What Physicists Do – March 11, 2019 – Dr. Lynn Cominsky
What Physicists Do – March 11, 2019 – Dr. Lynn Cominsky


[ Music ]>>Alright, we’ll begin. This is where I’ve been
half tempted to say, “The woman who needs
no introduction.” That’s how I wanted to
start out, but I’m going to do a full introduction. In honor of Dr. Lynn Cominsky,
our very own Dr. Lynn Cominsky. She is filling in because
our speaker originally for this date had to cancel. And as is, as is her MO, modus
operandi, Dr. Cominsky cares so much about this department
that she was willing to step in at the last minute. And I as a member of the
department am thrilled. Because I have never
seen this talk. And this is something
that, that, a talk that Dr. Cominsky gives. Well, [inaudible]
I wrote that down. But I, instead, I’m
personally thrilled. So this talk on, on the Science
of War and Peace is the topic. And it’s just perfect
for what physicists do. And I’m surprised it
wasn’t [inaudible] already. Dr. Cominsky is the Chair
of the Department of Physics and Astronomy here at SSU. And as we were just
talking about, for 15 years, that’s the longest tenure of
any Chair of the Department of Physics and Astronomy. So let’s actually,
we’ll give her– [ Applause ] Her bachelor’s degree is
from Brandeis University and her PhD is from MIT. Her early work was on X-ray, astrophysical X-ray
sources, transient sources. And X-ray binaries. She joined Sonoma State
University in 1986 and founded, more than a decade later. But founded the, the
pre-eminent Education and Public Outreach Group
here at Sonoma State. That group and because of Lynn’s
dedication and devotion to, to these topics in
science, in astronomy. Has worked on projects such
as the Fermi Space Telescope, the Swift Space Telescope. And more recently, LIGO, the Laser Interferometric
Gravitational Observatory. Her accolades are, as I put down
here, too numerous to mention. I [inaudible] almost
too numerous. And I looked at it, and I said, “They actually are too
numerous to mention.” So I cannot go through
her accolades. But a few things, she’s a
Fellow of the California Council on Science and Technology. She’s a, a Fellow of the
American Physical Society, and of the American
Association for the Advancement of Science, preeminent bodies. Recent awards she’s received
include the 2015 Sally Ride Excellence in Education award from the American
Astronautical Society. The 2016 Education prize from the American
Astronomical Society. And the 2016 Wang Family
Award from the CSU system. So let’s give a warm welcome
to our very own Dr. Cominsky. [ Applause ]>>Why, thank you. Yes, this is my pleasure
to give this talk today that I normally give
in the fall semester to the War and Peace folks. I’ve been doing it for,
gosh, at least 20 years, I would, I would guess. And you might wonder, well,
you know why am I posing with that statue of, or
the sculpture of Fat Man? It was just one of the
first nuclear weapons. My interest in all of
this nuclear stuff began when I was still a
postdoc at Berkeley. And I was looking
around for another job. And I had briefly toyed with
the idea of going to work at the [inaudible] National Lab. Because my thesis work which was about the thermonuclear
explosions in the surfaces of
neutron stars. And so a lot of the
physics is the same if you then have the
thermonuclear explosions, you know, in bombs. Like some of the [inaudible]. And so that made me a
very attractive candidate to that organization. And I was looking at
three different divisions of the organization to work at. The fission bond
building division, the fusion [inaudible] division,
and the policy division. That was the only one that
I actually thought of, that I might want to work at. And so I went out, and
I did a lot of research, and I do not have a
security clearance. So everything that I
know that I am going to tell you today is all
unclassified material. And so I went out and did a
lot of research to learn all about weapons as
opposed to neutron stars. And also to learn about a lot
of the politics that was going on with respect to things like nuclear nonproliferation
treaties. And they all, this
talk has evolved a lot over the past 20 years. And I’m not going to be able to tell you all the
different things that have been in this talk. All of these different years because some years
the talk is more about power plants, for example. One of my staff today reminded
me that it’s the anniversary of Fukushima accident in Japan. And so during the years when that was the top
nuclear [inaudible] news, I would talk more
about power plants. And I would talk
more about what, what happened at Fukushima. But every year, I
basically pick one topic that I think is the
most important topic from political point of view. And I end with that. And this, and this year
North Korea wins again. So sometimes it’s power plants,
sometimes it’s [inaudible], sometimes it’s North Korea. This year it’s still
North Korea. So with that preamble,
that, that exhibit is not at the art gallery anymore. But it was last fall
when I gave this talk in the War and Peace series. So I’m going to talk a
little bit about history. Then I’ll do a little bit about
physics, fission and fusion. And the effects of the weapons. And then I’ll spend the rest of
the time talking about what’s, what we know about what’s
going on in North Korea. So that won’t be
quite as physics-y. But there’s still
some physics in there. Okay, so where did atomic
weapons get started? Basically, World War
II, the timing of it. Coincided with what
physicists were finding out about the inner
workings of the atom. So this is, you know,
the late 1930s, say. And physicists that were
studying the atom figured out that it was possible to
release huge amounts of energy by either breaking apart or smashing together
the nuclei of atoms. Far more energy can be gotten
out of nuclear processes than can be released
in chemical reactions which only involve electrons. So what would Einstein do? [Laughter] By 1939,
many prominent, mostly Jewish physicists
had fled Europe and had come back
to live in the USA. And Einstein signed a letter
to Roosevelt, alerting him to the potential or
weaponizing nuclear reactions. But and so Pearl
Harbor happened in 1931. The USA did not really invest
very much in research into how to weapon the physics that the
people were doing in the lab. But after Pearl Harbor,
after December 7, 1941. They, US began the
Manhattan Project because they were really
worried that Nazi Germany, which also had all the
remaining non-Jewish physicists who were working on
nuclear reactions. Would be weaponizing
the science. And of course the Manhattan
Project was not going on in Manhattan. It was located near
Los Alamos, New Mexico. And but it was called,
it was like a code name. So most of the funding that went
to the Manhattan Project went to actually build the factories
to produce the materials that you would need
to make bombs out of. Not paid to the scientists
that were working on it because building
factories costs a lot more than paying some people. And the first successful
test was called Trinity, sometimes also called Gadget. And that was in July of 1945. In nearby Alamogordo,
New Mexico. Okay, so now some science. Nuclear physics versus
chemistry. Chemists, so here’s,
here’s a helium atom, right? Two neutrons, two
protons, two electrons. This is the, the board
version of the picture. And if we were going to be
doing chemistry on this, we’d be talking about
removing these electrons or adding more electrons. But if you want to do nuclear
physics, you’re talking about changing the nucleus. What’s in the nucleus. So either changing
the number of protons or the number of neutrons. The typical energies
involved in chemistry are of order electron Volts. You know one to ten
electron Volts. Because you’re dealing
with electrons and Volts are in
their potential. So electron Volts are a unit of
energy, roughly 1.6 times ten to the minus 19 joules. And joules are a standard
SI unit of energy. But nuclear physics, the typical
energies involved are millions of electron volts, or MeV. Capital MeVs. So for example, if helium
loses one of its protons, it becomes a different element
because the number of protons in the atom define
what element it is. So this particular one
here, this would be tritium. So it’s got two neutrons and one
proton which makes it hydrogen. But it’s very heavy hydrogen because it’s got
two neutrons in it. Or helium instead lost
one of the neutrons, and still had the two protons,
it would still be helium, but then it’s an
isotope of helium. It’s three helium. The, the weight comes
from the combined number of protons and neutrons. So the weight’s still the same. But what element it is depends on how many protons you
have in the nucleus. And yes, I’m in a room
with a Periodic Table! So that’s a great
thing for this talk. So some of the materials
which you’ll hear me talk about today include this
very heavy hydrogen, tritium. That’s one of the things
used in fusion weapons. Deuterium which is
regular heavy hydrogen with only one neutron in there. Also used in fusion weapons. Uranium, okay? So if you go out and you
do some uranium mining, and you get some rocks
out of the ground that have uranium in them. What you’re going to
find is that only 99% of that uranium is what
we call uranium 238. Now that’s not a particularly
useful isotope of uranium to use for nuclear weapons. What you really want for nuclear
weapons is the much less stable uranium 235. So in this top one, I
have something in red. That’s because it’s one of the main ingredients
for atomic weapons. So uranium 235 is only
less than one percent of what you would find in
that rock in the ground. That you just pulled
out of a uranium mine. But yep, that’s what you
need for both power plants and for fission weapons. And another main ingredient for
fission weapons is plutonium. But plutonium is not a
naturally-occurring element. You will not find it in
any rocks in the ground that can [inaudible] to mine. You may get instead in
power plants reactors where the uranium in power
plant reactors turns into waste that includes large
quantities of plutonium 239. Everybody doing good so far? Alright, so if we want
to get some uranium, we’re going to mine it as
ore from some open pits or some deep shaft mines. Sometimes you put some solutions
in there to get it out of there. And then you take it to a
mill, and you crush the ore. And you extract the uranium. Which leaves behind
a whole bunch of radioactive sludge, tailings. That just pile up and stay there in those states that
have the mines. And a lot of those
states who have the mines, the mines are located
in land that is part of a Native American
reservation. And so a lot of the reservations
are heavily contaminated with all of the leftover
stuff from the mining. That’s a whole other talk. Can’t go into that one now. But just making that point. So then you get this extracted
uranium, and you leach it out with sulfuric acid,
and you make this stuff called yellowcake. There’s a little picture of it. It’s also known as
uranium oxide. And then yellowcake is turned
into uranium hexafluoride gas. Which can be cooled
to make a solid so that you can transport it. And also compress it down a lot. And so that saves
on storage costs. So that’s how uranium
starts out. But if you want to
turn it into something that can be weaponized, you
then have to enrich the uranium. And what that means is you
have to enrich the fraction of the uranium 235, compared
to what you’d naturally find to make it useful
for your purposes. One you get up to, from
that less than one percent. Once you get the quantity of
uranium 235 up to five percent, you can make power plants. Out of that kind of uranium
that’s called low enriched uranium or LEU. But once you get more of the
90% of that isotope 235 compared to all the other isotopes which
are basically [inaudible]. That’s the highly
enriched uranium that you need to make weapons. And so there are many different
ways you can do that enriching of that isotope ratio. One common way in places that
have a lot of energy to spare. Is the gas enrichment method. And that is the method
that Iran uses. And part of the whole
Iran nuclear deal, another thing I don’t
have time to talk about. Was to limit the
number of centrifuges that Iran would have operating
to do that enrichment process. Okay, well that’s the deal that the current
administration pulled out of. So they’re still obeying the
deal because Europe didn’t pull out of the deal, all
the European countries. But just saying,
they have thousands of these stages of
these centrifuges. And they were not
using them all, and they could just turn them
back on again at any point. So there, because of
the weight different, when you have a centrifuge. Because of the weight different. The heavier stuff will
get flung to the outside and can be peeled off. And the later stuff
stays in the middle. And then you do another stage. And a little more
gets peeled off. Do another stage. And they have to go through
hundreds of thousands of stages to really get the
uranium enriched to the, with the 90% level. You can also do gaseous
diffusion. That’s the method that we use to do our uranium enrichment
here in this country. And that works on the principle that the lighted
things travel faster. So if you’re diffusing it,
it can go through things and get away from
the heavier one. That are slower. And also needs lots
and lots of stages. And then this one, electromagnetic isotope
separation. Was something that nobody in this country would ever have
used because we’re not sitting on a whole big oil field. But it turns out that
after the first Gulf War, when they found the hidden
nuclear facilities in, in Iraq. This is how they were doing
their uranium enrichment. This electromagnetic
isotope separation. Very energy-intensive thing
which is to put things in a big static electromagnetic
field and separate them that way. And so we weren’t
looking for that, right? So we were looking for evidence
that they were doing the things that we would have done. But they weren’t, because
they had huge oil fields that could provide lots
of power to do the work. And so they did in a way we
weren’t even thinking of. And as a historical tie,
we learned about this because we had a historical talk
in this series by Jay Davis. Who worked at Livermore, and who
was one of the people that went to Iraq after the first Gulf
War and restarted those things. And you can go back and look
at the historical records. But he’s also written
some articles about it if you look them up. Absolutely fascinating. Okay, well marching along here. So, so there is a piece of uranium that’s one inch
long, weighs ten grams. Here’s, here’s 235 uranium. Okay? It’s the major ingredient that you need for
chain reactions. And you see, you know
there’s three less neutrons. But uranium’s very, very dense. And when you’re done
with that enrichment, and you’ve kept all
the uranium 235. And you’ve put it on there
where you can turn it into a weapon or, or
a power plant fuel. All the depleted uranium,
the uranium that was left over that’s been depleted
of the uranium 235. So this [inaudible] uranium 238. That has been used to make armor
of tanks and the structures of the bonds themselves. This is very heavy and
very dense material. So it’s, you know
you’d think well great! We’ll make a tank
out of it and then, you know we’ll have this
nice impenetrable tank. Except it’s still radioactive. And so anybody that’s
sitting in a tank made of depleted uranium is exposing
themselves to health risks. From the danger of being
exposed to radioactivity. So that’s a whole other talk. Also don’t have time to give
that one, but I have given that one in the past about
the health effects of, of depleted uranium. And also all those tanks that
were left behind in Gulf Wars that were all made of that. And then they were all on fire, and all this stuff is
going up in the air. And anyway, it’s just
a big nasty mess. So I just wanted to clear up
some of that jargon for you. Okay, so now what
about fission weapons? Now this is the talk about
the physics of the weapons. Not the engineering. So I don’t really know
how to make a bomb, but I’ll tell you what I do
know about how the bombs work. So if you have an element,
so if you have a star, and it’s burning
fuel in its core. It can make the elements
up to iron. But to get energy out of
elements heavier than iron, what you have to
do is fiss them, fission them, break them up. By bombarding them
with neutrons. Okay? So here’s uranium 235. We’re going to shoot
some neutrons at it. And it’s going to break into
a bunch of pieces of stuff. And it’s going to
release more neutrons. And then if you can catch these
neutrons and send them back around to the uranium 235. Then you can get a
chain reaction going that will continue this process. Because every time you split
it, you get more neutrons in. [Inaudible] on the back end. Eventually the whole
thing just blows up. And that is what happens
in the first atomic weapons like Gadget or Trinity. Or Little Boy or Fat Man. So these were all A-bombs,
atomic bombs, fission bombs. This is a, a more scale models
of Little Boy and Fat Man. In the museum in New Mexico where they explain
a lot of this stuff. And so the interesting thing to
notice here is that the yields of all of these were in
the 15 to 20 kiloton range. So they have thousands of tons of conventional chemical
explosives. Right? So we also quote
the yield as the equivalent of how much or a regular
like TNT/dynamite kind of explosive you would need. To make that energy that
came out of that bomb. They don’t actually
tell you the energy. They just give you
the yield in terms of conventional chemical
explosives. And so for, for the
atomic bombs, this 20 kiloton yield is
basically what you get out of about a piece of
uranium this big. Like two pounds. So it only takes basically
a grapefruit-sized chunk of uranium 235 to be the
equivalent of 20,000 tons, and a ton is 2000 pounds. Right? So 20 million pounds
of conventional explosive. Which you know would fill
more than this room, right? And here you have just this
little [inaudible] of uranium that can give you
that much energy. It’s sort of amazing
when you think about it. So how do you make
an atomic bomb? Well, first you have to
get your enriched uranium. Then you have to somehow
squeeze it and confine it evenly and catch the neutrons
that are coming out of those initial
reactions, sending them back in. To make the chain reaction
with the uranium 235. And so it takes a
bomb to make a bomb. And usually you start
with a chemical one. And then you use the chemical
one to trigger the next stage which is basically
the fission reaction. So the Little Boy style, they
had some uranium 235 over here. And some more over here. This is the shotgun style. We have your chemical
explosive here. There’s your gun powder,
and something that’s going to inject neutrons into that. So you light this thing up, you
smash those two halves together. You inject some neutrons
at the same time. You have this tamper,
this casing. Around the whole thing,
holding it together. And touching those
extra neutrons and sending them back in again. And this all happens
in about a microsecond. And then it can’t hold
it together anymore. And then the bomb goes off. Okay, and there’s just a picture
from Hiroshima, the A-bomb. It’s called the A-bomb dome. It’s just like some remnants
that were left behind. Okay, so for the Fat Man style,
and also this is the style for Trinity, these
were spherical. So then what we have is we have
the uranium 235 in the middle. And we have the chemical
explosive all around the outside. And then you have a
casing all around that. And then at the center of this,
it’s not shown in the picture. But the center of this is
usually this thing called a [inaudible] golf ball. Which is a little
piece of [inaudible] that has a lot of
extra neutrons. And so if it’s squeezed,
the neutrons coming out, and that starts the
chain reaction. Right? So you squeeze,
you’re, you’re squeezing on it by imploding all of
this chemical explosives in a perfectly symmetric
and even way. So that it squeezes
down on uranium 235 in the middle to critical mass. And then that squeezes
the neutron generator, [inaudible] golf ball
thing in the middle. Get a big burst of neutrons at the same time you’re
squeezing the thing together. And that starts the
chain reaction. Until the thing blows
up a little bit later. So yes, the burst of neutrons
is timed from the moment of the maximum compression. So that’s your basic A-bomb. How they work, just the physics. I don’t really know
the exact engineering. Any questions about that
before I chage gears?>>Well, since there was two
types, I noticed the timeline. That’s really quick. I mean, you know talking
about the end of World War II. Like you develop it and let’s,
let’s get out and, and–>>Yeah, so they did
the test with Trinity. That was the Fat Man style. And then they were like, “Oh! Let’s try the other styles.” So then they did a little style which was the bomb they
dropped in Hiroshima. And then you would have thought,
“Okay, we could quit now. Because we’ve proven
that both designs work.” But then for whatever political
reason, the [inaudible] or something or they just had
some [inaudible] laying around and didn’t want to waste it. They decided to do the
Fat Man style over again. And dropped it on, on Nagasaki. So.>>So they had tested the–>>They’d already
tested this style. There was really no
reason to test it again. That was the, the Trinity test. So.>>How does the hydrogen
bomb work?>>Okay, that’s the next,
that’s the next one! We didn’t, we didn’t– .>>Was that [inaudible]
now the initial one to test it [inaudible]
in the war?>>Well, I mean they kind of,
the war wasn’t going to end if they didn’t drop
it, another bomb. I mean, that was the
political reason. This is a physics talk. Not all that great on the
politics but yes, there was lots of different rationales
going on back then. About why we needed to do
the Nagasaki bomb drop later. We already destroyed Hiroshima
and you’re [inaudible] that other design worked. So I don’t know. You know.>>But Hiroshima was
a test of that style?>>Hiroshima is a test of
the, of the shotgun style. That had not been
tested at Alamogordo, no. Because the only test at
Alamogordo was Trinity. And then [inaudible]
timeline, right? Right? So this was just like
three weeks later, and this was like three days later.>>One test and two active– ?>>Right, one test and
two active de, de– .>>Destruction.>>Destructions of cities.>>Yeah.>>Yeah. Okay, well moving
onto the fusion weapons. So we have our little
happy sun guy here. Because fusion is what naturally
occurs in the center of our sun. But in the case of our
sun is the huge mass of the sun that’s holding
everything together to allow these reactions
to occur. If you’re lighter than iron,
the way that you’re going to get energy out
of your nucleus. Is you’d have to put
two things together. But those two things, those two
deuterium atoms in this case. Which remember were basically
hydrogen with an extra neutron. They don’t want to be together
because they have plus charges in both nucleus,
both nuclei, right? So you have to overcome that
[inaudible] and repulsion and get those two plus
charges to get close enough that they will fuse, right? That’s not that easy to do. People keep trying to make
commercial fusion reactors. They keep trying to work on
fusion processes in the lab. To try to someday make a
commercial fusion reactor just like all of our current power
plants are fission reactors. And they have not been able
to do it successfully so far. By which I mean they haven’t
been able to get stuff to fuse for less energy to put into
the fusion than you get out of the fusion reaction. Right? So they haven’t
reached the break-even point with the fusion process. Where you get more energy
back than you put in. [ Inaudible ] So, so the basic
ingredients here for the fusion reactions
are this heavy hydrogen, very heavy hydrogen and
lithium, the next element on the Periodic Table. There it is over there. And these make the
so-called H-bombs, or hydrogen bombs, right? They’re H because deuterium and tritium are both
forms of hydrogen. And also these fusion
reactions are what we call thermonuclear reactions. Which just means that
they make a lot of heat. And the more heat you make,
the faster the reactions run. Which then makes more heat, which then makes the
reactions run faster. And you get your runaway in
that kind of feedback loop. Between the heat
and the ingredients. And so then you would
need less fuel which gives you more
efficient bomb. Because you get this
boosted reaction rate from the extra heat. Okay, so what’s the
secret of the H-bomb? Well, back, back when I was
first learning about this stuff. This was a whole big scandal. Because the secret of
the H-bomb was published in a bunch of newspapers. And now of course you
can just read it anywhere on the internet. But you know 20 years ago when I
first started giving this talk. This secret was not known. But I’ll tell you
what the secret is. The secret is light travels
faster than particles that you’ve just blown up. Right? Because light travels
faster than everything. And X-rays are a,
are a form of light. And so what happens
is we start off with, for example, the primary bomb. So here is, here’s the bomb
that is like a fission bomb. And it’s triggered by
a chemical bomb inside. So it’s very much like
the Fat Man style. And then as this starts to blow
up, it puts out a lot of X-rays. And the X-rays come down here,
and they bounce off the inside of the tamper, the casing. And they exert radiation
pressure because they’re [inaudible]
so they’re light. They have radiation pressure, and they squeeze the stuff
before it has a chance– . And then that helps
this stage ignite, the secondary stage ignites
in part due to the pressure of the X-rays bouncing
off the casing, squeezing down on the
material to make it critical. And so that is basically
the secret. Okay? So the X-rays squeeze it,
they heat this channel. It compresses it. It ignites this second
stage which is, which has got the
fusion material in it. Before this thing blows
the whole thing up.>>Are the explosions happening
before the bomb hits the ground?>>Oh, oh yeah. Yeah, all of these reactions
and stuff is happening, usually it’s more effective
to do it in the air, anyway. And I’ll show you why. As we get to the effects part. But there’s all sorts
of tricks you can play if you’re a bomb designer. For example, here’s,
here’s this thing, it’s the 1999 San
Jose [inaudible] so it really is 20 years ago
that this thing was published in the newspapers first. The secret stuff. Okay? So this, this particular
warhead has these two stages. And, and the, the fission
stage is the primary. And this is actually plutonium
fission boosted with tritium. So I mean you play
all these games. You can mix up the
fusion and the fission. If the fission produced
the fusion, the fusion boosts the fission. All these different
ingredient to get, if you’re getting really
fancy bomb designs. And then the second stage
is the so-called Teller-Ulam fusion device. This is Edward Teller
who was at Livermore. And at Stanford for his career. So you can read all
the details here. But, but basically
this is a fission bomb. This is a fusion bomb. This made the X-rays
come down here and help that thing go critical. The X-rays from the first
stage help the second stage go critical. So yes. Boosted fission. The fission’s boosted by
having some fusion in it. And the fusion’s triggered by having the fission
bomb next to it. And so you can imagine that
all these designs can get pretty complicated. And of course I don’t know
any of the classified details. So I’m just telling you what
you can find on the internet about the actual designs.>>I mean this is fascinating. I felt like I knew
something about this. But to know that the
[inaudible] is correct, right? To do this as a second
stage, you know I’m thinking of like the physics that
I knew about compression. They probably did all these
tests and it always blew up the fusion components. You couldn’t get the fusion
components to compress.>>Yes, you can imagine that could be a testing
cycle problem.>>That was likely a testing
cycle and it was the, the, the, the photons and, and –>>Right, getting, so getting
the radiation to come around and do the compression
in a spherical way so that you can actually trigger
that second weapon, right? Because if you squeeze a
little too hard this way, it will all go that way, right? And everything will just blow up
without finishing the process.>>Just want to mention, I
talked to my optics class. It’s hard to change the
direction of, of X-rays. And you have to have
these glancing blows.>>Right, so off of very
dense material that’s highly [inaudible] inside. Just like X-ray telescopes
are [inaudible]. Okay, so that’s how
you build the bombs. So why are atomic
bombs or hydrogen bombs so much worse than
chemical bombs? Well, first the amount
of heat and light energy that you release is at least
a thousand times greater. But more worrisome is that the
explosion itself is accompanied by invisible, harmful,
and penetrating radiation. And that radiation
persists and turns into what we usually
call radioactive fallout. And it will persist in the
atmosphere for days to weeks to years and in fact,
it’s still up there. From all the bomb tests in the
1960s that were done in the air. There’s still a layer of irradiated atmosphere
up there far enough. That’s just our ground-level
view of the Hiroshima cloud. So here, in case
you’ve not seen it. And hopefully this
will work, sound wise. Of course, maybe I have
the sound turned off on my actual computer. [ Bomb Explosion ] Alright, so there it is. So there you see– see all that
stuff getting sucked up there? See that ball of hot gas rising? It’s going to keep
rising until the pressure of that hot gas is equal to
the pressure of the atmosphere. Right? And the pressure of the
atmosphere is less as you go up. And that’s what makes
the mushroom. Now you see you’ve got
a big, hot ball of gas. Hot air expands, hot
anything expands. Hot gas in this case. As it expands, it’s evacuating
the area underneath it. So that makes a gap and
it sucks all the stuff up from the ground. To make the stem
of the mushroom. But the hot air itself rises like the bomb until
it gets equal. Because the pressure of
the air around it is more. So it’s keeping it
in a ball shape. Until it gets up to where
there’s less pressure. When you get high
enough in the atmosphere. And then there isn’t pressure
pushing on this ball shape of gas, and then it spreads out
and become like a mushroom top. In case you’re wondering where
the mushroom shape comes from. Okay? So the first effect is of
course just that incredible heat from just blowing this thing up. It’s, you know millions
of degrees. To make X-rays you need at least
ten million degrees hot plasma. That heat can become a fireball
that can then make firestorms. Because the heat expands and just [inaudible] don’t
need ten million degrees to light on fire. So they just start burning. And it just pushes
up the firestorm. Okay, I explained
the mushroom cloud. So the radiation, the invisible,
penetrating, harmful radiation that comes out from
these nuclear reactions. Includes alpha particles
which is just another name for doubly ionized
helium nuclei. Beta particles, which
is another name for positrons and electrons. Gamma rays which are an even
more energetic form of light than X-rays, and
fast-moving neutrons. And all of these things
are harmful to people. Okay? And they all come out,
and you can’t see any of them. But they can go right
through your skin. And in fact, alpha particles
are more deadly to people than electrons, for example. Neutrons, at least are neutral. So they’re not interacting
quite as much. Although the fast-moving
neutrons can also be very dangerous. And then, you’ve just
made this huge ball of gas where there didn’t
used to be from. That makes a shock front, a pressure shock
front that moves out. Okay? Pressure blast wave that then just collapses
all the buildings. And then all those radioactive
particles, the beta particle and the alpha particles
and the neutrons. They all stick to the
particles of the air or the dirt that got sucked up
that mushroom stem. And then it spreads out, and then they all
start to fall down. All those dust particles that
now are radiated, start to fall down all over the world. And 80% of it falls back
down in the first day. Ninety percent falls back
down in the first week. And then the rest of it is
still up there, basically. So there’s a picture of
some destroyed buildings. There’s a picture
of destroyed person. If you want to see what
happens from a certain size bomb on your city, Google, “nuclear
weapons effects calculator.” And you can pick a size bomb,
and it will show you the radius within which everything will
get destroyed, basically. And let’s just say for a
pretty modest-sized bomb. Like the kind that,
that we dropped on Hiroshima or Nagasaki. If you did the same thing,
it would take out all of San Francisco, and pretty
much the whole Bay Area.>>So how far away would you
have to be able to like live after burns like that? I guess for the Nagasaki.>>Well, you know,
there’s, there’s a lot of other issues, right? So there’s the nuclear
winter issue that you put all this
garbage up in the atmosphere. And it kills the sunlight
and then no plants grow. So maybe it doesn’t even
matter how far away you live. Because all the plants
are dead now. And then there’s this. The electromagnetic pulse, okay? So there’s another
thing that happens. So you just ionized
a huge chunk of air. And normally air doesn’t
conduct electricity very well. Although you might argue with
me if you lived in a place where there were winters. And you shuffled across carpet
so much and touched doorknobs. You would, you would experience
a little ionization of the air as you [inaudible]
shocked by the doorknob. But that isn’t terribly painful. But if you ionize a
huge amount of air. Then that plasma, the air
is turned into plasma. That conducts electricity
extremely well. And so where– and now you’ve
got all these electrons forming around through the air. And they’re just going to go
and find your nearest powerline. And make a huge power surge
on your entire power grid. And go into the grid and destroy
everything that’s connected to it. So it doesn’t matter too much
how far away you, you live. Because you probably won’t have
any electricity afterwards. Okay? In 1962 when they were
still testing bombs in the air, a 1.4 megaton air burst
knocked the lights out in Hawaii, 1000 miles away. And here’s a little,
here’s a little thing. So if you set the bomb off
30 miles above the ground. The electromagnetic pulse
will take out everything within a 500-mile radius. But if you raise the height above the atmosphere
even further. You can just have
one bomb that’ll wipe out the grid for the whole US. So, something to think about. And it doesn’t even have
to be attached to the grid. Anybody remembers, there
was this movie about Kansas. And they had these
people in cars that were just sitting there. And all of a sudden,
their cars died because and especially nowadays with everything being
computer powered, all the new cars, right? All those little chips
in your computers. No matter whether they’re
attached to a grid or not. They’re all toast. I mean, they are just going
to get zapped and destroyed. And none of that
stuff will work. So it doesn’t even have to
be attached to the grid. Just the pulse coming
through the air will wipe out pretty much anything
electrical. That we have. Certainly all of our
modern technology. And the people that, that
work on computer boards. They have to ground
themselves just because that little static shock
like the doorknob is enough to kill their computer chip. So imagine how much
damage this kind of weapon, kind of pulse can do to
any electrical devices.>>How, for that illustration,
how large is the, is the device?>>Oh, it’s just
your typical size. You know, a ten or
a hundred kilotons. Doesn’t even matter. I mean, you can look it up. I forget, but it’s, it’s
just a typical sized one. It’s not particularly a big one. Yeah. So, so why do we think
nuclear weapons are scariest, because they really
are scary, right? Most of the effects
are due to radiation so you can’t smell
them or see them. The damage to yourself by all
that penetrating radiation and the alpha particles,
the gas neutrons, et cetera. Can– those cancers can
take 20 years or– . If you’re not killed right
away, you can still die of cancer 20 years later from all the genetic
damage that you have. Forget about having kids
if you lived through that. And were zapped by
all that radiation. That’s not a good plan. A single bomb like Hiroshima
or Nagasaki, those small ones that we used to launch. Can kill 100,000 people
just with one bomb. That’s way more than a
conventional missile can do. It also doesn’t take
very much material right? Just a couple pounds
to make an explosion that can kill 100,000 people. However, it does take
a lot of engineering to make a bomb that
actually works. And so keep that in mind when
we’re talking about North Korea. So the sizes of the weapons
nowadays, so remember one, one kiloton is a thousand tons
which is two million pounds of the equivalent of
chemical explosive. It only takes two pounds to
make a 20 kiloton weapon. Today’s typical warheads
are 100 to 200 kilotons. But back when we were testing,
we were testing single warheads that had megaton range. And there were over 1700 of
[inaudible] tests in that era. Almost all [inaudible]
atmosphere before people realized this stuff
was not disappearing. It was going to stay up
there, some percentage of it. You know stuck to particles
in the upper stratosphere, one of those spheres up there. And, and the most recent North
Korean tests were in the range of 50 to 250 kilotons. We can tell because we can
measure the earthquakes. They’re testing underground. We can measure the size of
the earthquakes that are made by the seismic waves
from the bomb. So what about those North
Koreans, as I’m getting, getting to the end here? Yes, good timing. Okay, so 2006 is when North
Korea first reported its first underground tests. And that was just
a tiny earthquake. And we think that was
maybe half a kiloton. And the International Atomic
Energy Agency believes that they have made enough
weapons-grade plutonium to make at least five to 15 bombs. So that’s because if you
have power plants running. Then all of your
spent fuel turns into, a lot of it turns
into plutonium. We can then reprocess
that plutonium, get it out of the
spent [inaudible]. And turn it into weapons. So there’s definitely
a connection between peaceful uses
of atomic energy. And catch, catching
that waste products and turning it into weapons. Hence, the alarm recently raised
just last week about trying to get Saudi Arabia to have
some nuclear power plants. That was something that the
current administration has been working on. So in 2009, they
had another test, and this one was
about 13 kilotons. And then in 2010, they said that they had achieved
nuclear fusion. Now when we’re just looking at
earthquakes made by weapons, we can’t tell what kind
of bomb they just made if it’s fission or fusion. So I guess we would have
to take their word on that. It might really only have
been a boosted fission weapon. This is a weapon where you’ve
got deuterium, deuterium or tritium inside the shell
of your uranium or plutonium that will maybe double
the, the effective yield. And so depending on whose
measurements you’re taking, just based on earthquake
patterns and seismograph readings,
that’s where the 50 to 250 kiloton measurement
came out. Different experts have
different answers. But still, much bigger
than, than Hiroshima. And this is the path that
we think they’ve taken to develop their weapons. So this is from a New
York Times article. First, you try to make an
implosion atomic bomb, right? So this is like Fat
Man, like Hiroshima. Then you put some
boosting inside, right? So you put some deuterium
or tritium inside to boost the fission weapon. And then you can
actually make one where you’ve got a whole
layer of deuterium or tritium. And then you’ve got
some other stuff inside. So then you’ve got
a three-layer bomb. And finally, you can
get to a hydrogen bomb where you have the
atomic weapon. Triggering the fusion
weapon down below. And we, we do think that
North Korea has gone through this entire
chain of development. Based on the yield that
they have been getting. But then you also
need to be able to launch the bomb
at somebody, right? So what have they done in terms
of satellites and missiles? Well, in 2012 to
2016, they managed to launch some satellites
into earth orbit. Right? So if you have a rocket
and you put a satellite on it. And you can steer the rocket
so that you can launch things. Then it becomes a missile. So we call missiles
durable rockets. All the rockets I do with
my students you know don’t steer those. They are missiles. You are not allowed to do that. You just, they just go
up and down [inaudible]. Okay, but if you consider that
you’ve got yourself a missile. And the 2016 satellite
is still up there. And it was a clear
violation of UN resolutions. And so then they gave
them all these sanctions. But then through
2017, from 2016, they were launching missiles
every two to four weeks. And this is a picture of
one of their launches. And this is a picture of
their launching tower. And in 2017, they were
actually able to get missiles to go far enough that it
was getting seriously scary. Because these [inaudible]
12 missiles were able to go over Japan. And in fact, they did. They launched them
right over Japan. Totally freaking out the
Japanese, as you might imagine. So they were flying right over
Hokkaido, two different tests. And in the year, the year 2017. And so we now estimate that they
have a range for their missiles between 7000 and
9000 kilometers. And from North Korea
to California is about 9000 kilometers. Hence the worries of the people
on our coast, our West Coast, that we could be within
striking distance. And so if you go really high
up, you don’t get as far. But if you launch at
a lower trajectory, then you can go farther. When you’re going to
launch your records. Your, your rockets. But mostly, they
were having a lot of trouble launching
their rockets. And most of them were
blowing up before 2016. And so we weren’t too
worried until 2016. And then all of a sudden, they
started to work really well. And the reason we think that
all of a sudden they got better. Is because they seem to have
gotten their rocket engines from the Russians. So when the Soviet Union
broke up, there was a lot of rocket-building companies. And they used to
sell their rockets to the central USSR government. But now there’s just Russia,
and Russia didn’t want to buy anymore models, many
more rockets, rocket engines. And so these companies had
all these spare rocket engines lying around. And they were looking
for market. And apparently the, the
Russian gangsters were like funneling these
rocket engines out of the country
to other countries. And so we think a lot of
them made by this company, this name I’m not even
going to try to pronounce. We think a lot of them
went to North Korea. So this just sort of shows
what they used to look like. And then here’s, here’s
some more good pictures of what the rocket
engines look like. They’re all of sudden
started working. So that’s sort of scary. Yeah, the government
stopped buying them in 2006. And the company was really,
really broke by 2016. So then they were like, “Okay, let’s just sell off
some of them. And try to get some of
our money back instead of having these things
in the warehouse.” Alright, so what’s going on now. This is the only
peace part of my talk. What’s going on now
in terms of diplomacy. So one really good thing is
that Kim, Kim Jong Un who is in charge of North Korea. And Moon Jae In is in
charge of South Korea. Are having inter-Korean summits. Unless it’s intra– . Or whatever the right– . Whichever the right
direction is. Anyway, just with, North Korea and South Korea are
just meeting together. To try to make some
kind of plans. And those things have been
occurring pretty regularly and despite what’s
going on with the US versus North Korea summits. These summits are continuing, and they are continuing
to make progress. Then of course as I’m
sure you’ve heard. Kim Jong Un and President
Trump met in June 2018. And agreed, “To work towards
complete denuclearization of the Korean Peninsula.” And then Trump left that summit and said they’re
no longer a threat because they fell in love. And then they scheduled
a second summit which just happened
a couple weeks ago. And that one just
totally fell apart. And they didn’t sign anything. And I don’t know. Maybe their bromance is over. It’s hard to say. But after the first summit, North Korea announced it
was halting its missile and nuclear testing. And it would dismantle
several key sites. And in fact, as far
as we can tell, they have not resumed testing. They also signed a
pledge to close one of their test facilities. They blew up some tunnels. They said they were
willing to shut down their really big
enrichment facility if we would do something
nice for them. And then the nice things that
we did do is we stopped having direct military exercises
with South Korea. And they gave us back 55 crates
of remains from the Korean War. But meanwhile, they
just continued to build intercontinental
ballistic missiles. Even though they said
they weren’t going to anymore, but they did. And so then we have the
second summit recently. And Trump said that it
failed because they wanted to complete– us to completely
end our sanctions against them without them fully
denuclearizing. But meanwhile North
Korea claimed that they would dismantle
this same plant that they said they were
going to dismantle before. If we would just get rid
of the economic sanctions. But nothing, no agreement
was reached. But we have documented proof that they are still building
new nuclear facilities in North Korea. And they started right after the
first summit ended, you know. We can see those things. We have spy satellites. You know on a happy note. No one, they have not
gone back to testing, and we are still not
conducting military exercises in the Korean Peninsula. So here’s an example of some
work that they did right after the first summit,
in July 2018. There’s a trailer that can hold
an intercontinental ballistic missile at their missile
assembly facility. So this is the kind that
can reach us, right? Intercontinental. This is the kind that has
the range to reach the US. So what do they want? Like what can we
bargain with them about? Well, they would still like us to officially end
the Korean War. Which is supposed to have been in this armistice
state since the 1950s. They would truly love it if we would remove
the economic sanctions that have basically made
all the North Koreans about four inches shorter
than all of the South Koreans because they’re all
starving to death. And they don’t have any
good food and nutrition. They would surely love it if we would take our
troops out of South Korea. They would of course like
to unify with South Korea. But I’m not so sure how happy
South Korea would be about that. But sort of like East
Germany and West Germany after the Cold War, right? East Germans were all starving,
and they had no industry. And the West Germans
are all thriving, you know modern society. They eventually got over
it and got together. And now both halves
of the country are, are pretty good except for
the Eastern part’s still sort of ugly. Anyway, they would like to be
respected as a nuclear power. Well I think they’ve
convinced everybody they are a nuclear power. And they claim they would like
everybody to be denuclearized, but I’m not holding my
breath for that one. Are we in danger from them? Right? So in order for them
to really threaten us. They must have a tested
long-range design, yes. Check. Tested long-range
auxiliary system, check. We don’t know about these ones because they haven’t really
launched a bomb at anybody. We don’t know whether they
can, if you launch the thing up and it starts to come down. And it’s time to blow it up,
did your thing hold together as it re-entered the atmosphere? Right? So if you want
to go intercontinental, you go out of the atmosphere,
you go back in the atmosphere. You want to blow it up when
you get over here, right? But if the heat shield
fails, and it doesn’t work. Then you just get a dirty bomb. And get pieces scattered all
over but no actual explosion. You have to be able
to steer that missile. You have to have the electronics
to be able to do that targeting. And that means miniaturize
electronics so that those [inaudible]. You have to have
that guidance system. And of course, you have to
actually want to bomb somebody. So what do you think? We will, we will adjourn there. And you can think about there. There’s lots of notes
here as well. Places you can go
for more [inaudible]. [ Applause ]>>Before the hour. I’d like to have a few
minutes for questions. Before we have a short break for
a long, extended [inaudible]. We’ll see if we can get a couple of questions with
the whole group. No pressure that this
has to be [inaudible].>>If a bomb was launched at the
US, would the, is there any way that the US could stop it?>>Okay, so that’s
a good question. If somebody launched a bomb
at us, could we stop it? Well, that certainly depends
on what kind of bomb it was and how it was launched. So originally, when I was
thinking about working at Livermore, that was
the era of Ronald Reagan as president, and Star Wars. Or what became known as
Star Wars because that’s when the movie was popular. It was really called the
Strategic Defense Initiative. And that was an idea where the
Russians with their fixed silos and their intercontinental
ballistic missiles. We knew exactly where
they were coming from. So if they launched them,
we would know exactly where they were going to go. We would launch something and
take it out before it got to us. Now you have a really
long time to do that. Because it’s coming all
the way from Russia. And it’s being launched from some place that’s
fixed in the ground. And you know where it is. So that was at least
theoretically possible. Although all of the studies
that the physicists did at the time said, “We’ll
never be able to do that.” You know, that’s just, that’s just really a very
difficult technical challenge. So then [inaudible]
vehicles and laser beams that can shoot at them. You didn’t have to
actually plow into it. You could just zap it with some
lasers or throw a bunch of stuff in the way and confuse
its guidance system. And make [inaudible] instead of
going where it’s supposed to go. And there were all these ideas that people had about
doing that. But that, that huge phase, that
huge amount of time you have to get to intercept
something coming from Russia, that doesn’t work. If you’re launching
a small missile from a submarine
somewhere off the coast. And you don’t even know
where it’s coming from. Right? So we have a submarine
launched ballistic missile. Or if you have a
ballistic missile on something that’s lurking
around in your country. That makes the targeting and
intercept process you know that much more difficult. Like impossible. And so that’s why not a lot of
work has been done on Star Wars. Or SDIs since those days. Because people that did those
studies concluded it just wasn’t going to work that well. Also you know since it takes so little materials
to make a weapon. We can just put one
in a suitcase and we can just take
it into some country. Smuggle it in somehow, right? Because you’re not X-raying
everything that’s coming through the ports to find traces
of radioactivity or whatever. And so how, you can’t
possibly intercept those if you can’t find them
until it’s too late. So yes, people are
still thinking about it. Trump has started
the Space Force now because he wants the
militarize space. He [inaudible] was not
militarized previously. The idea of would be
some sort of deterrent to the Star Wars thinking
that somehow we’re going to have these things up there. Waiting for somebody
to shoot bombs at us. And take them all out
before they get there. And it’s, it’s really,
really a hard problem. And I don’t think anybody
has some good solutions.>>Let’s do one more question
before the, the break. [ Inaudible ]>>Well, anything that
creates a little ionized plasma [inaudible] can make
a little bit of pulse. It’s just to make a super huge
one that’s really destructive takes a big [inaudible]. But you can, you know,
you can make that little. I mean, anytime you
shock a door knob, you are ionizing the
air with just that area. Right? So that is like a little
tiny electromagnetic pulse. That breakdown of the
air as, as the shock goes through your fingers to the
doorknob and back to you, right? But to make one on purpose, basically requires an
instantaneous ionization of the air which
means, you know. A whole bunch of energy has to
make [inaudible] to plasma from, from neutral molecules
to just [inaudible].>>We’re going to continue
after a short break.>>Can you explain the different
between that kind of radiation and nuclear radiation?>>Okay, so, so as everybody
that’s a physics major knows. Light has an entire
frequency spectrum. All the way from radio
waves to gamma rays. And it’s only when
you get to things that are higher energy
than visible light. Well, visible light
can damage people. That’s what sunburns are, right? But you also get sunburns
from the ultraviolet part. So mostly people think
of the harmful radiation as being anything with more
energy than visible light. Because if you shine a
flashlight on yourself, it doesn’t really
hurt or anything. But if you shine an
ultraviolet source on yourself for long enough. You will definitely
get a sunburn, right? So as the wavelengths of the
light get shorter, their ability to penetrate the skin goes up. And so that’s why we take X-rays of people’s broken bones
with X-rays, right? And we don’t tend to
use gamma rays too much in the medical setting. Although if you’ve heard of this
thing called the cyberknife, a lot of, a lot of tumor
targeting is done with beams of directed gamma
rays that all converge on wherever your tumor is. Right? So you put a gamma, put a bunch of gamma ray
beams through your head. Not enough to destroy the
brain as it goes through. But if they all meet at one spot and deposit their
energy at the tumor. Then you can take out the tumor
with the so-called cyberknife. Right? So like converging
gamma ray beams in your head. Kind of thing. So ionizing radiation,
in other words. Anything that’s more
energetic than visible light. Is the more harmful kind. That doesn’t mean that
microwaves can’t harm you, the whole, you know
[inaudible] thing. You know, microwaves vibrate the
water in your soup or whatever. And so you know if you were in
a microwave, all of the water in your body would, you know be
heating you up pretty quickly. So that could be
dangerous as well. But people don’t tend
to go sit in microwaves. So that’s not a commonly
occurring problem. But, but your cell phones
and TVs and you know that projector, everything
makes RF. Makes radio waves. They’re very long waves. They’re very unenergetic
on a per photon basis. And they’re not generally
regarded as harmful. Because they don’t
penetrate the skin. And they can’t ionize your cells
to make tumors or cancer sites. So but, but radiation
is not just light. It’s not just electromagnetic
radiation. Because people called, they
didn’t know what they were, but they called them
alpha, beta, and gamma rays. They thought they were all three
different kinds of radiation. Gamma rays are the only
ones that are really light. The alpha particles
are helium nuclei. The beta particles are
electrons or positrons. Those have mass. They don’t travel as fast, but
if you give them enough energy. And they’re traveling
fast enough, they can go through your skin. And they can deposit and
cause, you know start tumors. Right? So other things in the colloquial public
are called radiation. They’re not necessarily
electromagnetic radiation, right? There’s particle radiation. And of course sometimes
light acts like a wave. And sometimes light
acts like a particle. So that just confuses
it further. But yeah, but there are
other things that we, that we call radiation. When we’re talking about
bombs like alphas and betas that are also [inaudible]
that they have mass. And they’re not,
not a form of light.>>Awesome, thank you.>>Yes, Mackenzie?>>So say there was a bomb. And you said when
they’re traveling to different continents,
they have to exit the– .>>They go up out
of the atmosphere. You travel through
space, and you come back through the atmosphere again.>>What would happen if it ignited while it was
outside of the atmosphere? Would there be any effect on us?>>Oh, I mean, it
would still ignite. It would still make
a pressure wave. But it would be someplace that
it would be far enough away. That hopefully not much
would happen, right? So even if, the electromagnetic
pulse needs to have the molecules of
the air be ionized in order to get the currents
into the power grid. So if you’re up there
where there’s no air, there’s no molecules,
just get a big blast wave. Just an explosion. Stars explode all
the time in space where there’s a vacuum, right? But it, it’s not
anything that tends to– .>>So the ideal to — .>>If you’re going to
shoot it down or something. But see shooting it down means
you’re not letting it have the nuclear explosion. So, so the whole concept
of a dirty bomb is a bomb that is filled with
radioactive waste. And it doesn’t make
a nuclear explosion, it just spews the
waste everywhere. I mean, it’s a big radioactive
contamination problem whenever all of that stuff landed. Right? So that, so that’s a
totally different style of bomb. It’s still scary
because it’s radioactive. But it doesn’t like fall out, and it doesn’t make
you know firestorms and pressure blast waves. It’s just a normal sort of bomb that contaminates
a lot of stuff. Because it’s just threw a
bunch of radioactive material like hospital waste all over
the place kind of thing.>>I was going to say,
that sounds like a good way to get rid of [inaudible].>>The best way, I mean,
if you could afford it. Is just put it on rockets
and send it into the sun. Then it can’t hurt anything. Right? Just send
it really far away. Like out into space
on a one-way ticket. But that’s pretty
expensive way to clean up the nuclear waste problem. Especially when you
consider there’s just piles of nuclear waste sitting at pretty much every nuclear
power plant in the entire world. Because nobody knows
how to get rid of that. We just let it sit
there in pools, usually.>>With the North Korean
economy being so impoverished. Where do they get the
economic wherewithal to have the nuclear weaponry?>>They just do it. Right? I mean, that’s why
the people are starving. They don’t spend any money on
anything else in their country. Other than the military. And every country has a certain
amount of money or whatever. I mean, it’s a choice. It’s a political choice, right?>>Is any of their
technology homegrown? Or is it all purchased?>>I think it’s mostly all
sort of gifted or stolen or purchased for cheap. From other countries
that have already figured out how to do it. And at one point I think
they had some Iranians or something advising them
on how to build their stuff. Right? Or maybe it was the
Pakistanis, right? You know. Yeah, so
there’s, there are states that know how to do it. That, you know like
Pakistan or Iran. That go around encouraging
other bad-acting countries to do it, too. It’s not, not a pretty picture.>>Anyway, so you
mentioned in the A-bomb so people use uranium to — . [ Inaudible ] Make sure that uranium 235 will
actually absorb many neutrons and form uranium 238?>>Well now what it
normally does is it breaks it apart first.>>So I guess there’s so
many different reaction when you have 235?>>Yeah, I mean it,
it’s not that common because you know it’s just,
but it’s much more fissile. It, you need much, you know, it can reach critical
mass and critical density. And it just takes a few
neutrons to blow it up. Right? So there are
certain elements that are just much better
for making bombs out of. Uranium 235 happens to be
a lot better than the 238. They’re both radioactive. If you’re just sitting there
and not disturbing them, they’re both radioactive. But the half-life of
uranium 238 is more than like ten billion years. Which is why it’s still
around in the rocks. Right? So uranium 235 is
a much shorter half-life. It’s still long. But it’s, that’s why
this, that’s why it’s not around in the rocks very much.>>As a follow up, how
would you get neutrons by themselves to shoot that?>>Well, you can just
make a neutron generator. It’s like a device that
somehow generates neutrons. But yeah, that’s a
whole other story. But or you can get this
[inaudible] and crunch them. And a bunch of neutrons
will spring out. I think that’s probably one
of those classified things that it’s not that
easy to find out. Although I could
try Googling it now. I bet you can find out
all this stuff now. Compared to when I first tried
to figure it out 20 years ago when there was no internet. [Inaudible] [ Inaudible ] Well, it’s one of the
nice things about the fact that I never had a security
clearance is I can talk about whatever I want. And nobody can give me
a lot of grief about it. My husband, on the other hand, he had a [inaudible]
clearance for a long time. And he used to work
out at Livermore on astrophysics projects. And so he could never
give a talk like this because he has had a
security clearance, right? So, but I never wanted
to get one just so I could keep going
around, educating people about this kind of stuff. But there’s, I’ve never
really had any personal or professional pushback. About the fact that it’s sort
of my hobby to educate people about this kind of stuff. I just felt, you know
I studied the policies. I decided I could not
participate in Star Wars. it was a totally stupid idea. And I probably wouldn’t
keep the job very long. Because they would
want me to say like, “Do Star Wars this way
instead of that way.” And I would be like,
“Don’t do Star Wars at all. It’s really stupid.” So I’m really glad that
I then got to just work on a different satellite
at Berkeley and I never had to go there. Because they were going
to pay me a lot of money. Took me about ten more years
before I made that much money in the academic world
[laughter]. For that job that I turned down. But, but it did launch
my interest in learning about all of this stuff. Which you know I continue
to educate people about. At least to the best of
my unclassified ability.>>Alright, we had a talk in
a series about nuclear winter and how that kind
of changed things. Once again, science is
informing the public. Could you speak a
little bit to, to that? The scientific push to
explain a nuclear winter?>>So, so nuclear
winter is what happens when you blow up everything. And you put a whole bunch of
stuff up in the atmosphere. And it stays there,
and it keeps the sun from getting down to the ground. To make the plants grow. And so then everything
is like winter. And then everybody
starves to death. On the other hand, it
would go a long way to combat global warming. [Laughter] I’m not
recommending it as an approach. But it’s definitely,
it, it’s like a, it’s like a super hyped-up
version of what happened when Mt. Pinatubo
went off, right? So that volcano put all
that stuff up in the air, and it actually did
slow global warming down for about three years. Because there was so much stuff
that filtered the sunlight that it, it kept the, the
warming curve from going up. It like plateaued
and then of course. The stuff all fell
down eventually. And then it went, global
warming started again.>>So nuclear winter
doesn’t last [inaudible]?>>No, nuclear winter would be
so much stuff from everything on the ground burning up. And putting up all this stuff in
the, you know that it would be for so long that we
would run out of food. And we would all die. Yeah. It wouldn’t just be
like an isolated thing, like one volcano going off. Even though that
was a big volcano. It would be like
everybody, like Russia and the US both bomb the heck
out of each other’s countries. Destroy it, everything. And put all that
stuff up into the air.>>And everybody dies.>>And everybody dies. On the whole planet. Not just in those countries. [ Inaudible ] Yeah, I mean, there’s, you know. If these, these, these
effects, the firestorms, the pressure waves, all of that. I mean, they happen over– . That’s why I said Google “nuclear effects
weapons calculator.” And you, you can see. I mean, it would take out the
entire San Francisco peninsula, just a single bomb. Everything would be flattened. You know everybody
would be killed. I mean, it’s, it’s
pretty dramatic. You know considering
it’s just this much stuff that’s combusting. So yeah. Not a good–>>Is uranium being, still
being actively mined here in the United States?>>Is uranium still
being actively mined? I think it is. I do think it is. Because we still
have power plants. And other countries
have power plants. Like France has lots
of power plants. Japan has lots of
power plants still. So you need.>>There’s still a big fight in
New Mexico on the reservations. But a, a worse fight is that
nobody can figure out what to do with the waste that’s
been generated since the power plants started. And so it just sit
there and pools. And sometimes they
put it in cans. And they like put the cans
in concrete and put them into some mountain in
[inaudible], it’s in Nevada. The problem is we have
no, I mean, the half-lives of these things are
millions of years. We don’t know how to make an
oil drum can to put stuff in. And it’s going to last
for millions of years and not let anything out, right? So they’re coming on
geology of those places like [inaudible] mountain to somehow encapsulate the
stuff they want to put in there. But then they found that there’s
water flowing through there. It can corrode the metal cans. And anyway, so no
one knows what to do. So they just leave it there. It still just sits there from
all the different power plants. All over. Big mess, really.>>Is there any way that
nuclear reactions or these kinds of explosions could
be used like, instead of as an explosive. Could it be used
as like an engine. So like to propel
something into space? Or [inaudible]?>>So yeah well so people
don’t use it as an engine to launch the rockets. But what they do have on the planetary satellites are
radioisotope thermal generators, RTG generators on the satellites
that just use the heat from a radioactive isotope. To create the power that you
need to run the satellite. Because you’re too
far from the sun. To use big solar panels
like we do on the satellites that go around the earth. So those radioisotope thermal
generators that they put on like the Cassini Mission
and things like that. you know they, they caused
a lot of alarm among people who were worried that,
that the rocket launch of Cassini would blow up. And the radioisotope
thermal generator would spew dirty-bomb-like stuff
all over the place. If it did blow up. But then of course it didn’t
and so it went to Saturn, and we don’t have to
worry about it anymore. But that was, that was a
concern of some people. And especially some
on this campus. Who we won’t mention, [inaudible] we won’t
mention them. Because I had a big
fight with them back when Cassini was being launched. About whether this should be
the number-one censored story. And whether people
should really be worried about humanity being
obliterated. Because NASA was launching a
radioisotope thermal generator. I wasn’t personally
worried about it. But others differed with me.>>I just have one
more question. One question about
in the seventies, when I was in elementary school. We had bomb shelter, like
nuclear bomb shelter.>>And there was a whole
duct tape thing too. You remember that?>>Yeah. Get some duct tape. It goes off and goes down here.>>And then duct
tape on your windows.>>Supposedly in a basement that I don’t think actually
exists now that I reflect on it. But now, like now
it seems even more. Threat seems even
higher than then, given North Korea’s ability to
at least launch rockets to us. Do you think we’re going to– Does, is anyone going to
implement that kind of–>>Are we going to go back to
having bomb shelters and stuff? Well remember what I said
about 80% of this stuff comes down in the first day. And 90% in the first week. So really, if you can just stay
indoors, you know, for a week. You’re going to miss most
of the worst fallout stuff. Assuming that the building
you’re in didn’t get blown apart by the [inaudible] or
burned by the firestorm. And if you’re far enough away. And you’re just worried
about the fallout. And you stay indoors for a week. You’ll probably have a
good chance of surviving. Of course you may not
have anything to eat. But you know, that’s
a whole other issue. Because all the food will be
contaminated just like the food at Chernobyl is still
contaminated. Anything that grows near there. Or Fukushima. You can’t grow anything in
either one of those places. And that wasn’t even
an explosion. But there’s still
not, [inaudible].>>Alright, with that,
let’s thank Dr. Cominsky. [ Music ]

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