The neutron spectra of nuclear facilities as the superposition of physically validated spectra

Neutron energy spectra in the energy range 10⁻¹⁰–18 MeV for 100 neutron fields of nuclear reactors and neutron generators are re-established. A method of forming the a priori spectrum in the form of the superposition of physically validated neutron spectra is used in the calculation. __________ Translated from Izmeritel’naya Tekhnika, No. 6, pp. 60–66, June, 2006.     

中子管充氚排气排风系统设计与使用

根据中子管生产的需要，设计一套充氚排气排风系统，经过长时间的使用效果相当好，提高了中子管生产效率和成品质量。     

A half century of radioisotope neutron sources in China

Near fifty years history of the development of radioisotope neutron sources in China is briefly reviewed. The structure design, preparing technology and production status of routine neutron sources including 210Po-Be source, 210Po mock fission source, 241Am-Be source, 238Pu-Be source, 252Cf spontaneous fission source and other special-shape neutron sources are summarized. In addition, the prospects of development on radioisotope neutron source in China are predicted from the needs of nuclear power construction, oil well-logging, neutron moisture gauges and neutron brachytherapy.     

High-fidelity MCNP modeling of a D-T neutron generator for active interrogation of special nuclear material

Fast and robust methods for interrogation of special nuclear material (SNM) are of interest to many agencies and institutions in the United States. It is well known that passive interrogation methods are typically sufficient for plutonium identification because of a relatively high neutron production rate from ²⁴⁰Pu [1]. On the other hand, identification of shielded uranium requires active methods using neutron or photon sources [2]. Deuterium-deuterium (2.45 MeV) and deuterium-tritium (14.1 MeV) neutron-generator sources have been previously tested and proven to be relatively reliable instruments for active interrogation of nuclear materials [3] and [4]. In addition, the newest generators of this type are small enough for applications requiring portable interrogation systems.Active interrogation techniques using high-energy neutrons are being investigated as a method to detect hidden SNM in shielded containers [4] and [5]. Due to the thickness of some containers, penetrating radiation such as high-energy neutrons can provide a potential means of probing shielded SNM. In an effort to develop the capability to assess the signal seen from various forms of shielded nuclear materials, the University of Michigan Neutron Science Laboratory’s D-T neutron generator and its shielding were accurately modeled in MCNP. The generator, while operating at nominal power, produces approximately 1×10¹⁰ neutrons/s, a source intensity which requires a large amount of shielding to minimize the dose rates around the generator. For this reason, the existing shielding completely encompasses the generator and does not include beam ports. Therefore, several MCNP simulations were performed to estimate the yield of uncollided 14.1-MeV neutrons from the generator for active interrogation experiments. Beam port diameters of 5, 10, 15, 20, and 25 cm were modeled to assess the resulting neutron fluxes. The neutron flux outside the beam ports was estimated to be approximately 2×10⁴ n/cm² s.     

Fast neutron beams--prospects for the coming decade

The present status of neutron beam production techniques above 20 MeV is discussed. Presently, two main methods are used; white beams and quasi-monoenergetic beams. The performances of these two techniques are discussed, as well as the use of such facilities for measurements of nuclear data for fundamental and applied research. Recently, two novel ideas on how to produce extremely intense neutron beams in the 100-500 MeV range have been proposed. Decay in flight of beta delayed neutron-emitting nuclei could provide beam intensities five orders of magnitudes larger than present facilities. A typical neutron energy spectrum would be essentially monoenergetic, i.e., the energy spread is about 1 MeV with essentially no low-energy tail. A second option would be to produce beams of (6)He and dissociate the (6)He nuclei into alpha particles and neutrons. The basic features of these concepts are outlined, and the potential for improved nuclear data research is discussed.     

Neutron and γ-radiation field characteristics for 14 MeV neutron generators used with a stilbene-crystal spectrometer

Neutron and γ-ray field characteristics have been examined for two 14 MeV neutron generators by the use of spheres and special cylindrical systems composed of various materials. Measurements have been made on the energy resolution of the spectrometer fitted with a stilbene scintillation crystal in relation to monoenergetic 14 MeV neutrons and the broadening of the monoenergetic neutron spectrum due to interaction with a target material block. __________ Translated from Izmeritel’naya Tekhnika, No. 5, pp. 53–57, May, 2008.     

High-sensitivity activation neutron detector

We demonstrate that neutron fluences of nearly 1000 cm^−2 can be measured when the fonctions of an activation detector and a device for recording induced activity are combined in one object i.e., a NaI(Tl) scintillation crystal. The beta radiation of the product from the¹²⁷I(n, γ)¹²⁸ reaction is detected with close to 100% efficiency by the crystal. The detector can be used in work with low-intensity sources of neutron fields such as neutron generators, radiosotope sources, and TOKAMAK devices.Translated from Izmeritel'naya Tekhnika, No. 2, p. 56, February, 1995.     

Spectrometer equipment for neutron spectra measurements in mixed neutron/photon fields

The paper describes spectrometer equipment in the IPPE experimental laboratory for neutron spectra measurement in mixed (n,γ) fields. The laboratory was founded in 1957 and it occupies a leading position in the field of nuclear facilities radiation spectrometry and benchmark experiments in Russia. Spectrometer equipment includes spectrometers based on the organic stilbene scintillator, hydrogen counter and Bonner balls. Basic fields of spectrometer application are mixed radiation neutron spectra measurement of radionuclide sources, of nuclear reactors and accelerators; study of neutron transfer through the material, including benchmark experiments and measurement of neutron spectra in the rooms of nuclear facilities.     

探测快中子的新技术(一)

概述了近年探则快中子的新技术，它们分别是：抑制γ射线、热中子和带电粒子的符合谱仪；高分辨、宽能量范围（0．1～15．0MeV）带正比计数器的3He夹心谱仪；含氢的纤维闪烁作用于抑制γ射线、中子位置分布和中子能谱测量，及合锂的纤维玻璃闪烁体用于长中子计数器测平均中子能量；中子的直接探测；用于中高能和重离子核物理的多元件阵列快中子探测器和极化仪；用于核核查的中子源影像探测器；高入射氚核能量和高能中子的伴随粒子技术等七个方面。它们对中子计量学的发展是重要的。     

乏燃料运输和储存容器中子屏蔽材料应用及研究现状

目的 了解国内外乏燃料运输和储存容器中子屏蔽材料的类型,整理分析现有中子屏蔽材料的性能和特点,为应用于乏燃料运输和储存容器的中子屏蔽材料的研发提供一定参考。方法 综述国内外应用于乏燃料运输和储存容器中子屏蔽材料的应用现状,对关键性能进行总结和比较,并提出其研究重点和发展趋势。结果 目前,硼化不锈钢、碳化硼/铝复合材料、硼铝合金、聚合物基复合材料和屏蔽混凝土等中子屏蔽材料已应用于乏燃料运输和储存容器。结论 随着核电厂高燃耗的发展趋势,未来乏燃料运输和储存容器对中子屏蔽材料的性能提出了更严格的要求,建议注重研发屏蔽性能优异、装配更换方便、耐辐照的中子屏蔽材料。     

T Violation in the weak scalar and tensor interaction: neutron and nuclei

The motivation and status of a search for time-reversal violation in nuclear and neutron beta decay are discussed. A new experiment for free neutron decay is proposed. A hitherto unmeasured amplitude, R, of the directional correlation J·( p×σ), between the neutron spin J, the electron momentum p and the electron spin σ, will be determined. An accuracy well below 0.01 can be achieved using an intense cold neutron beam and an electron tracking detector, where the spin sensitivity is provided by large angle Mott scattering. This study provides an unique access to the exotic scalar S and tensor T interaction. Finite values, or tight constraints on the time-reversal violating scalar components, can be deduced in a combined analysis of the proposed experiment and a precise determination of the tensor couplings from a recent study of ⁸Li decay. The great interest in weak scalar interaction is stimulated by a multitude of scalar bosons which are introduced in most extensions of the Standard Model.     

Controlled neutron field system at NIIAR reactors

The metrological support system for neutron measurements at nuclear reactors has been developed on the concept of controlled neutron fields applicable to organizations having a group of reactors. A metrological classification is proposed for the fields and the relation between them and also for approaches to certification. This controlled-field system has been set up at the NIIAR reactors for use in nuclear materials research. Data are given on neutron fields at five reactors.Translated from Izmeritel'naya Tekhnika, No. 8, pp. 62–63, August, 1995.     

Characteristics of polyethylene-moderated 252Cf neutron sources

Polyethylene-moderated ²⁵²Cf neutron sources were designed to produce neutron reference fields’ spectra that simulate the spectra observed in the workplaces within nuclear reactors and accelerators. The paper describes the neutron sources and fields. Neutron spectra were calculated by the Monte Carlo method and compared with experimental data.     

Superconducting MgB2 Thin Film Detector for Neutrons

The superconducting neutron detector using high-quality ¹⁰B-enriched MgB₂ thin films at higher operating temperatures has been proposed, where a resistance change induced by the nuclear reaction of neutron and ¹⁰B in MgB₂ is used to detect a neutron. Cold neutrons from a nuclear research reactor irradiated the MgB₂ detector, and the output voltage was clearly observed through a low-noise amplifier by using a digital oscilloscope. The out-of-equilibrium thermodynamics was investigated by means of the time-dependent Ginzburg-Landau equations by using the Earth Simulator.      

Neutron diffraction studies of nuclear magnetic ordering in copper

We have constructed a two-stage nuclear demagnetization cryostat for neutron diffraction studies of nuclear magnetism in copper. The cryostat is combined with a two-axis neutron spectrometer which can use both polarized and unpolarized neutrons. By demagnetizing highly polarized copper nuclear spins, the nuclei could be cooled below the ordering temperatureT _N60 nK, while keeping the lattice at a considerably higher temperature between 50 and 100 µK. The neutron beam increases the lattice temperature in the sample by a factor of two or more, thereby considerably shortening the time for measurements in the ordered state; both our calculations and the experiments yield 1 nW beam heating. Polarized neutron experiments show that the scattered intensities from the strong fcc reflections are severely reduced by extinction. This makes the sample not very suitable for further studies with polarized neutrons. By observing the (100) Bragg reflection, we have unambiguously proven antiferromagnetic ordering of the copper nuclear spins. Using a linear, position-sensitive detector, the time evolution of this peak was followed during the warm-up of the nuclear spin system. The peak intensity was found to depend strongly on the external magnetic field between zero and the critical fieldB _c=0.25 mT, indicating the existence of at least two antiferromagnetic phases. The results are compared to previous measurements of the magnetic susceptibility. Theoretical calculations do not provide a full explanation for our experimental data.     

New Neutron Shielding in the Edelweiss-III Experiment

In dark matter WIMP searches the fundamental background is due to neutron flux. Thus shielding plays a crucial role in attenuating this flux and consequently in suppressing nuclear recoil background events. The transition from EDELWEISS-II to EDELWEISS-III with a total fiducial mass of 24 kg and improved background rejection has required the modification of the neutron shielding. In this paper we describe the design of this new neutron shielding and give an estimate of the expected neutron rate in comparison with the EDELWEISS-II experiment.     

Parity-Violating Neutron Spin Rotation in a Liquid Parahydrogen Target

Our understanding of hadronic parity violation is far from clear despite nearly 50 years of theoretical and experimental progress. Measurements of low-energy parity-violating observables in nuclear systems are the only accessible means to study the flavor-conserving weak hadronic interaction. To reduce the uncertainties from nuclear effects, experiments in the few and two-body system are essential. The parity-violating rotation of the transverse neutron polarization vector about the momentum axis as the neutrons traverse a target material has been measured in heavy nuclei and few nucleon systems using reactor cold neutron sources. We describe here an experiment to measure the neutron spin-rotation in a parahydrogen target (n-p system) using pulsed cold-neutrons from the fundamental symmetries beam line at the Spallation Neutron Source under construction at the Oak Ridge National Laboratory.     

The energy spectrum of cosmic-ray induced neutrons measured on an airplane over a wide range of altitude and latitude

Crews of high-altitude aircraft are exposed to radiation from galactic cosmic rays (GCRs). To help determine such exposures, the Atmospheric Ionizing Radiation Project, an international collaboration of 15 laboratories, made simultaneous radiation measurements with 14 instruments on a NASA ER-2 high-altitude airplane. The primary instrument was a sensitive extended-energy multisphere neutron spectrometer. Its detector responses were calculated for energies up to 100 GeV using the radiation transport code MCNPX 2.5.d with improved nuclear models and including the effects of the airplane structure. New calculations of GCR-induced particle spectra in the atmosphere were used to correct for spectrometer counts produced by protons, pions and light nuclear ions. Neutron spectra were unfolded from the corrected measured count rates using the deconvolution code MAXED 3.1. The results for the measured cosmic-ray neutron spectrum (thermal to >10 GeV), total neutron fluence rate, and neutron dose equivalent and effective dose rates, and their dependence on altitude and geomagnetic cut-off agree well with results from recent calculations of GCR-induced neutron spectra.