Radioactive Boyscout: Real-Life Story of a Teenager's Quest for Nuclear Fusion

[FredGarvin]

Possibly a topic of conversation here...

Has anyone heard of this book / story? It really is amazing-scary. Possibly the most strange aspect about it, for me, is that it happened in my subdivision. I talked to a few neighbors who were there when things came to a head.



The original Harper's article is here to save you from buying the book.

http://www.geektimes.com/michael/culture/humor/items/Geekish/radioactive.html

It really is amazing how this kid got as far as he did.

 

[Morbius]

It really is amazing how this kid got as far as he did.

Fred,

Actually, I'm not AT ALL impressed with the young Mr. Hahn's
"accomplishments". First, the article states that, "..He had attempted
to build a nuclear reactor in his mother's shed following a Boy Scout
merit-badge project."

If he studied a little physics and nuclear engineering - he would see that
he went about his objective all wrong.

The article states that he put his Am-241 source in a block of lead,
presumably as shielding. If he had checked the Table of Nuclides, he
would have found that the decay mode of Am-241 is by emitting Alpha
particles:

http://sutekh.nd.rl.ac.uk/cgi-bin/CoNquery?nuc=Am241

If he had done his homework, he would have known that it is extremely
easy to shield alphas - they won't penetrate a piece of paper!

His knowledge of nuclear physics was faulty - witness his attempt at
Al27(alpha,n)P30 - attempting to induce a spallation reaction on Al27
with an alpha source? This kid must have been absent when they studied
about like charges repelling in school.

A reactor core is not just a bunch of radioactive materials all bundled
together. A reactor core has materials and geometry chosen for a
precise effect. The use of the word "critical" in describing a reactor is
because a properly designed reactor is a delicate balance between
neutron production and neutron loss. There was no understanding of the
physics of what he was doing.

This kid just assembled a bunch of radioactive material without any
logic or plan that made any sense as far as the laws of physics are
concerned.

Dr. Gregory Greenman
Physicist

 

[FredGarvin]

If you had read the story, you would have seen that he did this with, at best, a substandard high school education and, for the most part, one of his father's college science texts. This kid lacked every bit of sense on the planet, not just sense of the laws of physics. He was a degenrate. I was amazed he got as far as he did because of the happenings like how he posed as college professors and how he duped the NRC into giving him information.

 

[theCandyman]

I have not finished reading the story, yet, but what was everyone worried about and why did they take such precautions, Morbius?

 

[Morbius]

If you had read the story, you would have seen that he did this with, at best, a substandard high school education and, for the most part, one of his father's college science texts. .

Fred,

I DID read the story. I read it a long time back. We had this discussion
some time back on one of the science newsgroups; sci.physics, if memory
serves.

I was unimpressed then, and am still unimpressed.

This kid set out to build a breeder reactor; and he had absolutely no
concept of what a nuclear reactor was; let alone a breeder reactor.

He thought if he just cobbled together some radioactive material in
one spot - he would have a reactor.

I remember reading a book called "The Atom: Today and Tomorrow"
when I was in 5-th grade. I also used the address supplied in the back of
that book to get more information from the then AEC's Division of
Technical Information - including a booklet on "Nuclear Reactors".

From those readings then, I had a better grasp as to what a nuclear
reactor was, and how it worked; than this kid did.

I would expect that a high school student - even one from a substandard
school - to know enough to get some elementary texts on the subject
of nuclear reactors before attempting to build one.

No - this kid took the popular misconception that a reactor is just a
pile of radioactive material - and ran with it.

That doesn't connote anything praise-worthy, in my book.

Dr. Gregory Greenman
Physicist

 

[russ_watters]

I have not finished reading the story, yet, but what was everyone worried about and why did they take such precautions, Morbius?

They were worried about his materials, not his device.

 

[Morbius]

They were worried about his materials, not his device.

Russ is correct.

The worry is about the materials. He disassembled a number of smoke
detectors in order to get the radioactive Am-241.

The capsule that contains the Am-241 in a smoke detector contains a
warning to the user not to open that capsule.

It is just as if someone had run across a can of of arsenic, or some other
poison, labeled with the traditional "skull and crossbones" denoting a poison.

When one sees that symbol, anyone with a normal modicum of
intelligence should know not to proceed unless they know what they
are doing. The warning is there to protect you and the general public
from the dangers contained within.

This teen ignored those warnings and opened up the container. As long
as the Am-241 was contained within - it was of no danger to the public,
nor the teen. The alpha radiation that eminated from within the
container is very short range - because it loses energy very quickly.
That's why alphas can be stopped by a sheet of paper - or the dead layer
of skin surrounding your body.

Once the container is broached - then you have the prospect of someone
ingesting the Am-241. The short range and high LET - linear energy
transfer - of alphas [ meaning they transfer lots of energy per unit
distance traveled ] that was once an advantage if the alpha source
is external - now becomes a disadvantage.

If the alpha source - in this case, Am-241 - is ingested; then the alphas
are being emitted directly into living tissue. Because of the high LET -
alphas do a LOT of damage locally. They can tear delicate molecules
like DNA to shreds - and cause cancer.

Returning to my analogy - if a poison is safely secured in a proper
container - it is not a danger. If it is only removed from the container
and handled by someone who knows how to handle poisons - so that they
don't contaminate themselves and others; it is not a danger.

However, if an amateur that doesn't know what they are doing - ignores
the warning labels meant to protect them and the public in general - and
proceeds to open the poison and handle it improperly - then that person
is a public menance.

I don't believe in heaping any praise on someone with such disregard
for the dangers of poisons, nor radioactivity - especially when the
"adventure" was as ill-planned, and ill-conceived; as the one under
discussion here.

Dr. Gregory Greenman
Physicist

 

[ShadowKnight]

"It seems remarkable that David's story hasn't already wended its way through all forms of journalism and become the stuff of legend" - From the article

Stuff of legend? I don't think so... I never heard this story before and after reading it I can admire the kid's drive but the risk to himself and others in this manner isn't acceptable. Although he didn't need the lead shielding for the alpha radiation of the AM-241 (paper is enough to stop alpha as Morbius points out) the fact that he did it leads me to believe that he KNEW that the elements he was playing with were very dangerous. Also as soon as he realized that he was dedecting high amounts of radiotion through concrete and up to 5 houses away, he really should have told someone. It's one thing to put yourself in danger in the name of science but to knowingly risk many people around you isn't very ethical.

 

[hitssquad]

Irène Joliot-Curie and the radioactive boy scout

His knowledge of nuclear physics was faulty - witness his attempt at Al27(alpha,n)P30 - attempting to induce a spallation reaction on Al27 with an alpha source?

In 1935, Irène Joliot-Curie said she had induced neutron emissions via alpha irradiation of aluminum:
http://nobelprize.org/chemistry/laureates/1935/joliot-curie-lecture.html

• Aluminium can be transformed, by the capture of an alpha particle and the emission of a proton, into a stable silicon atom. On the other hand, if a neutron is emitted the product of the reaction is not a known atom.
  
  Later on, we observed that aluminium and boron, when irradiated by alpha rays do not emit protons and neutrons alone

 

[Morbius]

In 1935, Irène Joliot-Curie said she had induced neutron emissions via alpha irradiation of aluminum:
http://nobelprize.org/chemistry/laureates/1935/joliot-curie-lecture.html

• Aluminium can be transformed, by the capture of an alpha particle and the emission of a proton, into a stable silicon atom. On the other hand, if a neutron is emitted the product of the reaction is not a known atom.
  
  Later on, we observed that aluminium and boron, when irradiated by alpha rays do not emit protons and neutrons alone

hittsquad,

I'm aware of that - but look at the ENERGY required to do that!

Before the alpha can get close enough to the nucleus of the aluminum
atom for the alpha to be in range of the short ranged strong nuclear
force - the alpha has to overcome the mutual electrostatic repulsion
of the alpha and the nucleus. Therefore, there is a threshold energy
that the alpha has to have. If the energy is below the threshold - the
alpha doesn't make it close enough to the nucleus of the aluminum
before it runs out of energy and stops. It has to have an energy greater
than the threshold for the reaction.

The Curies used Radium as their alpha source - with a higher energy
alpha particle emission.

The 5.6 MeV alpha from Am-241 is BELOW that threshold energy of
the (alpha,n) reaction on Aluminum that the Curies induced. This is one
of the things the teen should have looked up before he chose Am-241
as his alpha source.

He chose Am-241 because it was convenient to get from smoke detectors-
NOT because it could do the job he intended it to do!

Dr. Gregory Greenman
Physicist

 

[theCandyman]

I have done a little extra reading in my text about biological effects of alpha particles. Is ionization of water in the body or destruction and mutation of DNA a more pressing problem? Or are they one in the same?

 

[Astronuc]

Cells contain water. Radiation ionizes water (radiolysis) which then may recombine to form peroxide, a powerful oxidizer (oxidant). The oxidants then interact with larger molecules, and in the case of DNA, they may break it - hence mutations. Oxidants also interact with enzymes, proteins and other macromolecules necessary for cell function, and the cell may then 'die'.

As the does of radiation increases, cell damage and mortality increase.

If a person survives (i.e. does not die), there is still a risk of cancer.

 

[hitssquad]

The Curies used Radium as their alpha source - with a higher energy alpha particle emission.

The 5.6 MeV alpha from Am-241 is BELOW that threshold energy of the (alpha,n) reaction on Aluminum that the Curies induced.

Interesting. Thank you for the clarification.

 

[Morbius]

I have done a little extra reading in my text about biological effects of alpha particles. Is ionization of water in the body or destruction and mutation of DNA a more pressing problem? Or are they one in the same?

Candyman,

In your readings about the biological effects of alpha particles; you should
come across a concept known as the "Quality Factor".

With respect to radiation, the term "dose" means "how much energy is
deposited per unit mass". The term "dose equivalent" is used for the metric
that describes how much biological damage is done.

The units of dose are "rads" [ = 100 ergs per gram ], or the SI unit is the
"Gray" [ = 1 Joule per kilogram ].

You get the "dose equivalent" by multiplying by the "quality factor".

The units of dose equivalent are "rems" and "Sieverts".

If you know the energy deposition dose in "rads" and you multiply by the
quality factor - you get a dose equivalent in "rems" [ rad equivalent man ].

If you know the energy deposition dose in "Grays" and you multiply by the
quality factor - you get a dose equivalent in "Sieverts".

So "rads" and "Grays" are both units for the same thing - and can be
converted one to the other.

"Rems" and "Sieverts" are both units of the same thing - and can be
converted one to the other. You can see both of these units used
side by side in the following table, courtesy of Idaho State University:

http://www.physics.isu.edu/radinf/radrus.htm

[The unit "mSv" is the abbreviation for the milli-Sievert; 1/1000-th of a
Sievert.]

The quality factor for photons is 1.

The quality factor for alphas is 20, if memory serves.

Therefore, alphas do 20 times the amount of biological damage per
unit of energy absorbed per gram; as do photons.

Courtesy of the Institute for Energy and Environmental Research:

http://www.ieer.org/sdafiles/vol_8/8-4/terms.html


Dr. Gregory Greenman
Physicist

 

[theCandyman]

The Curies used Radium as their alpha source - with a higher energy
alpha particle emission.

The 5.6 MeV alpha from Am-241 is BELOW that threshold energy of
the (alpha,n) reaction on Aluminum that the Curies induced. This is one
of the things the teen should have looked up before he chose Am-241
as his alpha source.

He used Radium as his later alpha source, would that react with the Aluminum? What is a "spallation reaction"?

 

[hitssquad]

Right said Fred and Irene

He used Radium as his later alpha source, would that react with the Aluminum?

We just went over that. Irène and Frédéric Joliot-Curie used radium to induce neutron emissions from aluminum. Here is Irène's Nobel lecture on the subject...
http://nobelprize.org/chemistry/laureates/1935/joliot-curie-lecture.html

...and here is Frédéric's Nobel lecture on the subject:
http://nobelprize.org/chemistry/laureates/1935/joliot-lecture.html

What is a "spallation reaction"?

"...A nuclear reaction in which light particles are ejected as the result of bombardment (as by high-energy protons)." (M-W Unabridged 3.0.) Spallation is distinct from fission where spallation might be thought of as more of a brute-force reaction involving kinetic hammering by the spallating particle and fission as a more elegant reaction involving initially absorption by the target nucleus of the fission-inducing particle.

 

[Morbius]

We just went over that. Irène and Frédéric Joliot-Curie used radium to induce neutron emissions from aluminum. Here is Irène's Nobel lecture on the subject...
http://nobelprize.org/chemistry/laureates/1935/joliot-curie-lecture.html

...and here is Frédéric's Nobel lecture on the subject:
http://nobelprize.org/chemistry/laureates/1935/joliot-lecture.html



"...A nuclear reaction in which light particles are ejected as the result of bombardment (as by high-energy protons)." (M-W Unabridged 3.0.) Spallation is distinct from fission where spallation might be thought of as more of a brute-force reaction involving kinetic hammering by the spallating particle and fission as a more elegant reaction involving initially absorption by the target nucleus of the fission-inducing particle.

hitssquad,

You got it. On both counts.

Dr. Gregory Greenman
Physicist

 

[theCandyman]

Sorry, but what I meant was the way in which he obtained his Radium. Was it concentrated enough to use? I remember hearing in my high school physics class that otherwise, Radium was obtained by boiling off big pots filed with something that contained Radium but that only very little Radium was obtained in this way.

 

[Morbius]

Sorry, but what I meant was the way in which he obtained his Radium. Was it concentrated enough to use? I remember hearing in my high school physics class that otherwise, Radium was obtained by boiling off big pots filed with something that contained Radium but that only very little Radium was obtained in this way.

Candyman,

The "Radioactive boyscout" used Americium-241 [ Am-241 ] as the
radioactive source of the alpha radiation.

Am-241 is found in smoke detectors. The Am-241 emits alpha particles
which are then detected by a radiation detector. Smoke interferes with
the transport of the alpha particles. When the smoke detector observes
that interference - it sounds the alarm.

The boyscout dismantled a bunch of smoke detectors to get his source of
radioactivity.

Dr. Gregory Greenman
Physicist

 

[Viper2838]

The radium that this kid found was from an old clock he bought.

"Inside he discovered a vial of radium paint left behind by a worker either accidentally or as a courtesy so that the clock's owner could touch up the dial when it began to fade. "- the story

Disregarding any other stupidity, why choose radium? If he was such a chemistry buff, he should have read about how Frédéric Joliot-Curie got cancer from carying a vile of the stuff around in his pocket. Not fun stuff to handle.

 

[hitssquad]

The safety of radium-226

If he was such a chemistry buff, he should have read about how Frédéric Joliot-Curie got cancer from carying a vile of the stuff around in his pocket.

Radium decays by alpha particle emission. Alpha particles are harmlessly stopped by the outer layers of human skin.
http://www.epa.gov/radiation/understand/alpha.htm


--
The health effects of alpha particles depend heavily upon how exposure takes place. External exposure (external to the body) is of far less concern than internal exposure, because alpha particles lack the energy to penetrate the outer dead layer of skin.
--

 

[Morbius]

The radium that this kid found was from an old clock he bought.

"Inside he discovered a vial of radium paint left behind by a worker either accidentally or as a courtesy so that the clock's owner could touch up the dial when it began to fade. "- the story

Disregarding any other stupidity, why choose radium? If he was such a chemistry buff, he should have read about how Frédéric Joliot-Curie got cancer from carying a vile of the stuff around in his pocket. Not fun stuff to handle.

Viper2838,

As hitssquad also replied - Radium is harmless outside the body.

The alpha radiation emitted by Radium is very easy to shield - it will
be stopped by the thickness of a piece of paper. Alpha radiation will
not penetrate even the dead layer of skin that surrounds your body.

Radium that is injested is very dangerous. The same characteristic
that makes alphas easy to stop - a high LET [ Linear Energy Transfer ]
means that the alpha particles deposit their energy in a very short
distance of travel - hence do a lot of local damage.

As long as you wash your hands after handling, in order to prevent
injestion [ or wear disposable latex gloves, in case you have a cut ],
and take reasonable care to prevent dispersal; Radium, and
other alpha sources are quite easy to handle safely.

Dr. Gregory Greenman
Physicist

 

[Norman]

Candyman,

In your readings about the biological effects of alpha particles; you should
come across a concept known as the "Quality Factor".

With respect to radiation, the term "dose" means "how much energy is
deposited per unit mass". The term "dose equivalent" is used for the metric
that describes how much biological damage is done.

The units of dose are "rads" [ = 100 ergs per gram ], or the SI unit is the
"Gray" [ = 1 Joule per kilogram ].

You get the "dose equivalent" by multiplying by the "quality factor".

The units of dose equivalent are "rems" and "Sieverts".

If you know the energy deposition dose in "rads" and you multiply by the
quality factor - you get a dose equivalent in "rems" [ rad equivalent man ].

If you know the energy deposition dose in "Grays" and you multiply by the
quality factor - you get a dose equivalent in "Sieverts".

So "rads" and "Grays" are both units for the same thing - and can be
converted one to the other.

"Rems" and "Sieverts" are both units of the same thing - and can be
converted one to the other. You can see both of these units used
side by side in the following table, courtesy of Idaho State University:

http://www.physics.isu.edu/radinf/radrus.htm

[The unit "mSv" is the abbreviation for the milli-Sievert; 1/1000-th of a
Sievert.]

The quality factor for photons is 1.

The quality factor for alphas is 20, if memory serves.

Therefore, alphas do 20 times the amount of biological damage per
unit of energy absorbed per gram; as do photons.

Courtesy of the Institute for Energy and Environmental Research:

http://www.ieer.org/sdafiles/vol_8/8-4/terms.html


Dr. Gregory Greenman
Physicist

Hello all,

To preface: I work on cosmic ray shielding (as a Ph.D. student) from a particle/nuclear physics standpoint, but I have only a very cursury knowledge of the biological effects these high energy particles have on cells, etc.

Are there any really good texts on the subject of the biological effects of high energy radiation that a physics graduate student with a couple of classes in microbiology (at undergrad level) can understand?

Thanks a lot for your help.
Cheers,
Norm

 

[Emfuser]

Hello all,

To preface: I work on cosmic ray shielding (as a Ph.D. student) from a particle/nuclear physics standpoint, but I have only a very cursury knowledge of the biological effects these high energy particles have on cells, etc.

Are there any really good texts on the subject of the biological effects of high energy radiation that a physics graduate student with a couple of classes in microbiology (at undergrad level) can understand?

Thanks a lot for your help.
Cheers,
Norm

You might benefit from looking for topics covered by health physics education programs.

It probably wouldn't hurt to look on http://www.nukeworker.com/ . The site is mainly for contract personnel in the nuclear industry (which I work in), but lots of those people are HPs or related functions and could probably point the way better than folks here.

 

[Morbius]

You might benefit from looking for topics covered by health physics education programs.

It probably wouldn't hurt to look on http://www.nukeworker.com/ . The site is mainly for contract personnel in the nuclear industry (which I work in), but lots of those people are HPs or related functions and could probably point the way better than folks here.

Norman,

For a professional scientist, a good resource would be to the
Health Physics Society, which is the professional society for
health physicists that specialize in radiation safety:

http://www.hps.org/

The Health Physics Society is one of the main debunkers of the so-called
"Tooth Fairy Project" which attempts to draw a correlation between
nuclear reactors and Strontium-90 found in baby teeth:

http://hps.org/publicinformation/ate/q616.html

Strontium-90 is in the environment due to atmospheric weapons tests
in the 1940s, 1950s, and very early 1960s. Since the half-life of
Strontium-90 is 29 years - it has been less than two half-lives since
the Partial Test Ban Treaty disallowed atmospheric nuclear testing.

Therefore, more than 25% of the the radioactive Stontium-90 released
in those tests has still not decayed and is still in the environment.

The National Cancer Institute issued a study in 1991 which shows that
areas around nuclear power plants do not have increase cancers.
After all, one receives more exposure to radioactivity from a coal
power plant:

http://www.ornl.gov/info/ornlreview/rev26-34/text/colmain.html

Please continue to listen to scientists, and not activists.

Dr. Gregory Greenman
Physicist

 

[theCandyman]

I saw the Radioactive Boyscout book in the library yesterday, so I decided it might be an entertaining read. The way it is written seems like it is more for teens and yound adults with little information or knowledge about chemistry or physics. Annoyingly, it is written in such a way as to make the nuclear industry look like an unsafe rabble of scientists and David seem like a genius child. The chapter I am on right now is talking about "disasters" and the cover ups of governments. More than anything it is bashing breeder reactors, the author even states that one could blow up like a nuclear bomb (is that even a realistic scenario?).

Also, about the above, the child did eventually use Radium to try and get Aluminum to emit neutrons. Did he succeed in this way making a "neutron gun"?

 

[Morbius]

I saw the Radioactive Boyscout book in the library yesterday, so I decided it might be an entertaining read. The way it is written seems like it is more for teens and yound adults with little information or knowledge about chemistry or physics. Annoyingly, it is written in such a way as to make the nuclear industry look like an unsafe rabble of scientists and David seem like a genius child. The chapter I am on right now is talking about "disasters" and the cover ups of governments. More than anything it is bashing breeder reactors, the author even states that one could blow up like a nuclear bomb (is that even a realistic scenario?).

Candyman,

No - a breeder reactor can't blow up like a bomb - nobody would design it
that way.

Breeders are fast reactors - they work on fast neutrons - neutrons with
high energy direct from the fission process. Fast reactors don't slow
the neutrons down to low energy as thermal reactors do.

Nuclear weapons also work on fast neutrons. That's where the scare
mongers try to justify the statement you read. However, just because
a fast reactor works on fast neutrons like a bomb does, doesn't mean
that it can explode.

It's like saying that your car uses the same technology as a "fuel-air"
bomb; the bombs the U.S. military has that vaporize a fuel like gasoline
over a large area and then ignites it. It can blow up a large area.

Well that same idea is used in the engine of your car. So if you use the
"logic" of the scare mongers - your car's engine can blow up and take
out a city block! Ridiculous! Nobody designs a car engine that could do
that.

Likewise, nobody designs a fast reactor that can blow up like a nuclear
weapon. In fact, one designs fast reactors like the Integral Fast Reactor
design that Argonne National Lab developed so that they don't blow up -
but rather shut down. Please see PBS Frontline's interview with
Dr. Charles Till of Argonne National Laboratory:

http://www.pbs.org/wgbh/pages/frontline/shows/reaction/interviews/till.html

I think you hit the nail on the head when you state that the book makes
the scientists and engineers that design reactors look like idiots. That
seems to be the tack - claim that the scientists and engineers are all
idiots that don't know what they are doing.

That way they can claim that the scientists and engineers don't know
enough not to design a fast reactor that doesn't explode like a bomb.

Hopefully people will not believe them. After all, airliners are designed
by engineers also - and people have enough confidence in those engineers
to fly in the machines they design. Why are aeronautical engineers
considered smart, and nuclear engineers considered dumb?

Dr. Gregory Greenman
Physicist

 

[Emfuser]

I saw the Radioactive Boyscout book in the library yesterday, so I decided it might be an entertaining read. The way it is written seems like it is more for teens and yound adults with little information or knowledge about chemistry or physics. Annoyingly, it is written in such a way as to make the nuclear industry look like an unsafe rabble of scientists and David seem like a genius child. The chapter I am on right now is talking about "disasters" and the cover ups of governments. More than anything it is bashing breeder reactors, the author even states that one could blow up like a nuclear bomb (is that even a realistic scenario?).

Also, about the above, the child did eventually use Radium to try and get Aluminum to emit neutrons. Did he succeed in this way making a "neutron gun"?

Yes, he succeeded in making a crude sub-critical pile that produced an appreciable multiplication for a household assembly. In the process, he also gave himself a pretty substantial dose of gamma radiation, beta radiation, limited alpha radiation, and neutron radiation. To those of us in the industry, it is somewhat fascinating that he could be sharp enough to accomplish what he did without realizing the danger he placed himself in.

 

[TOKAMAK]

Spallation is distinct from fission where spallation might be thought of as more of a brute-force reaction involving kinetic hammering by the spallating particle and fission as a more elegant reaction involving initially absorption by the target nucleus of the fission-inducing particle.

Just a quick question if I may: So would spallation be the appropriate term for the fissioning of the U238 tamper on a thermonuclear warhead? The U238 in the tamper fissions from the fast neutrons, but thermal neutrons won't have any effect (other than transmuting the uranium into neptonium, which will quickly decay to Pu239), correct?

 

[tehfrr]

The Uranium would still be fissioned. Spallation would be more of when a high energy particle blows a nucleus into pieces, rather than just splitting it into a couple of fission fragments.

Here would be a spallation reaction for example:

$$Ar^{40} + n_0^1 \rightarrow Na^{22} + 7protons +11 neutrons$$

I do not know how much spallation happens in an an atomic explosion; however, you mentioned fission. Uranium 238 (and thorium 232) are fissionable with fast neutrons, but spallation is different.

 

[Morbius]

Just a quick question if I may: So would spallation be the appropriate term for the fissioning of the U238 tamper on a thermonuclear warhead? The U238 in the tamper fissions from the fast neutrons, but thermal neutrons won't have any effect (other than transmuting the uranium into neptonium, which will quickly decay to Pu239), correct?

TOKAMAK,

As tehfrr stated, fissioning of U238 is not spallation - it is a fission reaction.

Or more specifically, it is a "threshold fission reaction".

An isotope like U-235 is said to be "fissile" - because it will fission with
low energy neutrons - that is the neutron need not bring with it any added
kinetic energy. Just falling into the nuclear potential well of a U-235
nucleus is enough to fission U-235.

An isotope like U-238 is said to be "fissionable". That is it will fission,
but only if the neutron has a kinetic energy above a certain threshold
value; which in the case of U-238 is about 1 MeV. If you have a lot of
high energy neutrons running around, U-238 will fission, and it is called
"fission" - same mechanism as U-235 - but just needs a little more energy.

Dr. Gregory Greenman
Physicist

 

[TOKAMAK]

Oh okay, I think I get it now. Thanks for the quick responses.