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.     

A Monte Carlo simulation and setup optimization of output ef f iciency to PGNAA thermal neutron using ~(252)Cf neutrons

We present the design and optimization of a prompt γ-ray neutron activation analysis(PGNAA) thermal neutron output setup based on Monte Carlo simulations using MCNP5 computer code. In these simulations, the moderator materials, reflective materials, and structure of the PGNAA252 Cf neutrons of thermal neutron output setup are optimized. The simulation results reveal that the thin layer paraffin and the thick layer of heavy water moderating effect work best for the252 Cf neutron spectrum. Our new design shows a significantly improved performance of the thermal neutron flux and flux rate, that are increased by 3.02 times and 3.27 times, respectively,compared with the conventional neutron source design.     

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.     

Improved slow-positron yield using a single crystal tungsten moderator

A well-annealed W(110) single crystal was used as a fast-to-slow positron moderator. The measured moderator efficiency at room temperature using a⁵⁸Co positron source in the backscattering geometry is =(3.2±0.4)×10^–3, roughly a factor of three better than for the best previously reported Cu(111)+S moderator. We find a stable positron moderation efficiency over a period of several weeks when maintained at pressures around 10^–9 Torr and an energy spreadE = 0.7 eV of the emitted slow positrons. An initial attempt was made to fabricate a hybrid Cu on W(110) moderator, which yielded of about 1.2×10^–3 after annealing.     

Experimental neutron flux measurements with a diamond detector at the QUINTA setup

The operational capability of a diamond detector used to measure the neutron spectrum by the response function on the QUINTA setup [1] installed at the proton beam of the phasotron [2] (Laboratory of Nuclear Problems, Joint Institute for Nuclear Research) was demonstrated in the energy interval of 2.1–20 MeV. The neutron-flux count rate was measured. The energy of neutrons was estimated at 7.4–25.7 MeV based on the diamond-detector response spectrum. The dependence of the diamond-detector response spectra on the angle between the proton beam and the line going through the detector and the center of the QUINTA setup was investigated. The angular anisotropy of the neutron flux was demonstrated. Measurements at different distances from the detector to the QUINTA setup were performed.     

Analysis of experimental data on the neutron yield from muons

Experimental data accumulated over 60 years of studying the yield of cosmogenic neutrons in a liquid scintillator (Y _LS), iron (Y _Fe), and lead (Y _Pb) were analyzed. This analysis revealed that the main part of the results on the yield Y _LS were overestimated by about 30%. With allowance for this circumstance, all experimental data can be described by the dependence Y(ē _µ, A) = b _n A ^β ē _µ ^α , where the product b _n ē _µ ^α stands for the energy spent by a muon on neutron production. The exponents of α = 0.78 and β = 0.95 are determined by the properties of the medium and by neutron production in showers.     

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.     

Monte-Carlo calculations for neutron yield from photonuclear reactions following bremsstrahlung in tungsten target

The photonuclear reactions of (γ, xn) or (γ, xnp) types can be used to produce high-intensity neutron sources for research and applied purposes. In this work a Monte-Carlo calculation has been used to evaluate the production yields of neutrons from the (γ, n) and (γ, 2n) reactions following the bremsstrahlung produced by 100 and 200 MeV electron beams on the tungsten target. Our calculations indicated that the neutron yield is an increasing function of the target thickness in a considered range from 1.5 to 2.5 mm.     

SILEX-I装置上激光-团簇聚变实验中子产额测量

超短超强脉冲激光与CD4团簇相互作用可以产生高能量的氘离子,从而产生DD聚变中子,这种团簇聚变中子源有着非常广阔的应用前景。在SILEX-I 100 TW飞秒激光装置上,超短超强脉冲激光与CD4团簇相互作用实现了DD核聚变。团簇聚变的中子产额是实验中最为重要的物理量,在实验中采用高灵敏的中子探测器对团簇聚变产生的中子进行了测量,在现有实验条件下测得中子产额为103。     

SILEX-I装置上激光-团簇聚变实验中子产额测量

 超短超强脉冲激光与CD4团簇相互作用可以产生高能量的氘离子,从而产生DD聚变中子,这种团簇聚变中子源有着非常广阔的应用前景。在SILEX-I 100 TW飞秒激光装置上,超短超强脉冲激光与CD₄团簇相互作用实现了DD核聚变。团簇聚变的中子产额是实验中最为重要的物理量,在实验中采用高灵敏的中子探测器对团簇聚变产生的中子进行了测量,在现有实验条件下测得中子产额为10³。     

A method for calibrating the confocal volume of a confocal three-dimensional micro-x-ray fluorescence setup

The measurement of the confocal volume of a confocal three-dimensional micro-x-ray fluorescence(3 D-XRF) setup is a key step in the field of confocal 3 D-XRF analysis.With the development of x-ray facilities and optical devices,3 D-XRF analysis with a micro confocal volume will create a great potential for 2 D and 3 D microstructural analysis and accurate quantitative analysis.However,the classic measurement method of scanning metal foils of a certain thickness leads to inaccuracy.A method for calibrating the confocal volume is proposed in this paper.The new method is based on the basic content of the textbook,and the theoretical results and the feasibility are given in detail for the 3 D-XRF mono-chromatic x-ray condition and the poly-chromatic x-ray condition.We obtain a set of experimental confirmation using the polychromatic x-ray tube in the laboratory.It is proved that the sensitivity factor of the 3 D-XRF can be directly and accurately obtained in a real calibration process.     

Project of the ultracold and cold neutron source at the WWR-M reactor with superfluid helium as a moderator

The WWR-M reactor of the Petersburg Nuclear Physics Institute provides a unique opportunity for creating conditions of low radiative heat release (～4 × 10^?3 W/g) at a sufficiently high neutron flux (～3 × 10¹² neutrons/(cm² s)). This opportunity can be implemented in the reactor thermal column, which represents a 1-m-diameter channel adjacent to the reactor core. This diameter of the channel allows the arrangement of the core gamma shielding made of bismuth (15 cm thick), a graphite premoderator (300 dm³) at a temperature of 20 K, and a converter with superfluid helium (35 dm³) at a temperature of 1.2 K. Calculations show that the heat release in the source (20 W) can be removed by pumping helium vapor, and the density of ultracold neutrons in an experimental trap will be ～10⁴ neutrons/cm³, which is higher than that of existing sources of ultracold neutrons by two to three orders of magnitude.     

On the theory of pneumotransport of beads in cold neutron moderator of the IBR-2 reactor

The paper presents some aspects of pneumotransport theory of solid ball motion along a pipeline of complex geometry having application for the pelletized cold moderator of the IBR-2 reactor. Motion equations for a ball carrying by gas flow along a round tube both smooth and rough, are obtained. Aerodynamics forces and momentum of forces, acting on the ball depending on its velocity are defined on the base of numerical modeling of ball movement, and analytical simplified model of pneumotransport of balls along round tube is created. This model meets the demand for practical application as it shows satisfactory agreement with experimental modelling of ball movement in a glass tube. One of important results of the work is giving proofs of irregular movement of ball along a tube stipulated by roughness of the tube side.     

Radiation hardening in niobium-dependence of the yield stress on neutron dose

Abstract

Niobium samples were neutron-irradiated at reactor ambient temperatures (approximately 50 °C for polycrystals and 90°C for single crystals) to doses from 4 × 10¹⁵ to 8 × 10¹⁸ neutrons/cm² (E> 1 MeV). The density and size distribution of radiation-produced defect clusters, observed by transmission electron microscopy, were measured in polycrystalline niobium over a range of doses from 2 × 10¹⁷ to 4.4 × 10^l8 neutrons/cm². The TEM results were correlated with yield stress measurements as a function of dose. The radiation hardening was analyzed on the basis of a planar dispersed barrier model. It was found that the observed increases in yield stress at low doses were consistent with the measured density and size distribution of the defect clusters, with a cluster strength of (0.5–0.8) Gb² (G, shear modulus; b, Burgers vector). This corresponds to strong barrier hardening. At doses above about 10¹⁸ neutrons/cm², the hardening rate decreased sharply; this apparent saturation is discussed in terms of the coarsening of defect clusters, dislocation channeling, and the effect of interstitial impurities.     

铟活化诊断氘氘中子产额不确定度分析

介绍了铟活化诊断氘氘中子产额的测量原理,分析了中子产额测量不确定度的来源及评定方法。中子产额测量不确定度主要由灵敏度标定不确定度、活化射线净计数不确定度、立体角测量不确定度及测量系统的随机误差等构成。评估了灵敏度标定过程中加速器中子与聚变中子能量差异、大厅散射中子本底等因素对灵敏度标定的影响,并评估了宇宙射线本底对活化射线净计数测量的影响。分析了中子产额处于不同量级时起主要作用的不确定度分量,提出了减小灵敏度标定不确定度的方法。以实验数据为基础,对具体的实验数据进行了分析计算。结果表明：利用伴随粒子法在加速器中子源上标定出铟活化测量系统灵敏度的相对标准不确定度为4.3%。中子产额低于1010时,产额测量不确定度大于7%,活化射线净计数误差是产额测量误差的主要来源;产额大于1010时,测量不确定度好于7%,中子产额测量不确定度主要由灵敏度标定不确定度引起。     

Uncertainties induced by statistical fluctuations in fast monoenergetic neutron yield measurements

A plastic scintillation detector was used to measure the yield of deuterium-deuterium (DD) neutrons or deuterium-tritium (DT) neutrons. Collisions of fast neutrons with hydrogen nucleus in a scintillator generated recoil protons, the energies of which were fully deposited in the scintillator. The statistical fluctuation of the protons' number and that of the protons' total energy were two sources of measurement uncertainty. Based on DT neutrons, this paper represents the algorithms of computing the probability density functions of the two sources. Uncertainties of the measurement induced by statistical fluctuations were finally computed by constructing the probability density functions of the proton number and that of the neutron number.