Coal analysis using the pulsed neutron generator

A prototype of elemental analyzer for coal has been developed by using a PFTNA (pulse fast thermalneutron analysis) system. The PFTNA technology is based on the reactions such as (n, γ), (n, n'γ), (n, Pγ), etc. byexamining the characteristic gamma rays emitted. In our prototype a pulsed neutron generator provides 14 MeV pulseneutrons, which contribute to the separation of spectrum Ⅱ (the sum of capture and activation spectrum) fiom spec-trum Ⅰ (the sum of inelastic, capture and activation spectrum), and thus to the measurement of C and O contents incoal. Data management is completed by computer program using the least-square regression method. The experimentin Changshan Power Plant for 3 months showed that the precision of calorific value, whole water, volatile content andash content is 0.5 k J/kg, 1.0 wt%, 2.0 wt% and 1.5 wt%, respectively.

Pulse-shaping method for real-time neutron/gamma discrimination at low sampling rates

The Na I:Tl scintillator is an innovative material for dual-gamma-ray and neutron detection with a low ^(6)Li concentration.To achieve real-time n/γ discrimination,a zero-crossing time comparison algorithm based on trapezoidal pulse shaping was developed.The algorithm can operate efficiently at low sampling rates and was implemented on a single-probe portable digital n/γ discriminator based on a field-programmable gate array.The discriminator and Na I:Tl,^(6)Li detector were tested in a neutron-gamma mixed field produced by an ^(241)Am-Be neutron source to evaluate the performance of the algorithm.The figure of merits was measured as 2.88 at a sampling rate of 50 MHz,indicating that the discriminator with its embedded algorithm has a promising n/γ discrimination capability.Efficient discrimination at sampling rates of 40 and 25 MHz demonstrates that the capability of this method is not limited by low sampling rates.

A method of monitoring gas saturation in carbon dioxide injection heavy oil reservoirs by pulsed neutron logging technology

A method is proposed to characterize the fast neutron scattering cross-section ( s f) quantitatively by the combina-tion of inelastic gamma rays and captured gamma rays, so as to realize the gas saturation evaluation of CO_(2)-injected heavy oilreservoirs based on the three-de tector pulsed neutron logging technology. Factors influencing of the evaluation effect of thismethod are analyzed and the effectiveness of this method is verified by a simulation example. By using the Monte Carlo simu-lation method and the physical model of bulk-volume rock, the relationship between s f and CO_(2) saturation is studied, and thesaturation interpretation model is established. The influences of formation temperature and pressure, heavy oil density, bore-hole fluid and reservoir methane content on the evaluation results of CO_(2) saturation are analyzed. The results show that thecharacterization of s f by the combination of secondary gamma information can eliminate the influence of formation lithology,borehole fluid and methane content are the main factors affecting the quantitative monitoring of CO_(2) saturation, and the ef-fects of formation temperature and pressure and heavy oil density are negligible. The simulation example verified the feasibilityof the method for evaluating the CO_(2) saturation of CO_(2)-injected heavy oil reservoirs.

Study of the pulsed working characteristics of the penning ion source for neutron tubes

The pulsed working characteristics of the neutron tube ion source were studied experimentally. The principle and method of selecting the gas pressure and anode voltage were determined.

Anti-noise performance of the pulse coupled neural network applied in discrimination of neutron and gamma-ray

In this study,the anti-noise performance of a pulse-coupled neural network(PCNN)was investigated in the neutron and gamma-ray(n-γ)discrimination field.The experiments were conducted in two groups.In the first group,radiation pulse signals were pre-processed using a Fourier filter to reduce the original noise in the signals,whereas in the second group,the original noise was left untouched to simulate an extremely high-noise scenario.For each part,artificial Gaussian noise with different intensity levels was added to the signals prior to the discrimination process.In the aforementioned conditions,the performance of the PCNN was evaluated and compared with five other commonly used methods of n-γdiscrimination:(1)zero crossing,(2)charge comparison,(3)vector projection,(4)falling edge percentage slope,and(5)frequency gradient analysis.The experimental results showed that the PCNN method significantly outperforms other methods with outstanding FoM-value at all noise levels.Furthermore,the fluctuations in FoM-value of PCNN were significantly better than those obtained via other methods at most noise levels and only slightly worse than those obtained via the charge comparison and zerocrossing methods under extreme noise conditions.Additionally,the changing patterns and fluctuations of the FoMvalue were evaluated under different noise conditions.Hence,based on the results,the parameter selection strategy of the PCNN was presented.In conclusion,the PCNN method is suitable for use in high-noise application scenarios for n-γdiscrimination because of its stability and remarkable discrimination performance.It does not rely on strict parameter settings and can realize satisfactory performance over a wide parameter range.

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.

Measurements of the ^(107)Ag neutron capture cross sections with pulse height weighting technique at the CSNS Back-n facility

Silver indium cadmium(Ag–In–Cd) control rod is widely used in pressurized water reactor nuclear power plants,and it is continuously consumed in a high neutron flux environment. The mass ratio of ^(107)Ag in the Ag–In–Cd control rod is 41.44%. To accurately calculate the consumption value of the control rod, a reliable neutron reaction cross section of the ^(107)Ag is required. Meanwhile,^(107)Ag is also an important weak r nucleus. Thus, the cross sections for neutron induced interactions with ^(107)Ag are very important both in nuclear energy and nuclear astrophysics. The(n, γ) cross section of ^(107)Ag has been measured in the energy range of 1–60 eV using a back streaming white neutron beam line at China spallation neutron source. The resonance parameters are extracted by an R-matrix code. All the cross section of ^(107)Ag and resonance parameters are given in this paper as datasets. The datasets are openly available at http://www.doi.org/10.11922/sciencedb.j00113.00010.

Conceptual design of a Cs2LiLaBr6 scintillator‑based neutron total cross section spectrometer on the back‑n beam line at CSNS

To reduce the experimental uncertainty in the 235 U resonance energy region and improve the detection efficiency for neutron total cross section measurements compared with those obtained with the neutron total cross section spectrometer(NTOX), a dedicated lithium-containing scintillation detector has been developed on the Back-n beam line at the China Spallation Neutron Source. The Fast Scintillator-based Neutron Total Cross Section(FAST) spectrometer has been designed based on a Cs2Li La Br6(CLLB) scintillator considering the γ-ray flash and neutron environment on the Back-n beam line. The response of the CLLB scintillator to neutrons and γ-rays was evaluated with different 6Li/7 Li abundance ratios using Geant4. The neutron-γdiscrimination performance of the CLLB has been simulated considering different scintillation parameters, physical designs,and light readout modes. A cubic 6Li-enriched( > 90%) CLLB scintillator, which has a thickness of 4-9 mm and side length of no less than 50 mm to cover the Φ 50 mm neutron beam at the spectrometer position, has been proposed coupling to a side readout SiPM array to construct the FAST spectrometer. The developed simulation techniques for neutron-γ discrimination performance could provide technical support for other neutron-induced reaction measurements on the Back-n beam line.

The Neutron-Gamma Pulse Shape Discrimination Method for Neutron Flux Detection in the ITER

The neutron flux monitor （NFM）, as a significant diagnostic system in the International Thermonuclear Experimental Reactor （ITER）, will play an important role in the readings of a series of key parameters in the fusion reaction process. As the core of the main electronic system of the NFM, the neutron-gamma pulse shape discrimination （n-γ PSD） can distinguish the neutron pulse from the gamma pulse and other disturbing pulses according to the thresholds of the rising time and the amplitude pre-installed on the board, the double timing point CFD method is used to get the rising time of the pulse. The n-γ PSD can provide an accurate neutron count.

Measurement and simulation of the leakage neutron spectra from Fe spheres bombarded with 14 MeV neutrons

Iron is commonly used as a structural and shielding material in nuclear devices. The accuracy of its nuclear data is critical for the design of nuclear devices. The evaluation data of ^(56)Fe isotopes in the latest version of the CENDL-3.2 library from China was significantly updated. This new data must be tested before it can be used. To test the reliability of this data and assess the shielding effect, a shielding benchmark experiment was conducted with natural Fe spherical samples using a pulsed deuterium–tritium neutron source at the China Institute of Atomic Energy(CIAE). The leakage neutron spectra from the natural spherical iron samples with different thicknesses(4.5, 7.5, and 12 cm) were measured between 0.8 and 16 MeV after interacting with 14 MeV neutrons using the time-of-flight method. The simulation results were obtained by Monte Carlo simulations by employing the Fe data from the CENDL-3.2, ENDF/B-VIII.0, and JEDNL-5.0 libraries. The measured and simulated leakage neutron spectra and penetration rates were compared, demonstrating that the CENDL-3.2 library performs sufficiently overall. The simulation results of the other two libraries were underestimated for scattering at the continuum energy level.

核爆炸早中期电磁脉冲产生的数值模拟方法

由于核电磁脉冲(nuclear electromagnetic pulse,NEMP)电场与爆炸当量、爆高、方位角、大气参数和观测位置等密切相关,NEMP产生的数值模拟是非常复杂的问题。本文评述了核爆炸电磁脉冲产生过程的数值模拟方法,包括NEMP产生的物理模型、γ射线和中子在大气中输运及康普顿电流源、大气电导率模型和电磁场求解方法;给出了NEMP的典型数值模拟结果,主要包括早期电磁脉冲和中期电磁脉冲联合模拟结果,并分析了早期电磁脉冲和中期电磁脉冲峰值、起止时间和频谱等特征参数。

基于强流脉冲离子束的中子辐照模拟装置及评价技术

依据高能原子辐照与中子辐照的初级离位原子(PKA)能谱相似性,基于TEMP-6M型强流脉冲离子束(HIPIB)系统,研发了一种中子辐照模拟装置,该装置以磁绝缘离子二极管伴生的强流脉冲二次电子束流实现0.1 MeV以上高能离子的高效率中和,获得动能为0.1~1 MeV、脉冲宽度为120~160 ns、脉冲辐照剂量为1012~10^(15)n/cm^(2)的强流脉冲原子或混合束,原子占比为85%~100%。通过辐照缺陷原位差热分析方法,快速确定材料缺陷数量、密度及dpa损伤速率等抗中子辐照性能评价指标。以核级AISI 304奥氏体不锈钢为例,计算PKA相似性定标曲线,采用220~280 keV的C原子等效1.8~2.3 MeV中子进行辐照模拟,调节名义束流能量密度0.5~4 J/cm^(2),实测辐照剂量范围为0.46×10^(13)~8.55×10^(13)n/cm^(2),热分析确定Frenkel缺陷密度为1.99×10^(16)~2.90×10^(17)/cm^(2),外推预测奥氏体不锈钢在1021n/cm^(2)中子剂量条件下的辐照损伤为500 dpa量级,适用于核电厂结构材料60年服役寿期评价需求。

反射中子对金属快中子脉冲堆特性参数的影响研究

快中子脉冲堆对墙壁反射中子比较敏感,反射中子会改变快中子脉冲堆波形,当反射中子较多时可能会对脉冲堆的运行安全造成不利影响。本文建立了考虑墙壁反射中子效应的点堆动力学方法、蒙特卡罗中子学计算方法和ANSYS热力学计算方法三者耦合的“核-热-力”耦合方法,并对含有墙壁反射中子效应的快中子脉冲堆Godiva-Ⅰ瞬态过程进行分析。结果表明:反射中子使脉冲后沿提高,使冲坪时的反应性变低,使堆芯位移、应力有所提高。

面向聚变中子探测的宽禁带半导体探测器关键问题与研究挑战

近年来国际聚变反应研究获得重大进展,选择抗位移能力强的宽禁带半导体探测器是推动聚变研究的关键技术之一.金刚石超宽禁带半导体具备卓越抗辐照和时间响应等特性,是聚变诊断特别是高能中子诊断的理想材料,碳化硅宽禁带半导体也可测量中子,且大尺寸外延技术更成熟,可覆盖聚变研究装置上的大规模应用.通过这两种宽禁带半导体辐射探测器的研究并实现自主可控的高性能器件制备,将显著提高我国核聚变反应测量系统的性能,支持我国在未来的全球能源革命中处于领先优势.本文将对这两种宽禁带半导体探测器在聚变中子探测应用场景下研制的关键问题和研究挑战进行探讨,助力我国聚变能源开发和应用.

脉冲束流下车载加速器中子源靶传热特性

为了研究不同脉冲束流频率下车载加速器中子源靶的传热特性及其热动态响应,通过调整脉冲束流的频率或脉宽对背部冷却微通道靶的传热性能进行模拟,并通过分析靶内部结构的热沉积分布,探究车载加速器中子源靶的热负载上限以及制约束流的因素。选用能量为2.5 MeV、峰值流强为10 mA的束流开展模拟,结果表明:当束流占空比保持在3%不变时,靶的最高温度呈周期波动,且存在上下包络;随着束流频率的上升,每个脉冲周期内靶的上包络温度逐渐下降,这是由于每个脉冲期间的热冲击下降所导致的;频率上升时,每个周期内加热时间与冷却时间同时缩短,导致其下包络温度在最开始增大后基本保持不变;靶的最高温度随着束流频率增加出现从锂层到中间层钽层的转移。该研究对于车载加速器中子源的束流参数选择和靶冷却设计具有一定的参考价值。

空间辐射位移效应西安脉冲堆中子试验平台及应用

空间辐射环境中的重离子、质子、电子等载能粒子辐照产生的位移效应是影响航天器在轨高可靠、长寿命运行的重要因素之一。基于中子辐照等效空间载能粒子产生的位移效应是评价航天器电子元器件抗辐射能力的重要手段。西安脉冲反应堆是空间辐射位移效应研究的重要平台,自建成以来,为国内多家器件生产、系统研制、型号应用等单位在抗辐射加固设计、考核评估、效应机理等工作中提供了重要支撑。本文综述了电子器件位移效应机理与敏感性、位移效应中子等效试验方法和西安脉冲反应堆中子试验平台及其典型应用。

台南气田脉冲中子-中子测井解释方法及应用

为评价水侵后台南气田的储层水淹状况,在套管井中规模应用脉冲中子-中子测井技术。研究井筒内积液、水淹层放射性增强、套管尺寸变化等影响因素对脉冲中子-中子测井曲线的影响及其校正方法,形成基于逐步剥离法和SIGMA—RATGN交会图法的储层饱和度定量解释方法。依据驱油效率、含水饱和度、校正后的热中子俘获截面值,建立台南气田气层水淹级别评价标准。新方法有效提高气层识别准确性和储层饱和度解释精度,水淹层评价符合率达92.3%,为台南气田稳产提供技术支持。

空气泡沫驱和二氧化碳驱注入剖面测井方法适用性分析

空气泡沫驱和二氧化碳驱是低渗透油田三次采油的重要技术手段,为有效研究注入层位的吸入情况,需要进行注入剖面测井评价,但空气泡沫液的不稳定体系特征和二氧化碳的超临界状态特性区别于常规水驱流体,常规的测井方法需要进行适用性评价研究。在对已有注入剖面测井方法的原理适用性研究的基础上,发现八参数注入剖面测井方法在二氧化碳和空气泡沫驱中适用性良好,脉冲中子氧活化可用于二氧化碳注入剖面测井,常规同位素示踪测井方法在空气泡沫驱和二氧化碳驱中适用性不良,分布式光纤测井方法适用性强,在二氧化碳和空气泡沫驱具有良好的应用前景。

热中子成像系统在页岩油开发中的应用

热中子成像系统是一种脉冲中子套后饱和度测井技术。当某些井未能进行常规裸眼测井时,应用热中子成像系统可以获取套后测井资料,实现对单井油水层的评价,为后续射孔等工作提供依据。在阐述热中子成像系统工作原理和技术特点的基础上,介绍了其在页岩油开发中的应用成果。利用热中子成像资料,可以评价储层物性和脆性矿物含量,进行储层分类、识别优质储层。通过分析热中子成像系统在压裂前、压裂后的测井信息,对比压裂前后储层孔隙度、含油饱和度的变化情况,可以有效评价压裂效果。研究结果可为改善油田开发效果、提高页岩油采收率提供技术支撑。

全谱饱和度测井仪中子发生器工作性能影响因素研究

全谱饱和度测井仪PSSL是一种广泛应用于油田水淹状况识别、剩余油分布确定及增储挖潜措施中的先进套后测井仪器,在国内外取得良好的应用效果。中子发射器作为PSSL仪器的核心部件,其工作性能的稳定性直接决定了测井资料的质量和仪器使用的可持续性。本文对PSSL全谱测井仪的中子发生器组成结构及工作原理进行研究,对中子发生器工作性能的影响因素进行分析、总结性能改善措施,提高仪器工作性能,延长仪器使用寿命,提升测井资料质量,同时增加仪器应用收益。