AbstractA 2.45 MeV neutron time-of-flight spectrometer is under design and construction for the measurements of neutron energy spectra from the JT-60U Tokamak. This paper describes the results from the Monte Carlo code, McTOF, which was written for the simulations of the response functions of the spectrometer. The spectrometer consists of two fast plastic scintillators (50 and 1800 cm2; thickness, 2 cm) located on a constant time-of-flight sphere. By introducing a second time-of-flight sphere, it was found that if the first scattering scintillator was tilted an angle of 70° (utilizing the properties of the second sphere), the resolution of the instrument improved by more than 30%. For a given standard set-up of the spectrometer, the resolution was obtained as 105 keV (4.3%) with an efficiency of 2.8×10−2 cm2. This means that for high JT-60U neutron yields (∼1016 n/s), five to 10 neutron spectra can be measured per plasma pulse. The simulated response functions showed a Gaussian distribution. The parameters of the Gaussian could then be expressed as third-degree polynomials in the source neutron energy interval 1.6–3.6 MeV. This implies that, to extract the measured neutron spectrum, a quick procedure for the folding of a guessed source neutron energy spectrum and an analytical value of the response function can be made.
摘要：一台用于测量JT-60U托卡马克装置中子能谱的2.45 MeV中子飞行时间谱仪正在设计和建造中。本文介绍了蒙特卡罗程序McTOF的模拟结果，该程序用于计算谱仪的响应函数。谱仪由两块快塑料闪烁体（面积分别为50和1800 cm²，厚度均为2 cm）组成，它们位于一个恒定飞行时间球面上。研究发现，通过引入第二个飞行时间球面，并将第一块散射闪烁体倾斜70°角（利用第二球面的特性），谱仪的分辨率提高了30%以上。对于标准配置的谱仪，其分辨率可达105 keV（4.3%），探测效率为2.8×10⁻² cm²。这意味着在JT-60U的高中子产额（约10¹⁶ n/s）条件下，每次等离子体放电可测量5至10个中子能谱。模拟得到的响应函数呈高斯分布，其参数可用源中子能量在1.6–3.6 MeV区间内的三次多项式表示。这表明，通过将猜测的源中子能谱与解析响应函数进行快速折叠，即可提取实测中子能谱。