Re: fissile versus fissionable

[rkathren@tricity.wsu.edu (Ron L. Kathren)]

No offense, but, regrettably, the DOE Orders, as is the case with 10CFR20,
sometimes play a little fast and loose with accepted scientific definitions.  

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>          We at the DOE use a slightly different definition of 
>          fissile/fissionable.  For example, in DOE Order DOE5480.24 
>          "Nuclear Criticality Safety," the definition used is:
>          
>          "Fissionable Material. Nuclides capable of sustaining a 
>          neutron-induced fission chain reaction (e.g. uranium-233, 
>          uranium-235, plutonium-239 ......."
>          
>          Thus you can see, that in the DOE usage, fissile material is a 
>          subset of fissionable material.
>          
>          Rey Bocanegra
>          Senior Radiological Technical Advisor
>          DOE Richland Ops Office
>          (509) 372-2868
>
>
>______________________________ Reply Separator
_________________________________
>Subject: fissile versus fissionable
>Author:  dj_strom@ccmail.pnl.gov at -MailLink
>Date:    1/24/97 12:16 PM
>
>
>Gary Damschen has it right: fissile material can have fission induced by 
>thermal neutrons, while fissionable materials require fast neutrons for 
>incuded fission.  Here's some insight, though: for even-Z nuclides (Th, 
>U, Pu, ...), an odd A (mass number) implies an odd N (number of 
>neutrons).  For odd-N nuclei, the addition of another neutron completes 
>a Pauli spin pair (spin up, spin down), which is an energetically more 
>favored quantum state than adding a neutron to an even-N nucleus.  Thus, 
>the odd-A nuclei for U (233, 235) and Pu (239, 241, 243) tend to be 
>fissile, while the even A nuclei are merely fissionable.  A look a the 
>neutron-induced fission cross-section for U-238 shows a threshold of 1 
>MeV.
>          
>The opinions expressed above are my own, and have not been reviewed or 
>approved by Battelle, the Pacific Northwest National Laboratory, or the 
>U.S. Department of Energy.
>          
>Daniel J. Strom, Ph.D., CHP
>Staff Scientist
>Health Protection Department K3-56
>Pacific Northwest National Laboratory 
>Battelle Boulevard, P.O. Box 999
>Richland, WA 99352-0999 USA
>(509) 375-2626
>(509) 375-2019 fax
>dj_strom@pnl.gov
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