A method of spin assignment of neutron resonances based on capture gamma-ray detection

Coceva, C.; Corvi, F.; Giacobbe, P.; Carraro, Giorgio

doi:10.1016/0375-9474(68)90833-6

Cited by 81 publications

(17 citation statements)

References 20 publications

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“…All these new methods make use of information contained in the γ cascade following neutron capture. It is an old idea [38], but improvements in neutron sources, detectors, and data acquisition apparatus has led to large improvements over previous results. For example, in the case of 95 Mo neutron resonances, applying these methods with a single pair of low-efficiency C 6 D 6 detectors increased the number of firm resonance J π assignments from 32 [39] to 218 [25] in this very difficult case.…”

Section: New Experimental Techniquesmentioning

confidence: 99%

Neutron resonance data exclude random matrix theory

Koehler

Bečvář

Krtička

et al. 2012

Fortschritte der Physik

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Key words Porter-Thomas distribution, random matrix theory.Almost since the time it was formulated, the overwhelming consensus has been that random matrix theory (RMT) is in excellent agreement with neutron resonance data. However, over the past few years, we have obtained new neutron-width data at Oak Ridge and Los Alamos National Laboratories that are in stark disagreement with this theory. We also have reanalyzed neutron widths in the most famous data set, the nuclear data ensemble (NDE), and found that it is seriously flawed, and, when analyzed carefully, excludes RMT with high confidence. More recently, we carefully examined energy spacings for these same resonances in the NDE using the ∆3 statistic. We conclude that the data can be found to either confirm or refute the theory depending on which nuclides and whether known or suspected p-wave resonances are included in the analysis, in essence confirming results of our neutron-width analysis of the NDE. We also have examined radiation widths resulting from our Oak Ridge and Los Alamos measurements, and find that in some cases they do not agree with RMT. Although these disagreements presently are not understood, they could have broad impact on basic and applied nuclear physics, from nuclear astrophysics to nuclear criticality safety.

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Section: New Experimental Techniquesmentioning

confidence: 99%

Neutron resonance data exclude random matrix theory

Koehler

Bečvář

Krtička

et al. 2012

Fortschritte der Physik

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“…For example, in some cases it is expected that the average number of γ rays in the de-excitation cascades between the capturing states and the ground state will be different for the two s-wave spins. In reality, the existence of other multipolarities will both broaden the multiplicity distributions as well as decrease the difference between average multiplicities for 3 − and 4 − resonances [6,7]. Detector effects also can cause changes in the measured multiplicity distributions.…”

Section: Introductionmentioning

confidence: 99%

Spin measurements forSm147+nresonances: Further evidence for nonstatistical effects

et al. 2007

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We have determined the spins J of resonances in the 147 Sm(n, γ) reaction by measuring multiplicities of γ-ray cascades following neutron capture. Using this technique, we were able to determine J values for all but 14 of the 140 known resonances below E n = 1 keV, including 41 firm J assignments for resonances whose spins previously were either unknown or tentative. These new spin assignments, together with previously determined resonance parameters, allowed us to eV from an analysis of 147 Sm(n,α) data, we divided the data into two regions; 0 < E n < 350 eV and 350 < E n < 700 eV. Using neutron widths from a previous measurement (corrected for new unresolved doublets identified in this work) and published techniques for correcting for missed resonances and for testing whether data are consistent with a Porter-Thomas distribution, we found that the Γ 0 n distribution for resonances below 350 eV is consistent with the expected PorterThomas distribution. On the other hand, we found that Γ 0 n data in the 350 < E n < 700 eV region are inconsistent with a Porter-Thomas distribution, but in good agreement with a χ 2 distribution having ν ≥ 2 We discuss possible explanations for these observed non-statistical effects and their possible relation to similar effects previously observed in other nuclides. * Electronic address: koehlerpe@ornl.gov 2

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“…The average multiplicity is expected to be different for J − than for J + . This conjecture was established [1,2,3] by Monte Carlo simulations of the gamma-cascades following neutron capture. The J-spin effect on multiplicity, although not large for Mo, (∆M J / < M >∼ 7%), results in the separation of M J values of s-wave resonances into two different groups, corresponding to the two possible spin values J + = 3 and J − = 2.…”

Section: Methodsmentioning

confidence: 94%

Neutron capture reactions on Mo and Gd isotopes using the DANCE array

Mitchell¹

2008

Proceedings of Workshop on Photon Strength Functions and Related Topics — PoS(PSF07)

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The γ rays following the 94,95 Mo(n, γ)Mo reactions have been studied by the time-of-flight method with the DANCE (Detector for Advanced Neutron Capture Experiments) array of 160 BaF 2 scintillation detectors at the Los Alamos Neutron Science Center. The targets were enriched samples. The γ-ray multiplicities and energy spectra for different multiplicities were measured in s-and p-wave resonances up to E n = 10 keV for 94 Mo and up to E n = 2 keV for 95 Mo. Preliminary analysis assigned definite spins and parities in 96 Mo for about 60% of the resonances, while tentative spins and parities were assigned for the rest of observed resonances. In 95 Mo the parities were determined for the observed resonances, confirming previously known assignments. Workshop on Photon Strength Functions and Related Topics

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A method of spin assignment of neutron resonances based on capture gamma-ray detection

Cited by 81 publications

References 20 publications

Neutron resonance data exclude random matrix theory

Neutron resonance data exclude random matrix theory

Spin measurements forSm147+nresonances: Further evidence for nonstatistical effects

Neutron capture reactions on Mo and Gd isotopes using the DANCE array

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