Neutron Total Cross Sections Research Articles

Design study of the imaging beam line at J-PARC MLF, ERNIS

Abstract We have a plan to build an imaging beam line, Energy-Resolved Neutron Imaging System (ERNIS), at Materials and Life Science Experimental Facility (MLF) at Japan Proton Accelerator Research Complex (J-PARC). In pulsed neutron imaging, we use characteristic features of the neutron total cross section, depending on the neutron wavelength, to get sample information such as crystallographic structure and nuclide composition. One of the most important items to be determined for a beam line at J-PARC is the choice of moderator among coupled, decoupled, and poisoned moderators. From the wavelength resolution point of view, we decided to use the decoupled moderator, which could cover major experiments performed at a pulsed neutron source. Here, we discuss the structure of the imaging beam line at beam line 22 of the J-PARC neutron source as well as the arrangement of insertion devices and the experimental area.

Wavelength dependent neutron transmission and radiography investigations of the high temperature behaviour of materials applied in nuclear fuel and control rod claddings

Abstract Neutron radiography was used for the investigation of the nuclear fuel and control rod cladding behaviour during steam oxidation under severe nuclear accident conditions. In order to verify the hypothesis that the unexpectedly high neutron cross-section found after oxidation of Zircaloy-4 in wet air containing 10% steam is caused by a strong hydrogen uptake, the wavelength dependence of the total macroscopic neutron cross-section of the specimens was measured. The characteristic dependence for hydrogen was not found, which is a proof that hydrogen is not absorbed significantly. The data agree mostly with the behaviour expected for β-Zr. Examinations of control rod simulators annealed until the failure in single-rod tests were performed. In order to separate the effect of the neutron absorber and control rod structure materials, radiographs taken with different neutron spectra were combined. This procedure clearly showed that the local melting resulting from the eutectic reaction between the stainless steel control rod cladding and the Zircaloy-4 guide tube is the reason for the failure.

Neutron diffraction measurements of residual stresses in a 50 mm thick weld

Residual stresses were determined through the thickness of a 50 mm thick ferrite steel weld plate using neutron diffraction. Whereas the limiting penetration depth for iron-based alloys is about 25 mm in the most typical neutron diffractometers, we significantly enhanced the penetration depth up to 50 mm with 2 mm spatial resolution by using the neutron wavelength of 2.39 Å. The selected wavelength minimizes the total neutron cross-section and beam attenuation, thereby, maximizes the neutron fluxes at depth. Two-dimensional mapping of the residual stresses shows that significant amounts of the tensile longitudinal stresses (over 90% of yield strength) were developed along the heat-affected zone of the weld.

Sensitivity analysis of neutron total and absorption cross sections within the optical model

Distinct maxima and minima in neutron total and absorption cross-section uncertainties when optical-model parameters are varied have been observed in large-scale covariance calculations. These features were seen over a wide mass range (20--210) and for energies up to 20 MeV. Here we investigate the physical origin of the observed patterns over an extended energy range (1 keV to 200 MeV). We have calculated the sensitivity of the cross sections for a specific nucleus ($^{56}\mathrm{Fe}$) to variations of the 15 parameters of a standard global optical potential parametrization, and have also carried out calculations for alternative global optical potentials over the original wide mass and energy ranges. We find that simple physical descriptions can be found in two energy ranges. Below approximately 100 keV, the patterns arise from the interplay of the $s$- and $p$-wave single-particle resonances. Above approximately 4 MeV, a single-phase-shift approximation (the Ramsauer model) describes the observed behavior. We discuss the potential importance of such sensitivity studies for further development of optical potentials.

Determinations of niobium and palladium resonance cross-sections by time-of-flight transmission experiment

The neutron total cross-sections and resonance parameters of Niobium (Nb) and Palladium (Pd) were measured in the neutron energy regions from 0.1 eV to 100 eV by using the time-of-flight method at the Pohang Neutron Facility, Korea, which consists of an electron linear accelerator, a water-cooled Tantalum (Ta) target with a water moderator, and a 12.06 m long time-of-flight path. A 6Li-ZnS(Ag) scintillator with a diameter of 12.5 cm and a thickness of 1.6 cm was used as a neutron detector, and high purity natural Nb and Pd metallic sheets with thickness of 15 mm (0.0833 atoms/barn) and 1 mm (0.0068 atoms/barn) respectively, were used for the neutron transmission measurements. The notch filters composed of Cobalt (Co), Indium (In), and Cadmium (Cd) were used to estimate the background level and also to calibrate energy. In order to reduce the gamma-ray background from Bremsstrahlung and from neutron capture, we employed a neutron-gamma separation system based on their different pulse shapes. The resonance parameters of natNb and natPd were obtained from the transmission ratio by using the SAMMY code, which utilizes both Doppler and resolution broadening effects and Bayes’ generalized least squares technique. The present measurements were compared with the existing experimental and the evaluated reactions data files.

A differential time-of-flight spectrometer of very slow neutrons

A time-of-flight spectrometer of neutrons with energies of 0.05–2.50 μeV is described. This spectrometer has been tested by measuring the total and differential neutron cross sections for a number of materials—aluminum, copper, silicon, zirconium, polyethylene, 6LiF, and fluoropolymers—that are essential for experiments in physics of ultracold neutrons.

In-situ neutron radiography investigations of hydrogen diffusion and absorption in zirconium alloys

Abstract The fast and non-destructive character of neutron radiography provides the possibility of in-situ investigations of hydrogen uptake and diffusion in zirconium alloys. A special reaction furnace with neutron transparent windows was constructed. The method of quantitative hydrogen determination by neutron transmission measurements was calibrated for each experimental run. Additionally, oxygen is absorbed in the α-Zr phase and precipitated in the oxide layer. The calibration of the correlation between hydrogen and oxygen concentrations and total neutron cross-sections at room temperature and between 1123 and 1623 K are described. Results of in-situ neutron radiography investigations of hydrogen diffusion and absorption are presented in this paper. A linear dependence of the total macroscopic neutron cross section on the H/Zr atomic ratio as well as on the oxygen concentration was found. No significant temperature dependence of the total neutron cross-sections of hydrogen dissolved in β-Zr or oxygen dissolved in the α-Zr or precipitated in the oxide layer was found.

Neutron moderator development research at the low energy neutron source

The Low Energy Neutron Source at Indiana University completed its construction phase roughly three years ago, and one of the more active research thrusts at the facility since that time has been our attempts to advance the state of the art in neutron moderation. This research program includes basic materials characterization, especially total neutron cross-section measurements, as well as in-situ testing of the performance of various prototype moderators. This paper reviews a number of the more noteworthy results we have uncovered and describes the goals of the moderator development program at LENS.

Scattering law of a magnesium hydride moderator

Metal hydrides have long been considered possible moderator and pre-moderator materials for neutron sources. These materials have hydrogen density comparable to liquid hydrogen or light water. They usually do not undergo phase transitions in the desired operating range of 0–300 K, and display reasonable resistance to radiation damage. Magnesium hydride is such a simple, robust hydride system. To assess its neutronic usefulness as a moderator material, we determined experimentally the total scattering cross-section of the material. We compared our theoretical results to the experimental total neutron cross-section and to the data from quasi-elastic neutron scattering experiments, and produced a scattering kernel suitable for neutron transport calculations.

?Measurement of Fast Neutron Total Cross Sections on O, Si, and SiO2

?Measurement of Fast Neutron Total Cross Sections on O, Si, and SiO2

Cross section structure of 232Th in the unresolved resonance region

An analysis of the 232Th neutron total and neutron capture cross sections has been performed in the energy region between 4 keV and 140 keV. The experimental data are analysed in terms of average resonance parameters utilizing a new statistical method for modelling of the resonance cross section structure in the region of experimentally unresolved resonances. The method exploits the characteristic function of the R-matrix elements distribution in Wigner's theory of nuclear reactions. To improve the representation of the 232Th cross section, the neutron strength functions for s- and p-waves are fitted to the experimental data in order to reproduce their observable fluctuations in (4–140) keV. Our method offers analytical expressions even for nonlinear functionals (observables) of neutron cross section as a transmission ratio. These functionals are incorporated into the evaluation process as a simple benchmark test for verification of the 232Th resonance parameters.

Global phenomenological optical model potential for nucleon-actinide reactions at energies up to 300 MeV

A set of new global phenomenological optical model potential parameters for the actinide region with incident nucleon energies from 1 keV up to 300 MeV is obtained. They are based on a smooth, unique functional form for the energy dependence of the potential depths and on physically constrained geometry parameters. The available experimental data including the neutron total cross sections, nonelastic cross sections, elastic scattering cross sections, elastic scattering angular distributions, and proton reaction cross sections and elastic scattering angular distributions of $^{232}\mathrm{Th}$ and $^{238}\mathrm{U}$ are used. The new nucleon global optical model potential parameters obtained are analyzed and used to analyze the experimental data of nucleon-actinide reactions. It is found that the present form of the global optical model potential could reproduce both the neutron and the proton experimental data.

Measurement of neutron cross sections and resonance parameters of 169Tm below 100 eV

The neutron total cross-sections of thulium (169Tm) were measured in the neutron energy region from 0.01 eV to 100 eV by using the time-of-flight method at the Pohang Neutron Facility, which consists of an electron linac, a water-cooled tantalum target with a water moderator, and a 12 m time of flight path. Two thulium plates with different thicknesses were used for the neutron transmission measurement. The background level was determined by using a notch-filter of Co, In, and Cd sheets. The present measurement was compared with the previous ones, and a new set of resonance parameters of 169Tm isotope was obtained from the transmission rate by using the SAMMY code, with a comparison with the recommended parameters by Mughabghab.

Total neutron cross-sections for rare isotopes using a digital-signal-processing technique: Case study 48Ca

A digital-signal-processing method was developed and used to measure the total neutron cross-sections of 48Ca from 15 to 300 MeV. This technique allows for cross-sections to be obtained with high statistical accuracy even for samples that are an order of magnitude smaller than those used with conventional (non-digital) techniques. The isotopic and energy dependence of rare-isotope total neutron cross-sections are of considerable value for extracting the n/p asymmetry dependence of optical-model potentials.

Total neutron cross section for181Ta

The neutron time of flight facility nELBE, produces fast neutrons in the en- ergy range from 0.1 MeV to 10 MeV by impinging a pulsed relativistic electron beam on a liquid lead circuit (1). The short beam pulses (∼10 ps) and a small radiator volume give an energy resolution better than 1% at 1 MeV using a short flight path of about 6 m, for neutron TOF measurements. The present neutron source provides 2 · 10 4 n/cm 2 sa t the target position using an electron charge of 77 pC and 100 kHz pulse repetition rate. This neutron intensity enables to measure neutron total cross section with a 2%-5% statistical uncertainty within a few days. In February 2008, neutron radiator, plastic detector (2) and data acquisition system were tested by measurements of the neutron total cross section for 181 Ta and 27 Al. Measurement of 181 Ta was chosen because lack of high quality data in an anergy region below 700 keV. The total neutron cross - section for 27 Al was measured as a control target, since there exists data for 27 Al with high resolution and low statistical error (3).

Optical Model And Cross Section Uncertainties

Distinct minima and maxima in the neutron total cross section uncertainties were observed in model calculations using spherical optical potential. We found this oscillating structure to be a general feature of quantum mechanical wave scattering. Specifically, we analyzed neutron interaction with 56Fe from 1 keV up to 65 MeV, and investigated physical origin of the minima.We discuss their potential importance for practical applications as well as the implications for the uncertainties in total and absorption cross sections.

Preliminary results of new GELINA data for natural cadmium

The total neutron cross section of cadmium (Cd) is very large in the thermal neutron energy region which determines its special role in reactor technology. The first resonance of 113Cd at 0.178 eV is of high importance in the interpretation of Cd neutron cross section structure in the thermal region. The evaluated data files for Cd isotopes and particularly the resonance parameters do not correspond to the requirements of the advanced reactor technologies. To provide data for a new evaluation, a set of top quality transmission experiments has been designed and performed at the neutron time-of-flight facility GELINA at the Institute for Reference Materials and Measurements (IRMM) in Geel, Belgium. The measurements have been carried out at 26.45 m and 50 m flight paths of GELINA at 50 Hz, 400 Hz and 800 Hz working frequencies of the LINAC, using natural Cd samples with various thicknesses (purity 99.99% in Cd). The experiments at 50 Hz provide high quality data in the thermal energy region, from which we could extract the resonance parameters for the first resonance of 113Cd at 0.178 eV with high accuracy.Considering the transmission data obtained with various sample thicknesses as a source of additional information for low level cross section we validate a new approach for cross section description in this energy region.

Porosity effects on the neutron total cross section of graphite

For subthermal neutron energies, polycrystalline graphite shows a larger total cross section than predicted by existing theoretical models. In order to investigate the origin of this discrepancy we measured the total cross section of graphite samples of three different origins, in the energy range from 0.001 to 10eV. Different experimental arrangements and sample treatments were explored, to identify the effect of various experimental parameters on the total cross section measurement. The experiments showed that the increase in total cross section is due to neutrons scattered around the forward direction. We associate these small angle scattered neutrons (SANS) to the porous structure of graphite, and formulate a very simple model to compute its contribution to the total cross section of the material. This results in an analytic expression that explicitly depends on the density and mean size of the pores, which can be easily incorporated in nuclear library codes.

Measurements of neutron total cross-sections and resonance parameters of erbium at the Pohang Neutron Facility

We measured neutron total cross-sections of natural erbium in the neutron energy region from 0.2 to 120 eV by using the neutron time-of-flight method at the Pohang Neutron Facility, which consists of an electron linear accelerator, a water-cooled tantalum target with a water moderator, and a 12-m-long time-of-flight path. A 6Li–ZnS(Ag) scintillator with a diameter of 12.5 cm and a thickness of 1.6 cm was used as a neutron detector, and a group of high-purity natural erbium metallic plates with various thickness was used for the neutron transmission measurements. The present measurement was compared with the existing experimental and the evaluated data. The resonance parameters of 166Er, 167Er, 168Er, and 170Er in the neutron energy region below 120 eV were extracted from the transmission by using the multilevel R-matrix SAMMY code and were compared with the evaluated data from ENDF/B VII.0 and other previous reported results.

Investigation of solid [formula omitted], [formula omitted] and [formula omitted] for ultracold neutron production

We have investigated the properties of the ultracold neutron converter materials deuterium D 2 , oxygen O 2 and heavy methane CD 4 in the temperature range between 8 K and room temperature. The experimental program was performed at the FUNSPIN beamline of the Swiss Spallation Neutron Source (SINQ) at Paul Scherrer Institut (PSI). In this paper the measured cold neutron total cross-sections for D 2 , O 2 and CD 4 are presented.