ENTRY 14807 20230413 150614807000 1 SUBENT 14807001 20230413 150614807001 1 BIB 10 28 14807001 2 TITLE Thermal neutron fission properties of Np237 14807001 3 AUTHOR (A.Ghiorso,D.W.Osborne,L.B.Magnusson) 14807001 4 REFERENCE (B,TRANSU.EL.,,1639,1949) 14807001 5 REL-REF (I,,A.Ghiorso+,R,ANL-4048,1947) High-sensitivity 14807001 6 apparatus for fission counting, ionization chamber. 14807001 7 INSTITUTE (1USAANL) 14807001 8 FACILITY (REAC,1USAANL) Thermal column of Argonne heavy-water 14807001 9 reactor. 14807001 10 DETECTOR (IOCH) A fissionability was measured in a sensitive 14807001 11 ionization chamber inserted into thermal column of 14807001 12 Argonne reactor. 14807001 13 SAMPLE A thin sample was prepared by electroplating of 14807001 14 platinum foil. The mass of neptunium was determined 14807001 15 by alpha counting to be 142*10**-6 g. 14807001 16 METHOD The fission rate of 237Np was compared under 14807001 17 identical neutron-flux conditions with that of a 14807001 18 standard thin sample of 239Pu. A fission rate of 6, 14807001 19 000 fission per minute was observed in neptunium 14807001 20 sample. Assuming that all fissions are due to 237Np 14807001 21 and using the known thermal neutron cross section of 14807001 22 239Pu, the thermal neutron cross section for 237Np 14807001 23 was determined. This cross section is for fission by 14807001 24 neutrons with a Maxwellian distribution of energy 14807001 25 corresponding to a temperature of 293 degree K. The 14807001 26 thermal nature of neutrons was confirmed by a 14807001 27 measurement with cadmium shield that reduced counting 14807001 28 rate by a factor of 100 or more. 14807001 29 HISTORY (20230413C) BP 14807001 30 ENDBIB 28 0 14807001 31 NOCOMMON 0 0 14807001 32 ENDSUBENT 31 0 1480700199999 SUBENT 14807002 20230413 150614807002 1 BIB 3 8 14807002 2 REACTION (93-NP-237(N,F),,SIG,,MXW) 14807002 3 ERR-ANALYS (DATA-ERR) Conservative limit of errors, rather 14807002 4 arbitrarily. 14807002 5 (ERR-S,,3.) Not greater than a few percent. 14807002 6 (ERR-1) Error due plutonium present in neptunium. 14807002 7 (ERR-2,,3.) Self absorption of fission particles. 14807002 8 STATUS (TABLE,,A.Ghiorso+,B,TRANSU.EL.,,1639,1949) 14807002 9 page 1640 of B,TRANSU.EL.,,1639,1949. 14807002 10 ENDBIB 8 0 14807002 11 COMMON 1 3 14807002 12 ERR-1 14807002 13 B 14807002 14 0.001 14807002 15 ENDCOMMON 3 0 14807002 16 DATA 3 1 14807002 17 EN-DUMMY DATA DATA-ERR 14807002 18 EV B B 14807002 19 0.0253 0.019 0.003 14807002 20 ENDDATA 3 0 14807002 21 ENDSUBENT 20 0 1480700299999 ENDENTRY 2 0 1480799999999