First Observations of Cosmic Ray Neutrons by a Mini Neutron Monitor at Riyadh, Saudi Arabia

In April 2017, a mini neutron monitor (NM) was installed at King Abdulaziz City for Science and Technology (KACST) central Saudi Arabia (Riyadh;cut-off rigidity, Rc = 14.4 Gv) for continuous observation of the cosmic ray (CR) neutrons. The detector was built as a major aspect of the international scientific joint effort between the Centre of Space Research (North-West University, Potchefstroom, South Africa) and KACST. The recorded data correspond to low energy neutrons that primarily have energies lower than 20 GeV. In this paper, a brief description about the mini NM detector will be given. The influence of atmospheric pressure on the recorded CR neutrons was studied and the barometric coefficient was calculated and used to eliminate the pressure effects from the measured data. The obtained coefficient was consistent with those previously obtained by several investigators. The daily variation of the CR neutron was studied and characterized. Short-term CR periodicities, such as the 27-day period, and its two harmonics, were identified. The obtained periodicities are in agreement with those reported by different researchers. The obtained results from this detector have been compared to the existing 1 m2 scintillator detector showing comparable results. Long-term data from this detector will be of incredible significance to the research community to investigate several types of CR variations resulting from solar activity at such high cut off rigidity site.

Development of a spherical tissue equivalent proportional counter for neutron monitoring

A spherical tissue equivalent proportional counter(TEPC) for neutron monitoring has been developed. It was properly designed to produce a uniform electric field intensity around the anode wire. An internal ^(241)Am alpha source was adopted for lineal energy calibration. The TEPC was characterized in terms of dose equivalent response in a standard ^(252)Cf neutron field, and was tested with 2.45 MeV neutrons. Microdosimetric spectra, frequency mean lineal energy and dose-average mean lineal energy of 2.45 MeV neutrons were obtained and compared with FLUKA Monte Carlo simulation results. The measurement and simulation results agreed well. The mean quality factor and dose equivalent values evaluated from the 2.45 MeV neutron measurement were in good agreement with the recommended effective quality factor and ambient dose equivalent H*(10),respectively. Preliminary results have proved the availability of the developed TEPC for neutron monitoring.

High-precision and wide-range real-time neutron flux monitor system through multipoint linear calibration

The neutron flux monitor(NFM)system is an important diagnostic subsystem introduced by large nuclear fusion devices such as international thermonuclear experimental reactor(ITER),Japan torus-60,tokamak fusion test reactor,and HL-2 A.Neutron fluxes can provide real-time parameters for nuclear fusion,including neutron source intensity and fusion power.Corresponding to different nuclear reaction periods,neutron fluxes span over seven decades,thereby requiring electronic devices to operate in counting and Campbelling modes simultaneously.Therefore,it is crucial to design a real-time NFM system to encompass such a wide dynamic range.In this study,a high-precision NFM system with a wide measurement range of neutron flux is implemented using realtime multipoint linear calibration.It can automatically switch between counting and Campbelling modes with variations in the neutron flux.We established a testing platform to verify the feasibility of the NFM system,which can output the simulated neutron signal using an arbitrary waveform generator.Meanwhile,the accurate calibration interval of the Campbelling mode is defined well.Based on the above-mentioned design,the system satisfies the requirements,offering a dynamic range of 10~8 cps,temporal resolution of 1 ms,and maximal relative error of 4%measured at the signal-to-noise ratio of 15.8 dB.Additionally,the NFM system is verified in a field experiment involving HL-2 A,and the measured neutron flux is consistent with the results.

Development of a wide-range and fast-response digitizing pulse signal acquisition and processing system for neutron flux monitoring on EAST

The neutron count rate fluctuation reaches six orders of magnitude between the ohmic plasma scenario and high power of auxiliary heating on an experimental advanced superconducting tokamak(EAST).The measurement result of neutron flux monitoring(NFM)is a significant feedback parameter related to the acquisition of radiation protection-related information and rapid fluctuations in neutron emission induced by plasma magnetohydrodynamic activity.Therefore,a wide range and high time resolution are required for the NFM system on EAST.To satisfy these requirements,a digital pulse signal acquisition and processing system with a wide dynamic range and fast response time was developed.The present study was conducted using a field-programmable gate array(FPGA)and peripheral component interconnect extension for instrument express(PXIe)platform.The digital dual measurement modes,which are composed of the pulse-counting mode and AC coupled square integral's Campbelling mode,were designed to expand the measurement range of the signal acquisition and processing system.The time resolution of the signal acquisition and processing system was improved from 10 to 1 ms owing to utilizing highspeed analog-to-digital converters(ADCs),a high-speed PXIe communication with a direct memory access(DMA)mode,and online data preprocessing technology of FPGA.The signal acquisition and processing system was tested experimentally in the EAST radiation field.The test results showed that the time resolution of NFM was improved to 1 ms,and the dynamic range of the neutron counts rate was expanded to more than 10^(6) counts per second.The Campbelling mode was calibrated using a multipoint average linear fitting method;subsequently,the fitting coefficient reached 0.9911.Therefore,the newly developed pulse signal acquisition and processing system ensures that the NFM system meets the requirements of high-parameter experiments conducted on EAST more effectively.

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

To satisfy high-precision,widc-rangc,and real-time neutron flux measurement requirements by the International Thermonuclear Experimental Reactor(ITF.R),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 arc based on a field programmable gate array and the PXI Express platform arc designed to realize the neutron flux measurement with I ms time resolution and a fast response less than 0.2 ms,together with real-time timestamps provided by a timing hoard.The application of the wide-range algorithm allows the system to measure up to 10^10cps 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.

Fusion Neutron Flux Monitor for ITER

Neutron flux monitor （NFM） as an important diagnostic sub-system in ITER （international thermonuclear experimental reactor） provides a global neutron source intensity, fusion power and neutron flux in real time. Three types of neutron flux monitor assemblies with different sensitivities and shielding materials have been designed. Through MCNP （Mante-Carlo neutral particle transport code） calculations, this extended system of NFM can detect the neutron flux in a range of 10^4 n/（cm^2.s） to 10^14 n/（cm^2.s）. It is capable of providing accurate neutron yield measurements for all operational modes encountered in the ITER experiments including the in-situ calibration. Combining both the counting mode and Campbelling （MSV; Mean Square Voltage） mode in the signal processing units, the requirement of the dynamic range （107） for these NFMs and time resolution （1 ms） can be met. Based on a uncertainty analysis, the estimated absolute measurement accuracies of the total fusion neutron yield can reach the required 10% level in both the early stage of the DD-phase and the DD-phase, the absolute measurement accuracy full power DT operation mode. In the advanced would be better than 20%.

Compact lithium-glass neutron beam monitor for SANS at CSNS

A small-angle scattering neutron spectrometer for material research is under construction at the China Spallation Neutron Source. An intervening neutron beam monitor behind the sample is needed to measure the beam intensity in order to reduce the measurement uncertainty caused by beam fluctuation. Considering the mobility requirement and limited space, we proposed a compact monitor using a type of lithium-glass scintillator provided by China Building Materials Academy. Its performance was studied experimentally using ^(252)Cf and ^(60)Co sources.The neutron light yield of the selected scintillator was measured to be 5:3 × 10~3 photons/neutron. The feasibility of n-gamma discrimination using the charge comparison method was verified. By using the Geant4 toolkit, themonitor was modeled with precise physical processes including neutron tracking, scintillation, and optical photon transmission. The gamma sensitivity and detection efficiency were investigated in the simulation. It was concluded that a 0.5-mm-thick lithium-glass scintillator with natural lithium is an appropriate choice to satisfy both the neutron detection efficiency and gamma elimination requirements.

Dynamic linear calibration method for a wide range neutron flux monitor system in ITER

As a key part of the diagnosis system in the International Thermonuclear Experimental Reactor(ITER),the neutron flux monitor(NFM),which measures the neutron intensity of the fusion reaction,is a Counting-Campbelling system with a large dynamic counting range.A dynamic linear calibration method is proposed in this paper to solve the problem of cross-over between the different counting and Campbelling channels,and improve the accuracy of the cross-calibration for long-term operation.The experimental results show that the NFM system with the dynamic linear calibration system can obtain the neutron flux of the fusion reactor in real time and realize the seamless measurement area connection between the two channels.

Development of Prototype Neutron Flux Monitor for ITER

The prototype neutron flux monitor consists of a high purity ^(235)U fission chamber detector and a'blank'detector,which is a fissile material free detector with the same dimension as the fission chamber detector to identify noise issues such as noise coming from gamma rays.The main parameters of the fission chamber assembly that have been measured in the laboratory are confirmed to approach the technological level of the International Thermonuclear Experimental Reactor(ITER)in the near future.This prototype neutron flux monitor will be further developed to become a neutron flux monitor suitable for the operation phase of D-D fusion on the ITER.

Real-time wide-range neutron flux monitor for thorium-based molten salt reactor

A novel full-digital real-time neutron flux monitor(NFM) has been developed for thorium-based molten salt reactor(TMSR).The system is based on the highspeed,parallel,and pipeline processing of the field programmable gate array as well as the high-stability controller area network platform.A measurement range of 10~8 counts per second is achieved with a single fission chamber by utilizing the normalization of the count and Campbell algorithms.With the advantages of using the measurement range,system integrity,and real-time performance,digital NFM has been tested in the Xi'an pulsed reactor fission experiments and was found to exhibit superior experimental performance.

EAST托卡马克中子与伽马在线监测研究

为了实现对实验型先进全超导托卡马克(Experimental Advanced Superconducting Tokamak, EAST)装置聚变产物中子与γ射线的有效监测,建立了一套核辐射在线监测系统。在装置大厅内外区域共布置13个监测点,根据装置大厅内外辐射强度的差异,分别采用探测范围广、时间响应快和探测灵敏度高、工作稳定性强相结合的BF3正比计数管和氩气电离室。脉冲信号经前置放大器、运算放大器、脉冲甄别与成形后送入单片机处理,通过双绞线与以太网的混合组网方式将数据传输到采集机,利用LabVIEW采集软件实现对中子与γ射线实时剂量率及累积剂量的采集与存储。监测数据表明,放电时大厅内中子和γ射线剂量率在短时间快速升高,且距离主机越近剂量率越大。而大厅外辐射剂量率始终处于极低水平,几乎不受脉冲放电的影响。该监测系统满足了EAST托卡马克装置辐射监测需求,确保了人员与周围环境辐射安全,保障了聚变装置安全有效运行。

Probeam型医用质子治疗系统机房屏蔽分析与测量结果比较

质子治疗系统使用能量在70~250 MeV范围内的质子进行肿瘤治疗,损失或预期使用的质子与靶物体产生能量范围宽、角度分布差异大的中子谱,成为质子治疗系统屏蔽设计的主要考虑源项。本文采用点核模型估算Probeam型质子治疗系统机房外中子周围剂量当量率,与测量结果进行比较分析,验证屏蔽结构的有效性。

多功能旋转靶装置研究

针对D-D中子发生器采用静态水冷靶时中子产额不稳定、中子产额持续下降等主要问题,研制了一套多功能紧凑型旋转靶装置。装置采用一体化设计,结构紧凑、尺寸小,具备靶体高速旋转和水冷、靶点可视化监测、靶面温度实时测量、中子产额实时监测等功能。本文介绍了该装置的主体结构、功能设计和性能测试,以及靶结构对中子散射影响的模拟计算。性能测试结果表明,该装置真空度满足加速器运行要求,相比静态水冷靶,束流靶点中心最高温度明显降低,中子产额稳定度明显提高。模拟计算结果显示中子能谱峰展宽范围为0~0.0577 MeV,散射中子占比为10.53%~26.75%。本文还针对模拟计算结果和测量结果中存在的问题进行了分析,提出了改进和优化方案。

基于台山核电厂中子剂量监测实践的思考

介绍了台山核电厂近几年来开展的中子辐射监测以及中子剂量监测的相关实践,并基于实践情况开展了中子剂量监测的合规性分析,讨论了国内外法规和标准针对核电厂中子剂量监测的要求。分析认为,台山核电厂近年来对中子辐射开展的剂量监测实践符合国内相关法规和标准的要求,但是也发现目前国内针对核电厂中子辐射监测的法规和标准中未明确需要开展中子个人剂量监测的起测标准,国际原子能机构的一般安全导则以及国外部分国家在核电厂中子剂量监测方面有相对更明确的规定。建议我国相关部门针对核电厂中子剂量监测考虑补充相关指导条款,各核电厂应针对自身情况开展中子剂量监测评价。

Days of “Zero” level geomagnetic activity accompanied by the high neutron activity and dynamics of some medical events—Antipodes to geomagnetic storms

The links of many medical-biological events with high levels of geomagnetic activity (GMA) are widely discussed. In recent years, several medical phenomena were described in inverse distribution by time with GMA. Also a concurrent to GMA and solar activity force-cosmic ray activity (CRA) and closely related high energy neutron and proton fluxes are studied as a forces dominating at low GMA and solar activity in relation to considered medical events. The aim of this study was to explore the distribution of some important medical events on days with “Zero” GMA levels, accompanied by high CRA (neutron activity). Medical event data of the Grand Baku region (more than 3 mln inhabitants), Azerbaijan, with daily distribution on the time 1 Dec. 2002-31 Dec. 2007 was compared to daily GMA Kp indices in general (Kp > 0, 1837 days) and 34 days daily GMA indices Kp = 0. Daily CRA data was also compared using neutron monitoring data from two stations. Daily averaged data and their standard deviations on the mentioned GMA levels were compared and statistical significance was established. Results revealed a significant rise in the number of emergencies (n = 1,567,576) and total deaths number (n = 46,360) at the days of “Zero” GMA level. These days were accompanied by significant rise of CRA (neutron activity). For Sudden Cardiac Deaths (SCD, n = 1615) and cerebral stroke (CVA, n =10,054) the increase achieved strong trend to significance level. Acute Myocardial Infarction occurrence (morbidity) and trauma were also absolutely more registered at days with “Zero” GMA level, despite the small number of such days. The average Infection numbers show an inverse relationship with absolutely high registry at the “Zero” GMA level days. Study linking environmental physical activity levels and the human medical data shows that geomagnetic field variations accompanied by the increased level of cosmic ray activity, can have either direct or indirect adverse effects on human health and physiology, even when the magnitude of the geomagnetic field disturbance is extremely small or even is equal to zero. On days of “Zero” daily Kp indices describing Geomagnetic Activity, accompanied by high Cosmic Ray Activity (neutron activity), more medical emergencies and total death number (daily) occurred. Sudden Cardiac Deaths and Cerebral Stroke numbers show a strong trend to significant rise. Absolute increase of number of Acute Myocardial Infarction and less Infections, not achieving statistical significance, was also observed. These results are additional data for considering Cosmic Ray Activity (neutron activity) as an additional factor involved in time distribution of human medical events.

A study of PFBR auxiliary neutron source strength activation and its variability with respect to the neutron spectrum and 123Sb capture cross section

In fast reactors, the inherent neutron source strength is often insufficient for monitoring the reactor start-up operation with ex-core detectors. To increase the subcritical neutron flux, an auxiliary neutron source subassembly(SSA) is generally used to overcome this problem. In this study, the estimated neutron source strength and detector count rate of an antimony-beryllium-based SSA are obtained using the deterministic transport code DORT and Monte Carlo calculations. Because the antimony activation rate is a critical parameter, its sensitivity to the capture cross section and neutron flux spectrum is studied. The reaction cross section sensitivity is studied by considering data from different evaluated nuclear data files.It is observed that, because of the variation in the cross sections from different evaluated nuclear data files, the values of the saturation gamma(> 1.67 MeV) activity and neutron strength predicted by ORIGEN2 lie within ±2%.The obtained antimony activation rate and sensitivity to the neutron flux are partially validated by irradiating samples of antimony in the KAMINI reactor. The average onegroup capture cross sections of bare and cadmium-covered 123Sb samples obtained by the ratio method are 4.0 and 1.78 b, respectively. The results of the calculation predicting the activated neutron source strength as a function of operating time and sensitivity to the neutron spectrum in the irradiation region are also presented.

田湾核电站换料期间中子通量密度监测方式优化研究

针对田湾核电站换料期间中子通量密度监测方式的不足,研究了用源量程探测器取代换料监测量程探测器完成换料期间中子通量密度监测的优化方案。基于全进全出和堆芯倒料两种堆芯换料方式,应用蒙特卡罗程序MCNP模拟计算源量程探测器的响应,计算结果表明,当靠近源量程探测器位置的乏燃料组件达到一定燃耗深度时,源量程探测器中子计数率达到0.5 s^(-1),满足换料过程中子计数率监测要求,与测量值符合得很好。应用源量程探测器替代换料监测量程探测器监测换料期间中子通量密度是可行的。

磁约束聚变装置辐射监测系统概况

采用氘、氚燃料的核聚变反应会产生大量的中子、γ射线及活化产物等,对人员和环境的辐射安全产生影响。为了减小电离辐射带来的影响,需要准确掌握聚变装置核辐射场强度的时间与空间分布信息。世界上已建设的磁约束聚变装置,均根据其自身运行工况特点,建立了完整的核辐射监测系统来应对电离辐射带来的潜在影响。通过对磁约束聚变装置运行及维护期间辐射剂量的监测,获得实验场所与外围环境的电离辐射和放射性核素数据,为辐射安全防护管理提供数据支撑。基于对国内外磁约束聚变装置辐射监测系统的调研,本文归纳了此类装置主要的电离辐射源项及监测系统架构,进而介绍了磁约束聚变中子与γ辐射剂量的测量方法及常用探测器。最后综述了国内外核聚变装置辐射监测系统的研究状况,展望了未来核辐射监测系统的发展趋势与目标。

堆用SiC辐照温度监控器的研究进展

碳化硅(SiC)晶体可以用作无源监控器测量反应堆的中子辐照温度,在未来高温强辐射的先进核反应堆中具有重要的应用前景。SiC测温技术自20世纪60年代被首次提出以来,基于SiC结构、热学和电学性质的中子辐照效应,人们建立了宏观尺寸法、质量密度法、热导率法和电阻率法等各种SiC测温方法。本文首先综述了这些SiC测温方法的基本原理和工作特点,然后着重介绍了中国原子能科学研究院(China Institute of Atomic Energy,CIAE)SiC测温系统的研究进展,通过中子辐照诱导SiC晶格肿胀的理论计算,分析和验证了该系统测温结果的可靠性,探讨了进一步提高SiC测温效率的实验方法。

压水堆堆芯中子通量监测系统对比研究

压水堆堆芯中子通量监测系统主要用于实现对反应堆堆芯的中子通量密度、冷却剂温度及液位的实时在线监测,对核电站的安全稳定运行起着至关重要的作用。通过介绍目前国内压水堆核电站主要堆型中堆芯中子通量监测系统的应用情况,对比分析了该系统在结构组成、功能性能等方面的差异,为其优化设计提供借鉴。