Insights into Beta-Delayed Neutron Covariances by Tim Johnson, Libby McCutchan, and Alejandro Sonzogni
Comprehensive analysis and visualization of beta-delayed neutron covariances, fission yields, and their implications in nuclear physics applications. The research covers calculations of delayed nu-bar, neutron probabilities, and recommendations for various systems. Disagreements in fission yields for specific nuclides are also discussed.
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Beta Delayed Neutron Covariances Tim Johnson, Libby McCutchan, Alejandro Sonzogni National Nuclear Data Center
Chart colored by 235U fission yields, highlighted by Q n>0 Many n emitters have high fission yield values, in particular Br (Z=35), Rb (Z=37), I (Z=53) and Cs (Z=55) Beta Delayed Neutron CRP #2 - Alejandro Sonzogni
Link between basic and more macroscopic quantities used in applied nuclear physics d: Delayed nu-bar, number of neutrons for single fission event. It can be calculated as: d = CFYi Pni , about 0.015/fission for 235U CFY: cumulative fission yield. Pn: beta-delayed neutron probability. Pn and T1/2 values of beta-delayed neutron emitters are relevant in nuclear power and astrophysics. Beta Delayed Neutron CRP #3 - Alejandro Sonzogni
Following Loaiza et al. & Than Dat et al., the recommended delayed nubars (MF=1, MT455) are plotted for a number of systems. Beta Delayed Neutron CRP #4 - Alejandro Sonzogni
Same plot as before, for summation calculations using JEFF- 3.1 yields and ENDF/B-VII.1 decay data 238Np 235U 238U 232Th 241Pu 233U 239Pu 252Cf Beta Delayed Neutron CRP #5 - Alejandro Sonzogni
As before, but plotting lighter and heavier fission fragments contributions 238U 232Th Beta Delayed Neutron CRP #6 - Alejandro Sonzogni
As before, but with ENDF/B yields 237Np Beta Delayed Neutron CRP #7 - Alejandro Sonzogni
Disagreements in fission yields for 237Np ENDDF/B yields are larger than JEFF s for neutron rich nuclide Beta Delayed Neutron CRP #8 - Alejandro Sonzogni
Disagreements in fission yields for 237Np Beta Delayed Neutron CRP #9 - Alejandro Sonzogni
Disagreements in fission yields for 252Cf Beta Delayed Neutron CRP #10 - Alejandro Sonzogni
Disagreements in fission yields for 252Cf Beta Delayed Neutron CRP #11 - Alejandro Sonzogni
Delayed neutron activity Covariances Ad(t): Delayed neutron activity following the decay of an equilibrated system To obtain Ad(t), we solve the Bateman s equations: dNi(t)/dt=- iNi + ki Nk , with boundary conditions: dNi(0)/dt=0, that is, Ni(0)~CFYi/ i , then: Ad(t)= i Pni Ni(t) We use a Monte Carlo method, the only correlation in fission yields is that they are normalized to 2, and the branching ratios are normalized to 1. Beta Delayed Neutron CRP #12 - Alejandro Sonzogni
Delayed neutron activity Covariances For N histories, we obtain Adi(tk), so the average value would be: <Ad(tk)>= N-1 Adi(tk) The uncertainty as: Ad(tk)= <Ad(tk) Ad(tk)> - <Ad(tk)><Ad(tk)> And the covariance matrix: (Ad(tk), Ad(tj) )= kj=<Ad(tk) Ad(tj)> - <Ad(tk)><Ad(tj)> Beta Delayed Neutron CRP #13 - Alejandro Sonzogni
Delayed neutron activity for 235U Beta Delayed Neutron CRP #14 - Alejandro Sonzogni
Delayed neutron activity uncertainty for 235U Beta Delayed Neutron CRP #15 - Alejandro Sonzogni
Delayed neutron activity divided by Keepins values Beta Delayed Neutron CRP #16 - Alejandro Sonzogni
Delayed neutron activity correlations for 235U Beta Delayed Neutron CRP #17 - Alejandro Sonzogni
Six group parameters fit In the ENDF-6 libraries, the delayed neutron activity is given as a sum of 6 or 8 exponential terms: Ad(t)= ai exp(- i t) In order to properly propagate uncertainties, we not only need the uncertainties in ai and i, but also the correlations: < ai ak >, < ai k >, < i k> For each history, we fit Ad(t) with a Keepin-like function, using Keepin s parameter as a starting point. Beta Delayed Neutron CRP #18 - Alejandro Sonzogni
Six-group fit Beta Delayed Neutron CRP #19 - Alejandro Sonzogni
Six-group fit The ak have uncertainties in the 10-17%, while the k in 2- 10%, due to a more uncertain fission yield data Beta Delayed Neutron CRP #20 - Alejandro Sonzogni
Chi-square distribution of the fits Beta Delayed Neutron CRP #21 - Alejandro Sonzogni
6-group Parameters Correlation Matrix 4 & 5 correlation a2 & a4 anticorrelation Beta Delayed Neutron CRP #22 - Alejandro Sonzogni
Conclusions Delayed nu-bars and neutron activities have been very precisely measured. In summation calculations decay data is of good quality, but there are problems in the fission yields data. Our work test the relatively short-lived (T1/2 < 100 s) subset of fission yields. We look forward to the next generation experiments and the results of the current WPEC Subgroup. We will generate covariance matrices for all targets of interest. Beta Delayed Neutron CRP #23 - Alejandro Sonzogni
Advertisement: Possible next workshop on Modeling of Antineutrino Flux from Nuclear Reactors June 2016 Port Jefferson, NY Perhaps Tuesday 6/14 Thursday 6/16 Beta Delayed Neutron CRP #24 - Alejandro Sonzogni
Pt Jefferson BNL JFK Beta Delayed Neutron CRP #25 - Alejandro Sonzogni
Location: Pt Jefferson Village Center Hotel, about 100 yards away. About $140/night. Train to Manhattan and JFK, about 1:40 h and $25 round trip. Train station 1 mile from Hotel. Plenty of restaurants nearby Beta Delayed Neutron CRP #26 - Alejandro Sonzogni
