|WikiProject Physics||(Rated Start-class, High-importance)|
"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. 188.8.131.52 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)
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)
Pdbailey is correct, emmited neutrons do fall under the category of ionizing radiation. The introduction explaining them as "non-ionizing" is patently false. The confusion likely stems from the fact that an emmited neutron is not DIRECTLY ionizing radiation (cf it has no charge, and does not strip electrons). Neutrons do, however, function as a type of INDIRECTLY ionizing radiation by interacting with nuclei and altering atomic/molecular charge. This categoizes neutron radiation as ionizing.184.108.40.206 (talk) 17:20, 25 January 2011 (UTC)
== why not we try to read,explor and try to combine NEUTRONS AN X-RAYS? THERE ARE MANY CONDITIONS AND THINGS ARE SAME IN BOTH OF THEM?(momna naeem) == —Preceding unsigned comment added by 220.127.116.11 (talk) 12:00, 17 June 2009 (UTC)
Under the heading "Uses": we have this sentence: "Neutrons can also be used for imaging of industrial parts termed neutron radiography when using film, neutron radioscopy when taking a digital image, such as through image plates, and neutron tomography for three dimensional images." A bit awkward. It could be broken into two sentences, or maybe it just needs a comma after "industrial parts". Also: Under the heading "Cosmogenic neutrons" we have this sentence: "Most of them activate a nucleus before reaching the ground; a few react with nuclei in the air." What are you saying? Activating a nucleus is different than reacting with a nucleus? Clarify, please. c.pergiel (18.104.22.168 (talk) 02:39, 20 November 2009 (UTC))
If you insert capsules of OE3Li7 inside a closed container and into a thermal neutron test source and provide a container vent tube connection to the outside can you get a measureable amount of helium output?WFPM (talk) 20:32, 18 April 2010 (UTC)
Agreed, please change non-ionizing to ionizing, it really hurts my eyes and probatly someone put it in because of the missing charge of neutrons. —Preceding unsigned comment added by 22.214.171.124 (talk) 17:06, 19 January 2011 (UTC)
"Neutron radiation is a kind of ionizing radiation which consists of free neutrons. A result of nuclear fission or nuclear fusion, it consists of the release of free neutrons from both stable molecules and isotopes, and these free neutrons react with nuclei of other stable molecules to form new isotopes of previously non-isotopic molecules, which in turn produce radiation. This will result in a chain reaction of nuclear radiation, which makes radiation dangerous and harmful over great areas of space."
Neutron radiation is indeed a type of ionising radiation consisting of free neutrons, but that is where the truth and the lead for this article depart company. It cannot be released by stable anything; it is a product of instability, as is all ionising radiation. "Molecules" are not involved in nuclear reactions, and something being called a "molecule" does not indicate that it is stable or unstable. In this article and in this context, "molecule" is without meaning; it is a chemistry term.
"Isotopes" are simply different forms of the same element; if something is an "isotope" it does not mean that it is radioactive. Almost all elements have more than one isotope and most elements have some radioactive isotopes. As I said, calling something an "isotope" does not mean that it is radioactive, and there is no such thing as "non-isotopic" in that sense; "stable" or "non-radioactive" would be the words you are looking for.
Neutron radiation can make other things that were not radioactive into radioactive things, and no other type of radiation can do that, but this can not spread in "a chain reaction of nuclear radiation". Only neutron radiation can make other things radioactive, but the radiation that it makes those things produce cannot then cause other things to become radioactive, repeating in an never ending chain. So even if a neutron bomb causes an area to become radioactive, the radiation that this area produces is not neutron radiation, and cannot make anything else radioactive. One neutron bomb cannot cause the entire Earth to become radioactive. The only time that type of chain reaction can occur is inside a nuclear weapon, and a neutron bomb is simply a normal nuclear weapon but instead of designing the weapon to keep as many neutrons as possible to keep the reaction going to make a bigger explosion and knock more buildings down, the designers let them escape. The explosion won't be as powerful, but there will be a larger dose of neutrons to kill people and leave buildings less damaged.
I noticed that Neutron spectrum redirects to this article. However, there is no mention about neutron spectrum in the article. Either a short explanation about neutron spectrum or a separate article would be appropriate. Otherwise the redirect does not make much sense. ––Nikolas Ojala (talk) 08:21, 10 May 2017 (UTC)