The neutron cross sections of thorium and the analysis of the resonances up to 1 keV

Asghar, M. I.; Chaffey, C.M.; Moxon, M.C.; Pattenden, N.J.; Rae, E.R.; Uttley, C.A.

doi:10.1016/0029-5582(66)90969-2

Cited by 23 publications

(10 citation statements)

References 14 publications

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“…For such large values of ν γ , a χ 2 distribution is very close to Gaussian in shape. One advantage of using a Gaussian rather than χ 2 distribution for the analysis is that data uncertainties ∆Γ γ can easily be included [27].…”

Section: Testing the Ptd With γ γ Datamentioning

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: Testing the Ptd With γ γ Datamentioning

confidence: 99%

Neutron resonance data exclude random matrix theory

Koehler

Bečvář

Krtička

et al. 2012

Fortschritte der Physik

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“…4 m diameter) and consists of a lami- reject the gamma-ray background. The Harwell five-glass scattering detector was used with a resolution of 5 nsec/m (Asghar et al, 1966a). 9) at a distance of 50 m from the neutron source.…”

Section: Values Ofmentioning

confidence: 99%

“…9) at a distance of 50 m from the neutron source. These Th data have been combined with trans mission and capture measurements to determine the resonance parameters and resonance integral of Th (Asghar et at., 1966a). in diameter by f in.…”

Section: Values Ofmentioning

confidence: 99%

Neutron Scattering and Capture Cross-Section Measurements

Rae¹,

Block²

1970

Experimental Neutron Resonance Spectroscopy

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“…For such large values of ν γ , a χ 2 distribution is very close to Gaussian in shape. One advantage of using a Gaussian rather than χ 2 distribution for the analysis is that uncertainties ∆Γ γ can easily be included [11].…”

mentioning

confidence: 99%

“…[11] to estimate most likely values for the means Γ γ and standard deviations σ N of the Γ γ distributions in the two energy regions. Resulting ML estimates are σ N = 4.67 ± 0.81, Γ γ = 52.0 ± 1.1, and σ N = 11.7 ± 1.5, Γ γ = 59.6 ± 2.0, for the lower-and upper-energy regions, respectively.…”

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confidence: 99%

Abrupt Change in Radiation-Width Distribution forSm147Neutron Resonances

et al. 2012

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We obtained total radiation widths of s-wave resonances through R-matrix analysis of 147 Sm(n, γ) cross-sections. Distributions of these widths differ markedly for resonances below and above En = 300 eV, in stark contrast to long-established theory. We show that this change, as well as a similar change in the neutron-width distribution reported previously, are reflected in abrupt increases in both the average 147 Sm(n, γ) cross section and fluctuations about the average near 300 eV. Such effects could have important consequences for applications such as nuclear astrophysics and nuclear criticality safety.PACS numbers: 24.30. Gd, 24.60.Dr, 24.60.Lz, 25.40.Lw In this letter, we show that total-radiation-widths (Γ γ ) extracted from R-matrix analysis of 147 Sm(n, γ) cross sections reveal an abrupt change in the shape and average value of the Γ γ distribution near E n = 300 eV. These observations are in stark contrast with theoretical expectations that both quantities should remain essentially constant across the resonance range and beyond.The effect reported herein occurs very near the same energy as previously reported abrupt changes in the α-particle strength-function ratio [1] for the two s-wave spin states and the shape of the reduced-neutron-width (Γ 0 n ) distribution [2]. Due to the difficulty of measuring the very small α widths, the former effect was of limited statistical significance. However, the effect in the Γ 0 n data was established at about the 99% confidence level using several different tests. These two previous effects remain unexplained.As we will show below, changes in the Γ γ distribution shape and average are established with very high confidence. That three such deviations from theoretical expectations could occur by chance in the same nuclide at the same energy must be vanishingly small. Therefore, it is virtually certain that significant departure from standard theory has been observed and that all three effects may have a common origin. Given the relative paucity of high-quality Γ γ data, similar effects may exist for other nuclides and, if so, could have far-reaching consequences for both basic and applied nuclear physics. For example, as we show below, these changes in the Γ γ and Γ 0 n distributions are reflected in abrupt increases in both the average 147 Sm(n, γ) cross section and fluctuations about the average that cannot be explained by the nuclear statistical model. As this theory is used to calculate cross sections for applications, similar differences in other nuclides could have important impacts in nuclear astrophysics and nuclear criticality safety.It is expected that Γ γ distributions for medium to heavy nuclides should be very narrow, and essentially constant across the resonance energy region. Expectation [3] that the Γ γ distribution should be very narrow arises from i) the very complex wave functions of states at high excitation characteristic of neutron thresholds and ii) the very large number of channels for γ decay. Condition i) results in partial γ-decay widths...

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The neutron cross sections of thorium and the analysis of the resonances up to 1 keV

Cited by 23 publications

References 14 publications

Neutron resonance data exclude random matrix theory

Neutron resonance data exclude random matrix theory

Neutron Scattering and Capture Cross-Section Measurements

Abrupt Change in Radiation-Width Distribution forSm147Neutron Resonances

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