Status of Subgroup 24

Transcription

1 Status of Subgroup 24 M. Herman National Nuclear Data Center, BNL for SG24 Brookhaven Science Associates

2 SG 24 membership M. Herman (BNL) - Chairman C. Mattoon (BNL) S. Mughaghab (BNL) P. Oblozinsky (BNL) M. PIgni (BNL) Y. Danon (RPI) R. Little (LANL) T. Kawano (LANL) P. Talou (LANL) D. Muir (ANL) D. Smith (ANL) R. Capote (IAEA) A. Trkov (Lubljana) H. Leeb (TUW) A. Ignatyuk (IPPE) E. Bauge (CEA) E. C. De Saint Jean (CEA) D. Rochman (NRG) A. Koning (NRG) - Monitor H. Hofmann (Eralngen) 2

3 SG 24 mandate Develop methodology for generating covariances in fast neutron region Implement covariance capabilities in the major nuclear reaction codes (EMPIRE, (Mc)GNASH, TALYS) Prepare covariances for a few test cases Consider correlation between resonance and fast region 3

4 Approaches to covariances in fast neutron region Deterministic Generalized Least Squares fitting (needs experimental data) EMPIRE/GNASH-KALMAN (accounts for experimental data) Stochastic Hybrid Binary accept/reject method (Koning, TALYS-MC) EMPIRE-Monte Carlo (MC) (no experimental data) Unified Monte Carlo (Don Smith) EMPIRE-MC-GANDR (accounts for experimental data) Backward-Forward Monte Carlo (Eric Bauge) 4

5 Covariance workshop at Port Jefferson June 24-27,

6 Issues addressed by SG24 during the last year Unrealistically low uncertainties in deterministic methods in presence of a large amount of experimental data Uncertainties of the model parameters (RIPL-3) Understanding physics of the minima in optical model potential ab-inito calculations of covariances for light systems: H.M. Hofmann n+d 6

7 Avoiding unreasonably small uncertainties model + many experimental data = low uncertainties How low? Lower than the smallest systematic experimental uncertainty although proper correlations are considered Lower than uncertainties adopted for standards! Lower than any user is going to buy Say % or less! 7

8 Avoiding unreasonably small uncertainties intrinsic model uncertainties/defects Systematic exp. uncertainty 3% R.W.Stooksberry(73) M.V.Pasechnik (80) P.Guenther (75) R.W.Finlay (93) KAMAN without scaling <2% KALMAN with scaling ~3% exp. systematic uncertainty preserved! (barn) Zr(n,tot) Incident Neutron Energy (MeV) "!/! (%) 8

9 Avoiding unreasonably small uncertainties intrinsic model defects (Leeb et al.) Similar scaling concept Extension to energy dependent scaling (remodeling) Factors deduced from experimental data for the neighboring nuclei 9 scaling factor model uncertainties in % (a) E (MeV) (b) E (MeV)

10 Avoiding unreasonably small uncertainties correlations within and among experiments (Leeb et al.) N uncorrelated points (no systematic uncertainties) => N -1/2 =>0 To avoid 0 uncertainty for infinite # of points we need systematic uncertainties (correlations) M uncorrelated experiments => M -1/2 =>0 To avoid 0 uncertainty for infinite # of points we need correlations among experiments Bayesian update requires lumping all correlated experiments into super-experiment (huge matrix!) Leeb et al. proposed approximate approach to include correlations among experiments in Bayesian update 10

11 Avoiding unreasonably small uncertainties hidden systematic uncertainties in experiments (Ignatyuk) Experimentalist often underestimate systematic uncertainties Experimentalist ALWAYS underestimate experimental errors Solution: calculate average over experiments calculate average deviation of each experiment from the average => hidden systematic uncertainty/error 11

12 Avoiding unreasonably small uncertainties hidden systematic uncertainties in experiments (Ignatyuk) U(n,f) Uncertainty, % statistic systematic Number of experiments 12

13 Model parameter uncertainties in RIPL-3 RIPL-3 provides uncertainties (not covariances) for the critical model parameters masses optical model parameters (globally) D-observed and gamma- and neutron-strength functions level densities GDR parameters (photon emission) presentated by R. Capote on Tuesday, June 23,

14 Understanding OMP minima minima are universal the first one - related to S-wave sensitivity changing sign the second one - interference between partial waves higher ones - Ramsauer effect presentated by M. Pigni on Tuesday, June 23,

15 Fission spectra covariances Talou, Madland and Kawano are currently working on producing covariance matrices for the prompt fission neutrons ( Los Alamos model combined with experimental data using Kalman filter) Kodeli, Trkov and Capote have applied a new Monte Carlo method to produce covariance matrices of the prompt fission neutron spectra for 235,238U and 239Pu neutron induced fission presentated by P. Talou on Tuesday, June 23, E n (MeV) 10 0 E n (MeV) 15

16 Topics: Quality assurance and users needs Issues in the resolved resonance region (scattering radius, systematic uncertainties) Low uncertainties from the theory point of view Low uncertainties from the practical perspective New evaluations covariances for fission spectra processing covariances; comparison of the codes 16

17 Conclusions Basic capabilities for generating nuclear data covariances in the fast neutron range have ben developed and implemented in the nuclear reaction codes used for data evaluation Capabilities to generate covariances in the fast neutron region have been established in several laboratories world-wide (e.g., BNL, LANL, IAEA, JAEA, IPPE Obninsk, NRG Petten) Inter-comparison of methods has been carried out in the frame of the SG24 and advantages and disadvantages of different methods have been understood. Nuclear reaction theory plays central role in the determination of covariances. Theory constraints provide also major source of cross-correlations among different reaction channels as well as among different isotopes. 17

18 Conclusions If no measurements are available estimates of covariances must resort to the theory. For such cases, uncertainties of the model parameters become critical (RIPL-3) Unrealistically low uncertainties have been rising justified concern of the users. Several reasons of low uncertainties have been identified and methods have been proposed helping to avoid low uncertainties. For some nuclei strong fluctuations are observed in a few MeV region. There is no consensus nor clear guidelines on how such cases should be treated if covariances are based on the model calculations. 18

19 Conclusions SG24 focused on the statistical nuclear reaction mechanisms (optical, compound nucleus, and preequilibrium models). This choice excludes from considerations light nuclei. In addition to the well established R-matrix fitting, ab-initio Resonating Group approach has been developed and successfully tested on the n+d system. Preparation of the covariances is affected by subjective evaluator's judgement. Uncertainties recommended by different evaluators may differ by as much as factor of 2. 19

20 Art of Covariances S 2 4 p r o v i d e d c a n v a s a n d brush I t s e v a l u a t o r s t u r n to paint