Measurement of cold neutron spectra using a model cryogenic moderator of the IBR-2M reactor

The method and results of an experiment to determine the cold neutron spectrum from solid mesitylene at moderator temperatures of 10–50 K are presented. This study was performed at the DIN-2PI spectrometer of the IBR-2 reactor. The objective of the study was to verify the system of constants used in the Monte Carlo simulation of cryogenic neutron moderators of the IBR-2M reactor and to obtain the cold neutron yield as a function of the moderator temperature. Satisfactory agreement between the experimental and calculated neutron spectra at a mesitylene temperature of 20 K has been obtained; the ratio of cold neutron intensities at 10 and 50 K is ∼1.8.     

Cold neutron moderator on an upgraded IBR-2 reactor: The first set of results

The first criticality of a new KZ-202 neutron moderator on the IBR-2M reactor is achieved. The moderator consists of thermal and cold units. The former is a room-temperature comb water moderator; the latter, a moderator using a mixture of aromatic hydrocarbons (mesitylene and m-xylene). The cold moderator is filled with granules of this mixture, which are supplied by a cold helium flow, and operates at 30 K. The combination of two units in one moderator makes it possible to simultaneously take the thermal and cold neutron spectra for extracted-beam spectrometers. The arrangement of the thermal and cold moderators is numerically optimized by the Monte Carlo method. The use of the cold moderator allows a 13-fold increase in the cold neutron intensity from its surface.     

Current status of advanced pelletized cold moderators development for IBR-2M research reactor

The world’s first advanced pelletized cold neutron moderator is prepared to be put into operation at the IBR-2M pulsed research reactor. It provides long-wavelength neutrons to the most of neutron spectrometers at the beams of the IBR-2M reactor. Aromatic hydrocarbons are used as a material for cold moderators. It is a very attractive material because of its high radiation resistance, good moderating properties, incombustibility, etc. It is shown that the idea of beads transport by a helium flow at cryogenic temperatures is successful. The recent progress and plans for moderator development at the IBR-2M reactor as well as the experimental results of beads transport are discussed in the paper.     

On the use of a composite moderator at the IBR-2 reactor: Advantages for the neutron-diffraction texture analysis of rocks

A unique cold moderator based on a mixture of mesitylene and m-xylene is developed for the IBR-2 pulsed reactor. If combined with a standard warm-water moderator, it provides a high neutron flux in a wide wavelength range. The advantages of the use of this composite moderator in neutron-diffraction texture analysis are discussed using the example of a sample of slate (formed from five minerals) studied using the SKAT diffractometer. The diffraction data obtained in experiments with warm-water and composite moderators are compared.     

Characteristics of the DIN-2PI spectrometer with a neutron concentrator

The basic characteristics of the upgraded DIN-2PI spectrometer are reported. Based on experimental data and numerical calculation results, it is concluded that a supermirror neutron concentrator, with which the DIN-2PI spectrometer is equipped, raises the density of the cold neutron flux at the sample almost by an order of magnitude. The use of a grooved moderator in channel no. 2 and upgrading of the core of the IBR-2M reactor increases the neutron flux density on the sample by about 40% more.     

Neutron experiments with cryogenic methane hydrate and mesitylene moderators

In this article we describe the experimental results of a methane hydrate moderator as well as as mesitylene moderator operated at a temperature around 20K at the JESSICA (Jülich Experimental Spallation Target Set-up In COSY Area) experiment at the Jülich cooler synchrotron COSY. For the first time the cold neutron spectrum of a methane hydrate moderator was experimentally investigated. A comparison with a solid methane and an ice moderator atT = 20 K will be shown. MCNPX simulations with new developedS(α,β) scattering kernels will be compared with experimental data. The applicability of mesitylene and methane hydrate as cold moderators at spallation neutron sources will be discussed.     

散裂中子源耦合慢化器的中子学研究

利用蒙特－卡罗方法研究了散裂中子源中耦合慢化器的中子学特性。给出了冷中子与热中子慢化器的中子能谱。甲烷慢化器提供了性能非常好的冷中子，在低功率的散裂中子源中得到了应用。计算了慢中子引出的角分布。由于较低的氢密度，液态氢的漫化能力低于水与液态甲烷，但是可以通过增加预慢化器来弥补这一问题。2cm厚的水预慢化器层可以大约减少热量在低温慢化器中的热量沉积33％而不破坏中子特性。     

On the possibility of investigations with very cold neutrons at pulsed sources

The possibility of investigations with very cold neutrons (VCNs) using the example of the IBR-2 pulsed reactor at the JINR FLNP is considered. Possible application areas and specific features of reactor characteristics for these investigations are briefly described. The results of detailed calculations of VCN generation in different cold moderators, VCN transport in neutron guides, and suppressing the contribution of delayed neutrons are presented.     

Concept of Small-Angle Diffractometer in Classical Configuration at the Cold Moderator of the IBR-2 Reactor

The possible concepts whereby a time-of-flight small-angle diffractometer optimized for a neutron moderator operating in the cold (at 30 K) and thermal (at 300 K) modes can be implemented at the IBR-2 reactor are studied on the basis of numerical calculations. Under cold conditions, the peak of the neutronbeam energy spectrum is shifted toward low energies (long wavelengths). This extends the sensitivity range of the instrument with respect to the sizes of the objects under study (1–100 nm and higher). A classical scheme enabling the separation of thermal/cold neutrons (E ~10^–3–10^–2 eV) from the background (formed mainly by fast neutrons), which is based on bent neutron-optical devices, is discussed. Due to restrictions imposed by the geometry of the beamline within which the instrument is planned to be located, a configuration with a short multichannel mirror device for beam bending (beam bender) is preferable. Simulation and optimization of the proposed small-angle instrument is carried out taking into account the real beamline geometry and the available space in the experimental reactor hall. A comparison of the setup has been made with the facility based on the curved neutron guide and the facility with direct view of the moderator.     

Sample to moderator volume ratio effects in neutron yield from a PGNAA setup

Performance of a prompt gamma ray neutron activation analysis (PGNAA) setup depends upon thermal neutron yield at the PGNAA sample location. For a moderator, which encloses a sample, thermal neutron intensity depends upon the effective moderator volume excluding the void volume due to sample volume. A rectangular moderator assembly has been designed for the King Fahd University of Petroleum and Minerals (KFUPM) PGNAA setup. The thermal and fast neutron yield has been measured inside the sample cavity as a function of its front moderator thickness using alpha particle tracks density and recoil proton track density inside the CR-39 nuclear track detectors (NTDs). The thermal/fast neutron yield ratio, obtained from the alpha particle tracks density to proton tracks density ratio in the NTDs, shows an inverse correlation with sample to moderator volume ratio. Comparison of the present results with the previously published results of smaller moderators of the KFUPM PGNAA setup confirms the observation.     

Neutron moderation in a bulk sample and its effects on PGNAA setup geometry

In a prompt gamma ray neutron activation analysis (PGNAA) setup, the neutron moderation in the bulk sample also plays a key role. This can even dominate the thermalization effects of the external moderator in some cases. In order to study the neutron moderation effect in the bulk sample, moderators with two different sizes of the sample were tested at the King Fahd University of Petroleum & Minerals (KFUPM) PGNAA facility. In these tests, the thermal neutron relative intensity and prompt gamma ray yield from the two moderators were measured using nuclear track detectors (NTDs) and NaI detector, respectively. As predicted by Monte Carlo simulations, the measured intensity of thermal neutron inside the large sample cavity due to the external moderator was smaller than that from the smaller sample cavity. Due to its larger size, additional thermalization of neutrons will take place in the larger sample. In spite of smaller thermal neutron yield from the external moderator at the large sample location, higher yield of the prompt gamma ray was observed as compared to that from the smaller sample. This confirms the significance of neutron moderation effects in the bulk sample and can thereby affect the PGNAA geometry size. This allows larger samples in conjunction with smaller moderators in the PGNAA setup.     

Optimization and Comparing a Different Various of Head Part of a Moderator of “Central” Direction for IBR-2 Reactor

The performance of the upstream moderator for neutron beams 1, 4, 5, 6, and 9 extracted from the IBR-2 reactor is simulated towards selecting its optimum configuration. For different moderator options, gain factors with respect to the existing comb-shaped water moderator are computed. Taking into account the technological issues in manufacturing a combined moderator, the scheme with optimal physical characteristics is selected.     

Instrumental design and expected performance of coupled-moderator near-backscattering spectrometer at J-PARC

A near-backscattering (n-BS) crystal-analyzer neutron inelastic spectrometer, DIANA, has been proposed for construction at Japan Proton Accelerator Research Complex. It has originally been designed to view a decoupled non-poisoned moderator in order to obtain high intensity and good energy resolution. Recently, we have reconsidered the instrumental parameters including the type of moderator, by performing Monte-Carlo simulations in order to obtain better performance. Among four virtual n-BS spectrometers on different beam sources moderators, a coupled-moderator-source spectrometer has shown the best performance, i.e. compared to the original DIADA design between ninefold and fivefold enhanced intensities have been obtained with 21%-better to 35%-worse energy resolutions.     

Monte Carlo calculations and experimental calibrations of Bonner sphere systems with a new cylindrical helium-3 proportional counter

The response functions to mono-energetic neutrons from thermal energy to 20 MeV of eight polyethylene moderating spheres with a cylindrical proportional counter were calculated with the MCNP-4B code for each moderator and confirmed by measurements in wide neutron fields (ISO), as Am–Be and ²⁵²Cf, and with the CANEL and SIGMA IPSN Cadarache (France) facilities, which simulate realistic field and thermal neutron response. With the described spectrometry system, we have carried out neutron measurements at different points from the annular zone inside the containment building of the Vandellòs II Nuclear Power Plant (Tarragona, Spain). The aim of this work is to present the results obtained during the sphere spectrometer development, with reference to the experimental and theoretical aspects and to show that our calculated spectra correspond to points of measurement compared with those obtained using the MORELPA code.     

Spectrum of vibrational frequencies of crystalline tungsten at temperatures of 293 and 2400 K

The slow neutron inelastic scattering spectra for a refractory (T _melt = 3680 K) Group VI transition metal of the Periodic Table, namely, tungsten, were measured for the first time in the range from room temperature to 2400 K. Measurements of the neutron scattering spectra of tungsten were performed on a DIN-2PI time-of-flight spectrometer installed at the IBR-2 reactor (Dubna, Russia). The sample was heated in a TS3000 K high-temperature thermostat. The spectrum of vibrational frequencies of the crystal lattice of tungsten at temperatures of 293 and 2400 K was determined from the measured neutron scattering spectra by the iterative method. A softening of the frequency spectrum of tungsten was observed with increasing temperature. This was explained by the increasing role of vibrational anharmonicity effects at high temperatures. The experimental results were compared with model calculations of the frequency spectrum of tungsten.     

Application of a cryogenic moderator in the REMUR neutron reflectometer

Examples of the application of a cryogenic moderator in the REMUR time-of-flight neutron reflectometer of the IBR-2 pulsed reactor (Dubna) are given. The results of two experiments are presented: spatial beam splitting upon reflection from a magnetically noncollinear film and the recording of a microbeam formed by a layered waveguide. A conclusion concerning the efficiency of the cryogenic moderator for experiments of this type is made.     

Small-angle neutron scattering study on the cold rolled steel sheets

The effect of cold rolling on the small-angle neutron scattering (SANS) pattern was investigated for low-carbon steels. Several cold rolled steel samples with different reduction ratios and annealed samples after cold rolling were respectively measured by SANS. The cold rolled samples presented anisotropic two-dimensional (2D) SANS patterns. From the 2D SANS patterns two kinds of 1D pattern were calculated: one was for the Q⊥RD (rolling direction), the other for the Q//RD. The scatterer sizes calculated from the 1D patterns by using a model fitting increased with the reduction ratio, for the Q⊥RD section only. The annealed sample presented an isotropic SANS pattern. It can be concluded that the dislocations produced during the cold rolling process accumulated around the precipitates and then caused anisotropic 2D SANS patterns.     

Physical design of target station and neutron instruments for China Spallation Neutron Source

The China Spallation Neutron Source(CSNS)is the first accelerator-based multidiscipline user facility to produce pulsed neutrons by tungsten target under collision of a pulsed proton beam with a beam power of 100 kW at a repetition rate of 25 Hz.In this paper,we focus on the physical design of CSNS target station and neutron instruments.Under optimized design,the flat tungsten target and the compact target-moderator-reflector coupling enhance effective cold and thermal neutron output from moderators.Three wing-type moderators supply four different characteristics of neutrons to 19 beamlines primarily for neutron scattering applications.Layout of neutron instruments are conceptually planned for total 20 beamlines,the configuration and specification have been determined for three day-one neutron instruments.All designs are optimized for the Phase I of 100 kW with a upgradable capacity to 500 kW.     

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根据第一壁后聚变中子通量和能谱的空间分布和 ITER 可能输出的聚变功率、聚变中子产额、第一壁(产氚包层)之后的中子通量的蒙塔-卡罗中子输运(MCNP)计算,对氦冷却固体增殖剂中子学和产氚包层模块(NT-TBM-HCSB)的聚变中子诊断提出概念性设计,本设计提出用固定位置微型裂变室探测器和可移动封装薄箔活化分析系统测量中子倍增器之后、固体氚增殖剂中及其后的中子通量;用可移动天然金刚石探测器的紧凑型能谱仪测量中子能谱。     

Time-of-flight neutron spectrometer for micro sample studies under high pressure

Abstract

A new neutron spectrometer for investigations of elastic and inelastic neutron scattering on polycrystal microsamples under high pressure in diamond and sapphire anvils cells is described. The spectrometer is operating at the IBR-2 pulsed reactor at JINR. The time-of-flight method and ring-shaped multicounter detector are used to register the scattered neutrons. Parameters and methodical peculiarities of the device and the examples of experimental studies are given.