235U(n,f) Cross Section Measurements: DER61, DER73, Wagemans & Deruytter

235U(n,f) cross section measurements for En< 12 eV by Deruytter and Wagemans S. Kopecky, A. Plompen and P. Schillebeeckx European Commission, Joint Research Centre (JRC), Geel (BE) C. Wagemans University of Gent (BE) Neutron standards meeting, IAEA, Vienna, 6 10 December 2021

235U(n,f) cross section measurements fE = ??? Cf Bf Cr Br rE Absolute measurements at SCK CEN Deruytter 1961, PhD Thesis and J. Nucl. En. 15 (1961) 165 Deruytter and Becker 1971, Nucl. Data for Reactors, Helsinki, 1971 Deruytter 1973, J. Nucl. En. 27 (1973) 645 ??? DER61 DER73 DER71a EXFOR entry 20189 20143 MONNET f(E) f,0 , If f,0, If Cf Bf Cr Br rE Relative measurements at GELINA fE = ? f(E) f(E) If f(E) Deruytter and Wagemans, J. Nucl. En. 25 (1971) 263 Wagemans et al., ND1979, Knoxville, p. 961 Wagemans and Deruytter, IAEA-TECDOC-335, p. 156 Wagemans et al., ND1988, MITO, p. 91 DER71b WAG79 WAG84 20131 21522 22080 GELINA WAG88 235U(n,f), Deruytter and Wagemans

235U(n,f): absolute cross section measurement, DER61 ? Cf Bf Cr Br v0 v fv = ??? : velocity calibration by Bragg edges ( Fe, Al, graphite, Be, Bi) 10Bv 1/v Chopper experiments at BR1 (2m FP) MONNET Energy dependence incident neutron beam : K based on 197Au(n, ) activation experiment : K = 2.708 (9) 10-3 (v0 = 2200 m/s, 1/v part) = 97.7 (5) b : f =0.888 (5) Detection efficiency for fission fragments Total number of 235U nuclides based on -counting using reference samples of same batch of material and produced under the same conditions : Nf derived from m = 1.833 (10) mg 235U No impact of T1/2 of 234U combined uncertainty of (K, f, Nf) : 0.85% K : 0.33 % f : 0.56 % Nf : 0.55 % GELINA 235U(n,f), Deruytter and Wagemans

235U(n,f): absolute cross section measurement, DER61 Data paper (see figure) f (v0 = 2200 m/s) = 586.5 (60) b (v0 = 2200 m/s, 1/v part) = 97.7 (5) b 1000 ? Cf Bf Cr Br v0 v fv = Exp. f (T/L) = a0 + a1 (T/L) f (454.545 ms/m) = 586.5 (60) b ??? 800 Re-analysed using original data f / barn 600 Separation correlated and uncorrelated uncertainty components 197Au(n, ) cross section from Dilg et al. (Z. Physik 264 (1973) 427) (v0 = 2200 m/s, 1/v part = 97.73 (10) b) with (v0 = 2200 m/s) = 98.68 (12) b f (v0 = 2200 m/s) = 586.7 (70) b 400 200 200 300 400 500 600 700 ((T/L) = 1/v) / (ms/m) Data base Axton f (v0 = 2200 m/s) = 589.4 (78) b Axton 197Au(n, ) : (v0 = 2200 m/s) = 98.65 (9)b GELINA 235U(n,f), Deruytter and Wagemans

235U(n,f): absolute cross section measurements, DER73 fv = ??? ??? Cf Bf Cr Br r : velocity calibration by Bragg edges ( Fe) 10?? 1/? Chopper experiments at BR2 (2m FP) Energy dependence incident neutron beam, (n,r) : (v0 = 2200 m/s) = 3835 (5) b Total number of 10B nuclides : weighting and 10B(n, ) experiments combined with chemical and isotopic composition from mass spec. Total number of 235U nuclides : absolute -counting without calibration of reference samples from the same batch of material influence T1/2234U = 2.446 (4)x 105 a Uncertainties due to systematic effects NB/NU : 0.38 % NB/NUwithout T1/2 / f : 0.14 % 10B(n, ) : 0.13 % Velocity calibration : 0.02% MONNET total without T1/2 : 0.43 % : 0.40 % 234U : 0.35 % combined : 234U GELINA 235U(n,f), Deruytter and Wagemans

235U(n,f): absolute cross section measurements, DER73 fv = ??? Cf Bf Cr Br r ??? Data paper f (v0 = 2200 m/s) = 587.6 (26) b If [0.02026, 0.06239] = 19.26 (8) b If [0.02, 0.06] not given and experimental data not available (yet) Uncertainty Counting statistics : 0.15 % Systematic effects : 0.41 % 10B(n, ) : (v0 = 2200 m/s) = 3835 (5) b 234U : T1/2 = 2.446 (4) x 105 a Re-analysed 10B(n, ) (v0 = 2200 m/s) = 3838 (6) b 234U T1/2 = 2.455 (6) x 105 a (DDEP) f (v0 = 2200 m/s) = 585.4 (25) (present standards: 10B(n, ) (v0 = 2200 m/s) = 3844 (32) b 586.4 (53) b) If [0.02026, 0.06239] = 19.19 (8) b If [0.02, 0.06] = 18.75 (8) b (using If1/If1 ratio from GELINA measurements, see further ) Value in data base Axton f (v0 = 2200 m/s) x T1/2 = 1439.1 (64) b original data (incl. 10B) = 1438.4 (64) b GELINA 197Au(n, ) : (v0 = 2200 m/s) = 98.65 (9)b 10B(n, ) : (v0 = 2200 m/s) = 3838 (6) b 234U : T1/2 = 2.457 (3) x 105 a Axton 235U(n,f), Deruytter and Wagemans

235U(n,f) absolute cross section measurements, DER61 & DER73 EXFOR entry DER61 DER71a f(E) f,0, If Deruytter 1961, PhD Thesis and J. Nucl. En. 15 (1961) 165 Deruytter 1973, J. Nucl. En. 27 (1973) 645 20189 20143 MONNET 595 Deruytter, exp Deruytter, weighted mean Axton (1986) Standards 2009 Standards 2017 Deruytter (1961 & 1973) Axton (1986) Standards (2009) : 584.3 (10) b Standards (2017) : 585.5 (24) b : 585.1 (16) b 590 : 587.3 (14) b f / barn JEFF-3.3 : 584.5 b ENDF/B-VIII.0 : 586.7 b 585 Deruytter et al. (1973) 580 1960 1980 2000 2020 0.06239 eV fE dE = 19.19 (8) b If1 = 0.0206 eV Year / a 0.06 eV fE dE = 18.75 (8) b If1= 0.02 eV 197Au(n, ) : (v0 = 2200 m/s) = 98.67 (10)b 10B(n, ) : (v0 = 2200 m/s) = 3838 (6) b 234U : T1/2 = 2.455 (6) x 105 a 235U(n,f), Deruytter and Wagemans

235U(n,f): relative cross section measurements at GELINA Cf Bf Cr Br rE fE = Experiments at GELINA: ? f(E) f(E) If f(E) Deruytter and Wagemans, J. Nucl. En. 25 (1971) 263 DER71b 20131 MONNET Wagemans et al., ND1979, Knoxville, p. 961 WAG79 21522 Wagemans and Deruytter, IAEA-TECDOC-335, p. 156 WAG84 Wagemans et al., ND1988, MITO, p. 91 WAG88 22080 Details: 11 eV WAG 79, WAG 84: optimised for resonance integralrelative to f(v = 2200 m/s) fE dE If3= 7.8 eV WAG 88: optimised for sub-thermal energy region 235U target Reference Frequency Pulse Width Moderator FP length Energy region EXFOR DER71b 40 Hz 1000 ns/40ns 2.8 cm Poly 8.0 m Electrodep. 0.01 20 eV 20131 GELINA Electrodep. WAG79 40 Hz 30 ns 2.8 cm Poly 7.8 m 0.02 30 keV 21522 WAG84 100 Hz 14 ns H2O (Be-can) 8.2 m Evaporation 0.02 30 keV WAG88 40 Hz 2000 ns CH4 (77 K) 8.2 m Evaporation 0.002 20 eV 22080 235U(n,f), Deruytter and Wagemans

235U(n,f): relative cross section measurements Cf Bf Cr Br rE fE = Experiments at GELINA: ? f(E) f(E) If f(E) MONNET Deruytter and Wagemans, J. Nucl. En. 25 (1971) 263 DER71b 20131 Wagemans et al., ND1979, Knoxville, p. 961 WAG79 21522 Wagemans and Deruytter, IAEA-TECDOC-335, p. 156 WAG84 Wagemans et al., ND1988, MITO, p. 91 (dedicated to sub-thermal energy region!) WAG88 22080 ?.????? ?? All data normalised to ?? ?? ??? = ?.???? ?? 0.06239 eV 0.06 eV GELINA Cannot be used to determine fE dE or If1= fE dE If1 = 0.0206 eV 0.02 eV 235U(n,f), Deruytter and Wagemans

Cross section at 2200 m/s or resonance integral E = Example: Cross section at 2200 m/s (based on fitting to data within same interval): k MONNET Estimated value + propagating only uncorrelated uncertainties, e.g. due to counting statistics 2 2 u i u i ? ? ?=? u = = u = ? ? ?=? n ? Resonance integral: Estimated value + propagating only uncorrelated uncertainties, e.g. due to counting statistics 2 u i 2 i ?= i=1 i n n I = i=1 uI= u i uI I= ? ? ?=? Equal bin widths GELINA No difference in relative uncertainty 235U(n,f), Deruytter and Wagemans

235U(n,f): relative cross section measurements 0.06 eV 11 eV 0.06239 eV Cf Bf Cr Br rE fE dE fE = fE dE If1= fE dE ? If3= If1 = 0.02 eV 7.8 eV 0.0206 eV Original Re-analysis Duran 0,f /b 0,f /b 0,f /b If1 /(b eV) If3 /(b eV) If1 /(b eV) If1 /(b eV) If3 /(b eV) If1 /(b eV) If3/(b eV) Deruytter, 1971 587.9 19.27 240.2 (21) 583.8 19.04 18.51 237.4 584.6 18.60 239.5 Wagemans, 1979 587.6 19.26 247.0 (30) 587.3 19.26 18.80 246.2 586.9 18.83 246.3 Wagemans, 1984 587.6 19.26 246.1 Wagemans, 1988 584.25 19.15 242.5 (20) 584.3 19.15 18.71 244.1 584.3 18.71 244.2 Problems with data from Deruytter (1971), see also footnote in paper Wagemans (1984) Using only data of Wagemans 1979, 1984 and 1988 197Au(n, ) : (v0 = 2200 m/s) = 98.67 (10)b 10B(n, ) : (v0 = 2200 m/s) = 3838 (6) b 234U : T1/2 = 2.455 (6) x 105 a If3/ If1 = 12.76 (8) If3/ If1= 13.06 (8) with If1 = 19.19 (8) b eV from Deruytter 1973: If3= 244. 7 (20) b eV 235U(n,f), Deruytter and Wagemans

Summary and conclusions Cross section measurements from Deruytter and Wagemans were reviewed absolute cross section data (at BR1 and BR2) are consistent and result in: f(v = 2200 m/s) = 585.5 (24) b corresponding to 0.06 eV fE dE = 18.75 (8) b eV MONNET If1= 0.02 eV experiments at GELINA were performed relative to the cross section at v = 2200 m/s or If1 to determine the integral: If3= 7.8 eV 11 eV fE dE = 244.7 (20) b eV 0.06 eV fE dE If1= 0.02 eV these GELINA data cannot be used to determine an absolute resonance integral e.g. the GELINA data from 1971 in the EXFOR data base are not consistent with the results in the publication. Therefore they are not recommended to be used in an evaluation An accurate determination of recommended cross section data, i.e. neutron standards, requires: traceable data including a separation of uncertainties due to random and systematic effects GELINA a careful study of experimental conditions (i.e. reading of related papers and reports) and uncertainty components possible re-normalisation using improved/updated reference data (e.g. half-live of 234U) cannot rely on automated procedures 235U(n,f), Deruytter and Wagemans