ENTRY 21256 19801024 00002125600000001 SUBENT 21256001 19801024 00002125600100001 BIB 15 50 2125600100002 INSTITUTE (2SWTWUR) 2125600100003 REFERENCE (J,NSE,27,85,6601) 2125600100004 (R,EIR-112,6703) 2125600100005 AUTHOR (H.R.VON GUNTEN,R.F.BUCHANAN,A.WYTTENBACH,K.BEHRINGER) 2125600100006 TITLE -THE DETERMINATION OF THE FAST FISSION CROSS SECTION 2125600100007 OF PROTOACTINIUM-233 WITH FISSION NEUTRONS.- 2125600100008 FACILITY (REAC ,2SWTWUR) RESEARCH REACTOR IN WUERENLINGEN, 2125600100009 (EIR), THERMAL REACTOR, 20 MW TH, RADIAL BEAM HOLE. 2125600100010 INC-SOURCE .U-233 TARGET AS NEUTRON FLUX CONVERTER. 2125600100011 INC-SPECT .FISSION NEUTRON SPECTRUM. 2125600100012 SAMPLE .PA-233 LAYERS ON PLATINUM DISKS, VARIOUS QUANTITIES 2125600100013 FROM 0.20 TO 1.76 CI (1 CI = 48 MICROGRAMS), DIAM 2125600100014 15 MM. FOR THE ABSOLUTE FLUX MEASUREMENTS THIN 2125600100015 THORIUM SAMPLES WERE USED (SAME GEOMETRY). THE 2125600100016 DETERMINATION OF THE COUNTER EFFICIENCY WAS CARRIED 2125600100017 OUT WITH U-235 AND (PA-233 + U-235)-MIXTURES, USING 2125600100018 AN U-235 STANDARD SOLUTION FOR PREPARATION. 2125600100019 METHOD .MEASUREMENT OF THE FAST FISSION CROSS SECTION OF 2125600100020 PA-233 BY COMPARING THE FISSION RATE OF A KNOWN 2125600100021 QUANTITY OF PA-233 TO THAT OF A KNOWN TH-SAMPLE, 2125600100022 USING BACK-TO-BACK FISSION COUNTERS. 2125600100023 .PRODUCTION OF PA-233 BY IRRADIATION OF THORIUM METAL 2125600100024 CHIPS IN THE REACTOR AND SUBSEQUENT CHEMICAL SEPARA- 2125600100025 TION. THE TARGET CONSISTS OF A 20 MM DIAM CYLINDER 2125600100026 FILLED WITH 10 G OF U-233 (AS U(3)-O(8)) AND IS 2125600100027 PLACED DIRECTLY IN FRONT OF THE COUNTERS. THE U-233 2125600100028 SERVES AS CONVERTER FOR THE NEUTRON FLUX AS WELL AS 2125600100029 ABSORBER FOR U-233 RESONANCE NEUTRONS. A 0.6 MM THICK 2125600100030 CADMIUM SHEET BEHIND THE CONVERTER SERVES AS 2125600100031 SHIELDING AGAINST THERMAL NEUTRONS. 2125600100032 DETECTOR (FISCH) DOUBLE (BACK-TO-BACK) PARALLEL PLATE TYPE 2125600100033 FISSION CHAMBER (ALUMINIUM) OPERATED AS A GAS FLOW 2125600100034 CHAMBER WITH AN ARGON(99 PC)-METHANE MIXTURE AT 1 ATM 2125600100035 PRESSURE. THE FIRST COUNTER CONTAINS ALTERNATIVELY 2125600100036 SAMPLES OF PA-233, TH-232, U-235, AND PA-233/U-235- 2125600100037 MIXTURES. THE SECOND COUNTER SERVES AS FAST NEUTRON 2125600100038 FLUX MONITOR AND CONTAINS UNIFORMLY PLATED DEPOSITS 2125600100039 ON ITS TWO CATHODES OF 4.47 RESP. 5.10 MG TH-O(2), 2125600100040 DIA 40 MM. THE CHAMBER IS SURROUNDED BY A SHIELDING 2125600100041 OF 100 MM LEAD AND 0.3 MM CADMIUM. 2125600100042 MONITOR (90-TH-232(N,F),,SIG,,FIS) 2125600100043 STATUS (NDD ) DATA TAKEN FROM NEUDADA. 2125600100044 HISTORY (800115T) G.C. 2125600100045 (800129E) 2125600100046 CORRECTION .CORRECTIONS FOR BACKGROUND, COUNTER EFFICIENCY, FLUX 2125600100047 VARIATIONS, HALF LIFE OF PA-233 (27.0 DAYS), SELF- 2125600100048 ABSORPTION OF FISSION FRAGMENTS IN THE SAMPLES, AND 2125600100049 THRESHOLD. 2125600100050 ERR-ANALYS .A DETAILED ERROR-ANALYSIS IS GIVEN. DATA CONTAIN THE 2125600100051 TOTAL ABSOLUTE ERROR. 2125600100052 ENDBIB 50 0 2125600100053 COMMON 2 3 2125600100054 EN-DUMMY MONIT 2125600100055 MEV MB 2125600100056 1.5000E+00 1.4200E+02 2125600100057 ENDCOMMON 3 0 2125600100058 ENDSUBENT 57 0 2125600199999 SUBENT 21256002 19801024 00002125600200001 BIB 3 6 2125600200002 REACTION (91-PA-233(N,F),,SIG,,FIS) 2125600200003 STATUS (NDD ) DATA TAKEN FROM NEUDADA. 2125600200004 CORRECTION .THE INTERFERENCE OF THE BETA BACKGROUND FROM PA-233 2125600200005 WAS ELIMINATED BY APPLYING HIGH ISCRIMINATION AND AN 2125600200006 APPROPRIATE CORRECTION FOR THE COUNTER EFFICIENCY AT 2125600200007 ZERO BIAS. 2125600200008 ENDBIB 6 0 2125600200009 NOCOMMON 0 0 2125600200010 DATA 2 1 2125600200011 DATA DATA-ERR 2125600200012 B B 2125600200013 7.7500E-01 1.9000E-01 2125600200014 ENDDATA 3 0 2125600200015 ENDSUBENT 14 0 2125600299999 ENDENTRY 2 0 2125699999999