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U.S. Department of Energy
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A MINATURE U$sup 238$ FISSION COUNTER

Technical Report ·
OSTI ID:4034298
A small, 0.25-in. diam. x 0.50-in. long, fast neutron fission counter probe employing highly depleted uranium as the fission material was developed. The isotopic analysis of the uranium is as follows: U/sup 238/ (essentially 100%) U/sup 236/ >s (0.03 plus or minus 0.02 ppm) U/sup 235/(0.90 plus or minus 0.20 ppm) and U/sup 234/ (0 04 plus or minus 0.02 ppm). The uranium was plated out of solution to a yield of approximately 1.72 mg/cm/sup 2/. Detailed measurements of the fast neutron flux in the Flexible Plastic Reactor (lO/sup 5/ to lO/sup 6/ neutrons/cm/sup 2//sec), obtained with the U-238 fission counter, show it to be insensitive to both thermal neutrons, even without a thermal (Cd) shield. and to highenergy (>5.3-Mev) gamma rays. The gamma sensitivity, photofission of the U/sub 3/O/sub 8/, was checked in ihe critical assembly by making a fast neutron flux scan with red phosphorus (1/2-in. x 1/10-in) pellets. Since the (n,p) threshold reaction in phosphorus ( approximately 1 Mev) is approximately the same as the (n.f) reaction in U/sup 238/ the two scans should yield, as is found to be the case, identical results provided there is no appreciable influence of photofission in the U/sub 3/O/sub 8/. (auth)
Research Organization:
Knolls Atomic Power Lab., Schenectady, N.Y.
DOE Contract Number:
W-31-109-ENG-52
NSA Number:
NSA-15-015753
OSTI ID:
4034298
Report Number(s):
KAPL-M-GDH-4
Country of Publication:
United States
Language:
English