# X-rays created by fission stage of a hydrogen bomb?
**URL:** https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761
**Category:** Factual Questions
**Created:** [May 30, 2019, 11:38am UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761 "2019-05-30T11:38:32Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@KidCharlemagne](https://boards.straightdope.com/u/KidCharlemagne)
#### Post date: [May 30, 2019, 11:38am UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/1 "2019-05-30T11:38:32Z")
I read that x-rays from the fission stage of an H-bomb are what sets off the fusion reaction. I thought fission primarily produced neutrons and gamma rays. How are x-rays produced and why do they (vs gamma rays) set off the fusion reaction? Thanks.
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### Author:  [@naita](https://boards.straightdope.com/u/naita)
#### Post date: [May 30, 2019, 12:17pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/2 "2019-05-30T12:17:43Z")
I am not a nuclear physicist but here’s my high school physics explanation aided by Wikipedia.
A single instance of fission produces neutrons and gamma radiation, but a fission chain reaction also produces incredible heat, and heat means thermal radiation. The hotter the result, the more energetic the bulk of the radiation. As per wikipedia:
> [@](#):
>
> A fusion explosion begins with the detonation of the fission primary stage. Its temperature soars past approximately one hundred million Kelvins, causing it to glow intensely with thermal x-radiation.
As to why it’s the X-rays and not the gamma rays causing the fusion my qualified guess is that it’s to do with absorption. Gamma rays are more likely to just pass on through, leaving the secondary x-rays to do most of the pushing. Yes, x-rays famously also go through stuff, but to a lesser degree than gamma, and there’s a lot of it.
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### Author:  [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)
#### Post date: [May 30, 2019, 12:20pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/3 "2019-05-30T12:20:24Z")
“x-rays” and “gamma rays” overlap in the wavelength regime. The distinction between the two is generally in the way they are created – X-rays are characteristically created by _bremsstrahlung_ – deceleration of particles, as in an x-ray tube. Gamma rays are characteristically generated by atomic fission or fusion. Sometimes it’s not separable exactly what’s responsible. For many uses the terms are essentially interchangeable.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [May 30, 2019, 1:37pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/4 "2019-05-30T13:37:41Z")
I imagine that X rays are more responsible for the fusion than gamma rays mostly just by virtue of there being more power in the X ray range than in the gamma range.
You’ve probably heard of fusion bombs being referred to as “thermonuclear”. That just means that the chain reaction is maintained by the extreme heat, rather than by neutrons in a fission bomb.
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### Author:  [@scr4](https://boards.straightdope.com/u/scr4)
#### Post date: [May 30, 2019, 1:53pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/5 "2019-05-30T13:53:18Z")
If I’m understanding [these](https://en.wikipedia.org/wiki/Plutonium-239#Nuclear_properties) [tables](https://en.wikipedia.org/wiki/Uranium-235#Nuclear_weapons) correctly, most of the energy from fission goes into kinetic energy of the new nuclei produced. And of course large nuclei would immediately collide, turning the kinetic energy into heat. At a temperature of millions of degrees, any material glows in the X-ray. (You can think of it as blackbody radiation, or you can - more correctly - think of it as electrons moving so fast that it emits X-rays through thermal bremsstrahlung.)
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### Author:  [@naita](https://boards.straightdope.com/u/naita)
#### Post date: [May 30, 2019, 2:20pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/6 "2019-05-30T14:20:30Z")
> [@scr4](#):
>
> If I’m understanding [these](https://en.wikipedia.org/wiki/Plutonium-239#Nuclear_properties) [tables](https://en.wikipedia.org/wiki/Uranium-235#Nuclear_weapons) correctly, most of the energy from fission goes into kinetic energy of the new nuclei produced. And of course large nuclei would immediately collide, turning the kinetic energy into heat. At a temperature of millions of degrees, any material glows in the X-ray. (You can think of it as blackbody radiation, or you can - more correctly - think of it as electrons moving so fast that it emits X-rays through thermal bremsstrahlung.)
Electrons, or nuclei? Not being a nuclear physicist I have this cartoon vision of the nuclei being accelerated so hard the electrons are just left behind circling nothing, like in a cartoon, but what actually happens to them, if they’re the ones emitting bremsstrahlung rather than the nuclei?
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### Author:  [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)
#### Post date: [May 30, 2019, 2:40pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/7 "2019-05-30T14:40:56Z")
I believe I once read that x-rays serve their role to initiate fusion in hydrogen bombs in part because they behave in some sense as a solid as they compress the secondary. Is this solid-like behaviour exhibited to the same degree by gamma (and/or other) types of EM radiation?
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### Author:  [@DPRK](https://boards.straightdope.com/u/DPRK)
#### Post date: [May 30, 2019, 2:56pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/8 "2019-05-30T14:56:50Z")
> [@KarlGauss](#):
>
> I believe I once read that x-rays serve their role to initiate fusion in hydrogen bombs in part because they behave in some sense as a solid as they compress the secondary. Is this solid-like behaviour exhibited to the same degree by gamma (and/or other) types of EM radiation?
A body surrounded by a uniform electromagnetic radiation field will be compressed; is that what you mean?
Photons have momentum, but in what sense are they solid?
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### Author:  [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)
#### Post date: [May 30, 2019, 3:06pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/9 "2019-05-30T15:06:22Z")
> [@DPRK](#):
>
> A body surrounded by a uniform electromagnetic radiation field will be compressed; is that what you mean?
Yes, I think.
> [@](#):
>
> Photons have momentum, but in what sense are they solid?
In a figurative sense insofar that they can compress macroscopic stuff?
Again, this is my recollection of something that I may well have misinterpreted. The best cite I can come up with quickly is [this one](https://fas.org/sgp/eprint/cardozo.pdf) (4th and 3rd last paragraphs on p. 1405). I seem to recall reading about it in a piece that was recounting the ‘eureka moment’ in Ulam’s idea for the bomb.
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### Author:  [@scr4](https://boards.straightdope.com/u/scr4)
#### Post date: [May 30, 2019, 3:36pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/10 "2019-05-30T15:36:18Z")
> [@naita](#):
>
> Electrons, or nuclei? Not being a nuclear physicist I have this cartoon vision of the nuclei being accelerated so hard the electrons are just left behind circling nothing, like in a cartoon, but what actually happens to them, if they’re the ones emitting bremsstrahlung rather than the nuclei?
I think the kinetic energy of the nuclei are quickly turned into heat, and at that temperature, that means everything turns into thermal plasma. Plasma means electrons and positive ions (including bare nuclei) are flying around separately. In this situation, electrons are moving much faster than ions, so they would be radiating a lot more energy.
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### Author:  [@KidCharlemagne](https://boards.straightdope.com/u/KidCharlemagne)
#### Post date: [May 30, 2019, 4:31pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/11 "2019-05-30T16:31:09Z")
The Wikipedia entry on the thermonuclear weapons states that “thermal x-rays” initiate fusion. What does “thermal” specifically mean in this context? I know radiation can be ionizing or thermal, and I certainly know what thermal means, but am confused about the need for a descriptor. Is the author just trying to say that’s is the heat rather than the capacity to break bonds that initiates fusion?
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### Author:  [@KidCharlemagne](https://boards.straightdope.com/u/KidCharlemagne)
#### Post date: [May 30, 2019, 4:34pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/12 "2019-05-30T16:34:16Z")
> [@KarlGauss](#):
>
> I believe I once read that x-rays serve their role to initiate fusion in hydrogen bombs in part because they behave in some sense as a solid as they compress the secondary. Is this solid-like behaviour exhibited to the same degree by gamma (and/or other) types of EM radiation?
Is this perhaps because since x-rays are less penetrative, they interact more with surface atoms and this has a compressive effect?
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [May 30, 2019, 4:41pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/13 "2019-05-30T16:41:24Z")
Radiation is not “ionizing or thermal”, and thermal X-rays would be both. “Ionizing” is a measure of the energy per photon (a rough measure, since different atoms will need different amounts of energy to ionize, but it’s usually good enough to be a useful distinction). “Thermal” is a description of how those energies are distributed. A laser (or maser or xaser or graser or whatever) is not thermal, because all of the photons are not at the same energy. Light from the Sun, by contrast, is (mostly) thermal, because there’s the right distribution: Most of the light is from a certain energy range around some peak value, with tails of lower and higher energies, according to a particular formula.
In particular, “thermal radiation” does not mean that it’ll heat up whatever it hits. _Any_ sort of radiation will do that. It also doesn’t mean specifically infrared: We only think of infrared specifically as “heat” because most of the things we think of as having heat (like fire and animal bodies) are in the infrared temperature range, but the visible light from the Sun or the X-rays in a nuke are similarly incandescence from other temperatures.
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### Author:  [@naita](https://boards.straightdope.com/u/naita)
#### Post date: [May 30, 2019, 5:05pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/14 "2019-05-30T17:05:18Z")
> [@scr4](#):
>
> I think the kinetic energy of the nuclei are quickly turned into heat, and at that temperature, that means everything turns into thermal plasma. Plasma means electrons and positive ions (including bare nuclei) are flying around separately. In this situation, electrons are moving much faster than ions, so they would be radiating a lot more energy.
Right, so the bremsstrahlung would be because some electrons are bumped so hard in the plasma they break light speed for the material?
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### Author:  [@DPRK](https://boards.straightdope.com/u/DPRK)
#### Post date: [May 30, 2019, 5:48pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/15 "2019-05-30T17:48:32Z")
> [@KidCharlemagne](#):
>
> Is this perhaps because since x-rays are less penetrative, they interact more with surface atoms and this has a compressive effect?
Handy Wikipedia says that the body will be compressed by the momentum of radiation it absorbs, of waves reflecting off the surface, and also of radiation it itself emits.
> [@](#):
>
> \*n the specific case of the pressure exerted on surfaces of a body in thermal equilibrium with its surroundings, at a temperature T: The body will be surrounded by a uniform radiation field described by the Planck black-body radiation law, and will experience a compressive pressure due to that impinging radiation, its reflection, and its own black body emission. From that it can be shown that the resulting pressure is equal to one third of the total radiant energy per unit volume in the surrounding space.
>
> By using the Stefan–Boltzmann law, this can be expressed as
>
> P[sub]compress[/sub] = u/3 = (4σ/3c) T[sup]4[/sup]
>
> where σ is the Stefan–Boltzmann constant.
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### Author:  [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)
#### Post date: [May 30, 2019, 6:00pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/16 "2019-05-30T18:00:34Z")
> [@DPRK](#):
>
> A body surrounded by a uniform electromagnetic radiation field will be compressed; is that what you mean?
>
> Photons have momentum, but in what sense are they solid?
Found it. From [Building The H Bomb: A Personal History by Kenneth W. Ford](https://books.google.ca/books?id=2xq3CgAAQBAJ&pg=PA8&lpg=PA8&dq=Hydrogen+bomb+ulam+insight+radiation+fluid&source=bl&ots=2sSW0iuG0w&sig=ACfU3U0p6f3zW5SPbT1rP-kHJNMlOST_Sg&hl=en&sa=X&ved=2ahUKEwjTpfXv6MPiAhWMmeAKHc0aDKYQ6AEwEXoECBcQAQ#v=onepage&q=Hydrogen%20bomb%20ulam%20insight%20radiation%20fluid&f=false): “(The radiation) can flow like a liquid and then push like a giant steel piston. No, not like steel. Stronger than steel.”
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### Author:  [@scr4](https://boards.straightdope.com/u/scr4)
#### Post date: [May 30, 2019, 6:41pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/17 "2019-05-30T18:41:24Z")
> [@naita](#):
>
> Right, so the bremsstrahlung would be because some electrons are bumped so hard in the plasma they break light speed for the material?
You’re thinking of Cherenkov radiation. [Bremsstrahlung](https://en.wikipedia.org/wiki/Bremsstrahlung) is just radiation from charged particles that are accelerated, e.g. when a high energy electron is deflected as it nears an atomic nucleus.
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### Author:  [@KidCharlemagne](https://boards.straightdope.com/u/KidCharlemagne)
#### Post date: [May 30, 2019, 10:40pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/18 "2019-05-30T22:40:15Z")
> [@Chronos](#):
>
> Radiation is not “ionizing or thermal”, and thermal X-rays would be both. “Ionizing” is a measure of the energy per photon (a rough measure, since different atoms will need different amounts of energy to ionize, but it’s usually good enough to be a useful distinction). “Thermal” is a description of how those energies are distributed. A laser (or maser or xaser or graser or whatever) is not thermal, because all of the photons are not at the same energy. Light from the Sun, by contrast, is (mostly) thermal, because there’s the right distribution: Most of the light is from a certain energy range around some peak value, with tails of lower and higher energies, according to a particular formula.
>
> In particular, “thermal radiation” does not mean that it’ll heat up whatever it hits. _Any_ sort of radiation will do that. It also doesn’t mean specifically infrared: We only think of infrared specifically as “heat” because most of the things we think of as having heat (like fire and animal bodies) are in the infrared temperature range, but the visible light from the Sun or the X-rays in a nuke are similarly incandescence from other temperatures.
I thought the range of electromagnetic waves that caused thermal radiation was roughly mid way to UV down to, but excluding, microwaves. Is the word thermal being used differently in the term “thermal x-ray?”. Maybe it’s best if I just ask - what other types of x-rays are there besides thermal?
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### Author:  [@DPRK](https://boards.straightdope.com/u/DPRK)
#### Post date: [May 30, 2019, 11:02pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/19 "2019-05-30T23:02:45Z")
The electromagnetic waves don’t _cause_ thermal radiation; they _are_ the thermal radiation. Hot matter emits electromagnetic waves. You can see this by heating up a piece of iron until it glows.
ETA in a bomb the fission is what starts heating things way up.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [May 30, 2019, 11:18pm UTC](https://boards.straightdope.com/t/x-rays-created-by-fission-stage-of-a-hydrogen-bomb/834761/20 "2019-05-30T23:18:14Z")
All sorts of distributions of energy are possible, only one of which is thermal. Most other distributions don’t have names, but one that does is a monochromatic source, in which all of the photons have the same energy (at least, approximately). Another one commonly encountered is a line source, which is basically a mix of a small number of monochromatic sources.
You can have thermal radiation anywhere in the spectrum. It’s just that, after some point, the temperatures become impractical for many purposes. A thermal X-ray source will have a temperature of a million degrees or so; a thermal microwave source will only be a few degrees above absolute zero. But both exist (and in fact the most perfect thermal spectrum we’ve ever observed is in the microwave range-- the Cosmic Microwave Background Radiation).
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