ENTRY 14673 20220117 14951467300000001 SUBENT 14673001 20220117 14951467300100001 BIB 13 57 1467300100002 TITLE Delayed neutrons from Pu239 1467300100003 AUTHOR (R.R.Wilson,R.B.Sutton) 1467300100004 REFERENCE (J,PR,71,560(1),1947) 1467300100005 #doi:10.1103/physrev.71.560 1467300100006 (R,LA-76,1944) Preliminary data. 1467300100007 REL-REF (O,12504002,J.W.Dewire+,R,LA-104,1944) Prompt neutrons.1467300100008 INSTITUTE (1USALAS) 1467300100009 FACILITY (CYCLO,1USALAS) 1467300100010 DETECTOR (BF3) Boron trifluoride ionization chamber. 1467300100011 SAMPLE 235U enriched sample, no details on 239Pu sample. 1467300100012 METHOD The number of delayed neutrons from Pu239 1467300100013 relative to the number from U235 has been measured by 1467300100014 means of a boron trifluoride ionization chamber 1467300100015 immersed in a block of paraffin. The sample of Pu239 1467300100016 was placed on one end of the bfs chamber and the 1467300100017 paraffin block was exposed to the direct beam of 1467300100018 neutrons from the cyclotron target about 10 ft away. 1467300100019 The strong neutron intensity, with the cyclotron on, 1467300100020 caused the grid of the first amplifier tube to drift 1467300100021 to such a negative voltage that nothing was recorded. 1467300100022 However, as soon as the cyclotron was turned off the 1467300100023 grid voltage would snap back to a sensitive bias 1467300100024 within a few milliseconds and the amplifier system 1467300100025 would then record boron disintegrations due to 1467300100026 delayed neutrons. The procedure, then, was to expose 1467300100027 the block to the cyclotron beam for 5 minutes and 1467300100028 then to count for 5 minutes with the beam off. This 1467300100029 was sufficient time for the delays to build up to 1467300100030 equilibrium during exposure and to die out completely 1467300100031 during the recording period. A sample of enriched 1467300100032 U235 prepared in as nearly as possible the same 1467300100033 geometry as the Pu239 was then substituted for the 1467300100034 Pu239 and the procedure was repeated. To determine 1467300100035 the contribution of the U238 in the sample, a disk of 1467300100036 uranium metal was substituted for the U235 sample, 1467300100037 and counts recorded. No sample at all gave no counts 1467300100038 at all. 1467300100039 ANALYSIS (DECAY) A comparison ionization chamber in which 1467300100040 known amounts of Pu239, enriched U235 and enriched 1467300100041 U238 could Be placed was inserted in the paraffin 1467300100042 block in the same position that the Pu239 or U235 1467300100043 sample had occupied. From the relative counts 1467300100044 recorded and the known cross sections one can 1467300100045 calculate that there are only 48 percent as many 1467300100046 delayed neutrons per fission from Pu239 as there are 1467300100047 from U235. 1467300100048 CORRECTION If one assumes the neutrons are all thermalized and 1467300100049 applies a correction, the percentage of delayed 1467300100050 neutrons from Pu239 relative to U235 is changed to 44 1467300100051 percent. It is difficult to draw any conclusions 1467300100052 about the delayed neutrons of U238 from the data. 1467300100053 ERR-ANALYS (DATA-ERR) Due to imperfect thermalization of neutrons 1467300100054 authors can only say that the proper ratio lies within 1467300100055 the range of 44-48%, and is probably about 46%. 1467300100056 HISTORY (20210114C) BP 1467300100057 (20220117A) BP: Added preliminary data reference and 1467300100058 updated authors. 1467300100059 ENDBIB 57 0 1467300100060 NOCOMMON 0 0 1467300100061 ENDSUBENT 60 0 1467300199999 SUBENT 14673002 20220117 14951467300200001 BIB 2 3 1467300200002 REACTION ((94-PU-239(N,F),DL,NU,,MXW)/ 1467300200003 (92-U-235(N,F),DL,NU,,MXW)) 1467300200004 STATUS (TABLE) page 560 of Phys.Rev.71(1947)560 1467300200005 ENDBIB 3 0 1467300200006 NOCOMMON 0 0 1467300200007 DATA 3 1 1467300200008 EN DATA DATA-ERR 1467300200009 MEV NO-DIM NO-DIM 1467300200010 2.53E-08 0.46 0.2 1467300200011 ENDDATA 3 0 1467300200012 ENDSUBENT 11 0 1467300299999 ENDENTRY 2 0 1467399999999