Neutron Capture Gamma-ray Spectra Research Articles

Evaluation of gamma-ray strength function based on measured gamma-ray pulse-height spectra in time-of-flight neutron capture experiments

In order to develop an evaluation method of gamma-ray strength function (GSF), neutron capture pulse-height (PH) spectrum of gold was employed, where it was measured with the NaI(Tl) spectrometer of AN-NRI installed at the Material and Life Science Experimental Facility in J-PARC. The neutron capture gamma-ray spectrum of gold was calculated using the nuclear reaction model code CCONE. In order to obtain the information on GSF from the measured data, a gamma-ray response function for the NaI(Tl) spectrometer was calculated by the Monte-Carlo particle-transport simulation code PHITS. As a result, the PH spectrum comparable with measured one was derived by applying the gamma-ray response function to the calculated gamma-ray spectrum. By evaluation with measured PH spectra, we obtained GSF which reasonably explains measured PH spectrum in the continuum region.

Neutron Capture Cross Section Measurement on91Zr at J-PARC/MLF/ANNRI

The neutron capture cross section measurement on 91Zr was performed at neutron TOF beam line ANNRI installed at J-PARC/MLF. Prompt capture gamma rays from the sample were detected with an array of large Ge detectors at a distance of 21.5 m from the spallation neutron source by the time-of-fligh (TOF) method. The neutron capture gamma-ray pulse-height spectra from the 182-eV p-wave resonance and the 292-eV s-wave resonance were obtained by gating on the TOF regions, respectively. Though the decay patterns of primary transitions from the capture state were quite different between resonances, the prominent characteristics common to both resonances was the very strong ground-state transition from the 935-keV state. Therefore, a ground-state transition method was applied to obtain the capture yield, so that the background components due to impurities were successfully eliminated. The preliminary result of the neutron capture cross section for 91Zr up to 5 keV is presented.

Measurement of neutron capture cross sections and neutron capture gamma-ray spectra of 93Nb, 103Rh and 115In in keV-energy region

The neutron capture cross sections of 93Nb, 103Rh and 115In were measured by the time-of-flight method in the energy region from 15 keV to 100 keV. A pulse-height weighting technique was employed to derive the neutron capture cross sections. The neutron capture γ-ray spectra were derived by unfolding the pulse-height spectra with the detector response functions.

Study on the keV neutron capture reaction in 56Fe and 57Fe

The neutron capture cross-sections and the radiative capture gamma-ray spectra from the broad resonances of 56Fe and 57Fe in the neutron energy range from 10 to 90keV and 550keV have been measured with an anti-Compton NaI(Tl) detector. Pulsed keV neutrons were produced from the 7Li\( (p,n)\) 7Be reaction by bombarding the lithium target with the 1.5ns bunched proton beam from the 3MV Pelletron accelerator. The incident neutron spectrum on a capture sample was measured by means of a time-of-flight (TOF) method with a 6Li -glass detector. The number of weighted capture counts of the iron or gold sample was obtained by applying a pulse height weighting technique to the corresponding capture gamma-ray pulse height spectrum. The neutron capture gamma-ray spectra were obtained by unfolding the observed capture gamma-ray pulse height spectra. To achieve further understanding on the mechanism of neutron radiative capture reaction and study on physics models, theoretical calculations of the \( \gamma\) -ray spectra for 56Fe and 57Fe with the POD program have been performed by applying the Hauser-Feshbach statistical model. The dominant ingredients to perform the statistical calculation were the Optical Model Potential (OMP), the level densities described by the Mengoni-Nakajima approach, and the \( \gamma\) -ray transmission coefficients described by \( \gamma\) -ray strength functions. The comparison of the theoretical calculations, performed only for the 550keV point, show a good agreement with the present experimental results.

Measurements of keV-neutron capture cross sections and capture gamma-ray spectra of 105Pd

The neutron capture cross sections and capture gamma-ray spectra of 105Pd were measured in the region from 15 to 100 keV and at 585 keV. A neutron time-of-flight method was utilised with an anti-Compton NaI(Tl) spectrometer and a 1.5-ns pulsed neutron source by the 7Li(p,n)7Be reaction. The capture yields were obtained by applying a pulse-height weighting technique to the observed net capture gamma-ray pulse-height spectra. The capture cross sections of 105Pd were derived with errors less than 5%, using the standard capture cross sections of 197Au. The evaluated capture cross sections of JENDL-4.0 and ENDF/B-VII.1 were compared with the present results. The evaluations of JENDL-4.0 and ENDF/B-VII.1 were larger than the present results by 3%–15% in the region from 15 to 100 keV and at 585 keV. The capture gamma-ray spectra of 105Pd were also derived by unfolding the observed net capture gamma-ray pulse-height spectra. The multiplicities of capture gamma rays of 105Pd were obtained from the capture gamma-ray spectra.

Nd-142のEn=550keVでの中性子捕獲断面積と捕獲ガンマ線スペクトルの測定

Nd-142のEn=550keVでの中性子捕獲断面積と捕獲ガンマ線スペクトルの測定

Se-74,76の550 keV中性子捕獲断面積と捕獲ガンマ線スペクトルの測定

Se-74,76の550 keV中性子捕獲断面積と捕獲ガンマ線スペクトルの測定

Evaluation of Neutron Capture Gamma-ray Spectra for 89Y, 93Nb, 127I, 133Cs, 141Pr, 197Au, natTl, and 209Bi

The neutron capture gamma-ray spectra for 8 nuclides, 89Y, 93Nb, 127I, 133Cs, 141Pr, 197Au, natTl, and 209Bi, were calculated by using the Hauser-Feshbach statistical model, and their results were compared with the available experimental data. Two dominant ingredients to perform the statistical calculation were the level densities described by the Gilbert-Cameron approach with an improved systematics, and the gamma-ray transmission coefficients described by gamma-ray strength functions. Although various gamma-ray strength functions with a Lorentzian formula have been developed by using the photonuclear data or a microscopic analysis, they have failed to reproduce the occasional anomalous bumps observed near or below a neutron binding. In this work, we could reproduce the bumps well by adding a Lorentzian with an energy-temperature dependent width into a giant electric dipole resonance with an enhanced generalized Lorentzian. In addition, we introduced a correction function so as to compensate for the shortcomings due to missing levels or level-cuts.

Variance reduction techniques for improved derived elemental concentrations from fitting prompt neutron capture gamma ray spectra

Advances in the post-acquisition neutron-induced gamma-ray-spectroscopy spectral fitting techniques provide a means for improving both the precision and accuracy of the elements measured in subsurface petroleum reservoir formations. Rigorous stepwise-elimination multiple regressions and a novel analytical hierarchy technique are examined using synthetic spectral logs and field data. These approaches lead to adaptive dimensioning of the least-squares spectral fitting process, which reduces the uncertainties associated with the elemental concentrations without sacrificing important contributions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A new facility for averaged resonance capture studies at the Omega West reactor

A facility has been developed at the Omega West reactor at Los Alamos to provide neutron beams of 2 and 24 keV average neutron energies. The neutron beam currents are comparable with those obtained at the Brookhaven high flux beam reactor. A three-crystal pair spectrometer has been developed to allow acquisition of high resolution primary neutron capture gamma ray spectra. This will be used for nuclear spectroscopy and structure studies.

Calculation of capture gamma-ray spectra for Ta-181 and Au-197

Abstract Neutron capture gamma-ray spectra for Ta-181 and Au-197 have been calculated using the level density derived from new low-lying level fitting and the Brink-Axel with a pigmy resonance profile function. Results were compared with the experimental data.

Evaluation of neutron capture gamma-ray spectra in hafnium and tantalum.

A method has been developed for evaluation of neutron capture γ-ray spectrum. It couples measured intensities of primary and secondary discrete—-ray with a γ-ray cascade model to calculate the unresolved part of the capture spectrum, and adds the discrete part and the unresolved part to obtain the whole spectrum. The cascade model uses the level density formula proposed by Gilbert & Cameron and the Brink & Axel form of El γ-ray profile function with a modification. This method was applied to thermal neutron capture spectra in six hafnium isotopes and 181Ta and was extended also to non-thermal capture spectra in 181Ta for 0.25 and 0.5 MeV neutrons with empirical assumptions. The calculated results were compared with experiments and agreement was good not only in terms of the gross structure, but also in terms of the fine structure which appears at high and low γ-ray energies.

An investigation of the 35Cl(n,γ)36Cl reaction

A detailed study of the neutron-capture gamma-ray spectrum for chlorine, above an energy of 1.6 MeV, has revealed a total of 234 transitions with intensity greater than 0.04%. Consistency tests indicate that the average energy uncertainty for the entire set of gamma rays is 0.1 keV. Data reduction was accomplished by invoking spectral deconvolution techniques with the result that many previously reported transitions were found to be multiplets. A decay scheme was derived by making use of both these new findings and the high energy precision attained for the transition energies. The proposed decay scheme accounts for more than 98% of the observed intensity and the energy of the levels included were found to have an average uncertainty of 0.08 keV. Based upon an error-free 15N neutron separation energy of 10 833.30 keV, the Q values for 35Cl(n,γ)36Cl and 37Cl(n,γ)38Cl were found to be 8579.82 (2) and 6107.85 (10) keV, respectively.

The Dependence of the Gamma-Ray Spectral Shape on the Neutron Energy Averaging Interval Size for the 181Ta(n,γ) Reaction

The dependence of the shape of neutron capture gamma-ray spectra on the neutron energy averaging interval size has been investigated for the 181Ta(n,γ) reaction. The effects of statistical fluctuat...

Non-statistical aspects of resonance neutron capture in103Rh

Measurements have been made of high-energy neutron capture gamma ray spectra from the 103Rh(n, gamma )104Rh reaction for discrete resonances up to 850 eV and for unresolved regions up to 6 keV, with the aim of investigating the reaction mechanism. Spins of stronger resolved s-wave resonances up to 1272 eV were assigned using low-energy capture gamma rays, and in some cases also using high energy gamma rays. A value was obtained for the neutron binding energy, and a level scheme was constructed for 104Rh states up to 1 MeV populated by primary transitions. The distribution of a sample of 1938 reduced partial radiation widths in spin 1 resonances were found. The averaged gamma -ray spectra up to 6 keV showed an enhancement in the region 6.0-6.2 MeV, confirming previous observations. No correlations were found between resonance reduced neutron widths and reduced partial radiation widths in any part of the gamma -ray spectrum.

Analytical sensitivities and energies of thermal neutron capture gamma rays II

A table of the analytical sensitivities of the principal lines in the thermal neutron capture gamma-ray spectrum from 0 to 3 MeV has been compiled for most of the elements. A tabulation of the full-energy, single-escape, and double-escape peaks has also been made according to energy. The tables are useful for spectral interpretation and calibration.

The change of nuclear orientation parameters related to pseudo-continuous neutron-capture gamma-ray spectra

Calculations of disorientation parameters, 〈 G 1〉, 〈 G 2〉 and 〈 G 4〉, carried out in two different ways for pseudo-continuous neutron-capture gamma-ray spectra are reported. In the first calculations a very simple model in which a constant number of dipole transitions is assumed was used. Secondly computer calculations were done with a more realistic model for level densities and transition probabilities. A computer calculations were done with a also gamma multiplicities were calculated. A comparison with experimental data is made.

Neutron capture gamma ray facility using an electron linear accelerator

A versatile facility for the study of resonance neutron capture gamma-ray spectra with high energy resolution is described. An electron linear accelerator is used to provide a pulsed beam of neutrons. Gamma-ray spectra are measured using a Ge(Li)-NaI(Tl) spectrometer. The gamma-ray pulse height and the neutron time-of-flight information are stored using an on-line computer. The salient features of the capture facility are described and spectra resulting from the capture of neutrons in natural tungsten are displayed.

The Application of a Gamma-Ray Cascade Model to the Calculation of Neutron Energy-Dependent Capture Gamma-Ray Production Cross Sections

A simplified cascade model for the calculation of neutron-capture gamma-ray spectra is compared with experiment. In the context of the model, the simplifying assumptions involve extrapolations of m...

Energy levels and configurations in 94Nb

In the high-energy thermal neutron capture gamma-ray spectrum of 94Nb, 83 gamma rays were observed between 4500 keV, and the neutron binding energy determined here to be 7229.5 ± 1.5 keV. A total of 71 low-energy gamma rays was observed from 30 keV to 1500 keV. These and previous data were used to develop a decay scheme. The presence of states arising predominantly from the following configurations is proposed: πg 9 2 v ( d 5 2 ) 5 2 3 , πg 9 2 v ( d 5 2 ) 3 2 3 , π ( p 1 2 ) − 1 ( g 9 2 ) 0 2 v ( d 5 2 ) 5 2 3 and, more tentatively, π ( p 1 2 ) − 1 ( g 9 2 ) 0 2 v ( d 5 2 ) 9 2 3 and πg 9 2 v ( d 5 2 ) 0 2 S 1 2 . Some preliminary assignments of spins and parities to other states have also been attempted. Calculations based on 90Zr and 88Sr cores both agree well with energies, spectroscopic factors and reduced M1 transition probabilities. The generally close agreement between the calculations involving different cores is surprising in view of the considerable differences in the two sets of wave functions. This is probably to be understood in terms of the ability of the effective nucleon-nucleon interaction to absorb the effect of configuration mixing.