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MIT courses, visit mitopencourseware@ocw.mit.edu. MICHAEL SHORT: So,
today we're going to get into the most politically
and emotionally fraught topic of this course
for stuff on chemical and biological
effects of radiation. Now that you know the units
of dose, background dose, we're going to talk about
what ionizing radiation does in the body, to cells,
to other things, and we're going to get into a
lot of the feelings associated with it. And by the end of this
lecture, or Thursday, I'm going to teach you
guys how to smell bullshit. Because we're going to go
through one of millions of internet articles about
things that cause cancer, that don't cause cancer. In this case, it's going to
be radiation from cell phones. So I'm going to try to
reserve at least 10 minutes at the end of this class for us
to go through a bunch of quote, unquote, studies and
misinterpretations of those conclusions. And I was going to pick my
favorite of the 44 studies, and looking through them all,
my favorite are all of them. AUDIENCE: [LAUGHTER] MICHAEL SHORT: So we'll see
how many we can get through. But let's get into
the science first, so you can understand a
bit about what goes on with ionizing radiation. Like radiation
damage in materials, radiation damage and
biological systems is an extremely
multi-time-scale process. Everything from the physical
stage, or the ballistic stage, of radiation damage
to biological tissues acting on femtoseconds,
where this is just the physical knocking
about atoms and creation of free radicals, these ionized
species, which in metals you wouldn't care about, in
biological organisms you do because then they
undergo chemical reactions from the
initial movement and creation of other
strange radiolytic species and the diffusion and
reaction of those things, which starts and
finishes in about a microsecond, before most of
these things are neutralized. And then, later on, the buildup
of those oxidative byproducts of these chemical reactions
undergo the biological stages of radiation damage. All of the free radicals
with biological molecules have reacted within
a millisecond. So radiation goes in, a
millisecond later the damage is done. Then you start to affect,
let's say, cell division. It takes, on average, minutes
for a rapidly dividing cell to undergo a division. That's when the
effects would first be manifest from a DNA mutation. But then it'd take
things like weeks, or years for these
sorts of things to manifest in a
health-related aspect. So, the division of one
cancerous cell into two won't change the way
your body functions, but the doubling in size of a
tumor that blocks other tissue absolutely would. And so, it all starts in
this sub-femtosecond regime, when most of you-- well,
for this entire year, we've been approximating
humans as water. We're going to continue
to do so for the purposes of these biological effects. So, let's say you, a
giant sack of water, gets irradiated by a gamma ray. And that gamma ray undergoes
Compton scattering. Which, now you know how to tell
what the energy of the Compton electron would be. We never talked about what
happens with the molecule where it came from. That molecule remains ionized. And since you're not especially
electrically conductive, they're not neutralized
immediately. And you can be left over
with either a free radical or an electron in
an excited state. And then what happens
next is the whole basis of radiation damage to
biological organisms. These free radicals can
then encounter other ones, and let's say an H2O+, can
very quickly find a neighboring water molecule, which they're
almost touching and form OH and H3O. This is better known as H+, and
that OH is a kind of unstable molecule. And these excited electrons
here can also become these H2O+'s, leading to this cascade
of what we call radiolysis reactions. There's a few of
them listed here, things like an OH plus
an aqueous electron, which could come from anywhere,
like Compton scattering, like any other biological
process that frees an electron, can make another OH-. So you can locally change
the pH inside the cell that you happen
to be irradiating. Or, let's say any of
these oxidative byproducts could encounter DNA. Rip off or add an electron to
one of the guanine, thymine, or other two or three
bases in DNA or RNA, then you've changed the
genetic code of the cell. In the progression of these
radiologists byproducts, like I mentioned, whether you
go by excitation or ionization, then you start to build up
these six species-- these five species tend to be--
or these six ones tend to be the ending
byproducts of a whole host of radiolysis reactions. And don't worry,
you're never going to have to memorize
all the radiolysis reactions because the mechanism
map is fairly complicated and there are multiple
routes to creating each one. But the ones that
are highlighted here in these squares,
are the ones that end up building up in your
body, things like peroxide. Has anyone ever put
peroxide on a wound before? What happens? Yell it out. AUDIENCE: It bubbles up. MICHAEL SHORT: Bubbles up. What happens when you
form peroxide in your body from radiation? AUDIENCE: It bubbles up. MICHAEL SHORT: Well,
luckily it doesn't quite bubble up on the
macro scale level, but it is a vigorous oxidizer. 90% H2O2 is used as rocket
fuel, as the oxidizing species in rocket fuel. You don't make 90% H2O2
from getting irradiated, but every molecule counts. Things like O2, you're
shifting the amount of oxygen in the cells. And then there's things like
these superoxide radicals, or H2O-, H2O+, or all these
other things that are available to rip off or add an electron
to something else that normally wouldn't have it. And the list of these
potential reactions, as well as their equilibrium
constants and activation energy, is huge. Here's half of it. Notice a lot of
these equilibrium constants shift really
strongly one way or the other. So, just because these
molecules are made, doesn't mean that
all of them end up staying and doing damage. But unless these rate constants
are either 0 or infinity, there's going to be some dynamic
equilibrium of these reactions. So, once in a while, some
of these free radicals will escape the cloud of
chemical change and charge and get to something else. Here's the other half
of the equation set. And it's under debate just
how many of these reactions there actually are. Like, how often would O2-
radicals combine with water, which you can see is not
quite set in the reaction, to form [? HO2 - NO2 NH+ ?] Kind
of a strange little reaction right there. Actually, a lot of
them are quite strange. You don't usually
think of them happening because these are very transient
reactions, whose byproducts do build up. And that's the chemical
basis for radiation damage to biological tissues. Now, once those
chemical products form, they have to move or diffuse. So you can actually calculate
or get diffusion coefficients for some of these
oxidizing species, as well as compute
an average radius that they'll remove before
undergoing a reaction. So this is part of
the basis for why alpha radiation is a lot more
damaging than gamma radiation. Chances are, if you incorporate
an alpha emitter into the cell, it does a whole bunch of damage. That damage consists of these
oxidative chemical species, that, if they're that far away
from neighboring atoms that happen to be in DNA, they
might do some damage. Whereas, isolated Compton
scatters and photoelectric exhortations from gamma
radiation, not so much. Chances are you hit random
water in the cell that isn't quite close to anything,
fragile, and not much happens. But you can also see this by
looking at charged particle tracks. These things can actually
be experimentally measured. By firing electrons into gel
or film or something like that, you can actually see
tracks of ionization and watch them as
a function of time. In this case, it's a simulation
of a charged particle track at different timescales. So, right here, this
10 to the minus 12 for the time in
seconds, tells you where these radiolysis
products are. And the N number, here, tells
you how many of those remain. So after a picosecond,
you can pretty much just trace out the path that the
electron took, starts off right here. What do you guys notice
about the density of the charged particle track
as it moves from the source to the end? AUDIENCE: It's much
more dense at the end. MICHAEL SHORT: It's much
more dense at the end. And why do you think that is? AUDIENCE: Stopping power. MICHAEL SHORT: OK. More than just-- yeah. Stopping power, yes, but
fill in the beginning and end of that sentence. Chris, do you have your hand up? AUDIENCE: [? It's all good. ?]
So, it's a charged particle, so it drops off most of it's
energy where it has the least amount of energy, so it does
the most damage [INAUDIBLE].. MICHAEL SHORT: That's right. So, you're actually
visualizing the change in stopping power as a function
of charged particle energy. It comes in, has a
very high energy. And it might knock a little
radiation damage cascade by hitting another
electron, which can have its own shower of ionization. And then it moves while doing
nothing, in this straight line, until it hits another one. And notice right
at the end, that's where the densest amount of
damage is done because that's where the stopping
power is the highest. It's also where the
energy is the lowest. So, this is where the worlds
of and physics collide. You can actually visualize
stopping power, like actually visually in gel or on
film or on a computer by watching these
charged particle tracks. And after 10 to the
minus 12 seconds, all the ballistics are over. Then you end up with
diffusion and reaction. So, it's going to be a balance
between these charged particles moving away from each other
and finding something else, or finding each other
and re-combining. And that's why, as you
go up in timescale, the particle tracks get
more and more diffuse and the number of these
remaining free radicals goes down until you level
out at about a microsecond, when all of the
different particles are so spread out
that there are none touching each other anymore. To refresh your memory a
bit from a few seconds ago, take a look at
some of the charge states of these
oxidative byproducts. Some of them plus, some of them
minus, sum of them excited, all over the place. So they can react
with each other, which is something you'd want
to encourage so that they don't go and find
something else, causing biological damage. There's a question on last
year's OCW problem set, that I'm not giving
you for this one, which is, calculate the
radiation resistance you would get by getting
cryogenically frozen. So here's a question
that I don't think a lot of cryogenicists
ask themselves, if you want to preserve
a human for 10,000 years and wake them up later,
how much radiation damage are you going to get? Ever think there's
a cryogenicist that ask themselves that question? I don't actually know. But it's not a question
I've ever heard before, which is why I made it
a problem set question. Because I know the
answer is not out there. I looked for a while. Let's switch particles
for a second and look at the charged particle
tracks from a proton. What differences do you
see between the proton and the electron
charged particle track? So, proton, electron. Proton, electron. AUDIENCE: There's no curve. MICHAEL SHORT: There's what? AUDIENCE: There's curve. It's straight. MICHAEL SHORT: Its straight. Why do you think it's straight? Why does anyone
think it's straight? AUDIENCE: They're bigger. MICHAEL SHORT: They are
bigger, more massive. So the same deflection, the
same transfer of momentum, to an electron using our beloved
hollow cylinder approximation thing, causes less of a change
in direction for a proton as it does an electron. The forces are the same. They're both just a plus
or minus 1 hitting a plus or minus 1 charge. But the mass is quite
different on the proton, so it doesn't get
deflected as much, which is why the
charged particle tracks are so straight. Now, what are these things here? What are those offshoots? AUDIENCE: [INAUDIBLE] MICHAEL SHORT: They're secondary
charged particle tracks. So, let's say a proton
hits an electron, that electron can have any
amount of energy, probably going to be lower
than the proton did. And it's going to cause
its own little damage cascade right there. And, just like before, you
can track the number of these charged particle trucks moving
from 5000 to about 1000, between, let's
say, 10 picoseconds and a little less
than a microsecond. And once these charged particles
have spread out or diffused away, chances are recombination
has gone down quite a bit and they're going to go
react with other things. And this is a perfect analogy
to radiation damage in metal. So, radiation damage in biology
is like radiation damage in material science. You have this initial
cluster of damage, in materials it's usually
vacancies or intestinals, in biology it's
charged particles. But when they're
in a dense cascade they can recombine
with each other. And the ones that
miss each other go off to find either other
defects in the material or other atoms in your cells. It's a very fitting analogy. Yeah? AUDIENCE: How come we don't
see like a denser [INAUDIBLE] to the proton
[INAUDIBLE] electrons? MICHAEL SHORT: Let's see. I don't know if we see the whole
charged particle track here. You're right, it doesn't
look like the density changes very much. You can't even really
tell where the source is. We may not be looking
at the whole thing. Here's another question. So, it's a 2 MeV proton. That scale bar is 0.1 microns. Let's do a quick simulation
to verify this idea. Luckily we have the
tools to do this, soon as I clone my screen. Let's use SRIM and find out what
is the range of 2 MeV protons in water. And if it's more than about a
micron, which is what's shown-- well, let's say,
that's 2 microns. If it's more than 2 microns,
what's shown on the screen, it means we're not
seeing the whole track. SRIM. Good, you can see it. So let's say, hydrogen at 2 MeV,
going into something consisting of H and O in a
ratio of 2:1, make sure its density is correct
for room temperature water, and let's look at a
range of 25 microns, because I kind of
already know the answer. AUDIENCE: [LAUGHTER] MICHAEL SHORT: Much
more than 25 microns. So, our initial
assertion was correct. Let's actually find
out what the range is. Let's put 40 microns. Whew, it's a little
more than I thought. Protons in water, at just 2 MeV. Let's fly tons of them. Wait til we get about 1,000. Look at the range. Make it bigger so
you can read it. 75 microns. 75.5 micron range. There you go. Let's go back to the big one. So, there you go. If this scale bar is 0.1
microns, you're looking about 2 of the 75 microns of
charged particle track. Interesting, no one picked
up that question last year, but I'm glad you did. I'm glad we were able to
show you where it comes from. So this will look
quite different if you're looking at the end
of the charged particle track. Cool. Good question. To look really,
really close up, you see a lot more of
this branching again. So whenever a proton strikes,
let's say another atom or an electron, you get your
own little dense damage cascade. And look at that, not
much until the very end when you get this cloud of
damage popping off at the end. So, yet more examples of the
physics that you've learned popping up in
biological systems. The difference is
it's water not metal, but otherwise
everything's the same. And then we get to
what's called G-values. I don't know why it's
called G, but I'll tell you what they mean. It's the number of each species,
per 100 MeV, found later, at let's say, 0.28 microseconds,
or typically 1 microsecond, for different particles
of various energies. These are relative
effectiveness' of these particles at different energies
to leave oxidative byproducts by. So there's a few things that are
wrapped up into these G-values. So, notice that, in
this case, here's a G-value for electron energy. At different
energies, you'll have different amounts of OH, H3O
in such, per 100 eV of energy. So the unit of
G-values here, it's like number of chemical
species per 100 eV of energy. So it's an energy normalized
measure of the effectiveness of radiation making chemicals. Does make sense to folks? If not, raise your hand
and I'll try to re-explain. OK. AUDIENCE: Please repeat it. MICHAEL SHORT: Yep. So a G-value, it's got units in
concentration per unit energy. And it's a measure
of how many chemicals a given particle will make
as a function of its energy. And these particles are the ones
that survive the recombination and end up diffusing
to other species. So, these G-values, it's
kind of like how many oxidative species are made that
go off and damage other things? Let's look at some
trends right here. For things like
OH, for electrons, what sort of patterns do
you notice in the data? And take a sec to parse
some of these numbers. Just look at the top three rows. What pattern do you see? AUDIENCE: Starts
high and then goes-- MICHAEL SHORT: Starts high,
goes low, goes high again. Why do you think that is? Straight from the physics. At super low energies,
100 eV electron, you'll make, on
average, 1 OH radical for every 100 eV of energy. As you increase in
energy, you start making fewer and
fewer per unit-- actually, that's not the
one I want to look at. That's a different species. Let's see. No, that is. OK. That follows the pattern
that we're looking for. AUDIENCE: Does the
high energy includes stuff that's created from
causing secondary cascades? MICHAEL SHORT: Oh, yeah. This is just total
number from everything. Right? It's just the number of each
chemical species left over after a microsecond. So what do you think could
cause this initial increase and then decrease
and then increase? AUDIENCE: Is it because
of the cross-sections of different particles? MICHAEL SHORT: Part of it. The cross-sections that also
go into the stopping power. That's part of the answer. So at really low
energies, you're already at your stopping power peak. And that way, for the little
bit of energy you have, chances are it's going to
ionize different things. Then as you increase
your energy, you have more and
more of that range of the particle in the
lower stopping power region. So, you'll have more
of the-- let's see. You'll have more and
more of that particle-- let me try and phrase
this quite well. Let's go back to the charged
particle tracks for electrons, and I'll get this--
yeah, here we go. So, when you're electron comes
in a really, really low energy, you're in that
region right there. Chances are you're
going to make a lot of those oxidative byproducts. And then as you go a
little higher in energy, you make fewer per
unit distance-- or you make fewer
per unit energy. You can think of that as
the spread, right there. But then also, as you
go way higher in energy, your ability to
ionize increases. So you've got that
sort of 1 over E term in stopping power
making things worse. And you've got
that log of E term in stopping power
making things better. And if we go back to
the data right here, for those top three
or four, it tends to follow that
trend pretty well. Now what about things like H202? What sort of trend
do you see there? AUDIENCE: The opposite. MICHAEL SHORT: The opposite. So, I'll give you a hint. H2O2 isn't directly
made by radiolysis, it tends to occur by reaction
of other radiolysis products. So it's like a
secondary chemical, not a primary produced chemical. So, why do you think H2O2
follows the opposite trend? AUDIENCE: It comes from
the-- not the decay, but like a reaction from one of
the previous ones, that there's more of that first
species there, that it hasn't reacted to form it yet. But once it is
lowered, that means it's made more of the H2O2. MICHAEL SHORT: Sure. AUDIENCE: And then vice versa. MICHAEL SHORT: Yeah. So, to rephrase what Sarah
said, in this energy range right here, you're producing
this fairly dense cascade of oxidative byproducts. When those reactions
occur, they tend to make things like
H2O2, something that's not made directly from
radiolysis, but indirectly from recombination
of those chemicals. And then as you raise the energy
more and more, to like 20 keV, you start making those primary
products more spread out. They're not as
close to each other. They don't recombine as much. They don't make as much H2O2. They'll tend, instead, to
spread out a little more. So more will survive. More of these primary
ones will survive, and not react to make as many
of the secondary ones. So, how is that explanation
fitting with you guys? Cool. So, it's a balance between
intermediate energies. You make a whole lot
of primary ones, which are so close that they react to
make the secondary species much more easily. As you raise the energy
of the particles going in, you make more isolated primaries
that can't find each other, and they don't make as many
secondaries per unit energy. Yeah? AUDIENCE: How come for like
the 100 eV H2O2 it's less? Because since it's making
a lot of the initial, or the primary,
byproducts, wouldn't you expect it to also make
a lot of the secondary because they're
also close together? MICHAEL SHORT: You might,
except at very low energies, our idea of stopping power
isn't quite as complete. So, by what other processes
can electrons lose energy at really low energies? You could have a deflection
without an ionization, right? Just a simple-- let's say,
you could have an excitation, you could have just
coulomb deflection, you can have neutralization. You can have all those really,
really low energy things that go on, that don't end up
producing as many ionizations. Because you need to produce
an ionization or an excitation to kick off radiolysis. So then, when you get
high enough in energy, and chances are you'll
ionize rather than undergo one of these really low
energy inner loss mechanisms, then you start making
more of the primaries, but densely, which make
more of the secondaries. Then as you go even
higher in energy, you still make
tons of primaries, but since they're
spread out more, since the stopping
power is lower, they don't find
each other and they don't make as many secondaries. So, let's look at some
other numbers and trends, different particles. First of all, for protons
and for alpha particles, note here that the
scales are in MeV. Whereas, the G-Value is for
electrons in the keV range, and for protons in the MeV
range are pretty much the same, on the same order of magnitude. Anyone have any idea why? AUDIENCE: They're heavier. MICHAEL SHORT: They're heavier. And then what does that lead to
in terms of a stopping power? AUDIENCE: They're
easier to stop. MICHAEL SHORT: They're
actually harder to stop. If they're heavier, than the
deflection of an electron doesn't stop them as much. And so that way, more of these
proton and alpha radiolysis products are going to
be more spread out. So you get the same
number per 100 MeV, in the MeV range, as
you do for electrons at a much lower energy. But then alphas also have
this interesting thing that they're doubly charged,
so that those coulomb forces, remember
it's by Z squared, so it's four times as strong. So, let's see, how
do they compare? Yeah. There aren't really enough
data to draw those nice trends that you could see
from electrons. But we do have some
other interesting trends in the G-values as a
function of temperature. So these right here are
G-values for H and OH by gamma rays, which
are two primary species. And here we've graphed them
as a function of temperature. Why do you think the
G-values, or the amount of radiolysis products that
survive a microsecond, increase with temperature? What's this a competing
force or a balance between? So once these products are
made, what are the two things that they can do? Anyone? AUDIENCE: Recombine or diffuse. MICHAEL SHORT:
Recombine or diffuse. Good. Which of these will
increase much more strongly with temperature? AUDIENCE: Diffusion. MICHAEL SHORT: Diffusion. If they spread out more at
higher temperature, then they'll separate from each
other and not recombine as much. So a whole bunch will
be made, no matter what, in a matter of femtoseconds. But at a higher
temperature, more of them diffuse away from each other
and survive the cascade, rather than recombining. And so that's why, when you look
at any primary species, H2 or H or anything like
that, you're going to see an increase in
G-values with temperature. What do you guys think
is going to happen to these secondary
byproducts with temperature? AUDIENCE: Decrease
with temperature. MICHAEL SHORT: Decrease. And why do you say so? AUDIENCE: Well, if they're
made from the primary products and the primary products are
surviving more because they're separating, then the secondary
ones are just going to be less. MICHAEL SHORT: Yeah. If the primary ones
are surviving more, you're not going to make
as many secondary ones. And that's just what we see. Number of free electrons
left, or especially things like the amount of H2O2, it's
all going to be in balance. And if more primaries
survive, you don't make as many secondaries
as a function of temperature. One, these heavy ones
are slower to diffuse. But two, they're
not made as much because the primaries escape
each others pull and go off to damage something else. In a reactor, this would be
metals causing oxidation. In a body this would be you. And so let's get into the
materials aspect of this to give you a more-- a less biologically
damaging view of what can
radiolysis really do. It's quite relevant to
all reactors, including the Fukushima reactor. The idea there is
that the reactor was flooded with seawater,
which introduces chlorine, which greatly
changes the balance of radiolytic byproducts. And this can actually
be directly studied. There's an experiment
just a few years ago-- two years ago, where
they wanted to figure out what is the influence of
radiolysis on corrosion? If you're making all of
these Hs and OH-s and H2O+s, does it change the
corrosion rate of materials in the reactor? So they built a
high-pressure cell, that they fill with
high-pressure, high-temperature water. And they've got this little disk
of metal with a thin membrane right there. It's thin enough that
protons can pass through it and cause radiolysis to occur
right in this little pocket where the water is. And so where the protons
are, you get radiolysis. Where the protons aren't,
you get regular old water corrosion. And the results are
pretty astounding. You can see the irradiated
zone in extra oxide thickness. So you can see where
the protons were because radiolysis
sped up the corrosion rate as a single effect. Right nearby, not
100 microns away, was the same water, at the same
temperature and pressure, just no protons and no radiolysis. To look at a cross-section,
you can very clearly see the difference
in oxide thickness way out in the unirradiated
zone or in the irradiated zone. And you can tell
right here how many protons there were,
until right over here where there were none. So it's a very striking
example of, well, this is what radiolysis
does in reactors. And we actually do
things in reactors to suppress radiolysis. We inject hydrogen gas. So there's a hydrogen gas
overpressure injected. One of the main reasons
is to suppress radiolysis. Because if I jump back to any of
these reactions, a lot of them involve H2. And if you dump a whole
bunch of H2 into the reactor, you push the reaction backwards
in the other direction. From straight up chemistry,
if you add a reactant and add a product, you
push the equilibrium in the other direction. That's why we do this in
terms of injecting hydrogen into light water reactors. And if you look at the
amount of hydrogen injected in a PWR, a pressurized water
reactor, which comprises 2/3 of the reactors in
the country, it's like 20 to 30 cubic centimeters
per kilogram of dissolved hydrogen. That's quite a bit. And the whole idea there
is to suppress radiolysis and suppress corrosion. So I find it to be pretty cool. So a knowledge of G-values
can keep your reactor from corroding. Then let's get into
the biological effects. In the end, for the
long-term effect it's all about what
happens to DNA. Because if a cell
mutates, it can either kill the cell so that
it can't replicate, or you can cause a
mutation that might make some sort of a change and
change the cell's function. And so you may imagine,
a lot of this stuff is done in LET, linear
energy transfer. Again, another word
for stopping power. If you look at the density
of these damaged cascades as a function of
stopping power, LET. You can see that for high-energy
electrons, or beta particles, they just bounce around
with a lot of distance between interactions, causing
very relatively little damage on the way. For Auger electrons,
again electrons, but at a much lower energy. They're at the end of
their stopping power curve and they cause a lot more
damage wherever they're emitted because already, they're
going to make a much denser damage cascade. Alpha particles just
go slamming through. It's like rolling a tank
through your cell pretty much. Because there's going to
be a ton of interactions from charged particle
interactions, you won't really change
the path of that alpha because an electron imparts
very little momentum to an alpha particle. And if DNA happens to be in the
way, it's going to get damaged. This is a lot of
the reason why there is relative effectiveness of
different types of radiation. We talked last week about
these quality factors, gamma rays are 1 electrons
tend to be pretty close to 1 alphas tend to be 20. Because the same
energy alpha particle will impart a ton more damage
locally than the same energy beta particle. So can you guys see visually
where these quality factors come from? Cool. And there's two types of DNA
damage, direct and indirect. Direct damage is
what you might think radiation comes in and
ionizes something in the DNA, either causing, let's say,
2 thymine-based bridge, like a kink in the
DNA, or destroying it or doing anything. But most of the damage
is done indirectly because the amount of
volume of DNA in your cells is extremely low. Has anyone ever done the old
high school bio experiment, where you extract
DNA from onions? AUDIENCE: Yes. AUDIENCE: Strawberries. MICHAEL SHORT: Strawberries. Anything? So how did you do it? Anyone remember
how this was done? AUDIENCE: Some
chemicals and stuff. AUDIENCE: You have to
mix in good solution with a bunch of good
stuff and [INAUDIBLE] MICHAEL SHORT: So you
take, let's say, an onion, mix it in solution
with a bunch of stuff, and you end up with
this gigantic booger, which happens to be DNA. It's like a
three-foot snot thing. But what was the volume
of the DNA compared to the volume of the onion? AUDIENCE: Quite small. MICHAEL SHORT: Quite small. There's not a lot
of DNA in cells. So the direct damage
route, while still there, comprises very little of
the damage done to tissue. Mostly it's indirect
because surrounding all DNA is the rest of
your cellular fluid, which consists mostly of water. And as we've seen all today,
water undergoes radiolysis. Those radiolytic byproducts can
diffuse, find their way to DNA, and cause the same
sort of ionization that direct radiation would do. And since that volume
is much larger, let's say the hollow cylinder
of water surrounding your DNA, this is the most likely
route to cellular damage. And-- Actually I want to skip ahead
to something real quick, you can actually use
that to your advantage because it can kill tumor cells. So tumors are rapidly dividing
masses of cancer cells. If those cells are
rapidly dividing, then DNA is being replicated
much more readily. So you can inject
something that will bind to DNA, like this
little chemical right here, this Iodine-125,
whatever, whatever, which mimics thymidine, something
that would be found in your DNA, but absorbs radiation
much better. So you can inject this
iodine-containing organic molecule, which
binds somehow to DNA. I'm not going to even
guess how it works. But, if you want
this to get damaged, then you want-- let's say, your
DNA to get preferably damaged, the tumors are
replicating faster, they're going to incur more
damage from the same amount of radiation. So the same process
that causes cancer can be used to cure cancer,
interestingly enough. And so, good, we do have
about 10 or 12 minutes to talk pseudoscience. So now that you know
a little bit about how radiation can cause
cancer and mutations and you know a lot of the
physics behind how much energy do you need to
cause an ionization, let's start knocking off
these questions one by one. So, this field,
more than any, is fraught with garbage,
absolute garbage science. I won't even say pseudoscience
because that almost makes it sound half legit. Garbage, misinterpretations,
lies, poorly done studies, misinterpretations of
abstracts and conclusions. And today I'd like to
focus on cell phones and do they cause cancer? Very hot topic. There's lots of people with
predetermined agendas that want to say all electromagnetic
radiation is bad and we should go back
to an agrarian society where nothing happened. Well, I'll give you a
hint, Cambodia tried that and it didn't turn out too well. People have interesting notions
of what's real and what's not. So let's start looking
at some of these. There's an article written by
this fellow, Lloyd Burrell, around November, 2014. It looks like it was
republished somewhere in 2016. Let's just start
looking at the facts. So, what I want to
start doing here is cultivating your nose to
be able to smell bullshit because this is a lot of what
you're going to be doing, in terms of public outreach. As nuclear scientists
you will be called on to provide expert advice and say
whether things are real or not, explain why, and do it
in an empathetic way so as not to make
people feel stupid. Because it's very easy for
someone to read this and think, yeah, I should be afraid. Cell phones cause cancer. It's a natural reaction to feel. Let's take a look at
some of these facts. Cell phones emit microwave
radio-frequency radiation. True or false? AUDIENCE: True. MICHAEL SHORT: True. Yeah. These are microwave
emitters, or RF emitters. What sort of energy is
microwave radiation emitted at? Just give me an order of
magnitude, MeV, eV, keV. AUDIENCE: MeV? MICHAEL SHORT: Little MeV. Fractions of an eV. It's far beyond
the visible range in the lower energy spectrum. Can a milli-electron-volt photon
cause an ionization directly? AUDIENCE: No. MICHAEL SHORT: No. Microwaves and RF
non-ionizing radiation. They can cook things
by heating up water, but they do not cause
ionizations the way that ionizing radiation does. This radiation has an ability
to penetrate our bodies. True or false? AUDIENCE: Yeah, [INAUDIBLE] True. MICHAEL SHORT: True. It gets through us, right? Radio waves are going
through us all the time. Our governments do virtually
nothing to protect us from these dangerous. AUDIENCE: Technically,
but what dangers? MICHAEL SHORT:
Technically, true. Yeah. So this is a classic example
of fear mongering, taking a bunch of facts,
putting them together to elicit an emotional
response that is incorrect. And because the emotional
part of the brain kicks in far faster than logical
part of the brain, that's how we're wired, it elicits a
reaction with a predetermined conclusion. And yet, there is strong
evidence, multiple peer reviewed studies-- I'm not even going to read
the rest of the sentence because I don't want to
go on record saying it as if it were true. Let's, instead,
look at the studies, because that is the stuff
that we should trust. AUDIENCE: [INAUDIBLE]
44 studies. MICHAEL SHORT: 44 studies cited. And let's look at
some of the reasons. Let's see, there's
a little bit-- I have to make it
a little smaller. Can you guys still
read that at the back? Or actually, no, make
it a little bigger and forget the sidebar. That's better. OK. I was going to pick a
couple of these to show you and I started going through
them and my favorite ones are all of them. Most of the studies are
perfectly legitimate, some of them are not. Most of the interpretations
by this Lloyd fellow are absolutely wrong,
and either done ignorantly, which
somewhat forgivable, it can be hard to parse these
studies, or intentionally. We don't know which one. Let's look here. "Telecoms giant," et
cetera, "commissioned an independent study--"
404, not found. Let's go to the next one. We can't conclude
anything from that. The Interphone Study found
that: "regular cell phone use significantly increased
the risk of gliomas," some type of tumor, "by 40% with
1,640 hours or more of use." Let's look at the key figure,
taken from this paper, and blow it up so
you can see it. What do you guys notice
about this figure? AUDIENCE: [INAUDIBLE] AUDIENCE: It's so [INAUDIBLE]. MICHAEL SHORT: Forget
the low resolution. We can't knock that
because it might be a copy. No error bars. And what does most
of this cell phone use-- and the unit
not shown here is, I think it's like hours of use? AUDIENCE: It's all
about the same. It's basically all the same. MICHAEL SHORT: Yeah. AUDIENCE: [INAUDIBLE] by
any chance [INAUDIBLE] AUDIENCE: The never is
actually closest to the 1. MICHAEL SHORT:
Except for this one. Blue line is odds ratio. A lot of these things are
given in OR, or odds ratio. Let's say the
fractional-- or let's say the multiplying factor
for increased risk of finding cancer in the variable group
compared to the control group. And control and variable
are interesting topics I want to make sure people have. So we have the Interphone Study
cited in many of these papers. Let's see. OK. Garbage, garbage,
opinions, opinions. Let's go find the study. This is something I wish people
did more, is go to the study itself. Yeah, the Interphone Study. AUDIENCE: Overall,
no increase in risk. [LAUGHTER] MICHAEL SHORT: We'll make this
bigger to make it more obvious. So many people-- this article's
been cited almost 500 times. I don't know in what capacity
because I haven't looked up every citation. But a lot of what this
site and other sites do is cite the Interphone Study to
say cell phones cause cancer. Read the conclusion. AUDIENCE: Rise of an era. Prevent [INAUDIBLE]
interpretation. MICHAEL SHORT: Yes. So this study is
not a bogus study. The study was done
correctly, reporting ORs, these odds ratios, with
95% confidence intervals. If you just look at
the numbers itself, oh man, 1.15 odds ratio, 15%
higher incidence of cancer, with a confidence interval
that includes less and more. So you cannot conclude with 95%
confidence that this data is correct. And the authors
very honestly say, no conclusion can be drawn,
require further investigation. What does this Lloyd fellow say? AUDIENCE: Cancer. MICHAEL SHORT: Cancer. Yeah. An either accidental or
deliberate misinterpretation of the data. OK, let's go to numbers 2 and 3. I don't need those anymore. Let's see, number 2. Oh, we did number 2. Number 3, again from
the Interphone Study. We can discount that
because we've now read the conclusion of
the study and looked at a bit of the difference. AUDIENCE: [INAUDIBLE] MICHAEL SHORT: Number 4,
"Harmful Association Between Cell Phone Risk and Tumors." AUDIENCE: [INAUDIBLE] MICHAEL SHORT: Let's see. AUDIENCE: It says
there's possible AUDIENCE: Possible. Studies providing a
higher level of evidence are needed [INAUDIBLE]. MICHAEL SHORT: Again,
honest authors. I applaud the authors for
taking a controversial topic, doing a fair bit of data,
with at least enough metadata analysis, I think the sample
size is OK, and then saying, higher level of
evidence is needed. What does the internet say? It takes the one
sentence that they want to support their
predetermined conclusion. Very dishonest, if you ask me. Number 5. Oh, this is fun. OK. What does number 5 say? AUDIENCE: Does this not
just make you angry? MICHAEL SHORT: Huh? AUDIENCE: Does this not
just make you angry? MICHAEL SHORT: Yes it
does make me angry. This is why I'm
showing it to you. - infuriating, right? But some of the
comparisons between what the folks on the internet
will say with the sentence that they want to
say- and then you go to the actual
study, which they do give you the link for,
"a consistent pattern of increased risk associated
with wireless phones." What does the study say? Take a sec to parse this. I'll make it a little bigger. When you see an odds ratio
of, let's say, greater than 1. And see a confidence interval-- AUDIENCE: Oh, holy crap. AUDIENCE: Oh! [INAUDIBLE] MICHAEL SHORT: Yeah. Again, another odds ratio and
another confidence interval. Another odds ratio, another
confidence interval. AUDIENCE: [INAUDIBLE] MICHAEL SHORT: Interesting. The one interesting
part is for what they call ipsilateral
cumulative use, which means a tumor found on
the same side of the head as the cell phone, there is
actually a confidence interval that seems to be significant. So, I'm not going
to trash this study. I'm going to say it's
not quite conclusive. It doesn't go out and say
cell phones cause cancer, despite this fellow
coming out and saying cell phones cause cancer. OK, moving on to
number 6, was a 404. Let's just confirm. Wasn't able to get
it an hour ago. Oh, it's back. OK, let's see what it does. I don't even know what
this one's going to do. AUDIENCE: [INAUDIBLE] AUDIENCE: Potential [INAUDIBLE] AUDIENCE: Possible
association with [INAUDIBLE] AUDIENCE: What's heavy
mobile phone use? MICHAEL SHORT: Heavy
mobile phone use, yeah. Well, they'll define that
somewhere in the article. So, some of these studies,
it's like OK, there's interesting
viewpoints to be seen. They shouldn't be
ignored just because we have this predetermined
conclusion that cell phones don't cause cancer. It's important to go and
actually look at the studies and decide for yourself. Let's get into the fun ones. Number 7. "A recent study on 790,000
middle aged women found that, "women who used cell phones
for ten or more years were two-and-a-half times more
likely," et cetera, et cetera. "Their risk increased
with the number of years they used cell phones." Let's look at the study. OK, That's. Not the study, so we need
to go find the study. And that's another news
article about the study, we need to go find this study. Ah, finally. AUDIENCE: The study. MICHAEL SHORT: The study. AUDIENCE: The study. MICHAEL SHORT: Read
the conclusion. AUDIENCE: What the-- I'm so bad. [LAUGHTER] AUDIENCE: I don't think
the people writing these articles are actually
like reading these-- MICHAEL SHORT: No, I
don't think so either. AUDIENCE: They just
look at the title and they're like, [INAUDIBLE] MICHAEL SHORT:
So, the best thing that you can conclude
about these sorts of people is that they're not reading the
studies and reporting on them. If they are reading them
and not getting it right, no, not everyone can
parse the science. If they're reading them,
understanding them, and cherry picking the facts in order
to support their conclusion, that to me should be criminal. We do live in a country where
there's freedom of speech. You're free to say
whatever you want, as long as it's not hate
speech of various kinds. It doesn't have to be right. You also don't have to listen. So just because you
have freedom to talk, doesn't mean people have
an obligation to listen. And this is the problem
with a lot of this. So I think my-- yeah, my notes for this study
was just kind of the F word. It was, how do you
get the conclusion from this internet
article, which wrote an article
about an article about an article about a study,
when the conclusion says, with an excellent sample
size not associated. OK. We have like five or
seven minutes left, so let's skip ahead. I had a fun one for number 12,
cancer of the pituitary gland. Let me get rid of
the other stuff. AUDIENCE: [INAUDIBLE] MICHAEL SHORT:
Oh, does that look like a surprisingly
familiar figure? AUDIENCE: Cool. MICHAEL SHORT: It's another
article about the same study. Let's just confirm. AUDIENCE: [INAUDIBLE]
articles about-- MICHAEL SHORT: Oh, look at that. AUDIENCE: [INAUDIBLE] papers. MICHAEL SHORT: That right
there was the article written about the study, where
the other link was an article, written about
the article, written about the study. OK. What else? Next one. Let's just keep going
in number order. Israeli study about
thyroid cancer. AUDIENCE: [INAUDIBLE] MICHAEL SHORT: OK. AUDIENCE: [INAUDIBLE] MICHAEL SHORT: This appears
to be a blog, so let's search for the word "Israel." AUDIENCE: [INAUDIBLE] MICHAEL SHORT: OK, but
first the news article. So take a sec to
parse some of this. "The incidence of thyroid cancer
has been increasing rapidly in many countries, including
the US, Canada, and Israel." I mean, one thing
to say-- let's say, case control research on
this topic is warranted. Sure. No one's going to refute a
claim that, hey, maybe we should study something properly, right? Let's go a little further down. Let's try to find
the actual study. Where is this study? Interesting. The main point of the study is
that thyroid cancer and cell phone usage are going
up at the same time. AUDIENCE: Wow! MICHAEL SHORT: This
is the point where I like to say correlation does
not imply causation, and hammer that point home by going to one
of my favorite blogs, Spurious Correlations. You can find any data set that
correlates with any other data set. AUDIENCE: [INAUDIBLE] MICHAEL SHORT: Let's
look at some examples. US spending on science,
space, and technology correlates with a 99.79%
correlation of suicides by hanging, strangulation,
and suffocation. AUDIENCE: [INAUDIBLE] MICHAEL SHORT: Correlated, yes. Causal, I don't think so. [INTERPOSING VOICES] MICHAEL SHORT: Yeah. Divorce rate in Maine correlates
with per capita consumption of margarine. AUDIENCE: [LAUGHTER] Michelle,
[INAUDIBLE] margarine. MICHAEL SHORT: You can find
a link between anything and anything else if you just
search the data long enough without searching for a
mechanism or a reason. AUDIENCE: That's cool. Can we look at the age of
Miss America below this? MICHAEL SHORT: Oh, OK. Age of Miss America
correlates with murders by steam, hot vapors. [LAUGHTER] AUDIENCE: [LAUGHTER] MICHAEL SHORT: Clearly, we
should ban the Miss America pageant or make them older. AUDIENCE: Yeah, [INAUDIBLE]. MICHAEL SHORT: Or the other
way around, make them younger. Maybe this is why we
have toddlers in tiaras, it's to stop murders by steam. Oh, my God. OK. AUDIENCE: [INAUDIBLE] MICHAEL SHORT: So
this is, again, the point where you
have to ask yourself, what are the other confounding
variables in this study? Why else could thyroid
cancer be going up? Anyone? I can probably come
up with like a hundred different possible reasons. AUDIENCE: [INAUDIBLE] MICHAEL SHORT: Any sort
of other chemicals? Let's say, more industrial
runoff, more urbanization, smog, inhalation, some amount,
let's say, I don't know, iodine released from Chernobyl
making its way through. Now, that would have had
like a 30-day half-life. AUDIENCE: [INAUDIBLE] MICHAEL SHORT: Yeah, that's
also got to pretty much decay by now. Yeah, there could be
any number of reasons. And just to say cell phones and
thyroid cancer are correlated, is like saying this. What else? AUDIENCE: [INAUDIBLE] MICHAEL SHORT: This I
think might actually have something to-- AUDIENCE: [LAUGHTER] MICHAEL SHORT: There
might be a link here. Revenue generated
by arcades kids with computer
science doctorates. Again, just a correlation. AUDIENCE: [INAUDIBLE] AUDIENCE: Sociology
doctorates-- [LAUGHTER] MICHAEL SHORT: Ah,
look at the amazing-- it's got all the same humps. And everything. All right, I think
I've made the point. AUDIENCE: Actually,
I like the margarine and the divorce rate one MICHAEL SHORT: Let's go on
to some of the other studies, let's say, number 15. 11 of 29 cases of
neuroepithelial tumors, cell phone users accounted
for 11 of them." 11 of the 29 people in the study
that got this type of tumor used cell phones. What's wrong here? AUDIENCE: Who doesn't
use cell phones? People use cell phones. Everybody uses cell phones. They don't think about anything
else that could have happened? MICHAEL SHORT: No, no. Here, I think the
study is flawed. What is the worst
part about this study? AUDIENCE: [INAUDIBLE] AUDIENCE: It's only 29 cases. AUDIENCE: It's 29 cases. MICHAEL SHORT: 29
cases, sample size. If you get 11 out of 29
and say half of the tumors we saw were attributed
to cell phones, that is not a proper conclusion. AUDIENCE: How are you
going to [INAUDIBLE] it to a cell phone [INAUDIBLE]? MICHAEL SHORT: Let's
see, number 17. Ah, OK. Another Israeli
study that talked about parotid gland cancers
and salivary gland cancers. My note to this is
read the last sentence. AUDIENCE: [LAUGHTER] [INAUDIBLE] AUDIENCE: Like, I'm sure there's
other factors [INAUDIBLE] [INTERPOSING VOICES] AUDIENCE: They cause cancer. MICHAEL SHORT: The blog
says, cause cancer. The data says, no
causal association. So again, almost
criminally ignorant. How many times did
you have to miss the last sentence, the
conclusion of the article, to pick the part that you want? AUDIENCE: But everything you
read on the internet is true. You know, it's [? illegal. ?] MICHAEL SHORT: All I
can say is everything that you read on the
internet was written. That's the best I can say. Number 20, we don't even
have to go to the study here. AUDIENCE: [INAUDIBLE] MICHAEL SHORT: Oh, boy. AUDIENCE: [INAUDIBLE]
machine learning [INAUDIBLE].. MICHAEL SHORT: Let's check
the study to make sure that the quote is actually
correct, but before-- AUDIENCE: [INAUDIBLE]
Oh, my God. MICHAEL SHORT: Four women. AUDIENCE: It's just the one. AUDIENCE: Study four women. Looks like it might [INAUDIBLE] MICHAEL SHORT: Yeah, by the
prestigious publication, Hindawi, which
sends me more emails than I read their articles. So let's look at the abstract. Of all four cases, they
are a case studies, so striking
similarity, how hard do you think it would be to find
four women with a certain type of breast tumor? There's a lot of women
in the world, right? AUDIENCE: Yes. MICHAEL SHORT: And breast
cancer is one of the leading causes of cancer in women. It wouldn't be hard to cherry
pick four people to get the same conclusion you want. Oh, and there's
another correlation, out of 108 billion humans
that have ever lived and have been exposed to ionizing
radiation, all of them died at some point. AUDIENCE: [LAUGHTER]
At some point. MICHAEL SHORT: At
some point, yeah. every human that's
ever lived has died. And every human
that's ever lived had been exposed to
ionizing radiation. AUDIENCE: [INAUDIBLE] AUDIENCE: It must be true. [INAUDIBLE] MICHAEL SHORT: Perfect
correlation, no causation. Let's see, two more. I think we have
time for two more. This is kind of fun. An eye cancer study. All right, let's just go-- "found elevated
risk for exposure to radio frequency
transmitting devices." AUDIENCE: Are
these real studies? Don't the authors
get mad that people are using their studies wrong? MICHAEL SHORT: I'm sure
the authors do get mad, but what are you going
to do about some person on the internet, right? You can send a nasty letter
to the magazine, which might reject it as hate mail. OK, on the blog. AUDIENCE: [INAUDIBLE]
very strong-- MICHAEL SHORT: What does it say? Elevated risk for
exposure in the study. AUDIENCE: People only get
excited by some crazy person. AUDIENCE: [INAUDIBLE]
it's about. [INAUDIBLE] MICHAEL SHORT: I don't think I
have to make my point anymore. We've gone through
about half of them. I encourage the rest of you guys
to go through the other half. And to the people, like
this Lloyd Burrell, I say check your facts. What you're doing is
criminally incompetent. With the way that people
are misleading the public to get whatever pre-gone
conclusions that they have from their emotions or
their funding sources or whatever the reason to
be, by misquoting facts you're absolutely
misleading people and spreading false science. Because, to me, the most
exciting moments in science don't end with the
words, "I told you so," but start with the words,
"that's interesting." So just because the
studies that you find don't support your
predetermined conclusions, doesn't mean you
should reject them. It means that you might
have to change your idea. So, on that note, I'd
like to stop here. We'll come back on
Thursday and go over the short and long-term
biological effects of radiation and look at some
more garbage science. Yeah? AUDIENCE: How do you feel
about those wireless chargers they have now? It's like a conductive
charger so it uses like a low-branch,
strongish magnetic field. MICHAEL SHORT: Mm-hmm. AUDIENCE: And people
are like, oh, my God. That's so scary. MICHAEL SHORT: I would
just say go to the studies. It's very easy to say put a
bunch of rats on a cell phone charger, turn it on,
and see what happens. I mean, the data doesn't lie. The reason might be a
little hard to figure out. Yeah. Yeah. So, I mean, another
thing is, when people have a predetermined-- I know it's a little
past 10:00, but no one's gotten up so I'll keep ranting. So a lot of this
neo-environmentalism going on has the predetermined
conclusion that only sources of power light on the Earth,
like solar and wind, that are renewable and such,
are the ways to go. And immediately dismiss
nuclear as not part of the environmental
solution, despite being part of the environmental solution. A large source of power
that's very efficient and doesn't admit any CO2. It might surprise them to
know that manufacturing wind turbines is a major
source of radioactivity. AUDIENCE: [INAUDIBLE] MICHAEL SHORT: Anyone
want to guess where? AUDIENCE: Rare-earth magnets. MICHAEL SHORT: Yes, thank
you, rare-earth magnets. The major cause of wind turbine
failure in the last decade has been the gearboxes
breaking down. Because in order
to extract power, you have to gear down those
giant turbines by quite a bit. And those gears, 300-feet up
in the air, tend to break down, they're hard to maintain. How do you fix it? Make stronger magnets. Put in rare-earth magnets that
electromagnetically harvest the energy, instead of gearing
it down and doing the same and you don't have
mechanical things grinding. What are rare-earth
magnets made out of? AUDIENCE: Rare-earths. MICHAEL SHORT: Rare-earths. Lanthanides, which happen
to be found with actinides, thorium,r whatever actinium
exists, radium, uranium, things with similar chemistry. What do you do when you extract
the rare-earths that you need from the rare-earth ore? You ditch the remains, which
are concentrated sources of these radioactive byproducts. Where do most radioactive-- I'm sorry, where do most
rare-earth magnets come from? AUDIENCE: China. MICHAEL SHORT: China. How is China's record on
environmental practices? AUDIENCE: Not [INAUDIBLE]. [INAUDIBLE] [INTERPOSING VOICES] MICHAEL SHORT: Spotty, at best. AUDIENCE: Questionable. MICHAEL SHORT: Yeah. So, again, one of those
things where people say, oh, wind power has absolutely
no effect on the environment. Check the radioactivity
of making windmills. AUDIENCE: I want you
to tell the Sierra. MICHAEL SHORT: I don't know if
the Sierra Club would listen. AUDIENCE: [INAUDIBLE] MICHAEL SHORT: I have
heard murmurs or rumors of them coming around to
the idea of nuclear power. There's an article that said
they switched positions, then there was a counter
article, followed a day later, that says, no, that
was a rogue actor. They don't reflect the
views of the Sierra Club. The problem is with all
these neo-envrionmentalists and cell-phones-cause-cancer
people and food-irradiation-is-evil
people, you'll find them cherry picking
data to support the conclusion that they already
felt they wanted. And when confronted with
overwhelming evidence to the contrary. They don't change their view. And that to me is the
best thing about science. If you prove to me
that you're wrong, I will say, thank
you, not [INAUDIBLE].. AUDIENCE: [LAUGHTER] MICHAEL SHORT: So, there you go. All right, I'll see
you guys on Tuesday.
