34,210
Or you crank up the
voltage like crazy,

810
00:37:34,210 --> 00:37:38,410
so that any count of any energy
causes an intense ionization

811
00:37:38,410 --> 00:37:41,205
cascade and a huge
current pulse.

812
00:37:41,205 --> 00:37:43,330
And this is the basis behind
cheap Geiger counters,

813
00:37:43,330 --> 00:37:45,370
like the ones we build
in our department.

814
00:37:45,370 --> 00:37:48,580
Those old Soviet
SPM 20 tubes that

815
00:37:48,580 --> 00:37:52,240
have actually been survived
being stepped on and crushed.

816
00:37:52,240 --> 00:37:54,970
As long as the electrodes don't
short out, they still work.

817
00:37:54,970 --> 00:37:56,845
So there's a few folks
in the department that

818
00:37:56,845 --> 00:37:58,548
have clearly bent Geiger tubes.

819
00:37:58,548 --> 00:38:00,340
One of them looks like
they've been chewed,

820
00:38:00,340 --> 00:38:02,280
but they still work.

821
00:38:02,280 --> 00:38:05,010
Because any sort of anything
interacting with a gas

822
00:38:05,010 --> 00:38:07,830
will cause an ionization
cascade, which is immediately

823
00:38:07,830 --> 00:38:10,590
sucked into the electrodes
by a high voltage

824
00:38:10,590 --> 00:38:14,485
and collected as a current pulse

825
00:38:14,485 --> 00:38:15,860
And that's just
a cutaway of what

826
00:38:15,860 --> 00:38:17,330
it looks like on the inside.

827
00:38:17,330 --> 00:38:19,520
And this is the circuit
for a Geiger counter.

828
00:38:19,520 --> 00:38:23,480
There is a voltage, a resistor,
a capacitor, and a tube.

829
00:38:23,480 --> 00:38:25,960
That's all you need.

830
00:38:25,960 --> 00:38:27,670
Everything else in
the MIT Geiger counter

831
00:38:27,670 --> 00:38:30,280
is there to make
lights and sound.

832
00:38:30,280 --> 00:38:31,930
It's just for fun.

833
00:38:31,930 --> 00:38:34,570
But the actual Geiger counter
itself can be made incredibly .

834
00:38:34,570 --> 00:38:37,960
Compact the bigger the
tube, the more radiation it

835
00:38:37,960 --> 00:38:39,460
will catch, just
because of its size

836
00:38:39,460 --> 00:38:43,090
but otherwise, as long as you
get the voltage high enough

837
00:38:43,090 --> 00:38:46,210
to cause this ionization
cascade, it works.

838
00:38:46,210 --> 00:38:47,335
It's really, really robust.

839
00:38:49,832 --> 00:38:51,790
So I want to skip ahead
for some of that stuff,

840
00:38:51,790 --> 00:38:54,640
and then talk about how do
you measure dose in humans.

841
00:38:54,640 --> 00:38:58,150
Who here has seen one of these
TLDs, or Thermoluminescent

842
00:38:58,150 --> 00:38:58,990
Dosimeters before?

843
00:38:58,990 --> 00:39:00,850
Our reactor trainees have.

844
00:39:00,850 --> 00:39:03,035
And you've worked on
nuclear stuff too, right?

845
00:39:03,035 --> 00:39:03,910
AUDIENCE: [INAUDIBLE]

846
00:39:03,910 --> 00:39:05,560
MICHAEL SHORT: You've got one
in the vault. Wait, Kristen,

847
00:39:05,560 --> 00:39:07,145
what about you,
since you've worked--

848
00:39:07,145 --> 00:39:09,456
AUDIENCE: We had one with
a little crystal in it.

849
00:39:09,456 --> 00:39:11,248
MICHAEL SHORT: That's
exactly what this is.

850
00:39:11,248 --> 00:39:12,467
AUDIENCE: [INAUDIBLE]

851
00:39:12,467 --> 00:39:13,300
MICHAEL SHORT: Yeah.

852
00:39:13,300 --> 00:39:14,175
And you can shake it.

853
00:39:14,175 --> 00:39:15,287
It rattles, right?

854
00:39:15,287 --> 00:39:15,870
AUDIENCE: Yep.

855
00:39:15,870 --> 00:39:17,752
[INAUDIBLE]

856
00:39:17,752 --> 00:39:18,710
MICHAEL SHORT: Exactly.

857
00:39:18,710 --> 00:39:20,200
So this is how these work.

858
00:39:20,200 --> 00:39:23,920
This stands for a
Thermoluminescent Dosimeter.

859
00:39:23,920 --> 00:39:25,900
And converting from
Latin to English,

860
00:39:25,900 --> 00:39:29,890
that means if you heat it, it
produces light proportional

861
00:39:29,890 --> 00:39:31,570
to the dose that it gets.

862
00:39:31,570 --> 00:39:34,090
So these little
crystals, aluminum oxide

863
00:39:34,090 --> 00:39:37,060
or some sort of assault
or whatever have you,

864
00:39:37,060 --> 00:39:43,240
something that creates
permanent ionized defects,

865
00:39:43,240 --> 00:39:46,210
they will relax when you
heat them, giving off light.

866
00:39:46,210 --> 00:39:48,610
And then you use a light
counter to tell how much dose

867
00:39:48,610 --> 00:39:50,380
this crystal has received.

868
00:39:50,380 --> 00:39:53,890
And by putting different filters
in the way for different pieces

869
00:39:53,890 --> 00:39:56,508
and looking at the light
coming from different parts,

870
00:39:56,508 --> 00:39:58,050
you can tell different
types of dose.

871
00:39:58,050 --> 00:40:00,700
So one works for
betas, because betas

872
00:40:00,700 --> 00:40:03,130
can get through the little
hole in the detector,

873
00:40:03,130 --> 00:40:06,430
whereas this may help you figure
out gamma rays or neutrons

874
00:40:06,430 --> 00:40:09,440
of different energies.

875
00:40:09,440 --> 00:40:11,830
And who here has seen
one of these ring badges?

876
00:40:11,830 --> 00:40:13,790
Yeah, so again, the
reactor trainees.

877
00:40:13,790 --> 00:40:14,780
Great.

878
00:40:14,780 --> 00:40:17,610
If you shake them, you
hear a little rattling.

879
00:40:17,610 --> 00:40:18,900
Try it next time.

880
00:40:18,900 --> 00:40:20,460
They're usually pretty loose.

881
00:40:20,460 --> 00:40:23,040
It's a cheap plastic
crappy casting

882
00:40:23,040 --> 00:40:25,848
with a thermal luminescent
crystal in the inside.

883
00:40:25,848 --> 00:40:26,640
So again, shake it.

884
00:40:26,640 --> 00:40:27,960
It should rattle.

885
00:40:27,960 --> 00:40:30,110
If it doesn't, the
crystal might be missing,

886
00:40:30,110 --> 00:40:33,740
and you should
probably get a new one.

887
00:40:33,740 --> 00:40:36,620
So when you read a TLD,
you use this fancy machine,

888
00:40:36,620 --> 00:40:39,350
all it does is heat
it very carefully,

889
00:40:39,350 --> 00:40:42,320
and allow the electrons that
are trapped at a higher energy

890
00:40:42,320 --> 00:40:45,840
to jump back down,
emitting visible light.

891
00:40:45,840 --> 00:40:46,340
That's it.

892
00:40:46,340 --> 00:40:48,410
We've seen this process before.

893
00:40:48,410 --> 00:40:50,810
What happens after the
photoelectric effect?

894
00:40:50,810 --> 00:40:52,670
Electrons fall down
an energy and release

895
00:40:52,670 --> 00:40:56,480
light in the form of
X-rays or visible light.

896
00:40:56,480 --> 00:40:58,947
Same thing.

897
00:40:58,947 --> 00:41:00,530
And then let's talk
about, how can you

898
00:41:00,530 --> 00:41:03,950
use dosimeters for dosimetry
in medical applications?

899
00:41:03,950 --> 00:41:06,440
And let's take the
example of proton beam

900
00:41:06,440 --> 00:41:09,800
therapy, the new and
more upcoming replacement

901
00:41:09,800 --> 00:41:11,330
to X-ray therapy.

902
00:41:11,330 --> 00:41:14,240
It relies on the fact that
the stopping power of protons

903
00:41:14,240 --> 00:41:18,050
is extremely low, until they
reach the end of their range,

904
00:41:18,050 --> 00:41:20,090
like we talked about here.

905
00:41:20,090 --> 00:41:23,360
So again, we use protons
as armor-piercing bullets

906
00:41:23,360 --> 00:41:25,400
to get through the
person, drilling

907
00:41:25,400 --> 00:41:27,800
a little hole in the
process, and exploding

908
00:41:27,800 --> 00:41:29,390
once they reach the tumor.

909
00:41:29,390 --> 00:41:30,680
It's a nice quirk of physics.

910
00:41:30,680 --> 00:41:33,830
It's really an elegant
use of the stuff in 22.01

911
00:41:33,830 --> 00:41:36,840
to do damage where
you want it to.

912
00:41:36,840 --> 00:41:39,872
There's all sorts of other
methods of cancer treatment.

913
00:41:39,872 --> 00:41:41,580
Let's say you're
simple, and you can just

914
00:41:41,580 --> 00:41:43,680
go with excision, which
means cutting it out.

915
00:41:43,680 --> 00:41:45,900
Chemotherapy, which is
a pretty nasty process,

916
00:41:45,900 --> 00:41:49,200
and is usually used as a
backup for radiation therapy

917
00:41:49,200 --> 00:41:51,620
to catch whatever else
might be floating.

918
00:41:51,620 --> 00:41:55,920
X-ray therapy, which is still
used a lot, but hopefully

919
00:41:55,920 --> 00:41:57,480
will get phased out a bit.

920
00:41:57,480 --> 00:42:01,710
Brachytherapy, where you
implant a little seed of a beta

921
00:42:01,710 --> 00:42:05,100
emitter into an area
near where the tumor is.

922
00:42:05,100 --> 00:42:08,685
Let's say you have an easy
route of entry, like that way.

923
00:42:08,685 --> 00:42:10,560
Then you can implant
one of these seeds right

924
00:42:10,560 --> 00:42:11,430
where the tumor is.

925
00:42:11,430 --> 00:42:14,110
But if you can't have
an easy route of entry,

926
00:42:14,110 --> 00:42:18,043
that's where proton
therapy comes in.

927
00:42:18,043 --> 00:42:19,710
And as we've talked
about X-ray therapy,

928
00:42:19,710 --> 00:42:23,700
if you want to damage the tumor
more than the rest of the brain

929
00:42:23,700 --> 00:42:25,320
or the rest of the
person, you have

930
00:42:25,320 --> 00:42:27,300
to come in from
different angles so

931
00:42:27,300 --> 00:42:29,400
that the sum of all
the dose to this target

932
00:42:29,400 --> 00:42:31,570
is less than anywhere else.

933
00:42:31,570 --> 00:42:34,560
And X-ray therapy tends
to do a lot of damage.

934
00:42:34,560 --> 00:42:37,530
Well, you hear of X-ray therapy
causing hair loss in people.

935
00:42:37,530 --> 00:42:39,760
Well, yeah.

936
00:42:39,760 --> 00:42:41,160
You're going through the head.

937
00:42:41,160 --> 00:42:45,150
It's not good for your
hair follicles, either.

938
00:42:45,150 --> 00:42:46,560
And then there's proton therapy.

939
00:42:46,560 --> 00:42:48,270
We've talked about
it before, but not

940
00:42:48,270 --> 00:42:49,740
in the strict medical sense.

941
00:42:49,740 --> 00:42:51,720
And actually I'm going
to reveal to you guys

942
00:42:51,720 --> 00:42:54,390
an invention that we've got out
of our department that might

943
00:42:54,390 --> 00:42:55,903
help this go a little better.

944
00:42:55,903 --> 00:42:58,320
The way it works is you start
with a cyclotron, which I've

945
00:42:58,320 --> 00:43:00,195
already explained,
something that accelerates

946
00:43:00,195 --> 00:43:03,175
charged particles
to about 250 MeV.

947
00:43:03,175 --> 00:43:05,550
And we have one of these across
the river at Mass General

948
00:43:05,550 --> 00:43:06,980
Hospital.

949
00:43:06,980 --> 00:43:09,740
Send them through
bending magnets,

950
00:43:09,740 --> 00:43:12,600
and bend them up so that
they hit the patient.

951
00:43:12,600 --> 00:43:16,400
Then you move the patient
on this gurney or table

952
00:43:16,400 --> 00:43:19,040
so that-- and the entryf
can rotate anywhere,

953
00:43:19,040 --> 00:43:20,930
to come in from any
entry point, minimize

954
00:43:20,930 --> 00:43:22,880
the dose to the
rest of the patient,

955
00:43:22,880 --> 00:43:24,300
while frying the tumor.

956
00:43:24,300 --> 00:43:26,760
AUDIENCE: Is that
a scale diagram?

957
00:43:26,760 --> 00:43:29,304
MICHAEL SHORT: Yep, quite big.

958
00:43:29,304 --> 00:43:32,290
Yeah.

959
00:43:32,290 --> 00:43:34,870
It's pretty to scale, yeah.

960
00:43:34,870 --> 00:43:38,630
So time on this instrument
runs in the thousands per hour.

961
00:43:38,630 --> 00:43:40,960
If you go through the back
door and know the folks that

962
00:43:40,960 --> 00:43:42,640
run the thing and
no one is not being

963
00:43:42,640 --> 00:43:43,907
used for cancer treatments.

964
00:43:43,907 --> 00:43:45,490
Proton therapy can
run in the hundreds

965
00:43:45,490 --> 00:43:46,490
of thousands of dollars.

966
00:43:46,490 --> 00:43:48,073
This is one of the
millions of reasons

967
00:43:48,073 --> 00:43:49,375
we have medical insurance.

968
00:43:49,375 --> 00:43:51,490
It's because when you
need it, you want it.

969
00:43:51,490 --> 00:43:55,280
And these cyclotrons
aren't cheap.

970
00:43:55,280 --> 00:43:56,780
The way they work
is pretty simple.

971
00:43:56,780 --> 00:44:00,770
You inject ionized particles
through these D magnets,

972
00:44:00,770 --> 00:44:04,070
and they go faster and faster
and faster every time they

973
00:44:04,070 --> 00:44:05,960
cross this electric field.

974
00:44:05,960 --> 00:44:08,630
They bend at larger
and larger tracks

975
00:44:08,630 --> 00:44:10,930
through these magnets as
their energy increases.

976
00:44:10,930 --> 00:44:13,280
Than they exit out the
other side, getting

977
00:44:13,280 --> 00:44:16,780
delivered to the patient.

978
00:44:16,780 --> 00:44:18,470
And why protons versus X-rays?

979
00:44:18,470 --> 00:44:20,870
Well, I made it
quick Desmos graph.

980
00:44:20,870 --> 00:44:22,280
To say, let's say
you started off

981
00:44:22,280 --> 00:44:25,430
with a equivalent dose
of protons and X-rays,

982
00:44:25,430 --> 00:44:28,680
and you're trying to get to
a 40 millimeter deep tumor.

983
00:44:28,680 --> 00:44:29,680
This is why.

984
00:44:29,680 --> 00:44:31,430
This is the amount of
dose that the X-rays

985
00:44:31,430 --> 00:44:33,710
would give compared
to the protons

986
00:44:33,710 --> 00:44:36,277
in this highlighted
tumor region.

987
00:44:36,277 --> 00:44:38,360
Then you look at the dose
where X-rays and protons

988
00:44:38,360 --> 00:44:39,652
give to the rest of the person.

989
00:44:39,652 --> 00:44:43,390
It should be
graphically obvious.

990
00:44:43,390 --> 00:44:45,540
And you can do some tricks
with proton therapy.

991
00:44:45,540 --> 00:44:49,320
If you have a lung tumor, you
can vary the energy and time

992
00:44:49,320 --> 00:44:52,320
at each point, such that
you give a uniform dose

993
00:44:52,320 --> 00:44:53,370
to the tumor.

994
00:44:53,370 --> 00:44:54,960
So you can move that
[? Bragg ?] peak

995
00:44:54,960 --> 00:44:59,040
by degrading the proton energy,
by putting filters in line

996
00:44:59,040 --> 00:45:00,090
with the beam.

997
00:45:00,090 --> 00:45:02,620
You don't tend to like to
change the energy of the beam.

998
00:45:02,620 --> 00:45:04,710
So you can put things in
the way of the protons

999
00:45:04,710 --> 00:45:06,270
to slow them down.

1000
00:45:06,270 --> 00:45:08,940
And because when the
stopping power is very low,

1001
00:45:08,940 --> 00:45:11,760
the proton speed's very
high, and forward scattering

1002
00:45:11,760 --> 00:45:14,490
is preferable, putting
things in the way of the beam

1003
00:45:14,490 --> 00:45:16,290
pretty much just
slows them down,

1004
00:45:16,290 --> 00:45:19,112
but doesn't change
their direction.

1005
00:45:19,112 --> 00:45:21,320
That assumption breaks down
when the energy gets low.

1006
00:45:21,320 --> 00:45:23,240
But when the energy gets low,
you better be in the tumor

1007
00:45:23,240 --> 00:45:23,910
anyway.

1008
00:45:23,910 --> 00:45:26,780
And you want them to change
direction and explode out

1009
00:45:26,780 --> 00:45:30,350
and blast everything in sight.

1010
00:45:30,350 --> 00:45:33,230
The problem with
proton therapy is

1011
00:45:33,230 --> 00:45:35,630
that humans are not
biological organisms

1012
00:45:35,630 --> 00:45:37,820
at static equilibrium.

1013
00:45:37,820 --> 00:45:39,190
In other words, they're alive.

1014
00:45:39,190 --> 00:45:40,690
They tend to move.

1015
00:45:40,690 --> 00:45:43,720
Breathing is something I
like to do every few seconds.

1016
00:45:43,720 --> 00:45:46,170
Swallowing, maybe once
every couple of minutes.

1017
00:45:46,170 --> 00:45:47,830
And most of your
organs move around

1018
00:45:47,830 --> 00:45:50,343
and dance without
you controlling them.

1019
00:45:50,343 --> 00:45:52,010
It's really hard if
you're trying to hit

1020
00:45:52,010 --> 00:45:54,350
a tumor on a moving target.

1021
00:45:54,350 --> 00:45:57,300
That is the main problem
with proton therapy.

1022
00:45:57,300 --> 00:46:00,710
The solution right now, I like
to call it spray and pray.

1023
00:46:00,710 --> 00:46:03,870
You fire into the person,
hope that things don't move.

1024
00:46:03,870 --> 00:46:05,350
We know that they do though.

1025
00:46:05,350 --> 00:46:07,580
Those proton beams
are very narrow.

1026
00:46:07,580 --> 00:46:10,010
And let's say, for
abdominal patients,

1027
00:46:10,010 --> 00:46:12,080
let's say you happen to
be digesting something.

1028
00:46:12,080 --> 00:46:14,750
Your intestines will just
go krschlock like that

1029
00:46:14,750 --> 00:46:16,617
and get lunch where it's going.

1030
00:46:16,617 --> 00:46:18,200
This is one of those
reasons that they

1031
00:46:18,200 --> 00:46:21,050
say don't eat anything
before these procedures.

1032
00:46:21,050 --> 00:46:23,510
If you're not actively
digesting things,

1033
00:46:23,510 --> 00:46:26,460
then your abdomen won't
be moving as much.

1034
00:46:26,460 --> 00:46:29,960
Thoracic patients, better known
as the lungs or your thorax,

1035
00:46:29,960 --> 00:46:31,760
if you're from France.

1036
00:46:31,760 --> 00:46:32,760
My wife likes to make--

1037
00:46:32,760 --> 00:46:34,010
I like to make fun of my wife.

1038
00:46:34,010 --> 00:46:34,552
That's right.

1039
00:46:34,552 --> 00:46:36,920
Because she still refers to
this region as the thorax.

1040
00:46:36,920 --> 00:46:39,230
And I was like, I am
not a giant beetle.

1041
00:46:39,230 --> 00:46:41,930
But it is the medical
term for this.

1042
00:46:41,930 --> 00:46:43,550
You tend to breathe.

1043
00:46:43,550 --> 00:46:45,240
And if you actually
measure how much

1044
00:46:45,240 --> 00:46:47,000
you move when you
breathe in and out--

1045
00:46:47,000 --> 00:46:48,833
let's say you're trying
to fry a lung tumor.

1046
00:46:48,833 --> 00:46:50,300
That's a tricky proposition.

1047
00:46:50,300 --> 00:46:53,550
So how do you keep
the protons on track?

1048
00:46:53,550 --> 00:46:56,910
Ideally, some dosimeter
would be able to determine

1049
00:46:56,910 --> 00:47:01,110
absolute dose, and
it would be able to--

1050
00:47:01,110 --> 00:47:04,320
where on this list
of things is--

1051
00:47:04,320 --> 00:47:06,540
oh, there's even more
things I'd want here.

1052
00:47:06,540 --> 00:47:08,430
So ideally, if you'd
want a proton dosimeter,

1053
00:47:08,430 --> 00:47:10,950
you want it to be able to
measure things, provide

1054
00:47:10,950 --> 00:47:16,050
some data, not be orientation
dependent, and things like not

1055
00:47:16,050 --> 00:47:18,600
be toxic, be cheap
to build, but also

1056
00:47:18,600 --> 00:47:22,380
be able to turn on and off if
the tumor moves out of range.

1057
00:47:22,380 --> 00:47:25,330
And this problem
hasn't been solved yet.

1058
00:47:25,330 --> 00:47:28,060
Existing dosimetry
methods include

1059
00:47:28,060 --> 00:47:31,480
making calculations and hoping,
which is what we do now.

1060
00:47:31,480 --> 00:47:33,760
We do complex Monte
Carlo calculations

1061
00:47:33,760 --> 00:47:35,980
based on scans of
the patient, try

1062
00:47:35,980 --> 00:47:38,000
and map out how much
energy is going to be lost

1063
00:47:38,000 --> 00:47:39,280
and where to go in.

1064
00:47:39,280 --> 00:47:40,930
There's conventional
port films, which

1065
00:47:40,930 --> 00:47:44,080
means you put a film on the
entry of the patient, which

1066
00:47:44,080 --> 00:47:46,390
gives you an idea of
where the beam is, but not

1067
00:47:46,390 --> 00:47:47,965
necessarily where the organ is.

1068
00:47:47,965 --> 00:47:49,840
Let me get into some
pictures of these things

1069
00:47:49,840 --> 00:47:51,310
so you know what they look like.

1070
00:47:51,310 --> 00:47:54,660
Anyone ever put one of
these in your mouth before?

1071
00:47:54,660 --> 00:47:57,370
The sort of electronic
dosimeters, the X-ray

1072
00:47:57,370 --> 00:47:58,870
imagers that you
get at the dentist,

1073
00:47:58,870 --> 00:48:00,850
you bite down on one
of these, and you

1074
00:48:00,850 --> 00:48:02,260
get X-rays of your teeth.

1075
00:48:02,260 --> 00:48:04,210
That's great if you have
a place to put them,

1076
00:48:04,210 --> 00:48:06,790
but doesn't quite work
for proton therapy.

1077
00:48:06,790 --> 00:48:08,290
There are tissue
equivalent gels,

1078
00:48:08,290 --> 00:48:12,700
where you can cast a person in
gel, fire in the proton beam,

1079
00:48:12,700 --> 00:48:14,495
and see how deep
it goes, and then

1080
00:48:14,495 --> 00:48:16,120
hope that your tissue
equivalent gel is

1081
00:48:16,120 --> 00:48:17,950
equivalent to the tissue.

1082
00:48:17,950 --> 00:48:20,680
Usually it's pretty good.

1083
00:48:20,680 --> 00:48:21,790
There's silicon diodes.

1084
00:48:21,790 --> 00:48:26,080
You can implant a tiny little
diode or other semiconductor

1085
00:48:26,080 --> 00:48:28,930
device near or in the
patient, and measure

1086
00:48:28,930 --> 00:48:31,660
the change in band
gap, or the voltage

1087
00:48:31,660 --> 00:48:35,350
required to turn on conduction
in the semiconductor.

1088
00:48:35,350 --> 00:48:37,470
The problem is you can
only use them once.

1089
00:48:37,470 --> 00:48:40,113
Once you irradiate a piece
of silicon, it's irradiated.

1090
00:48:40,113 --> 00:48:41,530
And then you would
have to take it

1091
00:48:41,530 --> 00:48:44,800
out and stick another
one in with a big needle

1092
00:48:44,800 --> 00:48:47,830
to keep going.

1093
00:48:47,830 --> 00:48:49,930
There's optically
stimulated luminescence,

1094
00:48:49,930 --> 00:48:51,430
which means protons hit stuff.

1095
00:48:51,430 --> 00:48:52,870
Stuff creates light.

1096
00:48:52,870 --> 00:48:54,760
Light can be measured
in real time.

1097
00:48:54,760 --> 00:48:59,190
So you could implant a
little crystal like this TLD

1098
00:48:59,190 --> 00:49:01,090
or Thermoluminescent
Dosimeter, attached

1099
00:49:01,090 --> 00:49:03,250
to a fiber optic cable.

1100
00:49:03,250 --> 00:49:06,220
And in that way, you can
measure the amount of light

1101
00:49:06,220 --> 00:49:07,390
and preamplify it.

1102
00:49:07,390 --> 00:49:09,190
PM means-- what is it--

1103
00:49:09,190 --> 00:49:11,110
Photo Multiplier tube.

1104
00:49:11,110 --> 00:49:14,320
And use electronics and
software to calculate that light

1105
00:49:14,320 --> 00:49:16,090
and turn it into dose.

1106
00:49:16,090 --> 00:49:19,690
Problem is, this scintillation,
it's not very strong.

1107
00:49:19,690 --> 00:49:22,090
There's a lot that can
go wrong between where

1108
00:49:22,090 --> 00:49:26,860
the radiation is done and
where it can be collected.

1109
00:49:26,860 --> 00:49:30,700
Also implanted MOSFETs are
these metal oxide semiconductor

1110
00:49:30,700 --> 00:49:32,650
field effect transistors.

1111
00:49:32,650 --> 00:49:33,850
Same problem.

1112
00:49:33,850 --> 00:49:37,035
You can look at the
change in difference--

1113
00:49:37,035 --> 00:49:38,410
I'm sorry, the
change in band gap

1114
00:49:38,410 --> 00:49:40,997
as you irradiate these things,
or in the MOSFET voltage.

1115
00:49:40,997 --> 00:49:42,580
But again, you can
only use them once.

1116
00:49:42,580 --> 00:49:45,025
It's not like you
can reset them.

1117
00:49:45,025 --> 00:49:46,400
So the problems
with all of these

1118
00:49:46,400 --> 00:49:48,957
is we don't know what
dose the tumor gets.

1119
00:49:48,957 --> 00:49:50,540
If we know how much
we need to fry it,

1120
00:49:50,540 --> 00:49:53,810
but we don't know if we fried
it, the cancer could recur.

1121
00:49:53,810 --> 00:49:56,360
Or it may not respond
to the radiation.

1122
00:49:56,360 --> 00:49:59,090
These are liability terms
to say it didn't work,

1123
00:49:59,090 --> 00:50:01,580
but you can't sue us,
because we don't know why.

1124
00:50:01,580 --> 00:50:02,960
And you don't know why.

1125
00:50:02,960 --> 00:50:06,170
Or you may apply too much
dose to the surrounding tissue

1126
00:50:06,170 --> 00:50:08,360
and induce secondary tumors.

1127
00:50:08,360 --> 00:50:10,550
This is one of those things
that's not talked about

1128
00:50:10,550 --> 00:50:12,440
very much, except
in medical circles,

1129
00:50:12,440 --> 00:50:15,627
and my entire family happens
to be in medical circles.

1130
00:50:15,627 --> 00:50:17,210
So they confirmed,
yeah, this is true.

1131
00:50:17,210 --> 00:50:20,460
We don't know how many
times, if you treat a tumor,

1132
00:50:20,460 --> 00:50:22,040
or do you induce
another one that

1133
00:50:22,040 --> 00:50:24,740
will pop up five years
later in the same site.

1134
00:50:24,740 --> 00:50:28,100
All you may think is, OK,
it recurred, despite being

1135
00:50:28,100 --> 00:50:29,285
dead for five years.

1136
00:50:29,285 --> 00:50:30,410
It might not have recurred.

1137
00:50:30,410 --> 00:50:33,030
It might have made a new one.

1138
00:50:33,030 --> 00:50:35,590
You don't know the
dose rate versus time.

1139
00:50:35,590 --> 00:50:39,630
The existing in situ methods
haven't worked very well.

1140
00:50:39,630 --> 00:50:41,040
So we had another
idea, that I'll

1141
00:50:41,040 --> 00:50:43,110
go in the last
negative 1 minutes,

1142
00:50:43,110 --> 00:50:46,680
what we call the integrating
F-Center Feedback Dosimeter.

1143
00:50:46,680 --> 00:50:49,290
We just got the
patent filed on this.

1144
00:50:49,290 --> 00:50:51,990
Not accepted, but filed
with the US Patent Office.

1145
00:50:51,990 --> 00:50:53,490
It's pretty simple.

1146
00:50:53,490 --> 00:50:57,270
You send in calibrated
light into a little crystal

1147
00:50:57,270 --> 00:51:01,470
of something that creates these
color centers, or F-centers.

1148
00:51:01,470 --> 00:51:03,930
When it's irradiated, look
at the light coming out.

1149
00:51:03,930 --> 00:51:05,130
See what's absorbed.

1150
00:51:05,130 --> 00:51:08,310
You know how much
dose you've received.

1151
00:51:08,310 --> 00:51:10,650
And so look at
these three parts.

1152
00:51:10,650 --> 00:51:13,420
A is just an alkali
halide salt, better known

1153
00:51:13,420 --> 00:51:15,490
as table salt, sodium chloride.

1154
00:51:15,490 --> 00:51:19,090
B is some biocompatible casing
so your body doesn't reject it.

1155
00:51:19,090 --> 00:51:23,140
Calibrated white light source,
fiber optic connection cables,

1156
00:51:23,140 --> 00:51:24,910
and a spectrometer to
read the absorption.

1157
00:51:24,910 --> 00:51:28,180
These can be little
compact USB spectrometers.

1158
00:51:28,180 --> 00:51:30,310
And it relies on what's
called F-centers.

1159
00:51:30,310 --> 00:51:34,060
When you irradiate ionic
materials, they change color.

1160
00:51:34,060 --> 00:51:36,910
These defects produced by,
let's say, blasting out

1161
00:51:36,910 --> 00:51:39,730
a chlorine ion or a
sodium or potassium ion

1162
00:51:39,730 --> 00:51:41,310
are optically active.

1163
00:51:41,310 --> 00:51:44,260
Because you get differing
regions of electron density.

1164
00:51:44,260 --> 00:51:46,600
And you absorb certain
wavelengths of light

1165
00:51:46,600 --> 00:51:47,950
changing their color.

1166
00:51:47,950 --> 00:51:49,960
If you then send calibrated
light through it,

1167
00:51:49,960 --> 00:51:53,150
you can tell what happened,
how much dose there was.

1168
00:51:53,150 --> 00:51:55,140
And F-center creation
versus radiation

1169
00:51:55,140 --> 00:51:57,000
is extremely well known.

1170
00:51:57,000 --> 00:51:59,610
We've actually done some
preliminary tests on the Dante

1171
00:51:59,610 --> 00:52:02,610
accelerator here to show that
the amount of dose that you

1172
00:52:02,610 --> 00:52:05,670
give in a fractional cancer
treatment on the order

1173
00:52:05,670 --> 00:52:09,690
of a kilogray or so does
cause the salt to respond very

1174
00:52:09,690 --> 00:52:11,460
strongly and produce a color.

1175
00:52:11,460 --> 00:52:13,770
And the best part is,
they relax on their own.

1176
00:52:13,770 --> 00:52:16,290
After anywhere from 5
seconds to a few hours,

1177
00:52:16,290 --> 00:52:17,970
the color just disappears.

1178
00:52:17,970 --> 00:52:19,380
Because the atomic
defects relax.

1179
00:52:19,380 --> 00:52:24,370
So you don't have to implant,
remove, reimplant, remove.

1180
00:52:24,370 --> 00:52:26,590
And you can enable
dose rate information

1181
00:52:26,590 --> 00:52:28,330
by putting multiple
salts in a row that

1182
00:52:28,330 --> 00:52:31,600
have different response
levels to these protons.

1183
00:52:31,600 --> 00:52:34,840
So by looking at the amount of
absorption in each wavelength,

1184
00:52:34,840 --> 00:52:37,210
you can tell not just the
dose, but the dose rate.

1185
00:52:37,210 --> 00:52:40,557
Calibrate your beam current.

1186
00:52:40,557 --> 00:52:42,390
And I'm going to skip
all the way to the end

1187
00:52:42,390 --> 00:52:43,780
to say how this would work.

1188
00:52:43,780 --> 00:52:47,160
So let's say you had one of
these IF2D dosimeters implanted

1189
00:52:47,160 --> 00:52:49,530
in your tumor, and
your heart was beating,

1190
00:52:49,530 --> 00:52:52,530
or your lungs were breathing,
or you were digesting something.

1191
00:52:52,530 --> 00:52:54,300
You could then feedback
this information

1192
00:52:54,300 --> 00:52:56,910
to the proton accelerator
to shut the beam off

1193
00:52:56,910 --> 00:52:59,010
when the tumor
moves out of range

1194
00:52:59,010 --> 00:53:02,560
and send in tiny little pulses
to say, hey, are you there?

1195
00:53:02,560 --> 00:53:06,930
Little micro second pulses to
say, microsecond of protons

1196
00:53:06,930 --> 00:53:08,230
isn't going to do much.

1197
00:53:08,230 --> 00:53:12,310
But if it senses the
IF2D back in range,

1198
00:53:12,310 --> 00:53:14,440
it then blasts continuously.

1199
00:53:14,440 --> 00:53:17,430
And as soon as the
IF2D says no more dose,

1200
00:53:17,430 --> 00:53:20,340
it starts just putting those
wake up pulses back on.

1201
00:53:20,340 --> 00:53:22,560
So this would be the
first feedback way

1202
00:53:22,560 --> 00:53:25,860
to apply proton therapy
without screwing it up.

1203
00:53:25,860 --> 00:53:28,890
You could also install
IF2D dosimeters

1204
00:53:28,890 --> 00:53:32,490
near the tumor,
outside the tumor,

1205
00:53:32,490 --> 00:53:35,490
and play the world's first
game of radioactive proton

1206
00:53:35,490 --> 00:53:36,630
Operation.

1207
00:53:36,630 --> 00:53:38,580
Don't hit the sides.

1208
00:53:38,580 --> 00:53:40,620
If you wonder if your
beam's on target,

1209
00:53:40,620 --> 00:53:43,260
you then steer it until it
doesn't hit any of the IF2Ds,

1210
00:53:43,260 --> 00:53:45,930
and you know you're right
through the gates on the tumor.

1211
00:53:45,930 --> 00:53:48,390
Very important for
certain sensitive tumors,

1212
00:53:48,390 --> 00:53:50,760
like chordomas,
spinal cord tumors,

1213
00:53:50,760 --> 00:53:55,650
which tend to happen in
infants and young children.

1214
00:53:55,650 --> 00:53:57,810
There's various ways
of treating those,

1215
00:53:57,810 --> 00:54:00,930
other than removal of the neck,
what you don't want to do.

1216
00:54:00,930 --> 00:54:02,912
They're extremely
difficult to operate on.

1217
00:54:02,912 --> 00:54:04,620
You don't want to give
radiation therapy.

1218
00:54:04,620 --> 00:54:07,050
So highly targeted
proton therapy

1219
00:54:07,050 --> 00:54:08,910
like this, making
sure that you fry

1220
00:54:08,910 --> 00:54:10,560
the tumor without
the surrounding

1221
00:54:10,560 --> 00:54:13,740
spinal cord and medulla,
would be probably

1222
00:54:13,740 --> 00:54:15,770
the way to go for this.

1223
00:54:15,770 --> 00:54:18,060
So I'm going to stop there,
because it's exactly 10.

1224
00:54:18,060 --> 00:54:20,000
It's also the perfect
stopping point.

1225
00:54:20,000 --> 00:54:24,138
And we'll pick up with
background radiation tomorrow.

1226
00:54:24,138 --> 00:54:25,930
I also want to let you
guys know that we'll

1227
00:54:25,930 --> 00:54:30,550
be doing our nuclear activation
analysis irradiations Friday

1228
00:54:30,550 --> 00:54:33,910
at the beginning of recitation,
and we'll finish up recitation

1229
00:54:33,910 --> 00:54:36,360
by doing the exam review.