ENTRY 14279 20170403 14271427900000001 SUBENT 14279001 20170403 14271427900100001 BIB 9 23 1427900100002 TITLE Nuclear Decay Properties of 256Fm 1427900100003 AUTHOR (R.W.Hoff,J.E.Evans,E.K.Hulet,R.J.Dupzyk,B.J.Qualheim) 1427900100004 REFERENCE (J,NP/A,115,225,1968) 1427900100005 #doi:10.1016/0375-9474(68)90657-X 1427900100006 INSTITUTE (1USALRL) 1427900100007 FACILITY (REAC,1USAGEV) General Electric Test Reactor, 1427900100008 Vallecitos, California. 1427900100009 INC-SPECT The energy spectrum consists principally of thermal 1427900100010 neutrons in this well-moderated reactor. 1427900100011 SAMPLE The 155Fm target material was separated from its 1427900100012 parent the beta emitter 255Es, which was present in 1427900100013 an einsteinium fraction of the following composition: 1427900100014 1.0 microg 253Es, 3.4x10**-5 microg 255Es. The 1427900100015 fermium was separated from the einsteinium by elution 1427900100016 from a column Dowex-50 resin with 0.4 M ammonium 1427900100017 alpha-hydroxyisobutyrate solution, pH = 3.85 at 85 1427900100018 degrees C. The target composition at the start of the 1427900100019 irradiation was 1.43x10**9 atoms 2SSFm and 1427900100020 1.21x10**10 atoms 253Es. The 253Es was present in the 1427900100021 target as a contaminant because of incomplete 1427900100022 chemical purification of the fermium. 1427900100023 DETECTOR (IOCH) 1427900100024 HISTORY (20170403C) BP 1427900100025 ENDBIB 23 0 1427900100026 NOCOMMON 0 0 1427900100027 ENDSUBENT 26 0 1427900199999 SUBENT 14279002 20170403 14271427900200001 BIB 5 31 1427900200002 REACTION (100-FM-255(N,G)100-FM-256,,SIG,,MXW) 1427900200003 METHOD (INTB,CHSEP) The total neutron exposure was 6 h at an 1427900200004 average flux of 8.6x10**13 n/cm2 sec, which was 1427900200005 determined by the activation of a cobalt wire. The 1427900200006 flux measurement is estimated to be accurate to +- 1427900200007 10%. After removal from the reactor, the target was 1427900200008 dissolved in 80% HCI - 20% ethanol solution and 1427900200009 treated to remove fission products. This solution was 1427900200010 saturated with HCl gas and loaded directly onto a 1427900200011 Dowex-50x12 (colloidal form) ion-exchange column. 1427900200012 Elution of the column with HCl-ethanol solution 1427900200013 resulted in the purification of the combined 1427900200014 einsteinium and fermium fraction from most fission 1427900200015 products, particularly the rare earths. The decay of 1427900200016 spontaneous fissions in the sample was measured by 1427900200017 counting in an ionization chamber with the amplifier 1427900200018 biased to record fission events only. In order to 1427900200019 calculate the neutron capture cross section of 255Fm, 1427900200020 the following cross section estimates were assumed 1427900200021 sigma(n,fission) = 200 b; for 256Fm, 1427900200022 sigma(n,destruction) = 20 b. However, the calculation 1427900200023 is insensitive to the values assumed since 1427900200024 neutron-induced reactions account for only 2% of the 1427900200025 destruction of 25SFm during the irradiation; the 1427900200026 remainder is due to alpha decay. In the case of 256Fm, 1427900200027 neutron-induced reactions account for < 10**-4 of the 1427900200028 destruction rate as compared to the 157 min decay. 1427900200029 ERR-ANALYS (DATA-ERR) No details on sources of uncertainties. 1427900200030 DECAY-DATA (100-FM-255,20.1HR) 1427900200031 (100-FM-256,157.MIN) 157 +- 2 min. measured by authors.1427900200032 STATUS (TABLE) page 232. 1427900200033 ENDBIB 31 0 1427900200034 NOCOMMON 0 0 1427900200035 DATA 3 1 1427900200036 EN-DUMMY DATA DATA-ERR 1427900200037 EV B B 1427900200038 0.0253 30.0 4.0 1427900200039 ENDDATA 3 0 1427900200040 ENDSUBENT 39 0 1427900299999 SUBENT 14279003 20170403 14271427900300001 BIB 3 13 1427900300002 REACTION (100-FM-257(N,G)100-FM-258,,SIG,,MXW,DERIV) 1427900300003 ANALYSIS Cross section estimate: The general trend for neutron 1427900300004 capture cross sections is to decrease with an 1427900300005 increase in mass number for isotopes of a given 1427900300006 element on the neutron excess side of stability. An 1427900300007 odd-even effect is also seen, e.g. the odd-mass 1427900300008 fermium isotopes have capture cross sections somewhat 1427900300009 higher than neighboring even-mass isotopes. Thus, we 1427900300010 may conclude that the capture cross section of 257Fm 1427900300011 for a well-thermalized reactor spectrum is less than 1427900300012 30 b. 1427900300013 STATUS (TABLE) page 232. 1427900300014 (DEP,14279002) 1427900300015 ENDBIB 13 0 1427900300016 NOCOMMON 0 0 1427900300017 DATA 2 1 1427900300018 EN-DUMMY DATA-MAX 1427900300019 EV B 1427900300020 0.0253 30.0 1427900300021 ENDDATA 3 0 1427900300022 ENDSUBENT 21 0 1427900399999 ENDENTRY 3 0 1427999999999