A multichannel spectrometer for detecting γ rays in a wide range of time intervals during pulse neutron irradiation

A versatile spectrometer has been developed for measuring the nuclear radiation spectrum in discrete time intervals. The design and operating principle of the spectrometer are described. Since the main logical part is based on a field programmable gate array, time intervals may be tuned in a wide range without changing the spectrometer hardware. The test experiments have demonstrated the spectrometer applicability for measuring the amplitude and timing parameters of the γ response when an analyzed sample is irradiated with a pulsed neutron flux. This device can be used to solve many problems of nondestructive testing, e.g., spectrometric neutron logging, detection of explosives, identification and characterization of fissile materials.     

decrease in the dead time of proportional counters of neutrons after exposure to pulsed fluxes of ionizing radiation

During irradiation of a proportional counter with a high-power bremsstrahlung flux, a high density of charged particles arises in the interelectrode gap owing to primary and secondary ionization. Charge separation in the interelectrode gap induces an internal electric field that leads to a decrease in the gas-amplification factor to a level below the neutron-recording threshold. The delay time of neutron recording (dead time) by the counter after a bremsstrahlung burst may exceed 100 µs. A device developed for switching a high voltage applied to the counter for the bremsstrahlung emission time is described, as are experiments on detection of prompt fission neutrons emitted after irradiation of the fissile substance with a pulsed bremsstrahlung flux. The results show that, when this device is used, the neutron-recording delay time decreases severalfold.     

Irradiation tests of ITER candidate Hall sensors using two types of neutron spectra

We report on irradiation tests of InSb based Hall sensors at two irradiation facilities with two distinct types of neutron spectra. One was a fission reactor neutron spectrum with a significant presence of thermal neutrons, while another one was purely fast neutron field. Total neutron fluence of the order of 10(16)?cm(-2) was accumulated in both cases, leading to significant drop of Hall sensor sensitivity in case of fission reactor spectrum, while stable performance was observed at purely fast neutron spectrum. This finding suggests that performance of this particular type of Hall sensors is governed dominantly by transmutation. Additionally, it further stresses the need to test ITER candidate Hall sensors under neutron flux with ITER relevant spectrum.     

Characteristics of the neutron field at the core center in the ИBB-2M water-moderated water-cooled reactor

The neutron spectrum has been measured at the center of the core in the ИBB-2M research water-moderated water-cooled reactor. A technique has been developed to measure the energy spectrum of neutrons in high-intensity fields (with a flux density of >10¹² cm^?2 s^?1) without recourse to fission detectors enclosed in boron shields.     

A thermal neutron detector based on single-crystalline silicon

It is shown that a change in the specific electrical conductivity (SEC) in silicon single crystals after irradiation and radiation defect annealing is directly proportional to the thermal neutron fluence. This fact is used as a basis of a method for measuring the neutron flux. In this case, the proportionality factor is dependent on the neutron spectrum, being independent of the initial SEC, which significantly simplifies detector calibration. In measurements of the thermal neutron fluence in terms of relative and absolute units, the rms was 4 and 8%, respectively.     

中子斩盘斩束效果的模拟计算

转盘式中子斩波器广泛地应用于飞行时间模式中子散射谱仪上,斩盘斩出的脉冲柬流特性直接影响着谱仪性能。为更好地进行转盘式中子斩波器的设计,采用Mcstas程序软件,分别对单盘和双盘的中子斩波特性进行了模拟计算。获得了相关物理参数对脉冲注量率和发散度的影响关系曲线。通过理论计算可以了解相关物理参数对斩波特性的影响,计算结果可为斩波器的理论设计以及相关物理参数的优化选择提供理论参考。     

Neutron Spectrum Measurements in the Vertical Channel of the IR-8 Research Reactor

Experimental results of neutron spectrum and neutron flux measurements in a dry vertical channel of the IR-8 research nuclear reactor at the Kurchatov Institute Russian Research Center are presented. The data were obtained using five sets of various activation detectors. The spectrum was reconstructed using the KASKAD computational program used in the method of integral neutron detectors. The results obtained make it possible to optimally plan the experiments on the irradiation and study of the radiation stability of various elements of the diagnostic systems of the International Thermonuclear Experimental Reactor (ITER) in the new irradiation channel of the IR-8 research reactor.     

Development of a thermal neutron detector based on scintillating fibers and silicon photomultipliers

We propose a technique for thermal neutron detection, based on a (6)Li converter placed in front of scintillating fibers readout by means of silicon photomultipliers. Such a technique allows building cheap and compact detectors and dosimeters, thus possibly opening new perspectives in terms of granular monitoring of neutron fluxes as well as space-resolved neutron detection.     

A study of structure inhomogeneities using a neutron double-crystal spectrometer according to the Warren technique: A review

A technique for examining inhomogeneities of materials on a neutron beam using a double-crystal spectrometer is described. The parameters of inhomogeneities are determined from the measured integrated attenuation due to small-angle scattering (the Warren technique for X rays). The theoretical basis for adaptation of this technique to neutron flux measurements is presented, and the scope of its applicability is outlined. Results from examining different materials using this technique are described. Proposals for developing a stationary express method for serial small-angle measurements are formulated.     

A method of measuring the neutron energy spectrum by activation detectors

This work is a preliminary step toward the study of physical properties of the ADS systems, in which a deeply subcritical active core is irradiated by a pulsed beam of relativistic deuterons.This work analyzes a general direct method of calculating a neutron energy spectrum using efficiency of reactions of activation detectors. Our interest was focused on the study of the influence of input experimental errors and uncertainty of cross sections on output errors. The experimental data are taken from the KWINTA experiment in JINR, Dubna. The obtained results of the neutron flux spectrum in range 0.7–200 MeV are compared with calculation results from the MCNPX code.     

Studying the spectrum of neutrons emitted from the LSDS-100 using a multiwire proportional fission chamber

A fast multiwire proportional fission chamber capable of detecting ∼10⁶ fission fragments per second was produced. Heptane vapor at a pressure of 15 mbar was used as a working gas. The full width at the base of the pulse from a fission fragment was ≤0.2 μs. The spectrum of the neutron flux density on the spectrometer surface was measured by the neutron slowing-down time in the lead of the LSDS-100 at neutron energies ranging from 18 eV to 11.3 keV.     

The Feasibility of Neutron Moderation Imaging for Land Mine Detection

Neutron moderation land mine detection involves irradiating the ground with fast neutrons and subsequently detecting the thermalized neutrons which return. This technique has been studied since the 1950s, but only using non-imaging detectors. Without imaging, natural variations in moisture content, surface irregularities, and sensor height variations produce sufficient false alarms to render the method impractical in all but the driest conditions. This paper describes research to design and build a prototype land mine detector based on neutron moderation imaging. After reviewing various neutron detector technologies, a design concept was developed. It consists of a novel thermal neutron imaging system, a unique neutron source to uniformly irradiate the underlying ground, and hardware and software for image generation and enhancement. A proof-of-principle imager has been built, but with a point source offset from the detector to roughly approximate a very weak uniform source at the detector plane. Imagery from the detector of mine surrogates is presented. Realistic Monte Carlo simulations were performed using the same two dimensional neutron imaging geometry as the detector in order to assess its performance. The target-to-background contrast was calculated for various soil types and moisture contents, explosive types and sizes, burial depths, detector standoffs, and ground height variations. The simulations showed that the neutron moderation imager is feasible as a land mine detector in a slow scanning or confirmation role and that image quality should be sufficient to significantly improve detector performance and reduce false alarm rates compared to non-imaging albedo detection, particularly in moist soils, where surface irregularities exist and when the sensor height is uncertain. Performance capability, including spatial resolution and detection times, was estimated.     

钢轨漏磁检测仿真分析及试验研究

为保障高速铁路的行车安全,针对现有高速铁路钢轨轨面伤损检测的需求,设计了一种携带有漏磁检测装置的钢轨探伤小车,并分析了钢轨探伤小车的结构组成和漏磁检测装置的检测原理。同时,在有限元分析软件 ＡＮＳＹＳ中建立了钢轨轨面漏磁检测的三维有限元模型,针对钢轨轨面主要的裂纹类和圆柱形缺陷,在软件中进行了钢轨缺陷的漏磁场特征仿真分析。通过计算分析,得出钢轨缺陷漏磁检测信号与传感器提离值、裂纹类缺陷长度、裂纹类缺陷深度、圆柱形缺陷直径、圆柱形缺陷深度的对应变化关系。最后,通过制备人工裂纹类和圆柱形钢轨缺陷,搭建起钢轨漏磁检测的试验平台,通过漏磁检测试验,验证了软件仿真结果的正确性。     

Online learning control for hybrid electric vehicle

Improvements in hybrid electric vehicle (HEV) fuel economy and emissions heavily depend on an efficient energy management strategy (EMS).However,the uncertainty of future driving conditions generally cannot be easily tackled in EMS design.Most existing EMSs act upon fixed parameters and cannot adapt to varying driving conditions.Therefore,they usually fail to fully explore the potential of these advanced vehicles.In this paper,a novel EMS design procedure based on neural dynamic programming (NDP) is proposed.The NDP is a generic online learning algorithm,which combines stochastic dynamic programming (SDP) and the temporal difference (TD) method.Instead of computing the utility function and optimal control actions through Bellman equations,the NDP algorithm uses two neural networks to approximate them.The weights of these neural networks are updated online by the TD method.It avoids the high computational cost that SDP suffers from and is suitable for real-time implementation.The main advantages of NDP EMS is that it does not rely on prior information related to future driving conditions,and can self-tune with a wide variance in operating conditions.The NDP EMS has been applied to "Qianghua-I",a prototype of a parallel HEV,using a revolving drum test bench for verification.Experiment results illustrate the potential of the proposed EMS in terms of fuel economy and in keeping state of charge (SOC) deviations at a low level.The proposed research ensures the optimality of NDP EMS,as well as real-time applicability.     

Measuring the neutron spectrum of the accelerator-based source using the time-of-flight method

The time-of-flight technique with a new method for generating short radiation bursts has been used to measure the neutron spectrum of the accelerator-based source with a stationary proton beam. Specific problems arising thereby and methods for solving them are described. The measured spectrum of neutrons in the reaction ⁷Li(p, n)⁷Be at a proton energy of 1.915 MeV is presented and compared to the calculation. This spectrum is shown to comply with the requirements for the neutron beam used in neutron capture therapy.     

First results of use of a scintillating-fiber position-sensitive detector for recording the target image in a 14-MeV neuron beam at the ISKRA-5 facility

The design of the scintillating-fiber detector is described, and the first results obtained in recording the target image in a 14-MeV neutron beam at the ISKRA-5 facility are presented. The scintillating-fiber position-sensitive detector has been designed for diagnosing laser fusion processes by recording the spatial distribution of thermonuclear neutrons escaping from the target. Position-sensitive detection is effected by conversion of neutron radiation into light in a scintillating fiber array. Discrimination of neutrons from γ rays by their time of flight and image intensification are performed with the aid of a frame camera. Images are recorded by a CCD camera. A technique for recording penumbra images is used for imaging at low neutron yields (3 × 10⁸−10¹¹).     

Neutron diagnostics for pulsed high-density thermonuclear plasmas

Time-resolved measurements of the neutron flux from the Scylla IV-P linear theta-pinch experiment have been made with scintillator-photomultiplier combinations. Calibration of the detectors is accomplished by a comparison of their time-integrated output with the total neutron yield measured using a foil-activation technique for which an accurate calibration has been established. The temperature of the Maxwellian ion velocity distribution that would produce the observed flux is obtained from the Maxwellian reactivity < sigmav >(DD) for D (d,n)He3 and measurements of the temporal evolution of the plasma column density and dimensions. This determination of the time history of the ion temperature is in good agreement with the plasma energy measured using other techniques.     

A Gaseous Radiochemical Neutron Monitor

Real-time neutron detection (monitoring) is based on the ability of atoms of inert radioactive gases generated by nuclear reactions to easily escape from the crystalline lattice of certain solid substances. An inert radioactive gas produced in a detector ampule is transferred by a carrier gas to a proportional gas-flow counter. The decay rate of the inert gas, which is uniquely related to the neutron-flux density in the ampule, is measured with this flow counter. This method is applied to monitor the neutron flux in the RADEX pulse neutron target driven by the linear proton accelerator of the Moscow Meson Facility at the Russian Academy of Sciences' Institute for Nuclear Research. By simultaneously using several nuclear reactions with different threshold energies of inert-gas production, it is possible to measure neutron spectra.     

Physical calibration of the LEND space-based neutron telescope: the sensitivity and the angular resolution

Results of physical calibrations of the LEND neutron telescope operating on board the NASA’s LRO lunar satellite since June 2009 are described. The main goal of the LEND telescope is to measure the epithermal neutron flux in polar areas of the lunar surface with a high (~10 km) resolution with the aim of determining the hydrogen distribution in the lunar regolith and detect the presence of water ice beds at the bottom of permanently shadowed lunar polar craters. The neutron detection efficiency and the effective area of the LEND detectors is experimentally estimated.     

基于低频电磁技术的管道缺陷检测方法研究

为了系统地研究基于低频电磁技术的管道缺陷检测方法,建立了其二维有限元模型。借助ANSYS参数化设计语言(APDL),进行了循环仿真计算,研究了不同尺寸缺陷的漏磁场分布;对漏磁场的信号进行微分处理,得到了所隐含的缺陷信息,并进行了实验验证。研究结果表明,该方法在锅炉水冷壁等管道缺陷的无损检测中有较强的实用性。