Talk:Neutron radiation
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"Fast neutrons on the other hand more often cause fission and so are useful in nuclear reactors and bombs"
I was under the impression that U-235 split more easily when under 'attack' by slow moving neutrons. I'm not so sure about Plutonium, though.
- Both are oversimplified. Ah me, where to start...! Andrewa 01:44, 26 Oct 2004 (UTC)
"A few reactors (fast neutron reactors) and all nuclear weapons rely on fast neutrons." A U235 bomb depends on slow neutrons to sustain the chain reaction, does it not. Arguably since no (few) U235 weapons exist, this sentence is still true, however it is slightly misleading. 136.159.97.136 21:24, 30 January 2006 (UTC)
What you need to understand is that the ratio of fission to activation (ng reactions) changes as a function of the neutron energy. For almost all actinides slow neutrons will favour absorption of neutrons without fission while when a fast neutron is absorbed then fission is more likely. This is why more Pu-241 will be made in a thermal reactor running on MOX than would be made in a fast reactor running on the same MOX mixture. Both the fission and activation cross sections tend to go down as the neutron energy increases. Hence as a result the critical mass for a moderated system is oftein much lower than for a bare metal sphere. I think that for Pu-239 that about 11 Kg is needed for a bare sphere to go critical while only about 350 g of Pu would be needed if powdered PuO2 was to be mixed with water in a beaker. In an atom bomb the process of moderation would take too long for it to occur, by the time that a neutron has been thermalised then the other neutrons generated as the same time as the hypothetical thermalised neutron (which has wandered off into some water or Be before coming back) will have already caused fission without having slowed down. The accident in Japan (around about Oct 1999) was stopped by removing the water jacket from around the fissile solution, but rather than being a system where one big pulse of fission occurs that was a system where a long almost steady power output was generated. The power output of that system was not constant as bubbles in the uranium solution formed. These reduced the effect of the water as a moderator so the power output dipped. When the bubbles went away the power increased, the bubbles were formed by the irradation of the water. One day I might add some graphs of cross sections for different reactions to wikipedia. If someone else wants to then look at the table of the nuclides which is in Korea (http://atom.kaeri.re.kr/), this has the cross section data for every isotope known to mankind. I would suggest that a fission vs capture ratio as a function of neutron energy graph should be drawn for U-235, Pu-239, Am-241 and U-238. These are likely to be very different in shape.Cadmium
"Neutron radiation is a form of ionising radiation though there is active debate because it is not directly ionizing like protons, photons, and electrons. This interaction is relatively rare, so neutron radiation is more penetrating than alpha radiation or beta radiation and gamma radiation" The rarity of "this interaction" is not why neautrons are more penetrating, it's their high mass and low (zero) charge. User: Nucleardave 0736 UTC 12 May 2005
How is it detected? - Omegatron 20:35, Jun 10, 2005 (UTC)
[edit] ionizing
Neutron radiation is ionizing! It makes ions via every slowing or capture mechanism. The only exception is when they are thermal (or even intermediate) and they are just acting as a gas until captured. Anyway, a recoiling nucleus is ionized (it looses all it's electrons! the most ionized it can be) it just wasn't ionized by having the electrons removed, it was ionized by being moved while it's electrons stayed put... I mean if you want to follow this line gammas are not ionizing b/c they just deposit their energy in an electron and an atom...--Pdbailey 05:30, 27 August 2005 (UTC)
