光电倍增管对14 MeV脉冲中子的直照响应

采用ING-103型DPF脉冲中子源产生的14.1 MeV脉冲中子对EMI两个不同型号的光电倍增管EMI-9815B和EMI-9850B进行了直照实验。针对DPF脉冲中子源产生中子脉冲的同时也会产生X射线脉冲的特点,采取了飞行时间法及吸收衰减法来消除X射线对中子脉冲的干扰。利用中子及X射线速度的差异,将光电倍增管放置在离源较远的测点位置,测得了X射线脉冲和中子脉冲时间上错开的双峰波形。通过在辐射通道内添加5 cm厚的铅吸收体有效地抑制了X射线峰,在离源较近的测量位置测到了干净的脉冲中子波形。根据实测波形,得到的光电倍增管EMI-9815B和EMI-9850B中子直照灵敏度分别为10-13与10-15量级,该结果与理论计算结果在量级上一致。     

光电倍增管对14 MeV脉冲中子的直照响应

 采用ING-103型DPF脉冲中子源产生的14.1 MeV脉冲中子对EMI两个不同型号的光电倍增管EMI-9815B和EMI-9850B进行了直照实验。针对DPF脉冲中子源产生中子脉冲的同时也会产生X射线脉冲的特点,采取了飞行时间法及吸收衰减法来消除X射线对中子脉冲的干扰。利用中子及X射线速度的差异,将光电倍增管放置在离源较远的测点位置,测得了X射线脉冲和中子脉冲时间上错开的双峰波形。通过在辐射通道内添加5 cm厚的铅吸收体有效地抑制了X射线峰,在离源较近的测量位置测到了干净的脉冲中子波形。根据实测波形,得到的光电倍增管EMI-9815B和EMI-9850B中子直照灵敏度分别为10^-13与10^-15量级,该结果与理论计算结果在量级上一致。     

光电倍增管中子直照灵敏度响应

 光电倍增管的中子直照响应对脉冲中子探测器的设计和实际应用具有重要影响。分析了中子束直接照射光电倍增管产生直照响应的过程和机理。中子与光电倍增管入射窗硼硅玻璃中的硼和硅发生(n,α)和(n,p)反应,导致窗玻璃产生荧光,从而使光阴极发射光电子。在5SDH-2小串列加速器上,选用9815B和9850B两种光电倍增管进行实验,得到了光电倍增管的中子直照灵敏度能谱响应曲线。结果表明：中子能量由低到高变化时,光电倍增管的中子直照灵敏度也随之增大;两种光电倍增管的中子直照灵敏度比值为1.9×10²~2.74×10²,该值与其相应的增益比量级一致。     

光电倍增管中子直照灵敏度响应

光电倍增管的中子直照响应对脉冲中子探测器的设计和实际应用具有重要影响。分析了中子束直接照射光电倍增管产生直照响应的过程和机理。中子与光电倍增管入射窗硼硅玻璃中的硼和硅发生(n,α)和(n,p)反应,导致窗玻璃产生荧光,从而使光阴极发射光电子。在5SDH-2小串列加速器上,选用9815B和9850B两种光电倍增管进行实验,得到了光电倍增管的中子直照灵敏度能谱响应曲线。结果表明：中子能量由低到高变化时,光电倍增管的中子直照灵敏度也随之增大;两种光电倍增管的中子直照灵敏度比值为1.9×102~2.74×102,该值与其相应的增益比量级一致。     

GaAs:Cr探测器对聚变脉冲中子诊断的灵敏度研究

 介绍了国产GaAs:Cr光电导探测器(简称PCD)在DT聚变中子辐射脉冲测量中的应用，利用PIN探测系统绝对测量结果，获得了GaAs:Cr PCD的14.1MeV中子直照灵敏度是1.5×10^-20C cm²/mm³，测量误差为±18%。此结果与理论预估和国外报道在误差内符合。     

GaAs:Cr探测器对聚变脉冲中子诊断的灵敏度研究

介绍了国产GaAs:Cr光电导探测器(简称PCD)在DT聚变中子辐射脉冲测量中的应用,利用PIN探测系统绝对测量结果,获得了GaAs:Cr PCD的14.1MeV中子直照灵敏度是1.5×10-20C cm2/mm3,测量误差为±18%。此结果与理论预估和国外报道在误差内符合。     

介质型脉冲高能中子探测器

首次报道一种基于反冲质子法和高速带电粒子在物质表面引起二次电子发射的高能中子探测方法,研制成功的新一代强流脉冲高能中子探测器,即介质型脉冲高能中子探测器.与传统的强流脉冲中子探测器相比,该探测器对中子的探测及信号的传输过程是在介质中完成的,因而不需要真空和高压也可以正常工作,并具有多项优异的物理性能.该探测器的输出信号来自于高能中子在聚乙烯转换靶产生的高能反冲质子和这些质子穿越电荷收集极表面时产生的部分二次电子.选择适当的卡阈吸收片和电荷收集极材料,二次电子在探测灵敏度中的份额及其随能量的变化可由实验测定.     

沟槽型硅微结构中子探测器的蒙特卡罗模拟研究

采用蒙特卡罗模拟方法研究了微结构参数、填充致密度等因素对沟槽型微结构半导体中子探测器（MSND）性能的影响规律,并开展了沟槽型MSND的优化设计研究。研究表明,随着沟槽间距的增加,MSND的探测效率呈下降趋势;当沟槽间距固定时,存在最优的沟槽宽度使得探测效率最大化;沟槽深度越大,探测效率越高。沟槽宽度和沟槽间距为15 m和5 m是一对优化的参数组合,可保证较高的探测效率和较平稳的系统甄别阈-探测效率曲线。当系统甄别阈取300 keV时,沟槽宽度、间距和深度分别为15,5 m和200 m时的MSND热中子本征探测效率可达37.77%,与平面探测器相比提高了9.2倍;对137Cs源662 keV伽马射线的中子-伽马射线甄别比可达4.1103,与平面探测器相比提高了23.7倍。本工作从理论上证明了MSND可解决传统平面型半导体中子探测器探测效率低的难题,同时可保持半导体探测器中子-伽马射线甄别容易的特点。     

沟槽型硅微结构中子探测器的蒙特卡罗模拟研究

采用蒙特卡罗模拟方法研究了微结构参数、填充致密度等因素对沟槽型微结构半导体中子探测器(MSND)性能的影响规律,并开展了沟槽型MSND的优化设计研究。研究表明,随着沟槽间距的增加,MSND的探测效率呈下降趋势;当沟槽间距固定时,存在最优的沟槽宽度使得探测效率最大化;沟槽深度越大,探测效率越高。沟槽宽度和沟槽间距为15μm和5μm是一对优化的参数组合,可保证较高的探测效率和较平稳的系统甄别阈-探测效率曲线。当系统甄别阈取300keV时,沟槽宽度、间距和深度分别为15,5μm和200μm时的MSND热中子本征探测效率可达37.77%,与平面探测器相比提高了9.2倍;对137 Cs源662keV伽马射线的中子-伽马射线甄别比可达4.1×103,与平面探测器相比提高了23.7倍。本工作从理论上证明了MSND可解决传统平面型半导体中子探测器探测效率低的难题,同时可保持半导体探测器中子-伽马射线甄别容易的特点。     

γ探测器中子灵敏度标定技术

叙述了γ探测器的14.1 MeV中子灵敏度标定原理和屏蔽方法,利用MCNP程序建模, 优化设计了对γ和中子高屏蔽性能的屏蔽体。 实验研究表明, 其信噪比最高达10∶1, 比测量点本身的信噪比1.35∶1提高了7倍, 从而实现了γ探测器的中子灵敏度标定。 It is introduced that a method and principle for calibrating 14.1 MeV neutron sensitivity of γ ray detector. A shield system for scattering neutrons and γ rays has been optimized by MCNP code. The experimental results show that the signal to noise ratio of the system is about 10:1, 7 times higher than the value of 1.35〖KG-*4〗∶〖KG-*4〗1 without shield system. Calibration of neutron sensitivity of γ ray detector is then accomplished.     

Analysis of the relationship between neutron dose and Cerenkov photons under neutron irradiation through Monte Carlo method

To theoretically explore the feasibility of neutron dose characterized by Cerenkov photons, the relationship between Cerenkov photons and neutron dose in a water phantom was quantified using the Monte Carlo toolkit Geant4. Results showed that the ratio of the neutron dose deposited by secondary electrons above Cerenkov threshold energy to the total neutron dose is approximately a constant for monoenergetic neutrons from 0.01 eV to 100 eV. With the initial neutron beam energy from 0.01 eV to 100 eV, the number of Cerenkov photons has a good correlation with the total neutron dose along the central axis of the water phantom. The changes of neutron energy spectrum and mechanism analysis also explored at different depths. And the ratio of total neutron dose to the intensity of Cerenkov photons is independent of neutron energy for neutrons from 0.01 eV to 100 eV. These findings indicate that Cerenkov radiation also has potential in the application of neutron dose measurement in some specific fields.     

Monitoring the energy variation of an electron linac using a Cerenkov detector

A new method to monitor the energy variation of a multi-energy electron linac by combining a Cerenkov detector and a CsI(Tl) detector is reported. The signals in the Cerenkov detector show an appreciable but different dependence on the energy of the electron linac from the traditional CsI(T1) detector due to the particular response of the former to charged electrons with high velocity above threshold. The method is more convenient than the HVL (half-value layer) method which is commonly employed to calibrate the energy of an electron linac for real time monitoring. The preliminary validity of the method is verified in a dual-energy electron linac with 6 MeV and 3 MeV gears. Moreover, the method combining the Cerenkov detector and the CsI(Tl) detector is applicable to probe the X-ray spectrum hardened by the inspected material and may serve as a novel tool for material discrimination with effective atomic number in radiation imaging.     

Simulation of natural radioactivity backgrounds in the JUNO central detector

The Jiangmen Underground Neutrino Observatory(JUNO) is an experiment proposed to determine the neutrino mass hierarchy and probe the fundamental properties of neutrino oscillation.The JUNO central detector is a spherical liquid scintillator detector with 20 kton fiducial mass.It is required to achieve a 3%/E(MeV)~(1/2) energy resolution with very low radioactive background,which is a big challenge to the detector design.In order to ensure the detector performance can meet the physics requirements,reliable detector simulation is necessary to provide useful information for the detector design.A simulation study of natural radioactivity backgrounds in the JUNO central detector has been performed to guide the detector design and set requirements for the radio-purity of the detector materials.The accidental background induced by natural radioactivity in the JUNO central detector is 1.1/day.The result is satisfied for the experiment.     

Monitoring the energy variation of an electron linac using a Cerenkov detector

A new method to monitor the energy variation of a multi-energy electron linac by combining a Cerenkov detector and a CsI（Tl） detector is reported. The signals in the Cerenkov detector show an appreciable but different dependence on the energy of the electron linac from the traditional CsI（Tl） detector due to the particular response of the former to charged electrons with high velocity above threshold. The method is more convenient than the HVL （half-value layer） method which is commonly employed to calibrate the energy of an electron linac for real time monitoring. The preliminary validity of the method is verified in a dual-energy electron linac with 6 MeV and 3 MeV gears. Moreover, the method combining the Cerenkov detector and the CsI（Tl） detector is applicable to probe the X-ray spectrum hardened by the inspected material and may serve as a novel tool for material discrimination with effective atomic number in radiation imaging.     

The contribution of Neutron and synchrotron radiation topography to the investigation of first-order magnetic phase transitions

Neutron and white beam synchrotron topography have proved to be valuable and complementary tools for the investigation of the coexistence of magnetic phases in single crystals. Neutron topographs indicate unambiguously which phase occupies a given region of the sample, whereas synchrotron radiation topographs give information about the coexistence-related lattice distortion and the dynamics of the phase transition. A few examples illustrate these capabilities. 1) Helimagnetic-ferromagnetic coexistence was followed in Tb and MnP by varying either the magnetic field or the temperature. The observed interfaces appear to result from competition between the elastic and magnetostatic terms of the total energy, the last term being dominant in the field-driven case. 2) The reorientational transition of hematite was shown to correspond, when spread over a wide temperature range, to a succession of abrupt transitions, probably related to an inhomogeneous incorporation of small amounts of impurities during growth. A similar feature also explains the occurrence of small ferromagnetic islands which remain in the helimagnetic phase of Tb.     

4He闪烁裂变中子探测器的中子灵敏度

对4He闪烁裂变中子探测器的中子灵敏度进行了理论和实验研究。采用蒙特卡罗方法模拟了不同能量中子和不同厚度裂变靶产生的裂变碎片在4He中的能量沉积,计算结果表明:中子在4He气中的能量沉积曲线和裂变碎片的能量沉积曲线能够互补,从而使探测器对中子的能量响应变得更平坦;探测器的中子灵敏度为10-15 Ccm2量级。并对探测器的中子灵敏度进行了实验标定,实验结果与理论计算结果较为一致。     

4He闪烁裂变中子探测器的中子灵敏度

对4He闪烁裂变中子探测器的中子灵敏度进行了理论和实验研究。采用蒙特卡罗方法模拟了不同能量中子和不同厚度裂变靶产生的裂变碎片在4He中的能量沉积,计算结果表明：中子在4He气中的能量沉积曲线和裂变碎片的能量沉积曲线能够互补,从而使探测器对中子的能量响应变得更平坦;探测器的中子灵敏度为10-15 Ccm2量级。并对探测器的中子灵敏度进行了实验标定,实验结果与理论计算结果较为一致。     

Neutron response study using poly allyl diglycol carbonate

The results of an experimental work aimed at improving the performance of the CR-39 nuclear track detector for neutron dosimetry applications are reported. A set of CR-39 plastic detectors was exposed to ²⁵²Cf neutron source, which has the emission rate of 0.68 × 10⁸ s⁻¹, and neutron dose equivalent rate 1 m apart from the source is equal to 3.8 mrem/h. The detection of fast neutrons performed with CR-39 detector foils, subsequent chemical etching and evaluation of the etched tracks by an automatic track counting system was studied. It is found that the track density increases with the increase of neutron dose and etching time. The track density in the detector is directly proportional to the neutron fluence producing the recoil tracks, provided the track density is in the countable range. This fact plays an important role in determining the equivalent dose in the field of neutron dosimetry. These results are compared with previous work. It is found that our results are in good agreement with their investigations.      

中子针孔成像点扩展函数模拟研究

应用Geant4系统对中子针孔成像的点扩展函数进行了模拟研究.建立了点扩展函数的数学模型,并将其分布图像与能量沉积数据的分布图像作了比较,可看出点扩展函数与能量沉积数据吻合得较好.研究结果表明,在一定偏移量范围内,拟合得到的点扩展函数更好,能得到较好的图像分辨率.通过对不同入射能量在一定偏移量入射下的点扩展函数讨论认为,入射能量增大虽然会增强图像的对比度,但会降低分辨率.