Radiative thermal neutron capture by natural sulfur

A series of experiments has been conducted at the Frank Laboratory of Neutron Physics (FLNP) of the Joint Institute for Nuclear Research (JINR) in order to study the possibility of determining the moisture content of coke using a standard neutron source. The proposed method is based on a measurement of the spectrum of prompt γ rays emitted when samples are irradiated by fast and/or thermal neutrons. The moisture content is determined from the area of the peaks of characteristic γ rays produced in the radiative capture of thermal neutrons by the proton (Eγ = 2.223 MeV) and inelastic scattering of fast neutrons by 16O (Eγ = 6.109 MeV). The 239Pu–Be neutron source (〈E n 〉 ~ 4.5 MeV) with an intensity of ~5 × 106 n/s was used to irradiate the samples under study. A scintillation detector based on a BGO crystal was used to register the characteristic γ radiation from the inelastic fast neutron scattering and slow (thermal) neutron capture. This paper presents the results of humidity measurement in the range of 2–50% [1, 2].

The reaction 171Yb(nth,2γ) was studied with the aim of extending the experimental database of intensities of cascades of two photons emitted sequentially after radiative thermal-neutron capture. An analysis of these cascade intensities permitted revealing the change in the structure of observed levels of the 172Yb nucleus versus the excitation energy and determining probable thresholds for the break of four Cooper pairs of neutrons below the neutron binding energy.

The Crab (Calibrated nuclear Recoils for Accurate Bolometry) project aims to precisely characterize the response of cryogenic detectors to sub-keV nuclear recoils of direct interest for coherent neutrino-nucleus scattering and dark matter search experiments. The Crab method relies on the radiative capture of thermal neutrons in the target detector, resulting in a nuclear recoil with a well-defined energy. We present a new experimental setup installed at the TRIGA Mark-II reactor at Atominstitut (Vienna), providing a low intensity beam of thermal neutrons sent to the target cryogenic detector mounted inside a wet dilution refrigerator Kelvinox 100. After the presentation of all components of the setup we report the analysis of first commissioning data with CaWO_{4} detectors of the Nucleus experiment. They show stable operation of the cryostat and detectors on a week-scale. Due to an energy resolution currently limited to 20 eV we use neutron beam induced events at high energy, in the 10 to 100 keV range, to demonstrate the excellent agreement between the data and simulation and the accurate understanding of external background. Thanks to these data we also propose an updated decay scheme of the low-lying excited states of ^{187}W. Finally, we present the first evidence of neutron-capture induced coincidences between BaF_2gamma -detectors installed around the dewar and the inner cryogenic detector. These promising results pave the way for an extensive physics program with various detector materials, like CaWO_{4}, Al_{2}O_{3}, Ge and Si.

A diffusion cloud chamber was built which had to be of a material with a relatively low macroscopic cross section for radiative capture of thermal neutrons. 61-S aluminum alloy was used. A polystyrene cylinder of a diameter a little smaller than that of the cylindrical body is used to insulate the sensitive region from the outside walls and to provide by means of a tape heater, the right temperature distribution along the boundaries of the sensitive region. (M.H.R.)

We have measured the cross section for radiative capture of thermal neutrons on $^{3}\mathrm{He}$. The measured cross section of 54\ifmmode\pm\else\textpm\fi{}6 \ensuremath{\mu}b is used to estimate the astrophysical S factor for the reaction $^{3}\mathrm{He}$(p,${e}^{+}$\ensuremath{\nu}${)}^{4}$He which gives rise to high-energy neutrinos from the Sun.

. The problem of introducing pulse neutron probing in the process of geological and geophysical studies has been updated. The main factors that increase the sensitivity and information content of pulse methods in comparison with stationary neutron methods have been considered. It has been shown that the efficiency of pulse neutron probing depends on the length of the probe, time and energy characteristics of the equipment used. The principal features of various modifications of pulse neutron probing for solving geological and geophysical problems have been noted. The aspects of the efficient use of pulse modification in neutron gamma-ray spectrometry and inelastic scattering of fast neutrons have been discussed. Improved modifications of neutron probing based on the complex application of instrumental signals arising from inelastic scattering of fast and radiative capture of thermal neutrons have been proposed

PROMPT GAMMA RAYS FROM RADIATIVE CAPTURE OF THERMAL NEUTRONS BY ELEMENTS FROM HYDROGEN THROUGH ZINC

The threshold electrodisintegration cross section and electromagnetic form factors of the deuteron are calculated by using the Argonne ${\mathit{v}}_{14}$ model for the nucleon-nucleon interaction to generate the bound- and scattering-state wave functions. The exchange-current operator is constructed to be consistent with the interaction model. The calculated electrodisintegration cross section is in good qualitative agreement with the experimental data over the whole measured momentum-transfer range, and is sensitive to the electromagnetic form factors of the nucleon. The calculated form factors appear to be in good agreement with the empirical values, although uncertainties in the isoscalar model-dependent exchange-current contributions and nucleon electromagnetic form factors prevent definite predictions to be made at high values of momentum transfer. Finally, the cross section for radiative capture of thermal neutrons on protons is found to be within less than 1% of the measured value.

A brief review is given of the contents of the Evaluated Database for Prompt Gamma Rays from Radiative Capture of Thermal Neutrons by Elements from Hydrogen to Zinc; this version also contains data for 32 Ge, 73 Ta, 74 W, 62 Sm, and 64 Gd.The evaluated data as well as the documentation were provided by R. S. Reedy and S. C Frankle (LANL, USA) and the software for retrieval was developed by V. Zerkin (IAEA-NDS).

With the aim to obtain information on the E1 and M1 photon strength functions at g-ray energies below the neutron separation energy, we studied two-step g cascades following the capture of thermal neutrons in 107 Ag. For this purpose, we undertook an experiment with the dedicated facility for two-step g cascades at the Rez ˇ research reactor. The obtained data were discussed in conjunction with previous results from resonance neutron capture measurements with the same isotope, obtained at the GELINA facility of the Institute for Reference Materials and Measurements. The cascade g decay of the 108 Ag compound nucleus has been simulated with the aid of the Monte Carlo algorithm DICEBOX assuming several models for photon strength functions. To interpret the results of the experiments, the outcome from these simulations was confronted with the observed cascade-related quantities. The results indicate that the E1 photon strength function below the neutron binding energy is suppressed with respect to the conventional Brink-Axel model and that the M1 and/or possibly E2 photon strengths may play an important role in the decay of compound nucleus at excitations below '3 MeV.

Neutron capture $\ensuremath{\gamma}$-ray spectra have been measured from the 7.76-keV $s$-wave and the 9.48-, 11.2-, and 14.4-keV $p$-wave resonances in $^{54}\mathrm{Fe}$. The 7.76-keV resonance spectrum is in excellent agreement with valence model predictions.NUCLEAR REACTIONS $^{54}\mathrm{Fe}(n, \ensuremath{\gamma})$, ${E}_{n}=1\ensuremath{-}18$ keV, measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$. $^{55}\mathrm{Fe}$ deduced resonances, levels, $J$, $\ensuremath{\pi}$, neutron separation energy. Enriched target, Ge(Li) detector. Comparison with valence model predictions.

Measurements have been made of high-energy capture gamma -ray spectra following neutron capture by 93Nb for discrete resonances up to 1 keV and for unresolved regions up to 6 keV, with the aim of investigating the reaction mechanism. Spin assignments have been made for s-wave and p-wave resonances using the low-level population method, and also using primary transitions. A determination of the neutron binding energy has been made, and a level scheme of 94Nb has been constructed for states up to 1520 keV populated by primary transitions. A significant correlation has been found between (d,p) intensities and average partial radiation widths to the same final states, for resolved p-wave resonances below 1 keV and for average regions at higher energies (up to 6 keV). The distributions of partial radiation widths for M1 and E1 transitions in s-wave and p-wave resonances were consistent with the Porter-Thomas prediction.

Parity non-conservation in radiative thermal neutron capture by protons

RECENT investigations have shown that crystal defects determine the fate of the fragments generated in solids by radiative thermal neutron capture as well as the kinetics of subsequent annealing reactions1,2. So far, there has been no experimental evidence for the influence of defects on the annealing of chemical damage produced in solids by irradiation. We have now obtained such evidence in the case of annealing in lead nitrate.

Isotope effects in radiative thermal neutron capture