Differential Cross Section Measurements at the University of Kentucky -- Adventures in Analysis

Transcription

1 Differential Cross Section Measurements at the University of Kentucky -- Adventures in Analysis J.R. Vanhoy, S.F. Hicks, B.R. Champine, B.P. Crider, E.A. Garza, S.L. Henderson, S.H. Liu, E.E. Peters, F.M. Prados-Estévez, M.T. McEllistrem, T.J. Ross, L.C. Sidwell, J.L. Steves, and S.W. Yates US Naval Academy, Annapolis, MD University of Dallas, Irving, TX University of Kentucky, Lexington, KY US Military Academy, West Point, NY CIELO / NEMEA7 1 Scott Lucas,EAWorldView

2 General Intro to the Laboratory Sample results for recent 23 Na, 54 Fe, nat Fe (n,n ) & (n,n g) Adventures in Analysis Ambiguities in Neutron Detection Efficiency attributed to 3 H(p,n) ds/dw The technique Choices for ds/dw Impact on Efficiency (E) Challenges in Normalizing (n,n g) What we did for 23Na(n,n g) What will we do for 54,56Fe? How well do we know the finite geometry corrections? Proving our correction code is rigorous Conclusion 2

3 Accelerator HVEC Model CN: 7 MV rf source p, d, 3 He, a, ions Authorized for 3H gas targets 1 ns pulse widths Basic Nuclear Science Nuclear Structure via (n,n g) Level Schemes & Transitions Spectroscopic Information DSAM Lifetimes (3He,ng) Applied Nuclear Science Differential (n,n ) Cross Sections 23 Na, 54 Fe, 56 Fe Detector Development Univ Guelph Univ Lowell RMD 3

4 scattering sample 3 H cell 4

5 Tungsten wedge 3H(p,n) Q= MeV 2H(d,n) Q= 3.3 MeV 3H(d,n) Q= 17.6 MeV Gas cell Beam line Na sample Typical adjustment of wedge with cell and sample 5

6 BGO HPGe g-ray Detection (singles setup) 6

7 (n,n ) TOF Setup Forward monitor Long counter Beam line Gas cell Copper shielding Neutron detector 7

8 Monitoring Neutron Production Counts Forward Monitor C 6 D 6 liquid scintillator Best choice for n angular distributions Views source neutrons from gas cell PSD cleanly identifies neutrons Long Counter(Hanson & McKibben 1947) Moderated BF3 tubes Generally used for excitation functions Insensitive to g-rays Insensitive to room thermals Placement at large angles reduces concern over resonances in LC efficiency. 74 Ge(n,g) 140-keV line in HPGe Measures prompt-thermal fraction during beam pulse Forward Monitor tof TOF Channel Number For absolute ds/dw values, use 1 H(n,n) for neutrons & for g-rays 8

9 Fitted Fe Spectrum n' + 56 Fe * 847 kev n + nat Fe n' + 56 Fe * 2085 kev n' + 54 Fe * 1408 kev 9

10 PRELIM ANALYSIS BY SALLY HICKS 54 Fe(n,n) Comparison with 6 databases Guenther Ann Nucl Energy (1986) 54 Fe at E n =3.0 MeV Exp 3.00 MeV Guenther 3.04 MeV Guenther 2.96 MeV 10

11 PRELIM ANALYSIS BY SALLY HICKS 56 Fe(n,n 1 ) using nat Fe 11

12 23 Na(n,n) 12

13 Inelastic Cross Sections --Two Techniques Counts Counts s n,n s n,n g 23Na(n,ng) E n =4.0 MeV, 125 o (n,n ) HPGe Channel Number s s - de excitation 23 Na n, n ' k - s feeders HPGe Channel Number 13

14 s (barns) s (barns) 23 Na(n,n g) Na(n,n 1 ) ENDF/B-VII E n (MeV) Na(n,n 1 ) JENDL E n (MeV) Comparison of inelastic (n,n k ) cross sections as determined from (n,n g) measurements with values in the evaluated nuclear libraries. ENDF over-predicts the data by ~15%, while the data track JENDL quite nicely. The JEFF library (not shown) undershoots the data by ~15%. Comparison of measured g-ray excitation functions with those of the GELINA/IRMM group [Rouki et al, NIM A 673, 83 (2012)]. UnivKY data points are in black. The agreement is striking considering the experiments use different normalization techniques and the neutron 14 energy resolutions are significantly different.

15 1 ADVENTURES IN ANALYSIS -- NEUTRON DETECTION EFFICIENCY 15

16 Long Counter 1 T-cell spectrum fit peak SAN12 FM spectrum fit peak SAN12 Main Detector relative Efficiency eff ( E n ) Yield ds FM dw Tpn ds dw 3H ( p, n) E n p eff ( E n ) 16

17 1 eff ( E Neutron detection efficiency Main detector Amplifier gain Thresholds PSD cuts Forward Monitor detector Amplifier gain Thresholds PSD cuts Variances arise Yield in 3 H cell spectrum (<<1%) Yield in FM spectrum (<<1%) Fit quality n ) Yield ds FM dw Tpn Knowledge of T(p,n) angular variation (3%??) Main Detector relative Efficiency E n = 3.6 MeV dataset 17

18 Sources for T(p,n) ds/dw H.Liskien & A.Paulsen M. Drosg G. Hale (p,p) (d,p) (n pol,n) (p,n) phase shift inter-comparisons (d,d) 4 He project (d,n) (n,p) (d pol,p) (d pol,d) (p pol,p) 18

19 1 T(p,n) at E p = 4.0 MeV 19

20 1 T(p,n) at E p = 5.0 MeV 20

21 1 Example Efficiency Curve E p =4.77 / E n,max = 4.0 Reaction Angular Range E scattered (MeV) Efficiency Curve for Ep=4.77 MeV / En = Na(n,n0) Na(n,n0) 23Na(n,n0) Normalization H(n,n) Same as above, but rescaled to accentuate differences. 21

22 1 Comparisons at Various Energies Table B.2 Comparison of the three approaches for T(p,n) upon the eff(en) Energy for Efficiency curve Comments 4.00 D has much better anticipated shape vs ENDF. LP tracks D but up to +9% in the MeV range 3.60 D has better shape than ENDF. LP and D almost exactly the same D has better shape than ENDF. LP and D almost exactly the same D has slight upturn, ENDF maybe better? LP at forward angles similar to ENDF 3.40 D better than ENDF. LP & D very similar LP & ENDF actually very similar with the exception of the MeV region where ENDF can be as such a 6% higher. D has a +6% buldge MeV. Here if I had to pick the best, I d guess the most realistic is ENDF or LP Very few points to judge with. Hard to make a call here. All very similar Dunno which one I d choose here. No basis to choose one over the other Dunno which one I d choose here. No basis to choose one over the other Dunno which one I d choose here. No basis to choose one over the other. E p < 4.0 MeV, no basis to chose one description over the other. E p > 4.0 MeV, Drosg and Liskien & Paulsen preferred. 22

23 2 ADVENTURES IN ANALYSIS -- CONVERTING g-ray YIELDS TO CROSS SECTIONS 23

24 Angle-Integrated XS (b) Angle-Integrated XS (b) 2 Scaling 23Na Yields to ENDF 56 Fe Cross Sections -- use g-rays from Fe sample to discover the conversion factor Na Corrected Yield s Na, g -rayi ~ Fe Corrected Yield # # Na Fe s Fe Comparison to evaluated data 26-Fe- 56 LANL,ORNL EVAL-SEP96 M.B.Chadwick,P.G.Young,C.Y.Fu CH99,FU86,Fu Fe(n,n 1 ) (MeV) E n E x 440 kev Fe(n,n 3 ) E x 2391 kev E n (MeV) 24

25 Conversion Factor 2 Scaling to ENDF 56 Fe Cross Sections Na Corrected Yield # Na s s Na, g -rayi ~ Fe Corrected Yield # Fe Fe s Na, g -rayi Na Corrected Yield g -rayi # Na brj transitionk s Fe Corrected Yield Fe, level j j transitionk # Fe 1.0E E (41) E+18 uncertainty ~ 6% 7.0E E E #Level. 2*Neutron Beam Energy wi xi x w 1 i 2 w s i 2 s i N wi xi ( N -1) - x w i 2 25

26 s (barns) s (barns) 2 23 Na(n,n g) Na(n,n 1 ) ENDF/B-VII E n (MeV) Na(n,n 1 ) JENDL E n (MeV) Comparison of inelastic (n,n k ) cross sections as determined from (n,n g) measurements with values in the evaluated nuclear libraries. ENDF over-predicts the data by ~15%, while the data track JENDL quite nicely. The JEFF library (not shown) undershoots the data by ~15%. Comparison of measured g-ray excitation functions with those of the GELINA/IRMM group [Rouki et al, NIM A 673, 83 (2012)]. UnivKY data points are in black. The agreement is striking considering the experiments use different normalization techniques and the neutron 26 energy resolutions are significantly different.

27 Use several samples in an attempt to average out the deficiencies of each? Unfortunately this produces better estimates rather than 2ndry standards nat Ti nat Si 27 Al 56 Fe 12 C 52 Cr 51 V Oblozinsky, Progress on Nuclear Covariances: AFCI-1.2 Covariance Library BNL

28 3 n ADVENTURES IN ANALYSIS -- ATTENUATION AND MULTIPLE SCATTERING CORRECTIONS MT McEllistrem MULCAT ( ) JR Lilley Monte Carlo Multiple Scattering Correction, CEA-DAM P2N (1980) DE Velkey, with Analytic & Monte Carlo Methids, NIM 129, 231 (1975) WE Kinney Finite Sample Corrections NIM 83, 15 (1970). 28

29 3 Multiple Scattering and Attenuation Correction using MULCAT init guess at `true ` finite sample Y ˆ s for a typical sample: S tot -1 ~ 16 cm double/singl = 10-4 triple/dble = 10-4 predict perturbed Y ˆ( ) finite samplecorrection R Issues Single element Extensive experience using the routine on medium-mass nuclei Limited # of s tot (E n ) values Elastic angular distribution used at one E n Runs **** histories alter `true`sˆ obtain continous fn 29

30 ratio MCNP MULCAT elas dsdw (mb/sr) mulcat-corrected mcnpx calculation: 12C ENDF ds/dw mulcat corrected, cm ENDFV/B-VII MeV Fasoli MeV Fasoli theta cm (deg) pseudo detector data cm Angle (deg) mulcat bef/aft mcnpx aft/bef 30

31 General Intro to the Laboratory Sample results for recent 23 Na, 54 Fe, nat Fe (n,n ) & (n,n g) Adventures in Analysis Ambiguities in Neutron Detection Efficiency attributed to 3 H(p,n) ds/dw The technique Choices for ds/dw Impact on Efficiency (E) Challenges in Normalizing (n,n g) What we did for 23Na(n,n g) What will we do for 54,56Fe? How well do we know the finite geometry corrections? Proving our correction code is rigorous Conclusion 31

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34 DATA REDUCTION OVERVIEW FOR (N,N ) & (N,N G) 34

35 n, ng Na (n,n g) spectrum Fe (n,ng) spectrum Extract g Peak Yields Extract g Peak Yields 1 Correct for Detector Efficiency Correct for Detector Efficiency Normalize to LongCounter*, #Na Normalize to LongCounter*, #Fe 2 Correct for n,g Atten & n Multiple scatt Correct for n,g Atten & n Multiple scatt 3 Obtain scaling factor using ENDF Cross Sections Convert to Cross Section 35

36 2 Na H C Na* C, 16 O, 17 O, 18 O Sample spectrum Container spectrum Polyethylene spectrum 3 Na Sample Cont. Extract Peak Yields Extract Peak Yields 1 Correct for Detector Efficiency Correct for Detector Efficiency 4 Convert to raw Cross Section 2 Correct for Atten & Multiple scatt 36

37 Sample spectrum Container spectrum Polyethylene spectrum 3 Na Sample Cont. Extract Peak Yields Extract Peak Yields 1 Correct for Detector Efficiency Correct for Detector Efficiency 4 Convert to raw Cross Section 2 Correct for Atten & Multiple scatt 37

38 3 Na H C Na* C, 16 O, 17 O, 18 O Sample spectrum Container spectrum Polyethylene spectrum 3 Na Sample Cont. Extract Peak Yields Extract Peak Yields 1 Correct for Detector Efficiency Correct for Detector Efficiency 4 Convert to raw Cross Section 2 Correct for Atten & Multiple scatt 38

39 3 Sample spectrum FM spectrum Container spectrum FM spectrum SAN12 SAN12 Na sample - wgt spectrum spectrum container spectrum wgt FM FM sample container SAN12 W lab FM Yield sample eff Na peak En # Na eff # Na ( E n ) ds dw raw f W lab f : absolute normalization factor MULCAT 39

40 H C Sample spectrum Container spectrum Polyethylene spectrum 3 Na Sample Cont. Extract Peak Yields Extract Peak Yields 1 Correct for Detector Efficiency Correct for Detector Efficiency 4 Convert to raw Cross Section 2 Correct for Atten & Multiple scatt 40

41 4 H C polyethylene spectrum FM spectrum Blank spectrum FM spectrum SAN12 SAN12 H poly container - spectrum spectrum spectrum FM wgt FM sample container SAN14 ds d W H W H, raw lab Yield FM eff f W lab H H peak En # H eff # H ( E n ) W tot W H dw f s W elas tot geometry # N # N geometry ENDF s tot ENDF s tot ENDF s elas ENDF ds dw elas o 0 ENDF ds dw elas 180 o MULCAT C mult scat factor MULCAT H mult scat factor ENDF s elas ENDF ds dw elas o 0 ENDF ds dw elas o 180 attenuation factor # weighted mult scat attenuation factor ds dw H, primitive ds dw H, raw atten C atten H multscat f r f s r s H, evaluated H, check s check ds dw primitive dw 41 (should get r = 1.00)

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43 Ambiguities in Neutron Detection Efficiency attributed to 3H(p,n) dsdw -- choices for dsdw -- FIG. 6. Comparison of the three reference T(p,n) cross sections at E p =4 MeV. The lower subfigure displays the percentage difference with respect to the DROSG parameterization. Differences between descriptions can be as much as ±10% and vary with angle. 43

44 1 Actually need ds/dw 3 H(p,n) (p,p) (d,p) (n pol,n) (p,n) phase shift inter-comparisons (d,d) 4 He project (d,n) (p pol,p) (n,p) (d pol,p) (d pol,d) solid line R-matrix analysis ds/dw predictable to <5% for cm < 50 o Really good for 50 o < cm < 140 o 44

45 ds/dw (mb/sr) ds/dw (mb/sr) 23 Na(n,el) (n,el) 4.00 MeV (n,el) 4.00 MeV MeV This Expt 3.97MeV TowleGilboy MeV Fasoli ENDF 3.97 ENDF 4.00 JENDL 4.00 JEFF 4.00/4.02 DATA theta,cm (deg) cm Angle (deg) Comparison of our elastic cross sections to previous measurements (top) and the evaluated nuclear libraries (bottom). The shape of ds/dw changes quickly at angles >80 o with energy and is sensitive to the reaction mechanism. 45

46 EVALUATIONS 23 Na(n,el) EXPERIMENTAL DATA (LEFT: There can be significant disagreements between the libraries for cross sections. RIGHT: Our measurements determine the best choices. Our measurements indicate that both the ENDF & JENDL libraries have good values for elastics, while only the JENDL properly describes the inelastic.) 46

47 Oblozinsky, Progress on Nuclear Covariances: AFCI-1.2 Covariance Library BNL

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