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visit MIT OpenCourseWare at ocw.mit.edu. MICHAEL SHORT: I
wanted to give you guys a survey of radiation
utilizing technology and tell you a little bit about
the way this department has changed the way it teaches. It used to be in our department
and probably everywhere else around the country
that first we teach you the theory of how things go
down and understand them, and then we can
teach you the context in which they're placed. This resulted in a rather boring
curriculum, in my opinion, having been one of
the ones that went through this actual curriculum. So for those who don't
know, I was an undergrad in this department. And while I learned a lot
of great things from folks, I also kept some mental notes
on what I would do differently, and now's the chance to do this. So instead, we've adopted
a context first theory second approach, which
means we tell you where we're going to show you
why should you pay attention to the rest of the semester. Then we fill out the rest of
the theory and fill in the gaps and then revisit the context
to show you what you've learned and how you can understand it. That's why today is going
to be a rather light class. So don't take any notes, just
listen, enjoy, ask questions. And I'm going to show you
some of the applications where we use radiation and
the principles of NSE and technology today. And for recitation
today since we haven't gone over any
technical material, we're going to be
heading to my lab to demonstrate one of these
things, a sputter coder which is a controlled system
for radiation damage which applies one material
to the other via the process of sputtering or actual nuclear
or ionic collisions that blast material, in this case,
gold, onto whatever you want to coat,
which in this case is a pile of pocket change. So we're going to make
some gold change today. So the motivation
today is really to get over two questions
is how can radiation be used for benefit and what
is the physics behind how it can be used? I'll be using a zircaloy fuel
rod, the same kinds that you'd see in a nuclear
reactor as the pointer because I'm not a fan of lasers. And this is actually
incredibly light. I can hold it out at the
end, not much visible shaking and I wanted you guys to see
and feel and try and bend what zircaloy actually is like. That's a piece the same diameter
and dimensions and stuff that you would see
in a nuclear reactor. So give it a slight bend. If you try really
hard, you can bend it. But notice how light it is. Notice how strong it is. It's about midway in density
between stainless steel and aluminum, but it's a hell
of a lot stronger than aluminum. It also has the added
benefit that it basically doesn't absorb neutrons. The real reason we use
zircaloys, zirconium alloys and reactors is that they
have very low interaction probabilities or cross-sections. And for those who don't know
what those are, in a couple of weeks we'll be defining
what a cross-section is. This stuff's pretty cool. Also what makes this
nuclear grade zircaloy and not just
regular zirconium is that there's no hafnium in it. Hafnium is chemically
very similar to zirconium, it also happens to be one of the
highest cross-section elements that there is. So you hide the
stuff that you need to be neutronically
transparent in reactors. It happens to be found in the
ground with the last thing you'd want in your
fuel cladding. In fact, you can use hafnium as
a control rod or control blade. So the difference in
chemistry and in cost between nuclear zirconium
what you've got there, and regular zirconium
is the hafnium has been taken out by some very
painful chemical separation. Usually you'd find
about 3% or 4% hafnium. So there's all sorts of
technologies that we use, the principles of nuclear
science and engineering. I'm just going to
say NSE from now on. You're all probably
pretty familiar with power and maybe familiar with
some of these other ones. Like medical isotopes
are the backbone of a lot of imaging
techniques to find and treat different maladies. Space is basically a giant
maelstrom of radiation so you can both use it and
have to shield from it. We'll go over some
of the crazier ways of shielding from space
radiation, actually today. Semiconductors. The way that the MIT
reactor made about 60% of its operating
budget until recently was by irradiating crystals of
silicon single, crystal bools or ingots of silicon, to
make what's called an n type semiconductor, via
the following reaction if I can find an eraser. I'm going to use the shorthand
that we talked about last time. Normally you would take
silicon and you add a neutron and you end up
forming phosphorus. I've not memorized the masses
of the isotope, but in the end this is actually a neutron
capture reaction, and then a resulting decay,
which produces phosphorus, which is what's
also known as an n type dopant. It's a sort of extra negative-- what is it? --a
negative charge type dopant that changes
the conductivity of the semiconductor. There's lots of different
ways of doping semiconductors. One of the best
and most uniform is to stick things in the reactor. So back when silicon
ingots were smaller, like 4 or 6 inches
in diameter, there was a constant train of
these things traveling through the reactor
getting irradiated and being sold and then cut up
into wafers to make devices. And it used to be
students or Europe jobs to load and unload those
things from the reactor. Now, it's not that dangerous. As long as you use the
right handling procedures, like put them on a cart,
pull the cart at arm's length and push like that,
your dose is very low. And that's because for a
given point source emitter, the dose you receive drops off
as 1 over r or the distance squared, which means
that your arm's length, let's say your arm
is about a meter, you can drop the
dose by quite a bit compared to what's
called the contact dose. Well, this poor fool held
the silicon ingots up to their chests like that. They were OK. They got about 10 months
of their yearly allowable radiation dose that won't induce
any additional risk of cancer. But to ensure that they would
not exceed that allowable dose, they became the administrative
assistant for the reactor for the next 10 months. So their job at the
reactor was to answer the phone, which is not
a radioactive activity, including at the reactor. First nuclear power. The reason why I know a
number of you guys are here is pretty simple. It's just a hot bucket of water. The way we make that
bucket of water hot is by putting uranium or other
fuel into these rods assembling a lot of them in a small
space where they then heat up by producing nuclear
fission, capturing the resultant kinetic energy
of the fission products and neutrons and everything
else that comes out and using it to either
heat up or boil water, that's then just driven through
a heat exchanger and a turbine. So aside from
everything on this side, it looks basically like any
other water cooled power plant. The difference is things get
toasty in a radioactive sense, but also pretty
well under control. And what's inside a reactor-- if you say this is the diagram
of a typical Pressurized Water Reactor or PWR where the
water is pressurized enough so as to stop boiling
from occurring, keeping the water liquid which has a
number of safety implications, you've got the core of
the reactor right here-- and these things right here
are called steam generators. It's nothing more than a heat
exchanger that generates steam. --and the steam generated in
here goes off somewhere else and drives the turbine. If you look inside
this reactor you'll notice a lot of different
fuel assemblies or fuel rods, including things like control
rods or shut down rods, rods made of neutron
absorbers like hafnium that we talked about,
or gadolinium or boron 4 carbide or any other
material with a high capture cross-section, meaning a high
probability for capturing a neutron rather than
letting it go from one fuel element to another to
produce more fission, to produce more heat. That's effectively
how a reactor works. So we went over a little
bit about the fuel. The fission and the
energetics is kind of cool. So let's say you start
off with uranium, probably the
fissile isotope 235, and you send in one neutron-- think it's 92. Don't quote me on that though. --and instead of undergoing
some sort of a capture reaction or something else, it can
split into what we call different fission products. And plus, anywhere
between two or three neutrons the usually
accepted number is an average of about 2.44
neutrons plus gamma rays, plus antineutrinos,
plus other energy and some occasional other stuff. The main point here is
these fission products-- if let's say you had
a uranium nucleus and it were to split in
half, fission products go in other directions,
they carry with them quite a lot of kinetic energy. And what we'll be doing a lot in
the second half of this course is watching to see how do
these highly energetic nuclei or atoms-- when they slam into
other atoms, how quickly do they lose energy? How far do they tend to go? These fission products
tend to stop in the fuel. Their range is going to be
on the order of nanometers. I don't even think
it reaches microns. But the neutrons
however, as we saw from looking at
Chadwick's paper, they can go pretty far,
usually on the order of around 10 centimeters
in a reactor before they go do something else. So it might make it
a few fuel rods over, and chances are get captured by
another uranium nucleus making more fission, more neutrons,
and some other fun stuff like gamma rays and neutrinos. Anyone not know
what a neutrino is? So a neutrino is a
very, very low mass but not massless as was found
I think like last year; almost speed of light particle
that's released as part of radioactive decay. They basically don't
interact with matter, but once in a while they do. What that means is that
they travel straight through everything. It's been estimated that
trillions of neutrinos from space are passing
through us per second and on average you won't
get a single interaction during a day. In fact, to detect
neutrinos they've had to fill old hollowed
out salt mines with water and fill them with photo
tubes in the hopes of catching two or three a day. What that means is if
someone turns on a reactor somewhere anywhere
in the world, it's releasing tons and
tons of neutrinos and if all of a sudden
you start to see two or three coming from
the same place, that's a rare event. That's something with some
statistical significance. And there's been projects in
our department using neutrino detectors to try and detect
where reactors are turning on anywhere in the world. So we've been able to sense that
the MIT reactor is next door from the building next door. I don't know how well
this is going to work when you get to farther distances. But the physics is
pretty much there. It's an engineering problem
to figure out, well, how do you detect
enough neutrinos to get a statistically
significant signal? That, far as I know,
has not been solved. Hopefully, by this
time next year it will. There's also control rods-- rods filled with absorbers,
like I mentioned before. If you want to stop
this nuclear reaction, you send in something like
hafnium or gadolinium or boron. So let's say, Boron-11,
like Chadwick knew, would be able to
capture a neutron. And then it would turn into--
what's the next one over? Well, sorry. That's a one and a zero. That's a five. That should turn into carbon-12. And then you've
captured the neutron instead of letting it
get into more uranium and cause additional fissions. So when something's
going wrong, or you want to control the power
level in the reactor, you insert control rods. They soak up the
neutrons, and make the reactor go subcritical. And we'll go over what all
these words mean in due time-- various points in the course. There's also coolant and
what's called moderation. Does anyone know what I mean
by moderation of neutrons? Yeah? What do you mean? AUDIENCE: It thermalizes them. MICHAEL SHORT: It
thermalizes them. And in other words,
it slows them down. Because the probability
that each uranium nucleus can capture a neutron depends
on the energy of the neutron. The cross sections
for interaction, which we give the symbol sigma
for the microscopic or sort of mass independent
cross section, they're functions of energy. They're extremely strong
functions of energy, over the energy ranges
we're interested in. Because we're interested in an
extremely large energy range. These neutrons tend to be
born at around 1 to 10 MeV, or Megaelectron Volts. And by the time they thermalize,
like you said, or reach roughly room temperature, kinetic
energy is of about 2,200 meters per second, they can be-- what is it-- a 40th or 0.025 eV,
fraction of an electron volt. So we're interested in nine
orders of magnitude of energy. And the cross
sections vary wildly over these nine
orders of magnitude. And I'll show you what some of
these look like pretty soon. And in this case, in the
case of light water reactors, like the PWR we saw, the
coolant and the moderator are basically the same thing. You guys remember how when
Chadwick put the paraffin in front of the neutron
source, he started to see more ionizations. That's because the paraffin
is a great source of hydrogen. So is water. Water is an ideal
coolant because it takes a lot of energy to heat
it up, and a lot to boil it. So you can store a lot of energy
with less of a temperature difference in water. And it's full of hydrogen.
And kinematically, it's easier for something
the size of a neutron and the mass of a neutron
to slow a neutron down. Because a neutron
hitting a proton can transfer up to all of
its energy ballistically. Then that proton won't move
very far because it's also got charge on it. If a neutron hits
something heavier, like stainless steel or
other stuff in the reactor, it cannot, by conservation
of energy and momentum, transfer all of its energy. That fraction is
actually pretty small. So you'll see. We'll actually calculate
what that fraction is. But it drops off
pretty precipitously as you start to get
heavier than hydrogen. And finally, there's
reflection and shielding. We'll get into shielding
in terms of how much stuff and how much matter does
it take to stop radiation from getting through. In some cases, you
can stop it all. In some cases, like gammas,
you technically never can. You'll just get what's called
attenuation or continuous removal of gamma rays. But chances are, you can't
remove every single photon from getting out. It's only a matter of how much
do you need it to get down to. And there's a neat aside. Who here has looked down into
a nuclear reactor before? Three of you. Wow. Four. OK. What did you see? AUDIENCE: Not that much. MICHAEL SHORT: Not that much. This is a particularly
powerful reactor known as the Advanced
Test Reactor, or ATR, at the Idaho
National Laboratory. You won't see any others
that look like this. One, because these
crazy-shaped fuel elements are not that easy to make. This is a test or
a research reactor where things get irradiated. It's about 125 megawatts. And the blue light
being produced is called Cherenkov radiation. It's from electrons
and things moving, or beta particles,
electrons, moving faster than the speed of
light in water. Now, as you know, you can't
exceed the speed of light in a vacuum. But things can move
through other media faster than the speed of light
in that medium, effectively producing optical
shock waves given off as little blue cones of
light for each particle. So when folks say, oh,
am I going to go green when I get near radiation? You can say, no,
you'll glow blue. They've just got the wrong
color on all the TV shows. And then onto fusion energy. Since most of us tend
to talk about fission a lot of the time, but
how many of you here are interested in
going into fusion? Usually, it's at
least half the class. And so I figured this used to
be a fairly fission-centric teaching style in
the department. And I think fusion
deserves equal time. Because about an
equal number of you want to go into fusion
to make it a reality. These reactors are laid
out fairly differently. What they'll be is a big,
hollow vacuum chamber that's shaped like
a donut or a torus, and lots of magnets
to confine a plasma or sort of a charged mess of
separated ions and electrons that whirls around in
millions of meters per second. Once in a while, these ions
and electrons, or especially these nuclei, will
collide with each other and undergo a fusion reaction,
or one of a few fusion reactions that I've
written up here for you. So in this case, there's no
elements with a symbol d or t. We're just using those to
refer to deuterium or tritium as a visual aid. But you should know that
they're deuterium and tritium from their atomic numbers. One, which means it's
an isotope of hydrogen. And their mass
numbers, two and three, which is not the mass
number for normal hydrogen. And in this case, when you
fuse deuterium and tritium, you can produce helium
and another neutron. And so then those
neutrons can be used to hit lithium,
which they'll usually have in what's called a breeder
blanket around the outside, which releases more tritium. So fusion reactors actually
can produce their own fuel. The trick is they're
radioactive gases, so containing them can be kind of tricky. You also need a way to get
the helium out of the reactor. But we have one of
these on campus. We have one of the only
three in the country. It's called the Alcator C-Mod. Have any of you guys seen
a tour of this place yet? Almost all of you. So for ever who hasn't,
do it this year. Because this may be the
last year of Alcator C-Mod's operation. That's not to say there
won't be the next fusion device on campus, but
there's one here right now. And it might be a while
before the next one's built. So if you haven't seen it yet,
go and see it this semester, definitely. The reason why
fission and fusion work from an
energetic standpoint, is if we look at the
binding energy per nucleon-- remember, last time we
mentioned the binding energy is the difference in energy. If you were to take, let's
say, a proton and a neutron from infinitely far away,
and bring them together to create a nucleus
of deuterium-- we'll call this D-- these two, the
energy of the proton plus the energy of the neutron,
the rest mass energies, rather, would be greater than the
energy of just deuterium. And that little bit
of mass that's changed is converted into energy. And this is what's known
as the binding energy. If we look at the binding
energy per nucleon or per proton or
neutron, we can get a relative ranking of how
tightly bound each nucleus is. So for the light
isotopes, smashing them together should liberate
excess binding energy-- or sorry, excess energy--
because you'll gain back some of that energy by the
conversion of mass to energy. Same thing over on this
side, just not as extreme of a gradient. If you were to split
apart heavy nuclei, like uranium-235, you can
release a little bit of energy in fission. And once you get
up here to iron, you can't go either
way, which is why, if you think about the
biggest fusion reactors that exist in the universe--
anyone know what they are? AUDIENCE: Stars. MICHAEL SHORT: Stars, right. They tend to hit cores
of iron before they either die out or
go all gravity crazy and become black
holes of supernovas, or whatever you will. This is kind of
the energetic limit for normal nuclear processes. Or if they become
a neutron star, then things get beyond
the scope of this course. I won't be explaining
neutron stars. There's a lot of medical
uses of radiation. I don't know if any of you
guys have seen these things. It's the only time I'll show
a tricky looking biology diagram, because it's kind
of interesting to note. These are what's called
brachytherapy seeds, little seeds of isotopes
that remit a certain type and energy of radiation selected
for their applicability, that can be implanted in the
body at the site of a tumor to deliver localized
radiation treatment. You can either go in through
existing ports on the human, and not having to drill
or cut a hole in someone, or they can be implanted
laparoscopically or surgically. So this way, if you don't
want to subject someone to a whole body radiation
dose or chemotherapy, or if you want to use it in
conjunction with chemotherapy, you can implant a tiny little
seed of a radioactive material in there to deliver a
certain dose to a tumor, and then take it out. And that way you
know very, very well what the dose is going to
be, because you can measure the activity or the number
of decays per second of that brachytherapy seed. And you know how it's
going to change over time. Because you know the
half-life of the particular isotope that you've looked at. There's also things
like imaging. You can have someone
ingest an isotope like technetium-99 metastable,
to highlight certain organs or things in the body
that you can then image later by their decay
gamma rays or other phenomena. It's also one of those reasons
why when you go in an airport, you have to tell them if
you've had a medical imaging procedure. Because a lot of these places
have radiation detectors. And if you are radioactive
and don't identify yourself, you will quickly be
identified and taken into the back room
to the probulator, or whatever they're going
to do at the airports. I don't know. I've never been searched I
don't plan on that happening. There's also X-ray
and proton therapy sending in well-known, well
energy-characterized radiation to fry tumors or other things. In the case of X-rays,
you're relying on what's called exponential attenuation. If you look at the
distance into a material, and you look at the
intensity of the X-rays-- say, at x equals zero,
this is your X-ray source. This is your incoming intensity. It falls off exponentially
with distance. You might then ask
yourself, all right, if my tumor is this deep, and
I apply that radiation dose to the tumor, what
about the rest? What about the part of
the body that the X-rays have to travel through in
order to get to that site? Anyone know how you would
deliver more X-rays to a tumor than the surrounding tissue? Anyone have any ideas? Yeah? AUDIENCE: Go from
different angles so the rays intersect
on the tumor. MICHAEL SHORT: Exactly. Go from different
angles so the rays would intersect on the tumor. I'll have a better diagram,
but I'll draw one for now. Let's say, that's the
eyes and that's the tumor. You can wear this helmet
where X-rays can come in from all different angles. And the X-ray emitter
would have to come in from different angles, so that
as all the rays intersect, this part gets fried the
most, while keeping you from getting too much radiation
to the rest of your brain and ceasing to function. There's also radio tracers. I think I already covered those. So imaging, we already showed an
image of what this looks like. The first X-ray
back in 1895 didn't have that good
resolution, but it was kind of striking
in that you could see the difference in contrast
between bones and tissue. I should replace this
with the X-ray of my foot that was my signing
bonus at MIT. My first day on
the job I went down to clean one of the old
rooms in Northwest 13, which is now where my labs are. And I moved a bunch
of boxes aside, and a 200-pound steel plate,
jagged cut with plasma torch, went down and smashed down
on the bones in my foot. And I had one of those temporary
feats of superhuman strength and was able to lift it up. I went back to try to lift it
up and couldn't move it an inch. I don't know how I
got out of the plate. The next thing I remember,
I was crawling up the stairs to go to the hospital. But I did get an
X-ray, and they were able to sense that
the pain in my foot was due to a hairline fracture. It was like a fracture in the
bones that basically came back together. But the improvement in
contrast resolution in X-rays is what differentiates
the ability to see a hairline fracture
from just the ability to see that you contain bones. And the reason for
this, and we'll be looking at a lot of
these curves in this course, is the differential absorption
or attenuation of X-rays, or any photons of any energy
through different types of matter. And so, for example,
here we have the ICRU standardized
average soft tissue attenuation, as well as bone. And you notice that
there's a few differences in these curves. So also, there's
some similarities. I'll note that these
actually have the same access to the same units. What do you guys notice that's
the same about these curves? How about the value? They're basically the same-- mass averaged with very
little differences. If you look at where it hits
the y-axis, about 3 times 10 to the 3rd, 3 times
10 to the 3rd. The curves follow
basically the same shape. What's the differences? So Sean, what do you think? AUDIENCE: Oh. That little jagged
[INAUDIBLE] out there. MICHAEL SHORT: These
jagged edges right here. Anyone have any idea why? And these reasons
go back to what you learned in
high school in 8.02 in terms of atomic
transitions, not nuclear. Anyone here remember the
k lines or the l lines? Or what was it-- the-- which emission series
were they called-- the different emission
lines that you can get from emission
or absorption spectra? It all has to do with
allowable electron transitions. And notice the units here are
in centimeters squared per gram. What's the main difference
between soft tissue and bone? AUDIENCE: Density. MICHAEL SHORT: Say it
loud enough so I can hear. AUDIENCE: Density. MICHAEL SHORT: Density. Bone tends to be a fair bit
denser than soft tissue. So these are mass-- what is it-- mass
normalized curves. But the fact is, if you have a
bone that has a higher density, then you're going to end
up with more absorption. In addition, you can use some of
these features and differences to your advantage. Like, if you choose a
photon with energy here, it might not be nearly as
absorbing in soft tissue as it would in bone. So by selecting the
mass of the thing you're trying to image
which you don't control, and the energy of the photon
which you can control, you can produce as
much possible contrast as you can between
two different things. Is everyone clear on
how that could work? Cool. We'll be going over why the
curves have these shapes, especially these jagged
edges pretty soon. And like you said,
this is how you irradiate a tumor with X-rays. Because you can't quite
control the amount of dose to any one part
unless you split it up into a whole bunch
of different rays. Proton therapy is
quite different. It's a newer technology. And it relies on very
well-known and distinct ranges of charged particles
to enter the body with very little
damage, stop and do their damage in the tumor, and
not come out the other side. They just require significantly
more expensive hardware. There's one of these at Mass
General Hospital, or MGH, down the road. It consists of a cyclotron or
a particle accelerator, which injects and speeds up protons so
that they're moving very fast, then sends it in a
beam through a bunch of bending magnets
and up to deliver the protons to the patient. The way this works is you
start injecting the beam. And as it goes through
these two magnets, or what's called dees,
every time it moves through the magnet,
it's a charged particle and a magnetic field. It has a fixed curvature. But every time it's accelerated
through this electric field it speeds up, so the curvature
gets greater and greater and greater. And it spins
outwards in a spiral until they exit the beam. And by deciding how
long they get to spin, you get to choose the
energy of the protons. Why does proton therapy work? This has to do with a
difference in interaction between charged particles and
photons, which have no charge. Charged particles
will lose their energy in a very well-known way,
what's called the stopping power formula, until they
actually stop in the matter that they are going through. Photons either scatter or
attenuate, or they don't. And you can't stop them all. So I want to run a quick Monte
Carlo simulation for you guys, and show you what protons
stopping in matter looks like. So this is a
program called SRIM, or the Stopping Range
of Ions and Matter. It uses the formulas that we'll
be deriving and developing in this class to calculate
the trajectory of protons in anything. So let's say, you are
made basically of water. So let's say, you consist
of hydrogen and oxygen in a stoichiometric
ratio of two to one. I think water approximates
humans pretty well. So we'll find out what the
range of these actual protons is in humans. So what we do know is that
it's a proton accelerator. And I know that
the MGH accelerator has an energy of 250 MeV, or
250,000 kiloelectron volts. And finally, we decide
how thick is the person? So how thick is a
person, typically? How many-- what units do we get? How many centimeters thick
is the average person? AUDIENCE: Forward
or from the side? MICHAEL SHORT: Let's go
the shortest distance in, so front to back. Maybe 10? Right? 10 centimeters? Not that much? Can it get halfway through you? Only has to go halfway,
because you can always lie in your stomach. All right. Let's go 10 centimeters. Most of the protons go
screaming right through you. You notice they don't
actually stop in the person. So you don't tend to irradiate
people with 250 MeV protons directly. You'll actually slow
down their energy to something a little more
reasonable, maybe 50 MeV. And then you can actually
watch each of these charged particle tracks being computed. As it hits, let's say,
imaginary nuclei or electrons, the paths will be
slightly deflected. But what's really
striking is they all tend to stop at
about the same place. That's the really cool
thing about charged particle interactions, is if you know the
charge, you know the nucleus, you know the energy, you
can calculate the range to within a very narrow margin. And what this is
doing is just flying. Looks like it's
done 70 ions so far. And it will keep on flying them
until either you hit the end-- let's say, we set it
to do 100,000 atoms-- or you just tell it to stop. Also, when you don't
have to draw the lines, it goes way faster. So let's let it get
maybe 300 or 400 ions, and we'll show you what the
average range of the protons looks like. How far do they go
before they stop? If we look at the
ion distribution it's pretty striking. All of the protons, except
it looks like one of them, stopped at a very fixed
depth of 41.9 millimeters with very little straggle, maybe
0.6 millimeters on either side. So depending on
the depth of the-- you can even get a deep, very
shallow, very small tumor if you get the
distance just right and the proton
energy just right. This is why proton
therapy centers are popping up all over the world. This is a much more
effective, though expensive, treatment for certain
types of tumors. At the same time, since
we're nuclear engineers, we may be concerned
with the amount of radiation damage being
done to different materials. And so this is kind of a
measure of how much energy the protons are losing
as they travel through. Notice, it's not zero. As soon as the protons
enter the person, they start to scatter
around, undergoing some different interactions. But they mostly don't lose much
energy until they reach almost their target depth. And what's called
the stopping power is very low at high energies, very
high at low energies, which means once they get slow
enough, they almost all stop right there at what's
called the Bragg peak. And that's the basis
behind proton therapy. And you'll be able to understand
why every feature of this curve looks the way it does by
the end of this course-- probably by the
end of this month. So let me stop that simulation
because we really could go on forever, but we won't. Then the question is, what do
you do if the tumor is too big? If the tumor is larger
than that straggling, you actually have to sweep
the energy of the proton beam. So you can vary the
energy continuously in what's called
intensity-modulated radiation therapy, where you change
the energy of the proton, sweep it back and
forth across the tumor to cover the whole thing. So you can sweep out in 3D
space the size of whatever you want to die, without
affecting the stuff that you don't want to die. So in this case,
let's say, you'll apply protons of a certain
energy for some point, and then another energy,
and then another energy. And you can maximize the
dose to a pretty flat level, while minimizing the rest
of the dose to the patient. So even while changing
energies, the most dose is done to the tumor,
and as little as possible is done to the
rest of the person. We already talked
about brachytherapy, but we didn't say why it works. This is the first
major topic we'll be talking about in this course. It relies on natural
radioactive decay. And for natural
radioactive decay, you need to understand
decay diagrams, which are energy level diagrams
of which isotopes turn into which others, by
which methods, and how much energy they release
in each type of decay. So for example, the
common one is iridium-192, a pretty biocompatible isotope
because it's, well, it's like a noble metal. And iridium-192 can decay
by one of three pathways and become platinum-192,
gaining a proton. Gaining a proton--
what has to happen for that to be conserved? So let's think about this. Let's say we have platinum-192,
which decays naturally into iridium-192. I can tell you, because we've
drawn the diagram to the right, it's going up one atomic number. So let's just say
that it had n protons, and it now has n plus 1. How do we balance
this nuclear reaction? What are we missing? Yep? AUDIENCE: [? Can the ?]
[? neutron ?] [? turn into ?] a [? proton? ?] MICHAEL SHORT: Can the neu-- OK. So there's a neutron
somewhere in this nucleus that turns into a proton. What are the three--
what are the things that we have to conserve
in any nuclear reaction? Yep? AUDIENCE: Just a question. Doesn't it go from
iridium to platinum, not platinum to iridium? MICHAEL SHORT: Yes. Thank you. I got that backwards. But the numbers are right. The symbols are wrong. Something else I'll
mention about this class. Please do stay on your toes to
correct silly things like that. I don't do scripts because
you didn't come here to see me read off
a piece of paper. Everything's live. All the derivations are
going to be live because its more interesting. It's certainly more
interesting for me to teach, so thank
you for catching that. And please do stay on your
toes if you something silly, especially if it's just not
the same as on the screen. So like Luke said,
we made a proton, or a neutron turned
into a proton. What's not conserved
in this reaction? Yep? AUDIENCE: Charge. MICHAEL SHORT: Charge. How do we balance that? Well, let's add some
other particles. There's got to be some
sort of radioactive decay. So what are our
choices of particles? Yep? AUDIENCE: An electron. MICHAEL SHORT: Sure. An electron. Or more specifically, we'll
call it a beta particle. Just like a gamma
ray is a photon that originates in the
nucleus, a beta particle is an electron that
originates in a nucleus. You can't tell it's a beta
particle just by looking at it. An electron is an electron. The only way you'd know
is either by its energy, or by because they're another
source of electrons nearby. So in this case,
we get beta decay. This looks fairly balanced. One thing that I'll
put in is beta decay is accompanied by
an antineutrino, but I did not expect
anyone to know that. I just wanted to make sure
it's up there for completeness. So what we're relying
on is the movement of these electrons, which are
high charge and low mass, which means they're very low range. Which means when you
implant a brachytherapy seed into a person, the
irradiation volume is only as large as the
energy of that beta particle will allow. The maximum energies
for these beta particles are given by the differences
between the starting and the ending energy. The way these diagrams
are constructed is your ending energy is
usually at an energy of zero, which we refer to as the
ground state of that isotope. And all of these are
relative energies in MeV, or megaelectron volts. So for example, this
iridium-192 has a 40% chance of decaying by beta
to platinum-192, which means the electron
can have up to 1.4597 MeV. And if we know its energy,
we know its maximum range. So selecting the right
isotope and the right activity for the right tumor
is quite important. Notice that there's
also other ways in which this thing can decay. It might release a beta
particle of a lower energy and reach what's called an
excited state of platinum-192, which can then decay by just
giving off this extra 612 keV of energy to
the ground state. So let's write that
nuclear reaction. Let's say we have
platinum-192, and I'll put a star to mention that it's
excited, becomes platinum-192. Where did the energy go? AUDIENCE: Gamma ray. MICHAEL SHORT: Gamma. So why do you say a gamma ray? AUDIENCE: Uh, because
that just seems to me like the biggest source
of energy that's released in a reaction like this? MICHAEL SHORT: So you
said it's because it's the biggest source of energy
that could be released? AUDIENCE: Well, it seems to
me, yeah, like, intuitively that would make sense. MICHAEL SHORT: OK. What do you think? AUDIENCE: Isn't it a
thing when an electron loses energy or drops an energy
level to release the proton? MICHAEL SHORT: Indeed. If an electron drops
down in energy levels, you'll have released
an X-ray or a photon. But that's not a gamma ray. It's not coming
from the nucleus. Yep? AUDIENCE: [INAUDIBLE]. Doesn't it have to be a
gamma ray because of-- like, that's the only way it can
conserve mass [? momentum? ?] MICHAEL SHORT: Exactly. So the question with this is,
what do we have to conserve? Mass momentum energy charge. If we have platinum-192
go into platinum-192, the mass is pretty
much the same. Yep. Question, Luke? AUDIENCE: What does it
mean to put platinum in the excited [INAUDIBLE]? MICHAEL SHORT: It means it's at
a higher energy nuclear state. It means that there is excess
energy in this nucleus. So the difference between
ground state or whatever of iridium-192 and the
ground state of platinum-192 is 1.4597 MeV. Notice I'm not rounding. Don't round. And we can end up with a beta
particle that doesn't quite release all that energy, leaving
some in the nucleus in what's called an excited state. It's analogous to
if you have, let's say, an atom of a, whatever
that happens to be. And since you started talking
about different electron energy levels, maybe this
atom is helium. And it only has two electrons. And one of them gained some
energy becoming excited up to the next energy level. Same thing, but on
the nuclear level, these excitations are
not in the eV range, they're in the MeV range. But you can think of it as a
precisely analogous process for the time being. There are excited
nuclear energy levels, and they can also decay
by photon emission-- in this case, gamma emission
because the masses are basically the same. Remember that the
rest mass energies might be slightly different,
but the charge is the same. There's no real
change in momentum because this is a nucleus
that started at rest. And this way the energy
can be conserved. Yeah, Sean? AUDIENCE: [INAUDIBLE] in
different cases, if they're excited, can they just go
through another decay process? MICHAEL SHORT: Absolutely. So there are multiple isomeric
transitions or gamma rays. So let's chart one of
the paths through here. There's a 14% chance that
iridium decays to this excited state, and it can then
decay by gamma ray to another excited state,
and then decay to ground. So there are lots of
different possible pathways. I've chosen a particularly
simple isotope because it fits on the slide. In your homework,
you're going to get to look at the decay
diagram for plutonium-239. There are not enough
pixels in this projector to show the full
complexity of that. So you'll have to
zoom in a little bit. But I'm not going to
ask you to do anything with it except for
look at the three most likely transitions out
of dozens, maybe scores, who knows? You guys will see. So that's a good question. Yeah. It can decay from an excited
state, to an excited state, to an excited state,
to an excited state, to an excited state and so on,
until it reaches the ground state. AUDIENCE: But does
it lose its energy, like, not by going
to ground state, but by decaying in some
more fission products? MICHAEL SHORT: It wouldn't
be fission products, but everything else
you said is, yes, it can continue to lose energy
by continuously undergoing radioactive decay. And we're going to go some of
this when we explore the early origins of the universe to say,
if you just started off with a soup of protons
and other things, you'd start to form all
the isotopes possible, and the shortest half-life
ones would then decay-- successive decays,
maybe multiple gammas or multiple betas or multiple
alphas at the same time-- I'm sorry-- in
sequence, until it reached something that was
stable, or stable enough that it's still around now. For example, there's no
stable isotope of uranium. There's no isotope of
uranium that will not undergo alpha or spontaneous fission. It's just that the
half-life is so long, that there's still some left
since the universe began. There's still a fair bit left. But you guys are going
to actually calculate as part of your homework
later in the course, how much uranium-235 was there
when the earth was born? And how much has
just disappeared because of the passage of time? So right now, it's
typically about 0.7% U-235 by isotopic composition. It was not the case
when the earth was born. But you guys will be
able to figure that out. Yeah, so good question. And have a rant from me,
I guess, in response. I'll try and keep my
answers a little shorter. Oh, here's a crazy one-- not particularly crazy, though. So this is molybdenum
99 decaying to technetium-99 metastable. There's lots of possible
decays, but the most likely one is right here. The state above the ground
state at about 140 keV, a fairly low-energy and
therefore more easy to detect photon. So if you notice, almost all
the other excited states, with a couple
exceptions, decay down to this 0.14 MeV excited
state, at which point you get decays to
the ground state. Those also have a
rather long half-life. It's a few days. So you can make
moly-99 in a reactor, transport it to a hospital,
feed it to someone, and use these 140
keV gamma rays, because they come
from the nucleus, to image whatever the
technetium will bond to. Yep, Carson? AUDIENCE: [INAUDIBLE]? MICHAEL SHORT: The M
stands for metastable. Now, where do you see it? This one. Yep. Because the direct decay-- you don't-- you never go from
molybdenum-99 to technetium-99 at the ground state. The M stands for metastable,
so it's an excited state. And metastable
tells you that it's got a pretty long half-life. All of these other states
are excited states. Metastable means it's
kind of, sort of, stable on, like, a human
time scale of things. It's not technically
stable, because stable would mean infinite
half-life or close enough. But metastable means
long enough to be detected or used, or
significantly longer than the others. Any other questions
before I move on? Cool. So you can use these to image
where something is in the body. For example, you can
use this to highlight certain organs,
highlight anything that will absorb technetium. Or if you attach, let's say, the
technetium to a type of sugar or something else that will
be uptaken by the body, you can see where it goes. And you can use
gamma ray imagers to make kind of heat
maps or radiation maps of where the technetium's
going to find what could be causing the problem. The problem is--
well, our main problem is there are huge
moly-99 shortages. Right now the only
economically viable way to make molybdenum-99
is in reactors. And there's only a few of
these places in the world that actually make them. And I don't see any on the US. We get ours from Canada. And these are slowly getting
closed down as we go. So the question
is, with millions of these diagnostic
procedures per year, where is the moly-99
going to come from? That might be where some
of you guys come in. If you can use the
knowledge from this course to figure out an energetically
and economically feasible way to make more
moly-99, you're rich. That's, you know,
life goal achieved. Space applications--
if we ever want to get off this earth for a
significant amount of time, we have to deal with
the fact that there's no atmosphere in
space to shield us from the high-energy protons
and other cosmic rays that would otherwise, well, destroy life. So there's a lot of
interesting ideas, and a lot of problems
with astronaut shielding. One of them is that the
protons are so heavy-- I'm sorry-- the protons are
so energetic that they're difficult to shield just
by mass attenuation. And the trick here is,
well, different radiation has different penetrating power. It depends on its
energy, but it also depends a lot on its charge. For example, alpha particles can
be stopped by a sheet of paper. These are the MeV
level helium nuclei. Like, if you hold an alpha
particle source in your hand, the dead skin on your hand stops
the alphas from getting in. Remember that, because I'm going
to be asking you a question later on to see who your
friends are and who they aren't. I don't know if anyone knows
what I'm talking about. But if you do,
don't give it away. Beta particles or electrons have
low mass and half the charge of an alpha particle. They can be able to
get through paper, even through a little bit of plastic. But a small bit of
metal can stop them. Gamma rays go right through. And notice that they've
been drawn not quite being stopped by
the concrete, which is a great shielding material. Because like I said before,
you can exponentially attenuate gamma rays. You can't with all certainty
stop every single one. So then how do you stop these
high-energy charged particles if the more energetic they
are, the more range they are? Boost your
electromagnetic field. So it's actually been
proposed to have spaceships with enormous magnetic fields
or electromagnetic fields around them to deflect
the protons away or around the ship. Because if you can't stop it
by putting matter in the way, rely on the fact
that they're charged particles, and will
curve around whatever has got a high electric
field around it. So this is one
way of, let's say, shielding deep space missions. If you can't put more stuff in
there because stuff is heavy, and launching stuff
into space is expensive, rely on electromagnetism. And there are also RTGs, or
Radio Thermal Generators, or Radio Isotope
Thermoelectric Generators, which are little balls of things
like plutonium or strontium that give off so
many alpha particles. And the alpha particles
have very low range. They deposit their kinetic
energy as heat in the material, and cause them to
glow on their own. If you produce enough heat,
if something's glowing red, you can use thermal electric
generators to capture that heat and turn it directly
into electricity. This is how things like
Voyager and, let's see, all the other space probes with
interesting names are powered. Once you're too far from the
sun for solar power to work, you need something
that doesn't turn off. So you can use RTGs,
which have long enough half-lives to produce
significant amounts of power for a long time, but
short enough half-lives so that their activity
is pretty high. And they release a lot
of energy as radiation. And that radiation is
heavy charged particles which you can capture as heat. So yeah, an actual little sphere
of plutonium that produces 100 watts just sitting there. There is no way to turn it off. That's the end of the sentence. It's plutonium. And finally, there's
nuclear rockets. If you think about using a
reactor for thrust instead of electrical energy,
the design of the reactor gets very different. For example, you can start
to let things get a whole lot hotter when there's no oxygen
in space to oxidize things. And your propellant
maybe would be liquid hydrogen that
doesn't burn, but goes through the reactor and gets
accelerated, turned into a gas with a high kinetic
energy, to fire out the back of the rocket nozzle
and provide the thrust that you need. And so it's nuclear
rockets that would really be the only feasible way without
bending space time, which I don't think we've
really done yet, in order to get to very distant stars. Like that planet they just found
orbiting Proxima Centauri-- four light years away. Pretty close, right? No. Not really. And if you think about how a
nuclear rocket mission would work, well, it doesn't have
to have nearly as much thrust, especially if you
start from orbit. Maybe use a chemical rocket
to launch yourself into orbit, and then spend half your journey
accelerating very, very slowly. And then turn the
rocket around, spend the other half of the journey
decelerating very, very slowly. So you need a long, constant
but low-level thrust for these long-live
nuclear missions. I'm going to stop
here because it's five minutes before the hour. We only have a few more of
these things to go through. But what I will ask
is you guys hang tight for the next few minutes
while these guys take the cameras apart. We're going to go
to my lab and see an application of nuclear
which, like I said, is plasma sputter coating. All right, everyone. So welcome to my laboratory. This is the Mesoscale
Nuclear Materials group, where we make and
break materials for nuclear technology,
usually not in that order. But whatever. We get it done somehow. And this is Reid Tanaka, one
of my graduate students, who has actually repaired
and going to show you the physical principles
and operation of a sputter coater,
which is nothing more than a controlled
radiation damage machine. And he'll be making
some interesting door prizes for you guys. REID TANAKA: Well, as
Professor Mike Short said, this is Professor Mike Short's. He calls it something else. I call it the home--
the rehabilitative home for old, orphaned equipment
and old graduates. All right. And so this is-- actually,
this piece of gear here, I did a little
research on it, and I think it was built
about the same time as I was entering
college 35 years ago. So about 1978, maybe 1980. That's how old this thing is. And now, so Professor Short
goes around, as all of us, and we scrounge and we scab
and we put stuff together. And you'll see that really
indeed, we do that a lot. So this part, we
put together out of a bunch of pieces of parts. If you look at it, and I'll
talk [? to it ?] a little bit. But there's a procedure
that we've got [? rigged ?] [? output. ?] But we
don't know [INAUDIBLE],, so we just sort of
throw them together. So what you're going to see
is a little demonstration of what a sputter coater is. You're going to see
a little [INAUDIBLE].. AUDIENCE: Could you
scoot in here, so we can [? hear your mic? ?] REID TANAKA: It's under vacuum
right now, vacuum pressure. This is our vacuum [? off. ?] AUDIENCE: Let me just-- here-- come right
here so you can see. REID TANAKA: [INAUDIBLE] Again,
there is another pressure indication, but
we don't actually trust that one [? too much. ?]
All right, without further ado, I'm going to power it on. We're going to [INAUDIBLE]
[? center ?] [? a ?] high voltage. It's argon in here. We've got argon supplies
in that bottle over there. And [INAUDIBLE] I just turn up
the high voltage power supply. Turning it up-- MICHAEL SHORT: Should
we get the lights, Reid? REID TANAKA: Voltage. Yeah. We can kill the lights. MICHAEL SHORT: I'll go get them. I'll just get them right
over where you are. REID TANAKA: And if you
see through this glass jar, it's going to be a
little bit of a glow. Some of you might be
able to see it already. MICHAEL SHORT: Oh, yeah. Come a little closer. From where I am, you start to
see the glowing purple plasma. So that's the ionization
of the argon causing it to electrostatically
accelerate towards the gold target. And that's blasting
off gold items that are then coating the
stuff that Reid's coating that you'll see in a sec. But this is a
controlled application of ionization and radiation
damage using a couple of kilovolt argon ion-- don't know if you call it a
beam, but at least in argon ion plasma. So there's a few
other things to note. Remember how we talked about
charged particles having a certain range in matter? Well, charged particles
in, let's say, low-energy particles
in the kV range do not have a very
high range even in gases, which is why Reid
has this vacuum pump connected. Otherwise, the argon
wouldn't make it to where it has
to do the damage. So when there's too
much gas in there-- shuts off. When there's not
enough argon in there, there's no argon
to do the damage. So we're actually exciting
about two kV ions. And their range is
higher than the distance they have to travel, so
they actually make it where they're supposed to go. And this is a kind of
direct application of NSE, along with a fair bit of
high voltage electronics. And that's pretty much
all there is to it. REID TANAKA: OK. So we have about two minutes if
you want to take a closer look and just [INAUDIBLE]. MICHAEL SHORT: Yeah. REID TANAKA: It's not
going to hurt you. MICHAEL SHORT: No. Get right in there. Do you want to see--
if you look underneath, you'll actually see
that blue glowing ring. That's actually a ring of gold
that's being hit by the plasma. And that's causing gold ions
to fire onto the target. REID TANAKA: You guys all took
chemistry at some point, right? Well, they tell you that
one of the great mysteries of the [? world ?]
[? as ?] [? we ?] [? know it's ?]
[? been solved-- ?] [INAUDIBLE] take something and
turn it into gold. Well, you should know that
only the nukes can do that. Right? Really, you got to get away
from all the electrons and all that other chemistry
stuff, and only the nukes. So if you really want to
turn something to gold, you got to join the
nuclear department. Just so you know that. Keep that in mind. MICHAEL SHORT: Has
everyone had a chance to get a close-up look? REID TANAKA: And I think we
got about another minute or so to let it run. MICHAEL SHORT: OK. Anyone have any questions
about what you're seeing here? AUDIENCE: Is it getting,
like, super hot in there, or-- MICHAEL SHORT: That's
a good question. The temperature does
not go up that much. There's certainly kinetic energy
turned into thermal energy as the argon hits the
gold, and the gold hits whatever you're
trying to coat. But the total amount of
energy, the density of that gas is extremely low. That's another reason
why in fusion reactors, the plasma is up to like
millions or tens of millions of Kelvin. There's just not a lot of it. So if you look at the total
amount of stored thermal energy in a fusion reactor,
it's quite low, even though the
temperature or the relation to the average kinetic
energy of the molecules is extremely high. So yeah. Good question. If you want, put your hand
up inside of the chamber. Is it warm? AUDIENCE: [INAUDIBLE] AUDIENCE: It's not warm at all. MICHAEL SHORT: Not at all. Yep. AUDIENCE: The
plasma is the argon? And where's the
gold coming from? From in that [? ring ?] MICHAEL SHORT: There we go. REID TANAKA: [INAUDIBLE]
we'll show you. MICHAEL SHORT: Yeah. We'll open it up and show you. So I'll get the lights on now. REID TANAKA: OK. [INAUDIBLE] AUDIENCE: Why isn't the
pressure [INAUDIBLE]?? REID TANAKA: What's that? AUDIENCE: The pressure changed. [INAUDIBLE] REID TANAKA: Yeah. From the point that we-- when
you walked in and saw that? AUDIENCE: Yeah. REID TANAKA: OK. The first thing--
so this had a sort of a static amount
of argon in it. And when I turned on the
voltage, the high voltage, that's to create the plasma. But then it has to get fed. And so what I ended up doing
with this little knob here, I probably should explain that,
is I was feeding it argon. That argon bottle from over here
it's going into this chamber. When you're feeding the argon
in, then the pressure came up. And if the pressure comes up
too high on this particular instrument, then it has an
automatic cut-off [? when ?] the high voltage [? cuts out. ?]
Because otherwise, you know, one of the reasons why it works
is because we have so few atoms in there. [INAUDIBLE] AUDIENCE: [? Good. ?] REID TANAKA: [INAUDIBLE] what
atmospheric pressure is in [? total? ?] AUDIENCE: 760. REID TANAKA: 760. [INAUDIBLE] Maybe we [? actually ?] have
a little bit of a [INAUDIBLE].. So this is that-- that's the gold ring. AUDIENCE: [? Neat. ?] REID TANAKA: And
in the chamber-- MICHAEL SHORT: You can put the--
you can put the ring facing down for stability if you want. REID TANAKA: What's that? MICHAEL SHORT: I
said, you can just put the ring lying flat down
if you want for stability. Yeah. REID TANAKA: And
in the chamber-- the purpose of having this,
actually, this machine, the main reason
that we use this for is if you have
something that you want to put into a scanning
electron microscope, and-- MICHAEL SHORT:
We're actually going to use one of those
in class, so-- yeah. REID TANAKA: You need to have
some kind of conductive coating on it. So if you're looking at--
[? especially ?] like [? biologic ?] [? stuff, ?] you
actually coat it with something that's conductive. So there you see, it has a gold
coat of about, I would guess, I think for as long
as we did it for, something on the level
of 200 [INAUDIBLE].. It's a pretty thin coat. MICHAEL SHORT: That's
all you need, though. REID TANAKA: Right. MICHAEL SHORT: Remember,
after quiz number one, we will be piloting--
well, two of you guys we'll be piloting a
scanning electron microscope down in the basement. And before we look at whatever
samples you want to see, whether it's one of your
eyelashes, dust on the floor, or a bug you found
or something, we'll want to coat in gold,
so that the electrons that we use for imaging
will have a place to go. We'll have a conductive path,
and they won't charge up, ruining the image. REID TANAKA: All right. I have a question. MICHAEL SHORT: Yeah? REID TANAKA: Is anybody--
was anybody here born this Millennium? Anyone? 2000 or later? Nobody. Anyone in 1999? Nobody in 1999? [INAUDIBLE] How about '98? You were born in '98? MICHAEL SHORT: There we go. REID TANAKA: All right. That would be-- [INAUDIBLE] brought my glasses. I've got that 1998 dime here. It's now gold-coated. And you can have it. [INAUDIBLE] [? too ?]
[? bad. If ?] [? somebody ?] [? wanted ?] [INAUDIBLE]
you got a quarter. You [? could lie ?] [? and ?]
[? say-- ?] But I guess you are the youngest [INAUDIBLE]. Yeah. All right. So you win this. Now, it'll rub off. AUDIENCE: OK. REID TANAKA: So
[INAUDIBLE] you-- AUDIENCE: [? I'll ?]
[? probably ?] keep it in a plastic bag. REID TANAKA: And-- MICHAEL SHORT:
[? Gold ?] [? change. ?] REID TANAKA: I
guess the other ones go to people that [INAUDIBLE]. Oh, no '97. How about a '96? You're a '96? [INAUDIBLE] AUDIENCE: [? There's ?]
[? three. ?] REID TANAKA: What's that? AUDIENCE: There's three '96s, REID TANAKA: Oh,
there's three '96s? OK. You get the-- you
get the [INAUDIBLE].. AUDIENCE: [INAUDIBLE]
over a year old. REID TANAKA: All right. Who wants the
nickel that's a '96? AUDIENCE: [INAUDIBLE]. REID TANAKA: You going
to arm wrestle for it? MICHAEL SHORT: There you go. Right in front of you, Reid. REID TANAKA: Well,
there's three of them. OK. MICHAEL SHORT: OK. REID TANAKA: [INAUDIBLE]. AUDIENCE: Thank you. REID TANAKA: And who
are the other two '96s? You're going to
have to arm wrestle. One gets a quarter,
but one gets the dime. MICHAEL SHORT: [INAUDIBLE]. Yep. REID TANAKA: That's the
only fair way of doing [? it, I think. ?] MICHAEL SHORT: That's not a
nuclear thing, but if it's fun. REID TANAKA: [INAUDIBLE]. Here you go [INAUDIBLE]. AUDIENCE: [INAUDIBLE]. REID TANAKA: And there is
the quarter [INAUDIBLE].. AUDIENCE: Thanks. AUDIENCE: [INAUDIBLE] MICHAEL SHORT: This one? AUDIENCE: [INAUDIBLE]. AUDIENCE: Yes. [? Because ?]
[? it ?] [? was ?] [INAUDIBLE].. MICHAEL SHORT: [INAUDIBLE]
actually [INAUDIBLE].. It's just-- AUDIENCE: It's
[? memorable ?] [INAUDIBLE].. REID TANAKA: OK. Yeah? AUDIENCE: So is that gold
deposited anywhere else in that chamber? REID TANAKA: Yeah. If you look-- actually, if you
look in the chamber, I mean, this is all- this is all
[? from it ?] [? being ?] [? sputtered. ?] And
if you look around-- I can turn this a little. Look at the glass. It gets on the glass, too. So it actually gets--
it gets everywhere. But it's mostly directed to that
area that you saw [INAUDIBLE].. I have another offer. Are you guys all nukes? You guys are all going
to be in the department? MICHAEL SHORT: All but one. REID TANAKA: Ah. AUDIENCE: [? Not me. ?] MICHAEL SHORT: But we
have a nuke enthusiast. So-- otherwise, wouldn't
be in this class. And anyone scared of nuclear
is probably not in this class. REID TANAKA: So obviously, it
was pretty easy for us to do. We have this machine here. If you're going to be
part of our department, if you want to just come
in, we can make you a-- we can make you a quarter, OK? I mean, I could
even supply them. I feel rich [? enough ?]
I can [INAUDIBLE],, because all this grad
student-- graduate school money I'm getting. MICHAEL SHORT: Nice. REID TANAKA: But--
anything else? MICHAEL SHORT: Any questions
for Reid on what you just saw? The goal is to sort of
give you a real life, you know, learn 22.01,
you'll understand how these things work, and
how you can modify them, create new stuff. That's the general idea. Same thing behind
looking at the electron microscope for the focused ion
beam, EDX elemental analysis. I want to bring what
we're teaching you to life as often as we can. Since we only got one
recitation a week, we'll be doing it
about that much. Once in a while I may
schedule some extra stuff as long as folks are available. But we're going
to try all we can to have days like this, where
you get to see what you're learning in real life. AUDIENCE: It was
called a sputter? REID TANAKA: Sputter coater. AUDIENCE: Sputter coater. REID TANAKA: Sputter coater. MICHAEL SHORT: It's because the
process of the argon hitting the gold is actually
known as sputtering, which is the blasting
off of surface atoms by energetic particles. It's a controlled form
of radiation damage. AUDIENCE: What's that Swagelok? MICHAEL SHORT: Swagelok. AUDIENCE: Swagelok. REID TANAKA: Yeah. AUDIENCE: So what's a Swagelok? REID TANAKA: Well-- MICHAEL SHORT: Do we
have any pieces here? Let's see. REID TANAKA: [? We ?] [? have ?]
[? lots. ?] [INAUDIBLE] if you go back [? around ?] [INAUDIBLE]
tubing that you see back in there. They're connected so
they don't [INAUDIBLE].. [INAUDIBLE] [? piping ?]
[INAUDIBLE].. It's proprietary-- MICHAEL SHORT:
They're all in use. REID TANAKA: --made by
the Swagelok companies to [INAUDIBLE]. MICHAEL SHORT: Oh, here we go. REID TANAKA: So I
don't know if Mike's going to take you around. AUDIENCE: [? Absolutely ?]
[INAUDIBLE].. MICHAEL SHORT: This
is Swagelok tubing. It's got a two piece
ferrule, which [INAUDIBLE] a metal-to-metal seal
for moving liquid or gas. And it takes an
insanely high pressure. So actually, over in the next
room, we can look on our way out, we've built a
reactor simulator, like an experimental
reactor that replicates all the conditions
except for the radiation. We had to make it entirely
out of Swagelok tubing, because this stuff can hold the
pressure and the temperature without deforming too much. So when you want to make it
absolutely airtight seal, use things-- Swagelok or things like it. AUDIENCE: Is it stainless steel? MICHAEL SHORT: This
is stainless steel. Yep. But they make it out of
titanium or other things, too. But stainless
steel works for us. AUDIENCE: That's cool. AUDIENCE: In a PWR, how
much pressure is there? MICHAEL SHORT: In a PWR, there's
150 atmospheres of pressure. It's also 150
atmospheres of pressure over in the room next door. AUDIENCE: [INAUDIBLE] MICHAEL SHORT: Like I said,
it's all the same conditions as a reactor except
the radiation. The pressure is what
makes it really dangerous. AUDIENCE: [INAUDIBLE] MICHAEL SHORT: Yeah. We'll look through one of the
few bulletproof glass shields. Because if anything
blows on that loop, it's like a proj--
it is a projectile. We've only had one explosion. There was no
temperature at the time, but it sounded like
a shotgun blast over the side of your shoulder. It was loud. AUDIENCE: You in the room? MICHAEL SHORT: The
loop was right here, and we were right
in front of it. Then the loop jumped
up maybe an inch. And we jumped up
about three feet. We got scared. That was what happens
when you improperly torque a high-pressure fitting. Because you've actually got
to tighten these nuts down to not too low and not
too high of a torque, otherwise, they don't seal. And usually, you only
find out that they don't seal when
they're approaching close to their rated thing. And you're like, great. It's at half pressure. It's OK. You reach 99%
pressure and kaboom. That's what happened. Cool. Thanks a lot, Reid,
for showing this to us and taking time out of your day. REID TANAKA: No problem. Anytime. MICHAEL SHORT: I hope
you guys enjoyed it. So no problems to work
through this week. That's going to change
starting Tuesday, next class. So have a good weekend. And I'll see you guys all
on Tuesday in Room 24-115, next to the room
where we were just in.
