ENTRY 30089 20080215 31253008900000001 SUBENT 30089001 20080215 31253008900100001 BIB 7 14 3008900100002 INSTITUTE (3RUMBUC) 3008900100003 REFERENCE (R,IFA-NR-33,(1970),197007) full information,but result3008900100004 revised following private communication. 3008900100005 (R,STI/DOC/10-125,37,197104) summary 3008900100006 (R,IFA-NR-22,196507) new method proposed 3008900100007 AUTHOR (C.Borcea, A.Borza, A.Buta, A.Isbasescu, L.Marinescu, 3008900100008 I.Mihai, T.Nascutiu, M.Petrascu, V.Savu, V.Simion) 3008900100009 TITLE Absolute measurement of Pu-239 fission cross-section 3008900100010 for 2200 m/s neutrons 3008900100011 EXP-YEAR (1970) 3008900100012 STATUS (APRVD) approved by Mihailescu (29 nov 1974) 3008900100013 HISTORY (19740124U) HDL. References added. 3008900100014 (19741218U) CA. -Status 'aprvd' added. 3008900100015 (20080305A) BIB section updated 3008900100016 ENDBIB 14 0 3008900100017 NOCOMMON 0 0 3008900100018 ENDSUBENT 17 0 3008900199999 SUBENT 30089002 20080215 31253008900200001 BIB 13 82 3008900200002 REACTION (94-PU-239(N,F),,SIG) 3008900200003 FACILITY (REAC) VVR-S reactor at Bucuresti 3008900200004 INC-SOURCE (REAC) horizontal channel with thermal neutron chopper 3008900200005 SAMPLE 99.88% Pu-239, 0.12% Pu-240. 3008900200006 Electrospraying of Pu-acetate on a 20-micron Al-foil, 3008900200007 radius= 10. mm, uniformity tested by collimated alfa 3008900200008 counting. Density = 2.543x10**16 atoms/cm2 +- 0.4% 3008900200009 METHOD (TOF) 2200 m/s neutrons selected by time-of-flight, 3008900200010 flight-path = 5.057 m for the Pu-target 3008900200011 5.378 m for the boron-target 3008900200012 channel-width = 16. micro-sec 3008900200013 N-flux determined absolutely with a thick B-10 3008900200014 target (transmission = 10**(-6)). Assuming the 3008900200015 B-10(n,alfa) branching-ratio as known, the absorbed3008900200016 neutrons were counted through the 477.4 keV gamma- 3008900200017 line of Li-7, using a Na-I spectrometer which was 3008900200018 calibrated with the 412. keV line of a gold-foil at3008900200019 the same position as the B-10 target. 3008900200020 Fragments were detected by counting the pulses from a 3008900200021 gaseous scintillation-chamber with a thick Pu- 3008900200022 this was calibrated against an ionization-chamber 3008900200023 with a thin Pu-target. Both chambers were set up 3008900200024 behind each other in the neutron-beam. The 3008900200025 efficiency of the ionization-chamber was assumed 3008900200026 = 1.+-0., after correcting for losses. 3008900200027 Density of Pu-nuclei in the thin target 3008900200028 was determined by measuring the alfa-activity in 3008900200029 low geometry using a silicon spectrometer which was3008900200030 calibrated using a standard point Pu-239 source in 3008900200031 a 2-pi geometry. 3008900200032 ANALYSIS The result of the experiment is 3008900200033 sigma =(2408.9+-0.92%) * eta * (1.E4 yrs)/hl * 3008900200034 * (1 - 0.002982 dge/keV) barns 3008900200035 where 2408.9 corresponds to the result reported in 3008900200036 IFA-NR-33, but increased by 0.3% for 3008900200037 losses due to threshold fission detection 3008900200038 (priv.com. Petrascu 71/5/17) 3008900200039 eta is the B-10(n,alfa) branching ratio 3008900200040 hl is the Pu-239 alfa-decay half-life 3008900200041 dge is the difference between the gamma-energies 3008900200042 of Li-7* and activated gold. 3008900200043 assuming 3008900200044 eta = 0.93692+-0.00006 from Deruytter+Pelfer 3008900200045 (J.Nucl.En. AB 21,833,1967) 3008900200046 hl = 2.4390E+4 years assumed in IFA-NR-33 3008900200047 dge = 67.3+-1.5 keV from Elliott+Bell (Phys.Rev. 3008900200048 74,1869,1948) 3008900200049 yields sigma = 740. +- 8. barns 3008900200050 Note= This result follows from correspondence between 3008900200051 A.J.Deruytter, H.D.Lemmel, and M.Petrascu. 3008900200052 The error does not include the half-life error, 3008900200053 and the half-life value requires updating after 3008900200054 a more reliable half-life of Pu-239 has been 3008900200055 established. 3008900200056 MONITOR See below under analysis. 3008900200057 PART-DET (FF) fragments 3008900200058 COMMENT For similar expt on U-235 see ENTRY 30140. 3008900200059 STATUS (TABLE) Information from IFA-NR-33-1970 revised 3008900200060 following private communications 3008900200061 HISTORY (19701207C) HDL 3008900200062 (20080215S) Dataset was restored. 3008900200063 CORRECTION Following correction-factors were applied 3008900200064 1) attenuation of neutron-beam due to chamber-walls 3008900200065 = 1/1.021 +- 0.25% 3008900200066 2) attenuation of the beam in air between fission- 3008900200067 chamber and boron-target = 1/1.010 3008900200068 3) a fotopeak-correction for the Li-7 gamma-line 3008900200069 = 1.03 +- 0.0001 (varying in different runs) 3008900200070 4) losses due to threshold fission detection 3008900200071 = 1.003 (Priv.Com. Petrascu) 3008900200072 5) an area correction = Pu/B target area ratio 3008900200073 = 1/1.013 +- 0.2% 3008900200074 plus other corrections smaller than 0.1% 3008900200075 ERR-ANALYS (ERR-T) given error consists of ERR-1 -ERR-4 and 3008900200076 statistical which error varies from one case to another3008900200077 (ERR-1) combined error of counting-rates 3008900200078 (ERR-2) Uncertainty in density and uniformity of the 3008900200079 target 3008900200080 (ERR-3) Uncertainty in efficiency of NaI 3008900200081 spectrometer(412keV) 3008900200082 (ERR-4)Uncertaint.due efficiency ratio 477.4keV/412.keV3008900200083 plus the errors of the corrections given above. 3008900200084 ENDBIB 82 0 3008900200085 COMMON 4 3 3008900200086 ERR-1 ERR-2 ERR-3 ERR-4 3008900200087 PER-CENT PER-CENT PER-CENT PER-CENT 3008900200088 0.7 0.4 0.4 0.2 3008900200089 ENDCOMMON 3 0 3008900200090 DATA 3 1 3008900200091 EN DATA ERR-T 3008900200092 EV B B 3008900200093 0.02526 740. 8. 3008900200094 ENDDATA 3 0 3008900200095 ENDSUBENT 94 0 3008900299999 ENDENTRY 2 0 3008999999999