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The article needs clean-up?? It looks fine to me now, and especially since the main concern re: "fissile" is in stuff that you can manufacture in large quantities, like we can do for U-233, U-235, and Pu-239. Does anyone know of any more isotopes?? 18.104.22.168 (talk) 06:57, 28 August 2008 (UTC)
- Yes, it does. It fails to list all fissile isotopes. Since there aren't that many of them, listing them all isn't hard. I could edit it if I would be reasonably sure I'm getting it right, but I don't. — Preceding unsigned comment added by 22.214.171.124 (talk) 12:48, 4 August 2013 (UTC)
How is 244 an odd number??? :-)
“Several … isotopes are known to be fissile, all of them having … odd atomic mass numbers. These include: … Curium-244”
I do not know the subject enough to relate oddness to fissilitude and, therefore, to fix the article. Oddly, my degree is in physics; I recall no rule postulating that only odd-weighing isotopes be fissile (no implication that there is no such rule). The reference  mentioning 244Cu as a fissile material is but a safety instruction, and it is OK for such documents to err on the “safe” side, so this reference is not convincing enough to me for a blank-minded edit.
- —  11:57, 11 February 2006 (UTC)
None of the nuclei 241Am, 237Np and 244Cm is fissile. All of them undergo fission after irradiation with fast neutrons, but not with thermal neutrons.
Furthermore, only 244Cm has an even mass number (244) and an even atomic number(96). Both 237Np and 241Am have an odd atomic number (93 and 95 respectively) and an odd mass number.
--Pgrouse 11:04, 5 October 2006 (UTC)
- Now, the article is stating that the "rule" for even N and odd # of neutrons is an "in general" rule - in other words, a "rule of thumb". I known as an engineer (M.S. Georgia Tech) that rules of thumb do tend to have exceptions - and sometimes, lots of them... 126.96.36.199 (talk) 06:57, 28 August 2008 (UTC)
- Also, considerations of fissibility for higher-order or hard-to-make actinides are not too relevent here, because they are impossible to collect large amounts of for making nuclear reactors and bombs.188.8.131.52 (talk) 06:57, 28 August 2008 (UTC)
The OE isotopes are unbalanced and less stable, and are fissable because they can be caused to fission by thermal neutrons. The EE isotopes are balanced and more stable (long halflived) and can only be fissioned with fast neutrons (>14Mev), and therefore are fissionable>WFPM (talk) 02:11, 21 April 2011 (UTC)
What does fissile actually mean?
The word fissile can be used to refer to any item which can be split. For example it is used in geology to refer to slates and shales. Should the definition be limited to the specific case of nuclear fission?? —Preceding unsigned comment added by 184.108.40.206 (talk) 16:06, 4 March 2008 (UTC)
- Well, now, the article is saying now at the top that it is an article about nuclear physics and nuclear engineering. Thus, for some other meaning of "fissile", you need to write your own article. 220.127.116.11 (talk) 06:57, 28 August 2008 (UTC)
- I have two comments on this point. First. this is about "fissile material" or "fissile isotopes." Perhaps the title could be changed accordingly. Second, there is another meaning of the term "fissile material" to mean material that can be used to make a nuclear weapons by supporting a fast fission chain reaction. In other words, the defining factor the ability to produce fission not with neutrons near zero energy but with neutrons as they emerge from a fission. I think it would be worth having a section reflecting this alternate definion. By this definition, any material with a bare critical mass is "fissile." That includes, for example, Np-237 and Pu-238.
- Suggest to any nuclear engineer that any material with a bare critical mass is fissile and they'll probably laugh in your face. But it's a widely held belief, and Wikipedia has probably been part of the problem.
- I have not yet discovered any authority for a good definition of fissile, despite asking many nuclear engineers (having worked for the AAEC in the past I still know some) and consulting every text they recommended. But both the term and the odd-even principle have been introduced in the very first chapter of most. It's a basic concept of both reactor and weapon design, and well understood but poorly defined. If that seems contradictory perhaps it's because we are speaking here about engineering rather than science! Andrewa (talk) 21:03, 3 May 2010 (UTC)
Neptunium-237 can sustain a chain reaction with fast neutrons, but rarely fissions with slow neutrons. Does this mean it is fissile or not? This also contradicts a sentence in the article stating that all fissile materials can sustain a chain reaction with both fast and slow neutrons. --JWB (talk) 05:16, 12 March 2009 (UTC)
In the technical sense Np-237 is not fissile, since it does not have a large fission cross section for thermal neutrons. But "fissile" material is commonly understood to mean material you can make a bomb from - i.e. that supports a fast fission chain reaction. In that sense NP-237 is fissile. NPguy (talk) 19:23, 12 March 2009 (UTC)
Good, but we need to address the second sentence of the article, and get references for each legitimate definition of "fissile". Also, is there commonly used terminology disambiguating being able to sustain thermal and fast neutron chain reactions?
The whole "odd Vs. Even" section
Did anyone notice that Jeopardy had a question last week relating the most important criteria in selecting U-235 was that it had an odd number of neutrons???
That whole section of the article is CONFUSING and, like someone said above, sounds way to much like a rule of thumb.
I am doing some research to try and clarify this point. Right now, from reading "Introduction to Nuclear Engineering" By J.R. Lamarsh (Prentice hall 3rd Edition) I can find no equivalent explanation for fissile behaviour and odd number of neutrons. He relates it solely to the number of neutrons per fission relased in a fuel mixture and the ratio of absorption to fission cross sections (See equation 3.51). of course, the underlying physics could still deal with # of nuetrons which is the point I am still researching.
In any case one line that DEFINITELY should be changed is the line about " More generally, elements with an even number of protons and an even number of neutrons, and located near a well-known curve in nuclear physics of atomic number vs. atomic mass number are more stable than others - and hence, less likely to undergo fission"
The well known line in nuclear physics is not a even to even neutron/ proton line... the line is # neutrons = # protons. As the Mass of the nuclei increases the "stable line" deviates further and further away from this line... regardless of if you have even or odd number of neutrons. what the line indicates is that as mass increases you need much more neutrons per proton in order to maintain stability. (i.e. you need the nuclear force to overcome the electromagnetic repulsion of the positeveloy charged protons). This includes isotopes with both even and odd numbers of neutrons thus it is not clear to me what point the article is trying to make. Do you mean closer to the line relative to isotopes of the same element?
Let's just hypothesize that An E isotope starts out with even number of proton/neutron pairs, so it can be balanced or not, depending on the number of extra neutrons. With an even number of extra extra neutrons you then have a relatively balanced EE type isotope which is the least unstable. However with an odd number of extra neutrons, you then have an unbalanced and therefor more unstable EO type isotope. In the case of an O type isotope, you start out with an odd number of proton/neutron pairs, which is unbalanced, and which cannot be completely balanced with extra neutrons, but can be less unbalanced with an odd number of extra neutrons (making an OE isotope) than it can with an even number of extra neutrons, (making an OO isotope). Of the 255 stable isotopes, approximately 150 are EE's, approximately 55 are OE's, and approximately 50 are EO's. So it's significant.WFPM (talk) 02:29, 21 April 2011 (UTC)
The whole "odd Vs. Even" section PART 2
Further research has told me that the odd-even concept in the article has some validity.
In the Lamarsh reference above see section 2.12 Nuclear Models, "Liquid Drop Model".
However, I beleive the concept as it relates to Fission (and thus fissile materials) is incomplete. I beleive a discussion of the formation of a Compound Nucleus, Binding Energy, and Fission is required... See Section 3.7 of Lamarsh "Fission". particularily useful is the table of "Critical Energies for Fission" is very useful. In this table, the change in Critical Energy as one alternates between even and odd numbers and the effect that this has on an isotope being fissile or fissionable is much mroe relavant than the generalized disucssion on stability that is now included in the article.
Seems to be an appropriate discussion of the phenomenon... I think it is a lot less confusing to disuss energy first, then bring in the odd-even concept. —Preceding unsigned comment added by 18.104.22.168 (talk) 13:30, 25 May 2009 (UTC)