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Naser
Coherent neutron source |
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It seems Plastic Magnets wasn't wacky enough. Time to dial the wack up to 11: behold the Naser! Neutron Amplification by Stimulated Emission of Radiation. Just the ticket for neutron holography, and shooting down nuclear warheads.
Pick an isotope of an element with an odd atomic number that decays
emitting a neutron. The nucleii will have a net spin. You can align the spins with a strong magnetic field (a Tesla or so) and some very low temperatures (about a mK). The enriched isotope is in effect an inverted population as in a laser: the nucleii are all in an energetic state but there is a kinetic barrier preventing them all going to a lower energy state at once. The decay that emits the neutron will probably have to emit a gamma ray if it is going to reserve energy and momentum.
We haven't got a lens or a mirror that works on photons or neutrons. Without a mirror, we are going to get our amplification in a single pass. Make the isotope into a wire or thin rod with one of the lattice axes running down the length of it. You can pull the isotope from a Czocralski furnace or run a zone furnace up and down it a few times. If your isotope is a metal with a hexagonal or face centered cubic structure, this will probably get a close-packed (1,1,1) axis running down the length of it.
We now apply the magnetic field. If you get this aligned with the crystalline axis, then you will probably get a neutron emitted close to the axis. There will be a number of other possible ways that the thing could decay while preserving the total spin, so as well as emitting the neutron along the axis, there are a number of other cone surfaces that it could lie on. However, if it is close enough to the close-packed lattice then the weak nuclear force may be enough to pull it onto the line. If the neutron lies along the line of nuclei, then the gamma ray will do the same. The gamma ray may cause a nucleus to emit its neutron and gamma in the same direction. By the time the pulse of neutrons has traveled 10 cms, the neutron beam should be coherent to less that an angstrom in 10 cms. That would give a spot 30cm diameter on the Moon. If the beam finesse is set by the nuclear width rather than the nuclear spacing, it could be a lot finer than that.
A high-power laser needs to have an initial source to start the amplification, and it needs to have shutters such as Pockels cells to stop an amplified pulse running in the reverse direction. It is not clear how we start the neutron pulse running in the right direction, We could possibly use a graded magnetic field so the amplification is greater starting from one end. When the thing has fired, the low temperature and the nuclear spin alignment will probably be destroyed, so we should not get a back-pulse. But don't stand behind it when you press the button just in case.
There. And if someone has built that, I will invent a hat-eating machine.
Laser triggered neutron beam?
https://pureadmin.q...njp_18_5_053002.pdf
[bhumphrys, Aug 21 2026]
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A hat-eating machine sounds like a lot more fun than whatever this is. Or how about A Coherent Nuggat Source? |
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I got excited so interrogated our pal Google who disappointingly maintains that neutron lasers can't be a thing, because neutrons are fermions, not bosons. |
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[Richard k] there's a link to an interesting paper; it's utter gobbledygook to me, about something they did at the Rutherford Appleton Lab. Please decode! |
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@bhumphrys Thanks for picking up on the fermion-boson thing. I am trying to remember this from about 1995 and I had left a chunk out. Something that decays emitting a neutron will probably a photon to satisfy energy and momentum balance. It is this photon that does the stimulation, and the weak force acting on the neutrons provides the focussing. I have altered the text. |
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The Rutherford-Appleton thing is doing a tiny bit of fusion. It is nothing like enough if you want to generate energy, but it is fine for generating a very short burst of neutrons. |
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So I've a suggestion: instead of calling it a 'naser' then, it could be a 'pnaser' (Photon-neutron laser), and similar to Psmith, the p is silent as in pshrimp. (Wodehouse). |
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I'm pretty sure the regular sort of mirror works because photons interact with it. |
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//Something that decays emitting a neutron will probably a photon// |
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Undoubtedly. {looks wise} |
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@bhumphrys How about 'gnaser' for gamma-neutron and the rest of it? I shall leave the name as it is for now, but 'gnaser' is good. |
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The Naser is a middle-Eastern barbering tool used to safely remove both nostril and exterior hairs from the generous Semitic nose. Northern Europeans are largely ignorant of this appliance, having little need for this treatment of their skimpy button noses. Partial clay plans were excavated from a site, but attempts to recreate the Naser resulted in injury to and embarrassment for the researchers. The Naser will remain a mystery unless neutrons can be harnessed to hygienically remove nasal hair. |
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The Gnaser (brutally shortened from Gnasher, then poorly transliterated from the Yiddish nosher, one who noshes, snacks) is a large universal masticator that has been miniaturized and adapted to eat hats. It is produced by the same folks who brought you "Hold My Beer" brand premedicated gauze dressings. |
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