Spark counting of particle damage tracks in neutron studies

Conclusion As shown by trial experiments, neutron detectors based on fissile nuclides and thin Lavsan foils can be used successfully in combination with a spark counter of tracks in a variety of neutron studies: measurements of the spatial distributions of the spectral characteristics of neutron fields of various kinds; measurements of integral and differential fission cross sections; in personal neutron dosimetry; etc. This method ensures that information from a large number of neutron detectors is obtained rapidly.Translated from Atomnaya Énergiya, Vol. 61, No. 1, pp. 35–40, July, 1986.     

钒自给能探测器中子响应计算方法

钒自给能探测器被广泛用作核动力反应堆的堆内固定式探测器,为堆芯中子注量率分布测量连续不断地提供信息。研究钒自给能探测器的响应电流计算方法,为堆芯在线功率分布监测与探测器设计优化提供理论依据。首先描述钒自给能探测器的响应机理与特性,然后基于Warren提出的理论模型,详细介绍中子响应电流控制方程及电子逃脱概率的计算方法,最后根据公开报道的典型钒探测器规格与实验数据进行数值模拟分析。结果显示,单位长度热中子灵敏度计算值与测量值相对偏差在±5%以内,论证了该方法的有效性与计算精度。     

铑自给能探测器延迟信号数字处理算法与实验研究

铑自给能探测器（RSPND）输出电流信号的慢响应特性严重影响反应堆内中子注量率的实时测量,不利于反应堆的控制和安全管理。采用反函数计算或各种补偿方法改进其响应特性,有利于RSPND的使用。本文研究了前向差分变换法、后向差分变换法、阶跃响应不变法及双线性变换法等4种数字处理算法,有效缩短了铑自给能探测器输出信号的响应时间,时间常数缩短到5 s以内。通过数字实验系统,验证了算法的正确性,为该探测器用于反应堆内中子注量率测量的快速响应提供了可行性。      

Development of a data acquisition and control system for the International Thermonuclear Experimental Reactor neutron flux monitor

To satisfy high-precision, wide-range, and real-time neutron flux measurement requirements by the International Thermonuclear Experimental Reactor(ITER), a data acquisition and control system based on fission chamber detectors and fast controller technology, has been developed for neutron flux monitor in ITER Equatorial Port #7. The signal processing units which are based on a field programmable gate array and the PXI Express platform are designed to realize the neutron flux measurement with 1 ms time resolution and a fast response less than 0.2 ms,together with real-time timestamps provided by a timing board. The application of the widerange algorithm allows the system to measure up to 10~(10) cps with a relative error of less than 5%.Furthermore, the system is managed and controlled by a software based on the Experimental Physics and Industrial Control System, compliant with COntrol, Data Access and Communication architecture.     

超快猝灭塑料闪烁探测器氘氚中子灵敏度标定

本文概要介绍了超快猝灭塑料闪烁探测器特性，并在不同闪烁体、光导和微通道板光电倍增管的组合条件下用１０ｎｓ脉宽的窄脉冲中子管对探测器的Ｄ－Ｔ中子灵敏度进行了标定。由这些标定数据推算出的探测器不同条件下的Ｄ－Ｔ中子灵敏度与实测数据在误差范围内是一致的。     

Optimization of moderator assembly for neutron flux measurement: experimental and theoretical approaches

A moderator of paraffin wax assembly has been demonstrated where its thickness can be optimized to thermalize fast neutrons. The assembly is used for measuring fast neutron flux of a neutron probe at different neutron energies, using BF03(U10and 200) and3He(U0.500)neutron detectors. The paraffin wax thickness was optimized at 6 cm for the neutron probe which contains an Am–Be neutron source. The experimental data are compared with Monte Carlo simulation results using MCNP5 version 1.4. Neutron flux comparison and neutron activation techniques are used for measuring neutron flux of the neutron probe to validate the optimum paraffin moderator thickness in the assembly. The neutron fluxes are measured at(1.17 ± 0.09) 9 105 and(1.19 ± 0.1) 9 105n/s, being in agreement with the simulated values. The moderator assembly can easily be utilized for essential requirements of neutron flux measurements.     

Simulation of the Characteristics of Multilayer Neutron Detectors

Multilayered detectors with several configurations MDN1.01 and MDN1.02 are described. The algorithm of the NEDSUM-2 code, which simulates the interaction of neutron fluxes with multilayered detectors and calculates their characteristics by the Monte Carlo method, is described. The computational results obtained with the NEDSUM-2 and PRIZMA codes agree with one another and with experiments performed at the Moscow Engineering Physics Institute and All-Russia Scientific-Research Institute of Technical Physics for real detectors MDN1.01 and MDN1.02. __________ Translated from Atomnaya Energiya, Vol. 99, No. 2, pp. 141–147, August 2005.     

核动力堆安全壳内外中子能谱和剂量测量

利用自制的多球谱仪测量了某核动力反应堆安全壳内外的中子能谱和剂量当量率。对安全壳外测量，中心探测器为球形^3He正比计数管；对安全壳内测量，中心探测器为球形金箔。系统的响应函数用MCNP程序计算，解谱程序为MIEKEB。为验证系统响应函数计算的准确性，进行了一些实验测量，并与理论计算结果进行了比较。结果表明，测量结果与计算结果在不确定度范围内相吻合。     

Activation Measurement of the Neutron Spectra of the BARS-5, IGRIK, and YAGUAR Reactors

A new approach is proposed and investigated for reconstructing the neutron spectra of reactors from activation measurements: the parameterization of the neutron spectrum is changed and the spectrum is represented in the form of a B spline. A Monte Carlo method is proposed for taking account of the distortions of the neutron spectrum by the measuring design of the detectors. The results of the activation measurements show that the approach developed can be used to reconstruct the neutron spectra of BARS-5, IGRIK, and YAGUAR reactors. __________ Translated from Atomnaya Energiya,Vol. 99, No. 3, pp. 177–184, September, 2005.     

Development of an high resolution neutron spectroscopy system using a diamond detector and a remote digital acquisition methodology

The need of performing high resolution fast neutron spectroscopy in a very harsh environment like that of the Radial Neutron Camera (RNC) of ITER, requires to develop new detectors and methodologies. Diamond detectors have been proved to be excellent candidates but the electronics needs a substantial improvement. Because of the high radiation level and the temperatures expected near the detector positions in the RNC, the electronics must be placed several meters away. A novel Fast Charge Amplifier (FCA) was developed that, connected to a diamond detector using several tens of meters of low capacitance coaxial cable, is able to produce fast output signals suitable to be processed by digital electronics. These fast output signals allow to operate at high count rates avoiding pile-up problems. This novel amplifier connected to a digitizer is here tested in the neutron energy range from 5 to 20.5 MeV using the mono-energetic neutrons produced by the Van de Graaff (VdG) accelerator of the EC-JRC-IRMM and by the PTB cyclotron. From the measurements the experimental response functions of the diamond detector at different neutron energies were obtained. The shape of the response functions have been compared with that predicted with a routine which was implemented for the Monte Carlo code MCNPX with the scope to validate the calculations versus the experimental data. The goal is to develop a tool which allows to calculate the diamond detector response functions also in term of absolute efficiency. This methodology along with the ability to measure at high reaction rates and the insensitivity to radiation damage launches the system described in this paper as a promising method for neutron spectrometry in the RNC of ITER.     

Experimental analysis for neutron multiplication by using reaction rate distribution in accelerator-driven system

Basic experiments are carried out in the Kyoto University Critical Assembly (KUCA) to study the nuclear characteristics of the accelerator-driven systems (ADS) and to establish a new neutron source for research. A method for measuring the neutron multiplication in the subcritical system is proposed by utilizing the reaction rate distribution obtained by the optical fiber detector. A comparison between the measured and calculated neutron multiplication shows agreement within a relative difference of 5% in most cases, through introducing certain correction factors.     

启明星1#次临界装置内不同位置探测器的中子计数率变化

在启明星1#次临界装置上进行了次临界外推实验,外中子源分别采用Am-Be中子源和252Cf中子源,放置在启明星1#次临界装置中心,中子探测器放置在次临界装置内不同位置,研究相对中子计数率的变化。实验测量结果表明:在启明星1#次临界装置不同位置的探测器测量得到的中子计数率变化不同,但对外推结果影响不大。     

Determination of the Neutron Energy Spectrum in a Fast-Reactor Core

A method is presented for measuring the energy spectra of neutrons in a fast reactor core using activational and fissioning detectors. The method is tested in an investigation of the characteristics of the neutron fields of nuclear reactors.     

Neutron-induced radiation damage in silicon detectors

Ion-implanted silicon pad detectors fabricated on different n-type and p-type silicon wafers with initial resistivities between 2.6 and 12.9 kΩcm were irradiated with neutrons of ~1 MeV energy, up to a fluence of 5×10¹³ n cm^-2. The evolution of diode leakage current and capacitance characteristics is presented as a function of the neutron fluence. The reverse diode current increases proportionally to the neutron fluence. There is evidence that the doping of the initial n-type material evolves towards intrinsic and inverts to an apparent p-type at fluences between 1×10¹³ and 3×10¹³ n cm^-2, depending on the initial silicon resistivity. There is also evidence that p-type material remains of the same conduction type with a slight increase of the acceptor doping with fluence. The signal shape and the charge collection efficiency for incident β particles were measured     

The use of resonance detectors for the investigation of neutron spectra in fast-neutron reactors

The possibility of the investigation of the low energy portion of the neutron spectra in reflecting fast reactors by activated resonance detectors is considered.Absorber difference and 1/v absorption methods are illustrated by an example of the measurement of the flux distribution of resonance neutrons with energies of 4.9 ev (Au¹⁹⁷) and 2.95 kev (Na²³) in the reflecting reactors BR-1 and BR-5. It is shown that the neutron spectrum region from one to several thousand electron volts can be studied in adequate detail with the aid of the set of detectors described.The authors express deep thanks to A. I. Leipunskii for interest in the work and to I. I. Bondarenko and V. V. Orlov for helpful advice and comments.     

Investigation of the two-phase flow in a boiling water reactor using neutron-noise technique

In this paper, the fluctuations of the neutron flux (“neutron noise”) of the Mühleberg BWR are investigated. Above 2 Hz, the noise measured by the in-core neutron detectors is driven exclusively by local fluctuations of the void fraction. Characteristic changes of the neutron-noise signature along the axis can be attributed to changes of flow pattern. By measuring the phase lag between pairs of axially placed neutron detectors, the transit time of the steam between the detectors can be evaluated. The measured transit times are applied to the study of two-phase flow in the core. The neutron-noise method has the advantage of providing in-core information under operational conditions.     

A system of benchmark neutron fields in research reactors

A system of benchmark neutron fields, which together with the special State standard gives unity and the required practical accuracy for reproducing the units of neutron flux density and fluence in nuclear reactors, is developed. The neutron characteristics of the fields and the foreign and domestic analogs are presented. 1 figure, 2 tables, 32 references. State Science Center of the Russian Federation—All-Russia Scientific-Research Institute of Physicotechnical and Radioelectronic Measurements. Translated from Atomnaya énergiya, Vol. 88, No. 5, pp. 378–387, May, 2000.     

Testing a system prototype for out-of-reactor monitoring of reactor power and its distribution in the core volume

Conclusion Prototype tests were performed for a representative set of reactor conditions: the power distribution was performed by a wide range of changes in the position of three groups of control and protection system regulatory devices, the A0 values were varied in the range from –0.40 to 0.16, and the coefficient of non-uniformity k_v in the range from 1.7 to 2.6. The results showed the high accuracy and effectiveness of out-of-reactor monitoring of the power and its distribution throughout the core volume.For an LWR, the out-of-reactor monitoring system assemblies can be placed in radiation shielding channels; for this three assemblies, each having three detectors, is sufficient. Chambers having an energy range of standard neutron flux monitoring equipment can be used as detectors.Determining the thermal power and the coefficients of nonuniformity of its distribution in the core does not begin to exhaust the possibilities for out-of-reactor monitoring. Algorithms already exist or are being developed which would allow increased accuracy in the monitoring of power and its distribution, localization of the region or fuel element with the greatest energy loading, detection of stuck control rods and nonfunctional thermal monitoring sensors, and diagnosis of fluctuations and position shifts of internal reactor vessel structures. Thus a reliable, cheap, rapdily responding core condition diagnostics systems can be constructed on the base of out-of-reactor detectors.Translated from Atomnaya Énergiya, Vol. 64, No. 3, pp. 174–180, March, 1988.