论文题目：低强度脉冲裂变中子探测技术研究
作者简介：欧阳晓平，男,1961年01月出生，1998年09月师从于复旦大学霍裕昆教授，于2002年07月获博士学位。
摘
要
本文对低强度脉冲裂变中子探测技术和介质型中子探测器的设计原理进行了系统的探索和研究。在国内首次研制成功三种适合于低强度微秒级脉冲辐射测量的探测器系统：1.狭缝式大面积PIN裂变中子探测系统；2.闪烁薄膜裂变中子探测器；3.夹层式统计增强型大面积厚PIN探测器阵列。这些探测器系统形成了低强度裂变中子测量较完整的技术体系，基本满足了国家试验在这一研究领域的需要。此外,发展了无源介质快中子探测器的探测理论，建立与完善了相应的探测技术。
脉冲裂变中子探测是低强度脉冲源辐射特性诊断的主要手段之一，诊断数据对认识和了解该类源产生过程、形成特性和再现机制具有重要意义。在这一研究领域，国外进行了大量的研究和探索，但至今未见公开的技术报道。而国内在这一领域的探索和研究才刚刚起步，几乎没有资料可参考借鉴。低强度脉冲裂变中子探测，要求探测系统具有高灵敏度、高n/g分辨、平坦的能量响应和绝对测量性能，其中子灵敏度比传统强流脉冲裂变中子探测系统最多要高出10个量级，测量范围覆盖10个量级以上，因此，测量要求高、技术复杂、难度大，被视为是一项具有挑战性和开拓性的重大课题。
本文首先研制成功狭缝式大面积PIN裂变中子探测系统和相关的实验技术。在传统裂变中子探测技术的基础上，本文首先提出了低强度脉冲辐射源中子诊断的狭缝探测概念。通过设计外延式铅狭缝准直器、研制大面积PIN探测器和大面积低本底裂变靶，把系统的裂变中子探测灵敏度提高到10-16
C.cm2，比原有的裂变中子探测系统灵敏度(10-21~10-22C.cm2)提高4个量级以上，并成功消除了伴随伽玛的干扰。通过建立性能参数测量的实验系统、方法和现场应用技术，解决了研制中的关键技术难题。
研制成功闪烁薄膜裂变中子探测器和相关的实验技术。为获得更高的中子探测灵敏度，本文采用M-C模拟方法，对有机薄膜闪烁体的中子、伽玛灵敏度随厚度的变化进行了大量的模拟计算，提出了低强度裂变中子诊断的闪烁薄膜探测概念。采用合理的结构设计，解决了伴随伽玛的干扰，研制了适合现场应用的薄膜探测器。同时，建立了探测器灵敏度等性能参数的测量方法和系统。实验表明，闪烁薄膜探测器灵敏度可高达10-12C.cm2，比原有裂变中子探测系统高9个量级，n/g
分辨可达15倍以上，并具有很好的能量响应。
研制成功夹层式统计增强型大面积厚PIN探测器阵列。为实施伽玛强度的绝对监测，进行n、g联合诊断并扣除中子测量中的g本底，本文提出了低强度脉冲源伽玛信号绝对测量的阵列探测概念，研制成功具有高灵敏度的夹层式统计增强型大面积厚PIN探测器阵列。其伽玛灵敏度比原有单片小PIN提高4个量级，并显示出良好的能量响应。
探索并发展了空气环境下无源介质快中子探测器的探测理论。提出了相关的理论模型，其要点是将空气中高速带电粒子在介质表面的二次电子发射产额视为纯介质表面发射产额和空气表面发射产额的线性组合。提出了探测器设计中，组成探测芯子的材料在给定能区的质子阻止本领必须互成正比的设计要求，进而发展了严格的介质中子探测器探测理论，通过多次现场应用检验，证明理论模型是正确的。介质探测器较之其它探测器，具有更为优越的性能，且结构简单、成本低，使用方便。
本文独立发展的三种探测器(系统)，构筑了独具特色的低强度脉冲裂变中子探测技术体系，在国家试验脉冲源性能参数诊断的应用中，获得了很有价值的脉冲中子、伽玛特征数据。特别是在这次实验中提供的中子增值率参数，突破了历年来无论国内或国外只能采用g间接测量中子增值率的传统，开辟了直接由中子测量中子增值率的新技术途径。这些探测系统的研制和应用成功，标志着低强度脉冲中子测试技术取得了重要突破，使我国核装置脉冲中子探测水平上了一个新的台阶。它们构成了独具特色的脉冲源裂变中子诊断技术系列，满足了国家研究的需要。其研究成果已获2项发明专利，另一项发明专利申请已受理。相关技术尚未见国内外公开报道。
关键词：低强度，脉冲裂变中子，辐射探测，n/g分辨，探测灵敏度，能量响应
This
thesis has conducted systematical studies on the detection of pulsed fission
neutron flux from a low-intensity and microsecond-duration radiation source.
Three types of devices have been explored and developed. Those are
slot-calibrated large area PIN fission neutron detecting system; foil
scintillator fission-neutron detector; and Teflon-sandwiched large area PIN
array. In addition, we have proposed novel principle for developing medium-type
fast-neutron detector.
Detection of fission neutrons from a
low-intensity radiation source is a frontier research subject with important
significance. From the measured results, one can get important information about
the fission neutron source, such as the generating process, formation mechanism.
In the research area, the foreign countries have conducted a lot of studies to
evaluate and improve their designs. However, those studies are highly
classified, therefore no public materials are available. In our country,
research in this area is still in the early-stage, and we have to do everything
from beginning. Detection of pulsed low-intensity neutron flux requires
development of sophisticated detectors, which have to possess high efficiency,
high n/g
discrimination, flat energy response and capability of conducting absolute
measurements. Furthermore, the detectors should be able to cover dynamic range
more than ten decades, and to achieve the highest efficiency with ten orders of
magnitude higher than that of the existing systems. All those requirements make
this task be a new challenge to explore.
First,
we have developed a novel detector with an outward-laid lead slot calibrator. By
designing the slot calibrator and developing large area PIN detectors as well as
large area fissionable target with thin Be substrate, this detecting system can
reach high neutron efficiency up to 10-16C.cm2, which is
about 4~5 orders of magnitude higher than that of the existing fission
detectors.
A
thin scintillatior foil detector for fission neutron measurements has been
developed and tested. Based on the large amount of Monte-Carlo calculations, a
concept of measuring pulsed neutron fluxes in high gamma-ray environments with a
thin plastic scintillator foil detector has been proposed. The developed
scintillator foil detector is proved to possess high efficiency, high n/g
discrimination and excellent energy response. The neutron detection sensitivity
can reach 10-12C.cm2, almost nine orders of magnitude
higher than the traditional fission detection systems, and the n/g
discrimination is reaching a factor of 15.
To
monitor the neutron and gamma flux simultaneously for combined n,g
measurements, a concept using high efficiency PIN detector array for gamma ray
measurement is presented, which sandwiches 10 PIN detectors and 11 Teflon disks.
The array has a detection sensitivity of four orders of magnitude higher than
individual PIN detector with size f20
and shows an excellent energy response.
Medium-type
pulsed fast-neutron detector is a kind of neutron detector which possesses much
better performances over the existing ones. Now we have developed a new kind of
medium-based detectors which can work at atmosphere environments. The physical
principle of these detectors was studied. Through proof-of-principle test and
applications in actual situations, this kind of detectors shows much better
performance than the old ones where the target has to be placed in the vacuum
environment.
In
summary, three kinds of devices have been developed, which constitute a
detection system for low-intensity pulsed fission neutron measurements. This
system worked very well and provided important parameters of neutrons and gamma
rays in applications in the national experimental research. The establishment of
the detecting technology for measurement of low-intensity pulsed fission
neutrons bridges the gap in the related research fields in the country. The
successful applications demonstrate an important breakthrough in the detection
of the low-intensity pulsed neutron source in the country. We have applied for
national invention patent for the three devices, among them, two have been
authorized, the third is accepted for evaluation.
Keywords:
Low-intensity, Pulsed fission neutrons, Radiation detection, n/g
discrimination, Detection sensitivity, Energy response
