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MICHAEL SHORT: Hey guys.

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So quick announcement, we're
not doing nuclear activation

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analysis today,
because the valve that

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shoots the rabbits
into the reactor

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broke and needs to be repaired.

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So we'll likely just
do this next Friday.

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And instead, we'll have
the whole recitation

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for exam review,
like I think we'd

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originally, originally planned.

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I also want to say thanks to
whoever said, please write

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lecture notes for this class.

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It's something I think
needs to be done.

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And I just now biked
back from meeting

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with a publisher, or
a potential publisher,

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to actually get this done.

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Because as I think as
you guys have seen,

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there's no one reading that
does this course justice.

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There are some
that are too easy,

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there are some
that are too hard.

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And there are giant
pieces missing,

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like most of what we're
going to go into today--

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sources of background radiation.

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And where do cosmic rays
come from, and what are they?

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So thanks to whoever said
that, because it spurred me off

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on a let's make this into
a book kind of thing.

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Want to quickly review
what we did last time.

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We went over all the different
units of dose and radiation

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exposure, from the roentgen--

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which is pretty much just valid
for those measurements in air.

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And I realized that yesterday
I brought in the civil defense

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dosimeter and passed
it to one person,

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and we didn't
continue bringing it.

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So I'll bring it to recitation.

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It's not in my bag.

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There is the unit
of the gray, which

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is just joules per kilogram.

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Which you can
calculate from stopping

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power or exponential
attenuation equations.

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This is where you
start, because it's

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how you get from
the world of physics

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to the world of biology.

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Into units of increased
risk, or sieverts,

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which is just gray times a
bunch of quality factors, which

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are either tabulated, or I'd
like to see somewhat better

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calculated.

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They are calculated sometimes,
but by empirical relations,

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because that's
usually good enough.

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Biomeasurements tend
to be pretty sloppy,

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and I'm not that upset that
these are empirical relations.

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I'm going to skip way ahead
past the detector stuff.

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We didn't quite finish
up the IF2D idea.

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I think this is where we
ended last time, where

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we were talking about
how do you detect dose

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during cancer treatment.

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And I was outlining one proposed
way that we're thinking of.

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Using this F-center
based dosimeter,

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which changes color
when it gets irradiated,

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you can implant it in the tumor.

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And as it moves from things
like breathing or swallowing,

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you could feedback
to the proton beam,

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and only irradiate
when it's in range.

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Or play nuclear operation,
and try not to hit the sides.

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However, whatever
you want to do.

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And there's multiple
implantation options for this.

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We've thought about things
like implanting a fiber optic

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cable into the tumor,
and then having a port

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on the side of you that could
do some in body spectrometry,

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which would be pretty cool.

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Could also put it all in a chip.

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You could have the emitter--

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either a broadband
or single color LED--

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the F-center, and the
spectrometer all in a chip

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that's implanted.

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And with radio frequency
power transfer,

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so you don't need to
put a fiber optic port

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and plug it into
the side of you.

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Or however it goes.

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And what we're doing
next in this development

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is nailing down what color
change is given by what dose--

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so the physics.

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Develop an on-chip version.

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Find a bio-compatible casing.

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We've done the IP part,
which is pretty cool.

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As you can see with
patent office at least

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has taken in the application.

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But it's neat that you need
to know pretty much everything

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you learned at MIT to pull
off a project like this.

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From the nuclear physics
stuff, to the material science,

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to the 22.071 electronics, to
the medical stuff for biology,

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to the financial stuff for econ.

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In order to pull off
an actual nuclear start

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up project like this, you need
everything you learn here.

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00:04:01,075 --> 00:04:03,720
Which is kind of
a neat case study.

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00:04:03,720 --> 00:04:06,980
But now let's get back into
what does a sievert really mean

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in terms of increased risk?

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Usually means the
increased risk of some sort

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of long-term biological
effect, whether it's cancer

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or some other genetic
effects-- let's say mutations--

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anything that would take
a while to manifest,

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and would manifest by slow
but steady cell division.

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And if you notice the
difference between adults

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and whole population,
let's see--

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yeah, sorry.

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You can see right
here that these--

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not very much dose.

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Let's say in the realm
of 10 to the minus 2

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sieverts can give you some
increased risk for cancer

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or some other effect.

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So we're talking on the
realm of 40 millisieverts

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or so would give you some
additional cancer risk.

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That's not a lot of dose.

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That's up to about the limit
of the occupational dose

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that you're allowed.

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So when we talk about
how much is too much,

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I've taken some excerpts
from this Committee

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on Radiation
Protection document.

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This is from Turner,
but the entire document,

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00:05:06,720 --> 00:05:09,240
as I mentioned, is up on
the learning module site.

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So you guys can see the actual
verbiage where this is defined.

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So your lifetime
dose should never

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exceed in tens of millisieverts
the value of age in years.

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Which means in some years if
you get a little bit less dose,

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you can get a
little bit more dose

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and still be
considered safe or not

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have any appreciable
increased risk.

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And while you're
working, you should never

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get more than about 50
millisieverts in a given year.

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How was it for
radiation workers?

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So for you guys,
what dose are you

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allowed per year
working at the reactor?

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AUDIENCE: About
five rem per year.

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MICHAEL SHORT:
Five rem per year,

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which is 50 millisieverts.

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Awesome, so it's--

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AUDIENCE: [INAUDIBLE] to
your eyes [INAUDIBLE]..

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MICHAEL SHORT: Oh sure, yeah.

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To jump back to that, if you're
saying that there's actually

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tabulated differences
for different organs,

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that's where they come from.

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Let's say you can take less
radiation to the same organ

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and get the same
dose in sieverts

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measured in equivalent risk.

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So I wouldn't be surprised
if these are the organs

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that you're not allowed
to irradiate as much.

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AUDIENCE: [INAUDIBLE].

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MICHAEL SHORT: I'm surprised
the eye isn't here.

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Does it say retina anywhere?

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Oh, OK.

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Well that's just one table.

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It's not necessarily
the complete answer.

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Yeah, so 50 millisieverts
isn't that much.

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Although if you think of it in
the old xkcd units of banana

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equivalent dose, eating
a banana gives you

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about 0.1 microsieverts.

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So you would have to eat
50,000 bananas in a year--

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no, I'm sorry, 500,000 bananas
in order to incur that.

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Well yeah, I was talking
to someone at dinner

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last night about
the banana burning

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experiment where we measured
the activity in becquerels.

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And then we can calculate
how much dose in sieverts

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it would take.

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And he said, how
many bananas would it

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take to get some
increased cancer risk?

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About double this.

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It would take about
a million bananas

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to give you about
100 millisieverts.

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And I said, you know
what else it would cost?

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And he goes, 100 millisieverts.

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No shit.

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And I said, that's right.

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Yeah.

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Yeah, he totally
didn't plan that,

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but it just worked out that way.

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Yeah.

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And then how much is too much?

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Let's say for the general public
for a background for excluding

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things like natural background
and medical exposures,

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you're not supposed to get about
more than one millisievert just

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walking about outside.

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And you don't tend to
get that much more.

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Why are medical exposures not
included, despite them being

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pretty radioactive procedures?

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Yeah?

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AUDIENCE: Because
they're very targeted.

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MICHAEL SHORT:
They are targeted,

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and so they could give a lot
of dose to certain organs.

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But the amount of
dose isn't necessarily

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00:08:00,540 --> 00:08:03,240
why we don't count
medical procedures.

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00:08:03,240 --> 00:08:05,016
Anyone have any idea?

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00:08:05,016 --> 00:08:05,796
Yeah.

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00:08:05,796 --> 00:08:08,004
AUDIENCE: Was it because
usually you wear a lead vest

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00:08:08,004 --> 00:08:09,690
if you're getting an X-ray?

200
00:08:09,690 --> 00:08:12,190
MICHAEL SHORT: In some cases,
like if you go to the dentist,

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00:08:12,190 --> 00:08:13,190
you'll get a lead X-ray.

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00:08:13,190 --> 00:08:17,200
But let's say you
get a chest X-ray.

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00:08:17,200 --> 00:08:21,400
Why don't we care that a chest
X-ray is way more than you get?

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Because these things
tend to save lives.

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00:08:23,840 --> 00:08:28,090
So you're absolutely willing
to get extra radiation exposure

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00:08:28,090 --> 00:08:30,640
that may have a delayed effect
if the immediate effect is

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00:08:30,640 --> 00:08:32,520
to save your life.

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00:08:32,520 --> 00:08:33,570
You had a question?

209
00:08:33,570 --> 00:08:35,539
Or no.

210
00:08:35,539 --> 00:08:36,159
OK.

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00:08:36,159 --> 00:08:37,830
Yeah, so we don't
count medical things

212
00:08:37,830 --> 00:08:41,500
because chances are you're
doing them to improve or save

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00:08:41,500 --> 00:08:42,000
your life.

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00:08:42,000 --> 00:08:43,860
So what's a little
bit of radiation

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00:08:43,860 --> 00:08:46,800
compared to let's say finding
the blood clot or the aneurysm

216
00:08:46,800 --> 00:08:48,600
or whatever it would take?

217
00:08:51,140 --> 00:08:52,310
And then how much is enough?

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00:08:52,310 --> 00:08:53,932
AUDIENCE: Yeah,
that's the table.

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00:08:53,932 --> 00:08:56,390
MICHAEL SHORT: This is the
table that you're familiar with?

220
00:08:56,390 --> 00:08:56,890
Yeah.

221
00:08:56,890 --> 00:08:58,910
They actually talk about
the lens of the eye.

222
00:08:58,910 --> 00:09:01,220
And that's a heftier dose.

223
00:09:01,220 --> 00:09:03,900
But also, the lens of the eye
is not a very massive organ.

224
00:09:03,900 --> 00:09:07,820
So this would mean do not stick
remaining eye in neutron beam,

225
00:09:07,820 --> 00:09:09,730
right?

226
00:09:09,730 --> 00:09:11,240
Or you've seen that
sticker, do not

227
00:09:11,240 --> 00:09:14,270
stare into a laser
with remaining eye.

228
00:09:14,270 --> 00:09:17,030
Yeah, the same goes for the
neutron beam ports coming out

229
00:09:17,030 --> 00:09:18,170
of the reactor.

230
00:09:18,170 --> 00:09:22,460
But the lens of the eye can take
a fair bit more dose per unit

231
00:09:22,460 --> 00:09:24,890
mass than the whole body.

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00:09:24,890 --> 00:09:28,260
The lens of the eye is not a
particularly fast developing

233
00:09:28,260 --> 00:09:28,760
tissue.

234
00:09:28,760 --> 00:09:32,390
It can cloud up with an insane
amount of radiation exposure.

235
00:09:32,390 --> 00:09:35,450
That would take a lot more
than 150 millisieverts to do,

236
00:09:35,450 --> 00:09:36,200
though.

237
00:09:36,200 --> 00:09:37,970
And then things like
500 millisieverts

238
00:09:37,970 --> 00:09:39,680
for skin, hands, feet.

239
00:09:39,680 --> 00:09:42,260
Pretty much just groups of
muscle, bone, and dead skin

240
00:09:42,260 --> 00:09:46,250
that not much is
going on biologically.

241
00:09:46,250 --> 00:09:49,000
Blood's flowing through
it, but that's about it.

242
00:09:49,000 --> 00:09:53,150
And notice that the regulations
do differ a little bit,

243
00:09:53,150 --> 00:09:55,280
but on the whole,
they're fairly similar.

244
00:09:55,280 --> 00:09:58,310
Same for the eye, same for
the feet, same for the year.

245
00:09:58,310 --> 00:10:00,030
Cumulative is a
little different.

246
00:10:00,030 --> 00:10:02,420
This says 10
millisieverts times age.

247
00:10:02,420 --> 00:10:04,358
This allows you a
little bit more.

248
00:10:04,358 --> 00:10:05,900
Whichever recommendations
you follow,

249
00:10:05,900 --> 00:10:08,000
they're all pretty similar.

250
00:10:08,000 --> 00:10:09,710
And our knowledge
of how much dose

251
00:10:09,710 --> 00:10:12,260
leads to how much
risk hasn't changed

252
00:10:12,260 --> 00:10:15,440
a ton in the last decade or so.

253
00:10:15,440 --> 00:10:18,280
There's been all sorts of
arguments for or against it.

254
00:10:18,280 --> 00:10:21,020
Has anyone heard of this
LNT or Linear No Threshold

255
00:10:21,020 --> 00:10:24,893
model of dose versus risk?

256
00:10:24,893 --> 00:10:26,310
This is something
we'll talk a lot

257
00:10:26,310 --> 00:10:27,690
about on the last day of class.

258
00:10:27,690 --> 00:10:29,490
This is the theory
that the amount

259
00:10:29,490 --> 00:10:32,070
of risk versus the
amount of dose is linear.

260
00:10:32,070 --> 00:10:35,580
And no threshold means that
every little bit of dose

261
00:10:35,580 --> 00:10:38,230
gives you additional risk.

262
00:10:38,230 --> 00:10:41,580
This is not supported
very much by science.

263
00:10:41,580 --> 00:10:43,950
I'd say it's not
supported by science.

264
00:10:43,950 --> 00:10:46,980
The converse argument is also
not supported by science.

265
00:10:46,980 --> 00:10:49,980
We just don't have the
statistics at super low doses

266
00:10:49,980 --> 00:10:51,720
to say what happens.

267
00:10:51,720 --> 00:10:55,260
But the official recommendation
is that there is a unit of dose

268
00:10:55,260 --> 00:11:01,840
that we define as nothing,
and it's 0.01 millisieverts--

269
00:11:01,840 --> 00:11:06,050
about 100 bananas--
per event, let's say--

270
00:11:06,050 --> 00:11:09,730
yeah, where does it say--
yeah, per source or practice.

271
00:11:09,730 --> 00:11:11,950
So eating 100 bananas
in one sitting

272
00:11:11,950 --> 00:11:15,100
is considered to give you
zero additional risk according

273
00:11:15,100 --> 00:11:16,840
to the official guidelines.

274
00:11:16,840 --> 00:11:18,610
So the guidelines
put in place do not

275
00:11:18,610 --> 00:11:20,680
follow the linear
no threshold model.

276
00:11:20,680 --> 00:11:23,440
But anyone that would claim
that one or the other model

277
00:11:23,440 --> 00:11:26,500
is absolutely correct has
either got a huge sample

278
00:11:26,500 --> 00:11:28,210
size of people that
we don't know about,

279
00:11:28,210 --> 00:11:30,280
or is probably
extrapolating beyond what

280
00:11:30,280 --> 00:11:32,630
the data will tell them.

281
00:11:32,630 --> 00:11:35,400
So you'll see this argument
flaring up quite a bit.

282
00:11:35,400 --> 00:11:37,900
For the last day of class we'll
have you read some arguments

283
00:11:37,900 --> 00:11:40,623
for and against the linear
no threshold model that

284
00:11:40,623 --> 00:11:42,040
aren't just blogs
on the internet,

285
00:11:42,040 --> 00:11:43,760
but they're actual
published articles

286
00:11:43,760 --> 00:11:45,250
that have passed peer review.

287
00:11:45,250 --> 00:11:47,042
And it's really hard
to tell exactly what's

288
00:11:47,042 --> 00:11:49,062
going on at low doses.

289
00:11:49,062 --> 00:11:50,770
But meanwhile, let's
focus on what you do

290
00:11:50,770 --> 00:11:52,870
get that we can measure.

291
00:11:52,870 --> 00:11:57,220
The actual contribution from
background levels is about 50%

292
00:11:57,220 --> 00:11:58,300
radon.

293
00:11:58,300 --> 00:12:01,330
This is a natural decay
product of radium.

294
00:12:01,330 --> 00:12:02,440
It's just everywhere.

295
00:12:02,440 --> 00:12:03,550
It's here right now.

296
00:12:03,550 --> 00:12:05,643
It's all through the atmosphere.

297
00:12:05,643 --> 00:12:07,060
This is why you
want your basement

298
00:12:07,060 --> 00:12:09,280
to be rather well
ventilated, because it's

299
00:12:09,280 --> 00:12:11,470
a heavy noble gas
that accumulates down

300
00:12:11,470 --> 00:12:13,678
in unventilated basements.

301
00:12:13,678 --> 00:12:15,220
So you don't actually
want your house

302
00:12:15,220 --> 00:12:16,887
to be sealed up super
tight, because you

303
00:12:16,887 --> 00:12:18,610
can have radon accumulation.

304
00:12:18,610 --> 00:12:21,610
Especially if you happen to
live near a granite deposit

305
00:12:21,610 --> 00:12:24,370
or on granite bedrock-- which
everyone in New Hampshire

306
00:12:24,370 --> 00:12:25,090
does--

307
00:12:25,090 --> 00:12:27,010
radon levels are
a little higher.

308
00:12:27,010 --> 00:12:28,510
There's actually a
story about a guy

309
00:12:28,510 --> 00:12:30,910
that used to work at a
nuclear plant somewhere

310
00:12:30,910 --> 00:12:31,660
in Pennsylvania.

311
00:12:31,660 --> 00:12:35,080
I don't know where, but he lived
on top of a pretty good granite

312
00:12:35,080 --> 00:12:38,680
deposit that was a few parts
per million radium more.

313
00:12:38,680 --> 00:12:40,930
So the radon levels in his
house or in his basement

314
00:12:40,930 --> 00:12:43,450
were much, much higher
than would normally

315
00:12:43,450 --> 00:12:44,880
be allowed for background.

316
00:12:44,880 --> 00:12:46,630
And this guy used to
set off the radiation

317
00:12:46,630 --> 00:12:49,220
alarms coming into work.

318
00:12:49,220 --> 00:12:51,350
Then he would breathe
the nice clean radiation

319
00:12:51,350 --> 00:12:55,010
free air in the plant and go out
without setting off the alarm.

320
00:12:55,010 --> 00:12:56,880
Eventually something
had to be done.

321
00:12:56,880 --> 00:12:59,450
I don't actually know what
was done, but if any of you

322
00:12:59,450 --> 00:13:02,670
can find that original story,
that would be pretty cool.

323
00:13:02,670 --> 00:13:05,940
Cosmic rays, another source
that you can't shield from,

324
00:13:05,940 --> 00:13:07,740
is about another 10%.

325
00:13:07,740 --> 00:13:10,650
And we'll talk a lot about
where these things come from.

326
00:13:10,650 --> 00:13:13,530
Terrestrial radiation, well
we'll count that as stuff

327
00:13:13,530 --> 00:13:16,160
in the soil, stuff
in the cinder block.

328
00:13:16,160 --> 00:13:18,990
Wood happens to be a fairly
radioactive substance

329
00:13:18,990 --> 00:13:21,090
pound for pound, but it's
not very dense compared

330
00:13:21,090 --> 00:13:23,320
to things like brick or--

331
00:13:23,320 --> 00:13:26,340
well, banana ashes is probably
about the same as wood.

332
00:13:26,340 --> 00:13:28,695
Internal, coming from you.

333
00:13:28,695 --> 00:13:30,570
You'll have this on
problems at number eight.

334
00:13:30,570 --> 00:13:34,170
Because you all now know your
internal radioactivity thanks

335
00:13:34,170 --> 00:13:36,210
to going to environmental
health and safety.

336
00:13:36,210 --> 00:13:39,750
Did anyone see anything
disconcerting in your spectra,

337
00:13:39,750 --> 00:13:43,350
other than a tiny
little potassium peak?

338
00:13:43,350 --> 00:13:45,500
Anyone?

339
00:13:45,500 --> 00:13:47,600
I'd say, ah, it's too bad.

340
00:13:47,600 --> 00:13:50,750
But that's great, especially
for you guys that work

341
00:13:50,750 --> 00:13:52,670
at the reactor.

342
00:13:52,670 --> 00:13:53,415
Medical X-rays.

343
00:13:53,415 --> 00:13:55,790
It's assumed that everyone
gets a couple of these a year.

344
00:13:55,790 --> 00:13:59,240
You all go to the dentist
and look for cavities.

345
00:13:59,240 --> 00:14:02,660
You break something, you may get
an X-ray of your hand or foot.

346
00:14:02,660 --> 00:14:05,940
And this is let's say an average
amount of medical X-rays.

347
00:14:05,940 --> 00:14:10,070
Then a little bit of stuff
leftover, consumer products.

348
00:14:10,070 --> 00:14:12,470
This isn't counting
things like Fiestaware,

349
00:14:12,470 --> 00:14:14,690
those orange glazed
plates and bowls

350
00:14:14,690 --> 00:14:19,770
that were painted with a
uranium based neon orange paint.

351
00:14:19,770 --> 00:14:23,270
So we also don't tend to
drink from Revigators anymore.

352
00:14:23,270 --> 00:14:25,878
Has anyone ever seen or
heard of a Revigator?

353
00:14:25,878 --> 00:14:27,790
AUDIENCE: Yeah, was this
in the '50s or '60s?

354
00:14:27,790 --> 00:14:29,360
MICHAEL SHORT: Or
even earlier, yeah.

355
00:14:29,360 --> 00:14:31,400
So back in the
'20s, people would

356
00:14:31,400 --> 00:14:34,580
put radium ore in these
containers and pour water in it

357
00:14:34,580 --> 00:14:36,620
and say, natural
radioactivity gets in.

358
00:14:36,620 --> 00:14:43,040
It cures croup or the Jimmy
legs or astigmatoid rheumatism,

359
00:14:43,040 --> 00:14:46,460
or whatever other quack
diseases there were in the '20s.

360
00:14:46,460 --> 00:14:49,130
You can still find them
on eBay, and that's not

361
00:14:49,130 --> 00:14:51,730
accounted for in today's
consumer products.

362
00:14:51,730 --> 00:14:54,975
But this all accumulates
the amount of dose

363
00:14:54,975 --> 00:14:56,350
that you tend to
get on your own.

364
00:14:56,350 --> 00:14:58,810
You might get a couple of
millisieverts a year of dose

365
00:14:58,810 --> 00:15:02,160
just from background, especially
depending on where you are.

366
00:15:02,160 --> 00:15:03,210
And the big one--

367
00:15:03,210 --> 00:15:05,850
whose spectrum I think you're
all familiar with by now--

368
00:15:05,850 --> 00:15:07,110
is that of radon.

369
00:15:07,110 --> 00:15:10,910
Because we saw most of
these peaks in the bananas.

370
00:15:10,910 --> 00:15:14,450
Anyone have any idea why you
would find so many radon decay

371
00:15:14,450 --> 00:15:15,800
products in bananas?

372
00:15:21,920 --> 00:15:23,360
Given that radon's
everywhere, we

373
00:15:23,360 --> 00:15:28,190
did notice elevated levels
of specifically bismuth 214

374
00:15:28,190 --> 00:15:32,810
and actinium I think 228
was the isotope we saw.

375
00:15:32,810 --> 00:15:35,420
Where would those come from?

376
00:15:35,420 --> 00:15:35,920
The what?

377
00:15:35,920 --> 00:15:36,880
AUDIENCE: The soil.

378
00:15:36,880 --> 00:15:38,230
MICHAEL SHORT: Absolutely, yeah.

379
00:15:38,230 --> 00:15:40,147
Whatever radium's coming
out from the bedrock,

380
00:15:40,147 --> 00:15:42,250
that radon has to come
up through the soil.

381
00:15:42,250 --> 00:15:44,530
If that happens to
decay in the soil,

382
00:15:44,530 --> 00:15:46,990
it makes lead,
bismuth, polonium,

383
00:15:46,990 --> 00:15:50,560
other heavy metals that are
taken by the plant's tissues.

384
00:15:50,560 --> 00:15:53,320
In addition, radon
daughter products

385
00:15:53,320 --> 00:15:56,257
can plate out on the
leaves themselves.

386
00:15:56,257 --> 00:15:58,090
So this is one of those
reasons that smoking

387
00:15:58,090 --> 00:16:00,160
is such a bad thing to do.

388
00:16:00,160 --> 00:16:02,200
Aside from the
chemical effects, you

389
00:16:02,200 --> 00:16:05,140
have giant fields of
high surface area tobacco

390
00:16:05,140 --> 00:16:07,250
that you then
concentrate and dry up

391
00:16:07,250 --> 00:16:08,500
into these tiny little sticks.

392
00:16:08,500 --> 00:16:11,230
You have an enormous
amount of leaf surface area

393
00:16:11,230 --> 00:16:14,530
and dry vegetation that has
taken all these radon daughter

394
00:16:14,530 --> 00:16:15,430
products.

395
00:16:15,430 --> 00:16:17,740
So most the dose
you get from smoking

396
00:16:17,740 --> 00:16:21,040
is lead, bismuth,
polonium, actinium, radium.

397
00:16:21,040 --> 00:16:22,360
Alpha emitters.

398
00:16:22,360 --> 00:16:25,360
As we saw last
time, to remind you

399
00:16:25,360 --> 00:16:31,030
guys of the quality factor
for alpha particles,

400
00:16:31,030 --> 00:16:33,050
it's as big as it gets.

401
00:16:33,050 --> 00:16:34,250
Anyone remember why that is?

402
00:16:38,640 --> 00:16:41,210
Why are alphas so damaging if
they get into your tissues?

403
00:16:41,210 --> 00:16:42,583
AUDIENCE: Because they're big.

404
00:16:42,583 --> 00:16:44,750
MICHAEL SHORT: They are
big, so they have high mass.

405
00:16:44,750 --> 00:16:45,450
And?

406
00:16:45,450 --> 00:16:46,370
AUDIENCE: Short range.

407
00:16:46,370 --> 00:16:47,745
MICHAEL SHORT:
Short range coming

408
00:16:47,745 --> 00:16:50,780
from their high relative charge.

409
00:16:50,780 --> 00:16:52,820
They have quite
high stopping power.

410
00:16:52,820 --> 00:16:54,770
And they will deposit
a lot of energy

411
00:16:54,770 --> 00:16:57,240
very close to where
they are emitted.

412
00:16:57,240 --> 00:16:58,460
So their range is very small.

413
00:16:58,460 --> 00:17:01,233
So that armor piercing
bullet analogy

414
00:17:01,233 --> 00:17:03,650
comes to just an armor piercing
bullet that explodes right

415
00:17:03,650 --> 00:17:05,420
out of the barrel of the gun.

416
00:17:05,420 --> 00:17:09,190
And they do quite a bit
of radiation damage.

417
00:17:09,190 --> 00:17:13,449
We jump back to the right slide
without inducing a seizure.

418
00:17:15,980 --> 00:17:18,500
I think we've looked before
at the radon decay chain.

419
00:17:18,500 --> 00:17:20,300
This is a simplified
version, because there

420
00:17:20,300 --> 00:17:22,640
are different branches or
different possibilities

421
00:17:22,640 --> 00:17:25,849
for decay, but some of them
have extremely low percentages.

422
00:17:25,849 --> 00:17:27,950
So this one's
simplified quite a bit.

423
00:17:27,950 --> 00:17:31,670
But it is whenever radon
decays, it gives off

424
00:17:31,670 --> 00:17:33,170
a bunch of alpha
and beta emitters

425
00:17:33,170 --> 00:17:37,970
that last anywhere from minutes
or seconds to days and so.

426
00:17:37,970 --> 00:17:40,220
For every radon atom
that you absorb,

427
00:17:40,220 --> 00:17:42,740
you end up getting four
or five alphas and betas,

428
00:17:42,740 --> 00:17:46,680
depending on how long it
stays into your system.

429
00:17:46,680 --> 00:17:48,520
And then mapping
out radon in the US.

430
00:17:48,520 --> 00:17:52,420
You have quite different
amount of radon dose

431
00:17:52,420 --> 00:17:54,380
depending on where you are.

432
00:17:54,380 --> 00:17:56,170
And I wanted to skip
ahead and overlay

433
00:17:56,170 --> 00:17:58,420
a couple of maps of the US.

434
00:17:58,420 --> 00:18:01,630
So this is a terrestrial--

435
00:18:01,630 --> 00:18:03,770
oh, I'm sorry,
that's the wrong one.

436
00:18:03,770 --> 00:18:05,260
Let's just look
at this one, yeah.

437
00:18:05,260 --> 00:18:06,700
Anyone notice any patterns here?

438
00:18:06,700 --> 00:18:08,590
Where do you tend to
get the most radon?

439
00:18:11,190 --> 00:18:14,070
What sort of features
would one live near when

440
00:18:14,070 --> 00:18:16,656
you get a lot of radon dose?

441
00:18:16,656 --> 00:18:17,600
AUDIENCE: Mountains.

442
00:18:19,785 --> 00:18:21,910
MICHAEL SHORT: Mountains,
which tend to be made of?

443
00:18:21,910 --> 00:18:22,577
AUDIENCE: Rocks.

444
00:18:22,577 --> 00:18:27,010
MICHAEL SHORT: Rocks, which
tend to contain a lot of radium.

445
00:18:27,010 --> 00:18:29,080
Especially granite
and other such rocks.

446
00:18:29,080 --> 00:18:33,430
The Conway granite, named after
up in Conway, New Hampshire,

447
00:18:33,430 --> 00:18:37,780
is about 52 parts per
million uranium or radium.

448
00:18:37,780 --> 00:18:39,550
So it's a fairly toasty rock.

449
00:18:39,550 --> 00:18:43,150
You can actually tell there
with your Geiger counter,

450
00:18:43,150 --> 00:18:45,100
if its count long
enough, that there

451
00:18:45,100 --> 00:18:49,060
is a little bit of radioactive
ore in that Conway granite.

452
00:18:49,060 --> 00:18:50,870
Not nearly enough
to matter at all,

453
00:18:50,870 --> 00:18:53,453
and certainly not enough to stop
you from making fancy kitchen

454
00:18:53,453 --> 00:18:54,238
countertops.

455
00:18:54,238 --> 00:18:55,780
But I wonder if
folks would buy those

456
00:18:55,780 --> 00:18:58,990
if they knew that there was 52
parts per million of something

457
00:18:58,990 --> 00:19:01,630
with a half life
of 9 billion years.

458
00:19:01,630 --> 00:19:03,863
I somehow think it
would matter to people,

459
00:19:03,863 --> 00:19:04,780
but it really doesn't.

460
00:19:04,780 --> 00:19:07,930
AUDIENCE: They put the radiation
symbol on it [INAUDIBLE]

461
00:19:07,930 --> 00:19:09,933
MICHAEL SHORT:
Yes, engrave that.

462
00:19:09,933 --> 00:19:12,100
If they made the radiation
symbol a little induction

463
00:19:12,100 --> 00:19:14,200
stove, that would
be pretty slick.

464
00:19:14,200 --> 00:19:15,640
Yeah.

465
00:19:15,640 --> 00:19:17,600
And then in terms of
relative radon risk,

466
00:19:17,600 --> 00:19:18,910
how much actually matters?

467
00:19:18,910 --> 00:19:19,900
I like this graph.

468
00:19:19,900 --> 00:19:22,600
Despite being difficult
to read, it actually

469
00:19:22,600 --> 00:19:25,330
shows how much the
average indoor level

470
00:19:25,330 --> 00:19:28,330
compares to all the different
things you could do.

471
00:19:28,330 --> 00:19:32,890
Like getting 2,000 chest X-rays
per year versus 100 times

472
00:19:32,890 --> 00:19:33,970
the average indoor level.

473
00:19:33,970 --> 00:19:36,280
That's about what I heard
that fellow in Pennsylvania

474
00:19:36,280 --> 00:19:39,520
had is like 100 or 80
times the normal radon

475
00:19:39,520 --> 00:19:44,200
levels from living underground
on this giant granite deposit.

476
00:19:44,200 --> 00:19:47,080
It's like getting 2,000
chest X-rays per year,

477
00:19:47,080 --> 00:19:50,230
or something like
smoking four packs a day.

478
00:19:50,230 --> 00:19:52,620
I know some people that do this.

479
00:19:52,620 --> 00:19:54,990
They don't tend to be that
afraid of the radiation

480
00:19:54,990 --> 00:19:58,290
that they're taking
in from smoking.

481
00:19:58,290 --> 00:20:04,200
But yeah, it's pretty insane
how much radiation you get.

482
00:20:04,200 --> 00:20:06,720
People are afraid to get one
chest X-ray, which is not even

483
00:20:06,720 --> 00:20:08,280
on this map.

484
00:20:08,280 --> 00:20:10,590
One chest X-ray
worth of radiation

485
00:20:10,590 --> 00:20:14,880
gives you much, much less than
living for a year in a house,

486
00:20:14,880 --> 00:20:16,577
which we all tend to do.

487
00:20:16,577 --> 00:20:18,660
Then if you live in a brick
or cinder block house,

488
00:20:18,660 --> 00:20:20,730
you actually get a fair
bit more radiation,

489
00:20:20,730 --> 00:20:23,460
because these are fairly
radioactive building materials.

490
00:20:23,460 --> 00:20:27,020
And I'll show you those
activity levels in just a sec.

491
00:20:27,020 --> 00:20:28,670
As far as exposure
sources, again,

492
00:20:28,670 --> 00:20:31,850
to look at the relative amount
of terrestrial gamma ray

493
00:20:31,850 --> 00:20:35,240
exposure, you can
correlate that pretty well

494
00:20:35,240 --> 00:20:39,920
with not green regions
on a topological map.

495
00:20:39,920 --> 00:20:42,860
So look at the really
low levels down here,

496
00:20:42,860 --> 00:20:47,810
correlates with low lying
vegetative areas around here.

497
00:20:47,810 --> 00:20:50,660
Colors are a little more
extreme on my screen,

498
00:20:50,660 --> 00:20:52,820
but you can see this is
all low lying right here.

499
00:20:52,820 --> 00:20:55,670
From Louisiana, Florida,
up the east coast,

500
00:20:55,670 --> 00:20:59,910
until you get to the
Appalachian Mountains and such.

501
00:20:59,910 --> 00:21:03,250
So pretty striking
correlations there.

502
00:21:03,250 --> 00:21:06,310
And it all comes from what we
call the primordial nuclides.

503
00:21:06,310 --> 00:21:09,760
These are unstable nuclides
that have such long half

504
00:21:09,760 --> 00:21:12,100
lives that they still
exist, despite the universe

505
00:21:12,100 --> 00:21:15,220
being 15 billion years
old, or whatever supernova

506
00:21:15,220 --> 00:21:19,690
formed our solar system being
five plus billion years old.

507
00:21:19,690 --> 00:21:22,090
Things that we've already
studied almost to death,

508
00:21:22,090 --> 00:21:24,190
like potassium-40.

509
00:21:24,190 --> 00:21:28,750
And you can see that's about
0.011% of all potassium

510
00:21:28,750 --> 00:21:30,940
is radioactive potassium-40.

511
00:21:30,940 --> 00:21:34,600
About 10% of which
gives off gammas in--

512
00:21:34,600 --> 00:21:35,650
what is it, 90/10?

513
00:21:35,650 --> 00:21:37,000
I forget the split.

514
00:21:37,000 --> 00:21:39,460
But can give off either
betas and then a gamma,

515
00:21:39,460 --> 00:21:41,860
or positrons and then a gamma.

516
00:21:41,860 --> 00:21:44,860
Then things like rubidium,
in the same column

517
00:21:44,860 --> 00:21:48,250
as sodium, potassium, and
cesium, so it behaves kind

518
00:21:48,250 --> 00:21:51,220
of like a salt-like element.

519
00:21:51,220 --> 00:21:55,610
There should be some for-- are
there any for chlorine too?

520
00:21:55,610 --> 00:21:58,070
Some of the other important
ones to note, oh, platinum.

521
00:21:58,070 --> 00:21:59,877
Does anyone has any
platinum jewelry?

522
00:21:59,877 --> 00:22:01,460
Does anyone have any
platinum jewelry?

523
00:22:05,020 --> 00:22:05,950
Good answer, yeah.

524
00:22:05,950 --> 00:22:06,850
I don't either.

525
00:22:06,850 --> 00:22:09,070
I teach at a college.

526
00:22:09,070 --> 00:22:11,710
Also, I don't like
wearing jewelry.

527
00:22:11,710 --> 00:22:14,110
But there'll be all sorts
of these primordial nuclides

528
00:22:14,110 --> 00:22:15,850
that you can't really
do anything about.

529
00:22:15,850 --> 00:22:17,030
They're just there.

530
00:22:17,030 --> 00:22:19,510
Note that the half lives
are really, really long.

531
00:22:19,510 --> 00:22:21,010
And as you know
now, the half life

532
00:22:21,010 --> 00:22:24,100
is going to be inversely
proportional to the activity.

533
00:22:24,100 --> 00:22:26,050
Despite almost all indium--

534
00:22:26,050 --> 00:22:31,210
look at that, 95% of the indium
that you'll find emits betas.

535
00:22:31,210 --> 00:22:33,880
Doesn't stop people from using
it as these awesome glass

536
00:22:33,880 --> 00:22:36,278
to metal seals for
vacuum components.

537
00:22:36,278 --> 00:22:38,320
Because once in a while
it might emit a beta ray,

538
00:22:38,320 --> 00:22:41,440
like a whole gasket
might emit a beta once

539
00:22:41,440 --> 00:22:43,270
every millennium or so.

540
00:22:43,270 --> 00:22:46,920
But these half lives
actually are measurable.

541
00:22:46,920 --> 00:22:48,880
And that begs the question,
are there elements

542
00:22:48,880 --> 00:22:51,960
with longer half lives that
are just too long to measure?

543
00:22:51,960 --> 00:22:54,580
You think what does it mean
to have a half life of 10

544
00:22:54,580 --> 00:22:59,260
to the 15 years, given that the
universe is on the order of 10

545
00:22:59,260 --> 00:23:02,470
to the 10 years old?

546
00:23:02,470 --> 00:23:04,600
Is it possible that
all nuclei will

547
00:23:04,600 --> 00:23:07,330
decay till the end of time?

548
00:23:07,330 --> 00:23:09,160
I've seen some
documentary such things

549
00:23:09,160 --> 00:23:11,770
and don't call this a science
that say, oh 10 to the 40 years

550
00:23:11,770 --> 00:23:13,840
from now, the last
protons decay,

551
00:23:13,840 --> 00:23:16,810
or the last whatever
elements decay

552
00:23:16,810 --> 00:23:19,490
into all protons and neutrons.

553
00:23:19,490 --> 00:23:21,220
Don't know if
that's true, but it

554
00:23:21,220 --> 00:23:24,460
does make me wonder, are some
of the other so-called stable

555
00:23:24,460 --> 00:23:28,670
elements just have
ridiculously long half lives?

556
00:23:28,670 --> 00:23:31,268
It's something to think about.

557
00:23:31,268 --> 00:23:33,640
So let's take a look at
the building materials,

558
00:23:33,640 --> 00:23:37,150
and see what's in the typical
things around us right now.

559
00:23:37,150 --> 00:23:40,120
You can see how much
granite, radioactive thorium,

560
00:23:40,120 --> 00:23:42,550
and potassium are in
these building materials.

561
00:23:42,550 --> 00:23:46,410
And how many usually is
measured in picocuries per gram.

562
00:23:46,410 --> 00:23:49,870
A picocurie is already less
than a becquerel per gram.

563
00:23:49,870 --> 00:23:57,000
Because a curie is what, 3.7
times 10 to the 10 becquerels.

564
00:23:57,000 --> 00:23:59,720
And a pico is a 10
to the minus 12.

565
00:23:59,720 --> 00:24:03,180
So things on the order of
a few picocuries per gram,

566
00:24:03,180 --> 00:24:04,690
a gram of that
material might emit

567
00:24:04,690 --> 00:24:07,360
one disintegration per second.

568
00:24:07,360 --> 00:24:09,100
Not a lot of radiation.

569
00:24:09,100 --> 00:24:11,920
But take a look at how much
potassium there is in granite.

570
00:24:11,920 --> 00:24:16,060
Nanocuries per gram, that's
getting into the integers

571
00:24:16,060 --> 00:24:18,130
worth of becquerels.

572
00:24:18,130 --> 00:24:22,620
If you look at wood,
check that out.

573
00:24:22,620 --> 00:24:25,844
Anyone heard of potash before?

574
00:24:25,844 --> 00:24:27,830
It's one of the ways
we get potassium.

575
00:24:27,830 --> 00:24:31,180
So if you take wood based things
and you burn them in a fire,

576
00:24:31,180 --> 00:24:33,130
you drive off all the
carbon in the water,

577
00:24:33,130 --> 00:24:36,460
you're left with these kind of
whitened salt and pepper ashes.

578
00:24:36,460 --> 00:24:37,390
That's potash.

579
00:24:37,390 --> 00:24:39,040
That's the ashes
left over in the pot

580
00:24:39,040 --> 00:24:40,332
after you burn stuff in a fire.

581
00:24:40,332 --> 00:24:42,202
They're quite potassium rich.

582
00:24:42,202 --> 00:24:43,660
So I think what
we'll do next year,

583
00:24:43,660 --> 00:24:45,662
instead of burning
a bunch of food,

584
00:24:45,662 --> 00:24:46,870
is just burn a bunch of wood.

585
00:24:46,870 --> 00:24:50,290
We'll have a nice bonfire,
collect the ashes.

586
00:24:50,290 --> 00:24:53,080
And we can see how much
potassium there is in wood.

587
00:24:53,080 --> 00:24:55,270
Which pound for pound,
if you see on this list,

588
00:24:55,270 --> 00:24:58,390
is the most radioactive
building material there is.

589
00:24:58,390 --> 00:25:01,270
Just that wood happens
to be pretty inexpensive,

590
00:25:01,270 --> 00:25:05,050
and consists mostly of water,
lignin, and other carboniferous

591
00:25:05,050 --> 00:25:06,340
materials.

592
00:25:06,340 --> 00:25:08,200
They don't have
carbon-14 on this list,

593
00:25:08,200 --> 00:25:10,200
but let's take a look at
some of the other ones.

594
00:25:10,200 --> 00:25:14,560
So sandstone cement has a
pretty toasty signature to it.

595
00:25:14,560 --> 00:25:17,500
Gypsum drywall.

596
00:25:17,500 --> 00:25:20,470
What is it, 13 parts per million
uranium in all the drywall

597
00:25:20,470 --> 00:25:22,830
you tend to find.

598
00:25:22,830 --> 00:25:24,075
Anyone scared yet?

599
00:25:24,075 --> 00:25:26,140
Because you shouldn't be.

600
00:25:26,140 --> 00:25:28,970
It's like I mentioned
before, this

601
00:25:28,970 --> 00:25:31,220
is the slide I want
to show to most folks

602
00:25:31,220 --> 00:25:33,050
in the general public.

603
00:25:33,050 --> 00:25:35,660
There is such a dose as nothing.

604
00:25:35,660 --> 00:25:37,830
And that's pretty much
what you get from,

605
00:25:37,830 --> 00:25:39,440
let's say, a day's worth of
being around these building

606
00:25:39,440 --> 00:25:39,890
materials.

607
00:25:39,890 --> 00:25:40,890
It's just about nothing.

608
00:25:44,522 --> 00:25:48,200
It's after the
building materials.

609
00:25:48,200 --> 00:25:50,470
There we go.

610
00:25:50,470 --> 00:25:54,150
Seawater is another great
source of radioactivity.

611
00:25:54,150 --> 00:25:58,410
Enough so that
people have actually

612
00:25:58,410 --> 00:26:03,125
proposed harvesting
uranium from seawater.

613
00:26:03,125 --> 00:26:05,000
So the total amount of
activity in the ocean,

614
00:26:05,000 --> 00:26:09,140
there's something
like 11 exabecquerels

615
00:26:09,140 --> 00:26:12,440
of radiation contained in
the uranium in the seawater.

616
00:26:12,440 --> 00:26:16,220
Which means you should be able
to have a gigantic trawler

617
00:26:16,220 --> 00:26:20,208
flying out around in the
ocean, and just floating

618
00:26:20,208 --> 00:26:22,250
through the seawater,
picking up atoms of uranium

619
00:26:22,250 --> 00:26:22,670
here and there.

620
00:26:22,670 --> 00:26:24,503
Because technically,
there's enough to power

621
00:26:24,503 --> 00:26:26,300
the world for like 2,000 years.

622
00:26:26,300 --> 00:26:28,410
The problem is the ocean is big.

623
00:26:28,410 --> 00:26:30,920
It doesn't stop people from
actually working on it.

624
00:26:30,920 --> 00:26:32,337
So it's neat to
think that there's

625
00:26:32,337 --> 00:26:34,430
a whole lot of
carbon-14 and tritium

626
00:26:34,430 --> 00:26:37,650
and uranium in seawater.

627
00:26:37,650 --> 00:26:39,690
300 picocuries per liter.

628
00:26:39,690 --> 00:26:42,598
Anyone have any idea why there's
so much more potassium activity

629
00:26:42,598 --> 00:26:43,890
than anything else in seawater?

630
00:26:47,590 --> 00:26:49,330
It's because it's salty, yeah.

631
00:26:49,330 --> 00:26:50,950
And potassium's
just like sodium.

632
00:26:50,950 --> 00:26:53,380
So there'll be a
fair bit of potassium

633
00:26:53,380 --> 00:27:00,300
in the seawater, 0.0117%
of which is potassium-40.

634
00:27:00,300 --> 00:27:04,030
And so last year, people asked,
what, uranium from seawater?

635
00:27:04,030 --> 00:27:05,360
How is that even possible?

636
00:27:05,360 --> 00:27:07,090
So this is the part
in the course where

637
00:27:07,090 --> 00:27:09,250
I'm going to pull out a
lot more recent papers

638
00:27:09,250 --> 00:27:11,920
to show you some of the
cooler innovations going on.

639
00:27:11,920 --> 00:27:14,290
So you could use this adsorbent.

640
00:27:14,290 --> 00:27:15,000
And adsorbent.

641
00:27:15,000 --> 00:27:20,060
Does anyone know what adsorption
means, not absorption?

642
00:27:20,060 --> 00:27:21,890
Adsorption is when
something sticks

643
00:27:21,890 --> 00:27:23,630
to the surface of something.

644
00:27:23,630 --> 00:27:25,880
Absorption with a B is
when it actually gets

645
00:27:25,880 --> 00:27:27,950
incorporated into the bulk.

646
00:27:27,950 --> 00:27:30,500
So folks are thinking about
making high surface area

647
00:27:30,500 --> 00:27:35,280
materials that can adsorb
selectively atoms of uranium.

648
00:27:35,280 --> 00:27:39,560
So you send out this huge
braided net, or a huge stack

649
00:27:39,560 --> 00:27:44,240
of adsorbing material with
a D, and just go around

650
00:27:44,240 --> 00:27:45,590
in the ocean.

651
00:27:45,590 --> 00:27:48,440
Attach them to tankers
or cargo ships,

652
00:27:48,440 --> 00:27:50,810
and just have them
pull in product

653
00:27:50,810 --> 00:27:53,150
as they go from coast to coast.

654
00:27:53,150 --> 00:27:56,180
And by actually changing around
the chemistry and the geometry

655
00:27:56,180 --> 00:27:59,300
of this, you can enhance
things specifically for uranium

656
00:27:59,300 --> 00:28:00,830
by about a factor of three.

657
00:28:00,830 --> 00:28:03,800
And this yellowcake right
here next to an actual ruler--

658
00:28:03,800 --> 00:28:05,930
that's 50 millimeters
right there--

659
00:28:05,930 --> 00:28:08,600
that was obtained
directly from seawater.

660
00:28:08,600 --> 00:28:11,938
So you can actually pull
yellowcake out of the ocean.

661
00:28:11,938 --> 00:28:12,980
Just not very much of it.

662
00:28:15,580 --> 00:28:18,810
And the way these work is there
are interesting compounds that

663
00:28:18,810 --> 00:28:22,530
selectively absorb uranium
into their structure,

664
00:28:22,530 --> 00:28:27,990
not by direct chemical bonding,
but by getting something close.

665
00:28:27,990 --> 00:28:30,990
For example, my wife tends
to study metals bonding

666
00:28:30,990 --> 00:28:31,740
to proteins.

667
00:28:31,740 --> 00:28:34,488
And it's not necessarily
always a full chemical bond

668
00:28:34,488 --> 00:28:36,030
like you might think,
but the protein

669
00:28:36,030 --> 00:28:39,570
can kind of wrap around a
metal ion, transport it places.

670
00:28:39,570 --> 00:28:41,530
Similar thing going here.

671
00:28:41,530 --> 00:28:43,590
I'm not going to
pontificate anymore

672
00:28:43,590 --> 00:28:46,200
on it because the title
has the word organic in it,

673
00:28:46,200 --> 00:28:48,380
and I am definitely
not an organic chemist.

674
00:28:48,380 --> 00:28:49,963
Don't want to tell
you anything wrong,

675
00:28:49,963 --> 00:28:52,583
but I do want to tell you you
can actually see this paper

676
00:28:52,583 --> 00:28:54,000
to find out what
sort of compounds

677
00:28:54,000 --> 00:28:55,958
selectively grab onto uranium.

678
00:28:55,958 --> 00:28:57,750
And if there's a seawater
floating through,

679
00:28:57,750 --> 00:29:01,200
and uranium happens to flow
nearby, it can bond to it.

680
00:29:01,200 --> 00:29:05,040
You can then somehow squeeze
out or burn off that adsorbent,

681
00:29:05,040 --> 00:29:07,535
and there you get uranium.

682
00:29:07,535 --> 00:29:09,160
Now let's talk about
what's in the body

683
00:29:09,160 --> 00:29:13,720
and interpreting the spectra
that you got from EHS,

684
00:29:13,720 --> 00:29:15,270
your full body spectra.

685
00:29:15,270 --> 00:29:16,870
If you take a look
at how much uranium

686
00:29:16,870 --> 00:29:19,030
there is in the body,
wow, there's some.

687
00:29:19,030 --> 00:29:22,330
Every one of you is got
about a becquerel of uranium

688
00:29:22,330 --> 00:29:23,480
in the body.

689
00:29:23,480 --> 00:29:27,080
But if you look at the relative
amounts, rate it was at.

690
00:29:27,080 --> 00:29:29,870
The only things that
really matter a ton,

691
00:29:29,870 --> 00:29:34,580
potassium-40, about 4.4
kilobecquerels per human.

692
00:29:34,580 --> 00:29:38,490
So each of you is giving
off 4,400 potassium gammas

693
00:29:38,490 --> 00:29:40,080
per second.

694
00:29:40,080 --> 00:29:42,770
Most of them just flow right
through all the other people.

695
00:29:42,770 --> 00:29:48,183
And then carbon-14,
about 3.7 kilobecquerels.

696
00:29:48,183 --> 00:29:50,600
Pretty interesting to know
just how much radioactive stuff

697
00:29:50,600 --> 00:29:52,070
you have in your own body.

698
00:29:52,070 --> 00:29:55,310
You will need this table
for homework number eight

699
00:29:55,310 --> 00:29:58,220
when I ask you a
pretty fun question.

700
00:29:58,220 --> 00:30:00,770
Then there's all the
various medical procedures.

701
00:30:00,770 --> 00:30:03,920
The ones that aren't counted in
your annual dose because they

702
00:30:03,920 --> 00:30:05,630
tend to save people.

703
00:30:05,630 --> 00:30:07,880
But now let's look at
the dose in millirem

704
00:30:07,880 --> 00:30:10,520
So if you want to figure out
what this is in sieverts,

705
00:30:10,520 --> 00:30:12,720
just divide by 100.

706
00:30:12,720 --> 00:30:17,880
So a regular old
chest X-ray, 0.1--

707
00:30:17,880 --> 00:30:19,620
let's see, how does it go?

708
00:30:19,620 --> 00:30:23,070
100 rem in a sievert.

709
00:30:23,070 --> 00:30:27,610
Yeah, so about 0.1
millisieverts, or 1,000 banana

710
00:30:27,610 --> 00:30:28,300
equivalent dose.

711
00:30:28,300 --> 00:30:29,620
Not terrible.

712
00:30:29,620 --> 00:30:34,350
Which is why if we go
back to that chart of all

713
00:30:34,350 --> 00:30:36,420
those relative
risks, if you look

714
00:30:36,420 --> 00:30:39,510
at the average indoor level,
it's like getting-- well,

715
00:30:39,510 --> 00:30:42,900
I would have to guess maybe
40 chest X-rays per year

716
00:30:42,900 --> 00:30:44,932
based on this
rather crude scale.

717
00:30:44,932 --> 00:30:46,890
And you're allowed to
get around a millisievert

718
00:30:46,890 --> 00:30:49,440
or a few millisieverts
of radiation per year.

719
00:30:49,440 --> 00:30:51,641
That sounds like it
checks out mathematically.

720
00:30:54,870 --> 00:30:57,540
Let's look at some of
the other crazier ones.

721
00:30:57,540 --> 00:30:59,070
Dental bitewing.

722
00:30:59,070 --> 00:30:59,640
Yeah.

723
00:30:59,640 --> 00:31:01,890
So anyone ever bite
down on something

724
00:31:01,890 --> 00:31:04,980
where you have to get an X-ray
through the side of your mouth?

725
00:31:04,980 --> 00:31:08,040
Quite negligible amount
of dose, yet they still

726
00:31:08,040 --> 00:31:10,630
put the lead apron on you.

727
00:31:10,630 --> 00:31:13,720
I'm guessing that's mostly
for show, because that's

728
00:31:13,720 --> 00:31:14,920
very, very little dose.

729
00:31:14,920 --> 00:31:20,350
It's well beyond the 0.1
microsieverts of something

730
00:31:20,350 --> 00:31:22,000
that counts as nothing.

731
00:31:22,000 --> 00:31:24,770
But there's not a lot of
dose going into these things.

732
00:31:24,770 --> 00:31:28,390
Let's see what really does
give you a whole lot of dose.

733
00:31:28,390 --> 00:31:34,030
10 millisieverts for a CT scan,
or a whole body CT screening.

734
00:31:34,030 --> 00:31:36,190
That's a pretty
hefty amount of dose.

735
00:31:36,190 --> 00:31:38,290
Right there with
one procedure you

736
00:31:38,290 --> 00:31:41,772
may get more than your normal
annual background dose.

737
00:31:41,772 --> 00:31:43,480
But if you're going
in to look for stuff,

738
00:31:43,480 --> 00:31:46,270
chances are you need to find
whatever you're looking for.

739
00:31:46,270 --> 00:31:47,200
So we don't count it.

740
00:31:47,200 --> 00:31:50,560
And it may give you a
slightly higher chance

741
00:31:50,560 --> 00:31:53,140
of developing cancer
much later down the line

742
00:31:53,140 --> 00:31:55,572
when that cell that
gets mutated divides.

743
00:31:55,572 --> 00:31:58,030
But it's probably going to save
your life in the next hour,

744
00:31:58,030 --> 00:31:59,270
or the next day.

745
00:31:59,270 --> 00:32:01,550
So definitely worth it.

746
00:32:01,550 --> 00:32:03,930
Let's see, the worst--

747
00:32:03,930 --> 00:32:05,820
what's the worst
procedure we can find?

748
00:32:09,980 --> 00:32:12,200
Noncardiac embolization.

749
00:32:12,200 --> 00:32:13,650
I don't know enough
biology words

750
00:32:13,650 --> 00:32:15,866
know exactly what that means.

751
00:32:15,866 --> 00:32:18,210
AUDIENCE: I know what
noncardiac means.

752
00:32:18,210 --> 00:32:20,990
MICHAEL SHORT: Yeah, I think we
all know what noncardiac means.

753
00:32:20,990 --> 00:32:21,690
Good.

754
00:32:21,690 --> 00:32:25,960
This isn't 7012.

755
00:32:25,960 --> 00:32:29,110
Nonmedical procedures-- or more
medical procedures, I'm sorry.

756
00:32:29,110 --> 00:32:30,700
Where's the techneitum scan?

757
00:32:30,700 --> 00:32:32,590
Yeah, notice how
many of these things

758
00:32:32,590 --> 00:32:35,830
have technetium imaging where
you'll inject technetium

759
00:32:35,830 --> 00:32:39,430
into a certain organ or a
certain vascular or lymph

760
00:32:39,430 --> 00:32:40,940
or whatever system.

761
00:32:40,940 --> 00:32:43,240
Some of these things can
give you a fair bit of dose.

762
00:32:43,240 --> 00:32:46,570
Like again, maybe a
heart stress rest test

763
00:32:46,570 --> 00:32:49,600
can give you double or triple
your normal background dose.

764
00:32:49,600 --> 00:32:52,060
This is why you have
to declare to airports

765
00:32:52,060 --> 00:32:54,310
if you've just had a
medical imaging procedure,

766
00:32:54,310 --> 00:32:56,830
because this is well more
than enough to pick up

767
00:32:56,830 --> 00:32:59,575
on any sort of airport
radiation monitor.

768
00:32:59,575 --> 00:33:01,450
So again, if you ever
get a medical procedure

769
00:33:01,450 --> 00:33:03,730
with any sort of
radiation, anything,

770
00:33:03,730 --> 00:33:08,260
do declare it, because
it's quite measurable.

771
00:33:08,260 --> 00:33:10,390
Then there's radiation
from altitude.

772
00:33:10,390 --> 00:33:13,210
I may have mentioned already
that the reason that pilots

773
00:33:13,210 --> 00:33:16,810
can't fly for a certain number
of hours is not fatigue,

774
00:33:16,810 --> 00:33:18,940
but it's radiation exposure.

775
00:33:18,940 --> 00:33:21,400
When you start to
look at how many

776
00:33:21,400 --> 00:33:25,750
microsieverts you get per
hour on the ground, 0.03.

777
00:33:25,750 --> 00:33:28,270
Right about down at that--
hanging around for an hour

778
00:33:28,270 --> 00:33:29,950
is a negligible dose.

779
00:33:29,950 --> 00:33:32,440
You go up to
international air travel,

780
00:33:32,440 --> 00:33:35,950
that goes up by a factor
of little more than 100.

781
00:33:35,950 --> 00:33:39,310
And so you get a fair bit
of radiation exposure.

782
00:33:39,310 --> 00:33:42,160
If you take your annual
allowable occupational

783
00:33:42,160 --> 00:33:47,160
limit of 50 millisieverts,
divide by 3.7 microsieverts,

784
00:33:47,160 --> 00:33:48,650
you're getting close to 86--

785
00:33:48,650 --> 00:33:49,150
what is it?

786
00:33:49,150 --> 00:33:51,948
How many hours in a year?

787
00:33:51,948 --> 00:33:52,970
Let's see.

788
00:33:52,970 --> 00:33:55,860
There's three times 10 of
the seven seconds in a year.

789
00:33:55,860 --> 00:33:57,640
So divide that by 3,600.

790
00:33:57,640 --> 00:33:59,680
That's getting on
the realm of 10,000.

791
00:33:59,680 --> 00:34:01,690
That's about the
conversion factor.

792
00:34:01,690 --> 00:34:03,403
So you can't spend
your life in the air,

793
00:34:03,403 --> 00:34:05,320
because you'd get too
much radiation according

794
00:34:05,320 --> 00:34:09,480
to the occupational risks.

795
00:34:09,480 --> 00:34:12,552
And so actually in addition to
some interesting measurements

796
00:34:12,552 --> 00:34:14,010
that have been
published in papers,

797
00:34:14,010 --> 00:34:15,719
we've actually had
students go out

798
00:34:15,719 --> 00:34:20,250
and build radiation altimeters
based on the MIT Geiger

799
00:34:20,250 --> 00:34:21,179
counter--

800
00:34:21,179 --> 00:34:23,012
removing the speaker,
of course, because you

801
00:34:23,012 --> 00:34:25,090
don't want to clicking
Geiger counter on a plane.

802
00:34:25,090 --> 00:34:27,480
That'd be kind of a
stressful situation.

803
00:34:27,480 --> 00:34:29,340
Let me show you one
example of these.

804
00:34:29,340 --> 00:34:32,670
Are also published from a paper,
but we have pretty similar data

805
00:34:32,670 --> 00:34:35,130
from-- if you want, to
go talk to Max Carlson,

806
00:34:35,130 --> 00:34:39,179
one of my graduate students who
hooked up his Geiger counter

807
00:34:39,179 --> 00:34:41,370
to an alarm clock--

808
00:34:41,370 --> 00:34:44,560
the case that had
[INAUDIBLE] in it.

809
00:34:44,560 --> 00:34:47,130
I think this was a poor
choice of case for a plane

810
00:34:47,130 --> 00:34:49,920
because it looks kind
of like a time bomb.

811
00:34:49,920 --> 00:34:54,270
But luckily nobody found it,
and he was able to get the data.

812
00:34:54,270 --> 00:34:56,280
But you can see just how
much more data you get.

813
00:34:56,280 --> 00:34:59,700
And you can correlate the height
that you're at with the dose--

814
00:34:59,700 --> 00:35:05,950
in this case, microroentgens per
hour or microrad depending on--

815
00:35:05,950 --> 00:35:10,180
what is it-- ambiguous unit
definition right there.

816
00:35:10,180 --> 00:35:11,590
But it's quite noticeable.

817
00:35:11,590 --> 00:35:13,690
So for those of you who
have built Geiger counters

818
00:35:13,690 --> 00:35:17,230
and have cell phones, and don't
want to have a fake time bomb,

819
00:35:17,230 --> 00:35:19,390
you can actually hook
in your Geiger counter

820
00:35:19,390 --> 00:35:21,330
to the microphone port
of your cell phone.

821
00:35:21,330 --> 00:35:23,230
And with a few available
radiation apps,

822
00:35:23,230 --> 00:35:27,220
you can actually monitor
your dose in microsieverts.

823
00:35:27,220 --> 00:35:29,710
Assuming that it all comes
from gamma rays, which

824
00:35:29,710 --> 00:35:31,880
is most of what a lot of
cosmic rays will produce.

825
00:35:31,880 --> 00:35:33,430
So it's a pretty
safe approximation

826
00:35:33,430 --> 00:35:35,650
that your dose in gray
flying on the plane

827
00:35:35,650 --> 00:35:37,600
is also your dose in
sieverts, because it's

828
00:35:37,600 --> 00:35:39,933
whole body, and its gammas.

829
00:35:39,933 --> 00:35:41,350
So I'd say try
this at home, kids.

830
00:35:41,350 --> 00:35:46,130
This is one of those things
I recommend you try out.

831
00:35:46,130 --> 00:35:48,830
Speaking of these cosmic rays,
where did they come from?

832
00:35:48,830 --> 00:35:51,220
Well, this is a question
that's been under debate,

833
00:35:51,220 --> 00:35:54,910
and was more completely
answered just a few years ago.

834
00:35:54,910 --> 00:35:58,330
They come from very high energy
particles from somewhere.

835
00:35:58,330 --> 00:36:01,060
It had been argued, do they
come mostly from solar flares,

836
00:36:01,060 --> 00:36:04,480
or did they come from
elsewhere in the galaxy?

837
00:36:04,480 --> 00:36:07,810
Mostly we're talking about
things like high energy protons

838
00:36:07,810 --> 00:36:09,640
or other charged particles.

839
00:36:09,640 --> 00:36:11,710
We're also talking neutrinos.

840
00:36:11,710 --> 00:36:13,330
Anyone know about
how many neutrinos

841
00:36:13,330 --> 00:36:18,790
are theorized to pass
through you every second?

842
00:36:18,790 --> 00:36:19,690
Trillions.

843
00:36:19,690 --> 00:36:21,110
Yeah, something like that.

844
00:36:21,110 --> 00:36:23,800
But they basically don't
interact with matter.

845
00:36:23,800 --> 00:36:25,760
As I showed you guys
near the beginning,

846
00:36:25,760 --> 00:36:29,710
it takes a gigantic salt mine
full of water and exploding

847
00:36:29,710 --> 00:36:33,250
photomultiplier tubes in order
to catch two or three neutrinos

848
00:36:33,250 --> 00:36:34,330
a day if you're lucky.

849
00:36:34,330 --> 00:36:36,430
So let's say those
don't really matter

850
00:36:36,430 --> 00:36:38,020
in terms of background dose.

851
00:36:38,020 --> 00:36:41,218
But when those high
energy particles interact

852
00:36:41,218 --> 00:36:43,510
with the oxygen and nitrogen
up here in the atmosphere,

853
00:36:43,510 --> 00:36:46,030
they produce a
shower and cascade

854
00:36:46,030 --> 00:36:50,850
of additional ionization
and high energy particles.

855
00:36:50,850 --> 00:36:54,870
So it's been said that solar
flares and such will accelerate

856
00:36:54,870 --> 00:36:57,210
charged particles
from the plasma

857
00:36:57,210 --> 00:36:58,890
in the sun towards Earth.

858
00:36:58,890 --> 00:37:02,100
They're deflected somewhat
by the magnetic field

859
00:37:02,100 --> 00:37:05,510
of the Earth, but they
tend to enter right here

860
00:37:05,510 --> 00:37:07,250
at the-- what is it?

861
00:37:07,250 --> 00:37:08,070
At the poles.

862
00:37:08,070 --> 00:37:11,210
I'm sorry, that's the simple
word I was looking for.

863
00:37:11,210 --> 00:37:16,820
Until recently in 2001, they
were looking specifically

864
00:37:16,820 --> 00:37:19,910
at the evidence for or against
the idea that coronal mass

865
00:37:19,910 --> 00:37:22,820
ejections-- which means
large ejections of mass from

866
00:37:22,820 --> 00:37:25,760
the outer layers, these
sparcer layers of the sun--

867
00:37:25,760 --> 00:37:30,080
was responsible for most charged
particles and cosmic rays.

868
00:37:30,080 --> 00:37:32,110
Skipping the stuff
that's not in bold,

869
00:37:32,110 --> 00:37:34,970
it appears to be that
the CME bow shock

870
00:37:34,970 --> 00:37:37,250
scenario has been overvalued.

871
00:37:37,250 --> 00:37:38,720
So for a while,
folks were saying

872
00:37:38,720 --> 00:37:42,020
most cosmic rays come from the
sun-- that's our nearest star.

873
00:37:42,020 --> 00:37:46,250
By making really, really careful
measurements of the energy

874
00:37:46,250 --> 00:37:47,690
and lifetime of
these cosmic rays,

875
00:37:47,690 --> 00:37:49,970
this has actually been
somewhat disproven

876
00:37:49,970 --> 00:37:52,970
that this is the major
source of cosmic rays, which

877
00:37:52,970 --> 00:37:54,810
is pretty cool.

878
00:37:54,810 --> 00:37:57,560
But let's talk about where
they actually come from.

879
00:37:57,560 --> 00:38:00,530
Reactions that you can
probably understand.

880
00:38:00,530 --> 00:38:03,290
So extremely high protons
enter the atmosphere.

881
00:38:03,290 --> 00:38:05,660
They all start as
high energy protons.

882
00:38:05,660 --> 00:38:08,150
And when protons are
high enough energy--

883
00:38:08,150 --> 00:38:10,430
and like I do probably
in every class ever,

884
00:38:10,430 --> 00:38:13,900
I'm going to pull up Janis
to show you something.

885
00:38:13,900 --> 00:38:16,690
They can undergo what's
called spallation.

886
00:38:16,690 --> 00:38:19,570
It's the same principle
that the Spallation Neutron

887
00:38:19,570 --> 00:38:21,910
Source at Oak Ridge
National Lab works on

888
00:38:21,910 --> 00:38:24,610
is shoot in extremely
high energy protons,

889
00:38:24,610 --> 00:38:26,690
out come neutrons.

890
00:38:26,690 --> 00:38:30,370
So as usual, it didn't
clone the screen right.

891
00:38:30,370 --> 00:38:31,690
So just bear with me for a sec.

892
00:38:36,557 --> 00:38:38,890
I'd like to, for probably the
first time in this course,

893
00:38:38,890 --> 00:38:42,425
switch databases to the
incident proton data.

894
00:38:42,425 --> 00:38:43,512
Is that actually working?

895
00:38:43,512 --> 00:38:44,456
OK, good.

896
00:38:47,760 --> 00:38:50,710
So we'll leave the
incident neutron data,

897
00:38:50,710 --> 00:38:54,270
we'll go to the
incident proton data.

898
00:38:54,270 --> 00:38:57,920
We'll stick with
the same library.

899
00:38:57,920 --> 00:38:59,360
Let's see how much they have.

900
00:38:59,360 --> 00:39:02,880
Not much, but enough to
matter, because there's

901
00:39:02,880 --> 00:39:07,240
a lot of nitrogen-14
up in the air.

902
00:39:07,240 --> 00:39:11,930
Let's see what happens when
protons hit nitrogen-14

903
00:39:11,930 --> 00:39:13,180
all the way at high energy.

904
00:39:13,180 --> 00:39:16,910
So don't quite know what a
negative cross-section refers

905
00:39:16,910 --> 00:39:17,410
to.

906
00:39:17,410 --> 00:39:22,190
But at high energies, this is
definitely a possible event.

907
00:39:22,190 --> 00:39:24,540
And let's see, there's not
a lot of cross-sections

908
00:39:24,540 --> 00:39:26,160
to look at here.

909
00:39:26,160 --> 00:39:28,670
Let's try oxygen-16.

910
00:39:28,670 --> 00:39:30,620
Not much.

911
00:39:30,620 --> 00:39:32,760
We'll stick to the slides then.

912
00:39:32,760 --> 00:39:35,520
So when a high energy
proton strikes a nucleus,

913
00:39:35,520 --> 00:39:37,290
it can eject neutrons.

914
00:39:37,290 --> 00:39:41,790
And those neutrons can then
cause activation reactions,

915
00:39:41,790 --> 00:39:44,820
and then emit things like
proton or tritium, leading to--

916
00:39:44,820 --> 00:39:47,100
that's where your
carbon-14 comes from.

917
00:39:47,100 --> 00:39:49,110
Comes from nitrogen-14.

918
00:39:49,110 --> 00:39:52,350
So in comes a high energy
proton, releases a neutron.

919
00:39:52,350 --> 00:39:56,550
That neutron hits nitrogen-14,
releases a proton,

920
00:39:56,550 --> 00:39:58,630
out comes carbon-14.

921
00:39:58,630 --> 00:40:01,170
So this is why it's being
constantly generated

922
00:40:01,170 --> 00:40:02,020
in the atmosphere.

923
00:40:02,020 --> 00:40:03,812
It's not like there's
a certain amount that

924
00:40:03,812 --> 00:40:06,270
was there at the beginning
of the universe and decays,

925
00:40:06,270 --> 00:40:09,150
because its half life
is only 5,700 years.

926
00:40:09,150 --> 00:40:11,370
So this is part of why
radiocarbon dating works,

927
00:40:11,370 --> 00:40:13,615
because we have cosmic rays.

928
00:40:13,615 --> 00:40:15,240
It's kind of a neat
connection to make.

929
00:40:15,240 --> 00:40:17,323
If there weren't cosmic
rays, all of the carbon-14

930
00:40:17,323 --> 00:40:21,720
would decay pretty quickly
in the universe time scale.

931
00:40:21,720 --> 00:40:25,350
And we wouldn't have this
form of radiocarbon dating.

932
00:40:25,350 --> 00:40:28,320
And then same thing for tritium
production in the atmosphere.

933
00:40:28,320 --> 00:40:30,830
This is where some of that
tritium naturally comes from,

934
00:40:30,830 --> 00:40:33,530
is it makes carbon-12-- which
is the normal form of carbon--

935
00:40:33,530 --> 00:40:36,080
but out come tritium,
which there is going

936
00:40:36,080 --> 00:40:38,750
to be some constant isotopic
fraction of tritium in all

937
00:40:38,750 --> 00:40:40,760
the world's hydrogen.
Some of it's being

938
00:40:40,760 --> 00:40:43,670
generated in real time.

939
00:40:43,670 --> 00:40:45,860
And we do have these
spallation sources on Earth.

940
00:40:45,860 --> 00:40:48,500
Like I mentioned, the
Spallation Neutron Source

941
00:40:48,500 --> 00:40:50,570
has a gigantic synchrotron.

942
00:40:50,570 --> 00:40:53,930
We've seen these before, which
just injects in this case

943
00:40:53,930 --> 00:40:58,100
protons, which circle around and
around and around, accelerating

944
00:40:58,100 --> 00:41:02,570
until some of them are
extracted and fire onto things

945
00:41:02,570 --> 00:41:06,740
like a liquid mercury target,
some neutron rich liquid metal.

946
00:41:06,740 --> 00:41:09,050
So you want something
that's very neutron rich.

947
00:41:09,050 --> 00:41:10,970
You want something
that's very dense.

948
00:41:10,970 --> 00:41:13,670
You want something that's fluid
so you can cool it better.

949
00:41:13,670 --> 00:41:16,070
And you want something with
high thermal conductivity.

950
00:41:16,070 --> 00:41:17,990
That's where the metal comes in.

951
00:41:17,990 --> 00:41:20,420
So a liquid metal you can
keep cool really well.

952
00:41:20,420 --> 00:41:23,900
Because when you're firing lots
of 800 MeV protons into it,

953
00:41:23,900 --> 00:41:26,795
you generate a tremendous
amount of heat.

954
00:41:26,795 --> 00:41:28,670
And this is what the
actual thing looks like.

955
00:41:28,670 --> 00:41:30,980
You can get tours of
this down in Tennessee

956
00:41:30,980 --> 00:41:32,948
at the Oak Ridge National Lab.

957
00:41:32,948 --> 00:41:34,490
Actually, I've driven
up here before.

958
00:41:34,490 --> 00:41:36,350
I recognize this from the map.

959
00:41:36,350 --> 00:41:38,680
That's pretty cool.

960
00:41:38,680 --> 00:41:40,560
So where the actual
neutron science stuff

961
00:41:40,560 --> 00:41:42,580
happens, where all
the scientists sit

962
00:41:42,580 --> 00:41:44,580
with their targets, there's
quite a bit of stuff

963
00:41:44,580 --> 00:41:46,050
going on behind it.

964
00:41:46,050 --> 00:41:47,910
So there is a gigantic--

965
00:41:47,910 --> 00:41:50,960
you can see that's a
parking lot for scale.

966
00:41:50,960 --> 00:41:54,420
There's a gigantic
linear accelerator

967
00:41:54,420 --> 00:41:57,090
shooting into the
synchrotron ring, which

968
00:41:57,090 --> 00:41:59,130
then fires the protons
here into the target

969
00:41:59,130 --> 00:42:03,720
into one of any number of end
stations, which creates a not

970
00:42:03,720 --> 00:42:07,230
quite push button, but
turn on-able pulsed neutron

971
00:42:07,230 --> 00:42:09,220
source, which is pretty slick.

972
00:42:09,220 --> 00:42:11,880
And again, parking
lot for scale.

973
00:42:11,880 --> 00:42:14,410
Takes a lot of magnets to
bend an 800 MeV proton.

974
00:42:16,722 --> 00:42:18,180
That's what it
actually looks like.

975
00:42:18,180 --> 00:42:21,670
Has anyone ever seen one
of these synchrotrons?

976
00:42:21,670 --> 00:42:24,525
Like at Brookhaven or at
Oak Ridge or at anywhere?

977
00:42:24,525 --> 00:42:25,900
They're quite
interesting things.

978
00:42:25,900 --> 00:42:28,570
The closest one
to us is the NSLS,

979
00:42:28,570 --> 00:42:30,700
or the National Synchrotron
Light Source version

980
00:42:30,700 --> 00:42:32,620
two at Brookhaven National Lab.

981
00:42:32,620 --> 00:42:34,973
It's like a 2 and 1/2 hour
drive down in Long Island.

982
00:42:34,973 --> 00:42:36,640
I don't know if they're
doing tours yet,

983
00:42:36,640 --> 00:42:38,770
but it's about a
kilometer around.

984
00:42:38,770 --> 00:42:40,780
And I was told they did
bike races around it

985
00:42:40,780 --> 00:42:42,447
to see who could beat
the protons, which

986
00:42:42,447 --> 00:42:44,920
of course everybody loses.

987
00:42:44,920 --> 00:42:47,200
But they are pretty
insane collections

988
00:42:47,200 --> 00:42:48,970
of magnets, vacuum equipment.

989
00:42:48,970 --> 00:42:53,140
And once in a while a
proton will pass through.

990
00:42:53,140 --> 00:42:55,177
And then there's the
spallation source itself.

991
00:42:55,177 --> 00:42:56,760
So this is what the
target looks like.

992
00:42:56,760 --> 00:42:59,040
There's going to have to
be liquid metal cooled in.

993
00:42:59,040 --> 00:43:02,892
And then out of here come lots
and lots and lots of neutrons.

994
00:43:02,892 --> 00:43:04,350
Enough neutrons
that you still need

995
00:43:04,350 --> 00:43:05,640
hot cells to deal with things.

996
00:43:05,640 --> 00:43:07,630
They're still quite
radioactive, inactivated.

997
00:43:07,630 --> 00:43:08,970
But it's not a reactor.

998
00:43:08,970 --> 00:43:11,220
Other ways of making neutrons.

999
00:43:11,220 --> 00:43:13,470
Speaking of, has anybody
seen the pulsed fusion source

1000
00:43:13,470 --> 00:43:18,240
that we have down
in Northwest 13?

1001
00:43:18,240 --> 00:43:18,870
No?

1002
00:43:18,870 --> 00:43:20,880
We have a pulse
neutron source that you

1003
00:43:20,880 --> 00:43:23,400
can come take a look at.

1004
00:43:23,400 --> 00:43:26,133
It's an electrostatic
fusion pulsed machine.

1005
00:43:26,133 --> 00:43:28,050
There's a whole bunch
of tritium and deuterium

1006
00:43:28,050 --> 00:43:31,440
in this palladium sponge,
what happens to hold hydrogen

1007
00:43:31,440 --> 00:43:33,450
and its isotopes very well.

1008
00:43:33,450 --> 00:43:36,240
And with a very quick pulse,
you can have a tiny pulse fusion

1009
00:43:36,240 --> 00:43:39,180
and generate about 10 to the
8th neutrons that actually is

1010
00:43:39,180 --> 00:43:41,100
a push button neutron source.

1011
00:43:41,100 --> 00:43:43,980
So if you want to see a
neutron source beyond reactors,

1012
00:43:43,980 --> 00:43:45,510
go down to the vault
in Northwest 13

1013
00:43:45,510 --> 00:43:47,070
and ask to see that.

1014
00:43:47,070 --> 00:43:48,780
We did a quick
experiment before trying

1015
00:43:48,780 --> 00:43:51,510
to activate cell phones
to see what was in them.

1016
00:43:51,510 --> 00:43:54,030
We did not generate
enough neutrons to do so.

1017
00:43:54,030 --> 00:43:56,400
But this cell phone has
definitely seen a few fusion

1018
00:43:56,400 --> 00:43:57,842
neutron pulses.

1019
00:43:57,842 --> 00:43:59,550
And we checked later,
it's not giving off

1020
00:43:59,550 --> 00:44:01,200
any residual radioactivity.

1021
00:44:01,200 --> 00:44:03,200
At least we can measure.

1022
00:44:03,200 --> 00:44:05,802
That was a fun
failed experiment.

1023
00:44:05,802 --> 00:44:07,010
And then comes the craziness.

1024
00:44:07,010 --> 00:44:09,650
Since it's about five
of, I want to get

1025
00:44:09,650 --> 00:44:12,450
into things that will
definitely not be on the exam.

1026
00:44:12,450 --> 00:44:15,590
So just sit back and enjoy
and stop taking notes.

1027
00:44:15,590 --> 00:44:18,740
Complete insanity can happen
with super high energy

1028
00:44:18,740 --> 00:44:19,890
electrons.

1029
00:44:19,890 --> 00:44:23,520
We've already talked
about Bremsstrahlung.

1030
00:44:23,520 --> 00:44:26,220
We have talked about
synchrotron radiation, where

1031
00:44:26,220 --> 00:44:29,170
you have a charged particle
going along a magnetic field

1032
00:44:29,170 --> 00:44:29,670
line.

1033
00:44:29,670 --> 00:44:33,190
It changes direction
and gives off X-rays.

1034
00:44:33,190 --> 00:44:37,660
We haven't talked about
inverse Compton scattering.

1035
00:44:37,660 --> 00:44:40,465
Interesting process here.

1036
00:44:40,465 --> 00:44:43,550
In comes a low energy
photon, hits an electron,

1037
00:44:43,550 --> 00:44:47,090
out comes a higher
energy photon.

1038
00:44:47,090 --> 00:44:49,340
Compton scatterings usually
think of as the other way

1039
00:44:49,340 --> 00:44:53,330
around, where a high energy
photon comes in, scatters off

1040
00:44:53,330 --> 00:44:55,880
an electron, loses energy.

1041
00:44:55,880 --> 00:44:58,190
In this case, a
high energy electron

1042
00:44:58,190 --> 00:45:00,410
colliding with a
low energy photon

1043
00:45:00,410 --> 00:45:04,858
can impart energy to the photon.

1044
00:45:04,858 --> 00:45:06,900
And you can actually
calculate-- or in this case,

1045
00:45:06,900 --> 00:45:08,600
I've just taken from a paper--

1046
00:45:08,600 --> 00:45:12,140
the energy gain from
inverse Compton scattering,

1047
00:45:12,140 --> 00:45:15,410
as well as whatever
cross-section there is.

1048
00:45:15,410 --> 00:45:18,020
And even though this is a
very infrequent process--

1049
00:45:18,020 --> 00:45:19,825
well, the universe
is pretty big,

1050
00:45:19,825 --> 00:45:21,200
and contains a
lot of things that

1051
00:45:21,200 --> 00:45:24,320
have magnetic fields
like stars and black--

1052
00:45:24,320 --> 00:45:27,880
whatever else happens
to have magnetic fields.

1053
00:45:27,880 --> 00:45:29,630
And you can identify
radio sources

1054
00:45:29,630 --> 00:45:33,050
by looking for these inverse
Compton scattered X-rays.

1055
00:45:33,050 --> 00:45:36,030
So the Chandra X-ray map,
I believe a piece of which

1056
00:45:36,030 --> 00:45:40,190
or a receiver for which is up in
the building in Porter Square.

1057
00:45:40,190 --> 00:45:42,930
If you guys go down three
stops on the red line,

1058
00:45:42,930 --> 00:45:45,530
you'll see this little area
full of Japanese noodle

1059
00:45:45,530 --> 00:45:48,197
shops, Lesley University,
a bunch of galleries.

1060
00:45:48,197 --> 00:45:48,905
And in a little--

1061
00:45:51,742 --> 00:45:54,200
I think it's still there-- and
a little sign that says, oh,

1062
00:45:54,200 --> 00:45:57,080
and there's the Chandra
X-ray Observatory.

1063
00:45:57,080 --> 00:45:57,668
Whatever.

1064
00:45:57,668 --> 00:45:59,210
They may or may not
have moved, but I

1065
00:45:59,210 --> 00:46:02,430
recommend you check it out.

1066
00:46:02,430 --> 00:46:04,570
And then what happens
to those electrons?

1067
00:46:04,570 --> 00:46:08,180
Well, they can actually decay.

1068
00:46:08,180 --> 00:46:09,840
Pretty interesting things.

1069
00:46:09,840 --> 00:46:12,080
And so some of this
inverse Compton scattering

1070
00:46:12,080 --> 00:46:15,080
has gone into the evidence
for or against where

1071
00:46:15,080 --> 00:46:17,690
cosmic rays come from,
because you should

1072
00:46:17,690 --> 00:46:21,080
see electrons of
a certain energy

1073
00:46:21,080 --> 00:46:22,925
after undergoing this process.

1074
00:46:25,850 --> 00:46:27,020
I think I will skip ahead.

1075
00:46:27,020 --> 00:46:28,530
Oh, I won't skip ahead.

1076
00:46:28,530 --> 00:46:32,010
And so what these
cosmic rays can produce

1077
00:46:32,010 --> 00:46:35,190
is what's called positive,
negative, or neutral pions.

1078
00:46:35,190 --> 00:46:37,860
Other subatomic particles
with masses somewhere

1079
00:46:37,860 --> 00:46:40,860
between protons and
electrons that themselves

1080
00:46:40,860 --> 00:46:44,440
can undergo different reactions
or different decays into muons.

1081
00:46:44,440 --> 00:46:46,170
And don't worry, muons
and pions and such

1082
00:46:46,170 --> 00:46:48,270
are not part of the
topic of this course.

1083
00:46:48,270 --> 00:46:50,640
But they do have
known lifetimes,

1084
00:46:50,640 --> 00:46:52,782
they do have known
masses and charges,

1085
00:46:52,782 --> 00:46:54,240
they do have known
stopping powers.

1086
00:46:54,240 --> 00:46:56,040
We should be able
to measure them.

1087
00:46:56,040 --> 00:46:59,160
And there is a cosmic muon
detector at Boston University.

1088
00:46:59,160 --> 00:47:01,290
Or rather, it's a
pair of detectors

1089
00:47:01,290 --> 00:47:03,690
that looks for this
coincidence of one muon

1090
00:47:03,690 --> 00:47:06,150
scattering off one
detector, or interacting,

1091
00:47:06,150 --> 00:47:08,970
and another particle being
sensed directly beneath.

1092
00:47:08,970 --> 00:47:12,503
So we can actually sense these
muons to confirm or refute

1093
00:47:12,503 --> 00:47:13,920
the theories about
where they come

1094
00:47:13,920 --> 00:47:17,140
from in terms of cosmic rays.

1095
00:47:17,140 --> 00:47:19,830
And these neutral
pions are what end

1096
00:47:19,830 --> 00:47:21,840
up creating these gamma rays.

1097
00:47:21,840 --> 00:47:25,570
I think they were around
the 70 something MeV range.

1098
00:47:25,570 --> 00:47:27,540
So if these theories
about them are correct,

1099
00:47:27,540 --> 00:47:29,730
we should be able to
sense these gamma rays,

1100
00:47:29,730 --> 00:47:32,700
and sense how many of them there
are as a function of energy.

1101
00:47:35,460 --> 00:47:36,810
That's not what I wanted to do.

1102
00:47:40,920 --> 00:47:42,600
Let me recreate
presentation mode,

1103
00:47:42,600 --> 00:47:45,840
because this is definitely
delving into the kind of stuff

1104
00:47:45,840 --> 00:47:47,310
that, well, I'm
not an expert in.

1105
00:47:50,110 --> 00:47:52,870
So a quick detour into
subatomic physics.

1106
00:47:52,870 --> 00:47:55,570
You guys probably have heard of
that protons and neutrons are

1107
00:47:55,570 --> 00:47:57,880
not the smallest building
blocks of matter.

1108
00:47:57,880 --> 00:48:01,330
They themselves can be composed
of quarks and antiquarks

1109
00:48:01,330 --> 00:48:03,910
with different charges
and different masses.

1110
00:48:03,910 --> 00:48:05,560
They're given different flavors.

1111
00:48:05,560 --> 00:48:07,780
I don't know who came up
with this terminology,

1112
00:48:07,780 --> 00:48:09,430
but it's kind of fun.

1113
00:48:09,430 --> 00:48:11,170
Things get kind
of whimsical when

1114
00:48:11,170 --> 00:48:13,420
you get into subatomic physics.

1115
00:48:13,420 --> 00:48:17,290
And these quarks and
the gluons between them

1116
00:48:17,290 --> 00:48:20,230
are what composes protons,
neutrons, in their antimatter

1117
00:48:20,230 --> 00:48:23,100
counterparts.

1118
00:48:23,100 --> 00:48:26,550
And these sorts of things can
also undergo their own decay

1119
00:48:26,550 --> 00:48:27,340
and reactions.

1120
00:48:27,340 --> 00:48:30,480
So when beta decay
occurs, it's actually

1121
00:48:30,480 --> 00:48:33,000
one of these up quarks
turning into a down quark

1122
00:48:33,000 --> 00:48:36,360
and releasing an electron
and an antineutrino.

1123
00:48:36,360 --> 00:48:40,050
But again, we're not going to
delve even deeper into this.

1124
00:48:40,050 --> 00:48:43,080
There are other particles
composed of other arrangements

1125
00:48:43,080 --> 00:48:44,380
of quarks.

1126
00:48:44,380 --> 00:48:48,780
So if you have just an up and a
down, you have a positive pion.

1127
00:48:48,780 --> 00:48:50,020
Which should have a charge--

1128
00:48:50,020 --> 00:48:53,580
I think one's 2/3
of one's minus 1/3.

1129
00:48:53,580 --> 00:48:54,990
Yep, that is correct.

1130
00:48:54,990 --> 00:48:58,800
So a plus pion should
have a charge of 1/3

1131
00:48:58,800 --> 00:49:00,420
the charge of an electron.

1132
00:49:00,420 --> 00:49:02,370
So if you know the
mass of some particle

1133
00:49:02,370 --> 00:49:04,260
because you know the
number of quarks,

1134
00:49:04,260 --> 00:49:06,090
and you know the
charge of it, you

1135
00:49:06,090 --> 00:49:08,873
should be able to calculate
its own stopping power.

1136
00:49:08,873 --> 00:49:10,290
And figure out how
many should get

1137
00:49:10,290 --> 00:49:12,270
through the atmosphere
and such, or how many

1138
00:49:12,270 --> 00:49:14,800
get absorbed in your detector.

1139
00:49:14,800 --> 00:49:17,310
And so when a very high
energy proton collides

1140
00:49:17,310 --> 00:49:20,070
with an atmospheric molecule,
it creates neutrons,

1141
00:49:20,070 --> 00:49:22,140
creates a shower of pions.

1142
00:49:22,140 --> 00:49:26,400
These neutral pions-- much like
electron positron interaction--

1143
00:49:26,400 --> 00:49:30,130
can produce their own gammas.

1144
00:49:30,130 --> 00:49:32,400
So they can spontaneously
decay from particles

1145
00:49:32,400 --> 00:49:36,450
that are mass into gamma
rays of pure energy.

1146
00:49:36,450 --> 00:49:40,140
Which then go on to create
their own shower of electrons

1147
00:49:40,140 --> 00:49:42,420
and positrons by
pair production.

1148
00:49:42,420 --> 00:49:45,540
Because as we saw, the higher
in energy you go for photons,

1149
00:49:45,540 --> 00:49:48,120
the more likely pair
production becomes.

1150
00:49:48,120 --> 00:49:49,660
And there you have it.

1151
00:49:49,660 --> 00:49:54,820
This is part of the 22.01 stuff,
but taken to the nth degree.

1152
00:49:54,820 --> 00:49:56,460
And then the evidence
for pion decay

1153
00:49:56,460 --> 00:49:59,670
comes from extremely
fine measurements

1154
00:49:59,670 --> 00:50:03,660
of the number of these pions
as a function of energy.

1155
00:50:03,660 --> 00:50:04,910
Or in this case, look at that.

1156
00:50:04,910 --> 00:50:08,110
They're-- what is it-- ergs per
centimeter squared per second.

1157
00:50:08,110 --> 00:50:09,765
What does that unit
physically mean?

1158
00:50:12,125 --> 00:50:13,250
Not going to get into that.

1159
00:50:13,250 --> 00:50:16,120
But at any rate, there
are different models

1160
00:50:16,120 --> 00:50:20,050
for how many of these pions
or their high energy gamma

1161
00:50:20,050 --> 00:50:22,085
decay products
should be observed.

1162
00:50:22,085 --> 00:50:23,710
And by looking at
those very carefully,

1163
00:50:23,710 --> 00:50:26,710
you can tell where
they came from.

1164
00:50:26,710 --> 00:50:29,680
Should they have come from
coronal mass discharges,

1165
00:50:29,680 --> 00:50:31,930
so we should know what energy
those protons should be,

1166
00:50:31,930 --> 00:50:33,675
or some other source

1167
00:50:33,675 --> 00:50:36,820
But I am going to stop
there, because it is five of.

1168
00:50:36,820 --> 00:50:40,540
So after that crazy detour, give
you guys 10 minutes to degas

1169
00:50:40,540 --> 00:50:44,440
and absorb some neutral
pion gamma decay products.

1170
00:50:44,440 --> 00:50:47,910
We'll meet upstairs in 10
minutes for an exam review.