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采用蒙特卡罗方法对235U裂变电离室进行模拟,在多个单能点及锎源中子场计算其响应值。MCNP4C的F4记录卡可计算出U片中的径迹长度,利用FM乘子卡将径迹长度转换为裂变计数,与U片放置处注量的比值即为该探测器的响应值。本文分别对高灵敏和低灵敏两个电离室的响应进行模拟计算,且在多个单能点进行理论计算,结果列于表1、2。经计算,在2.5MeV单能中子场,U片自吸收的影响约0.6%,探测器结构及空气的散射影响约5%。由表可看出,探测器自身对中子的散射影响在低能点的作用较大,在14.8MeV等高能处的影响较小。
The Monte Carlo method was used to simulate 235U fission ionization chamber, and the response values were calculated at multiple single-energy points and 锎 source neutron sub-fields. The F4 record card of MCNP4C can calculate the track length of U slice. The track length is converted to fission count by FM multiplier card. The ratio of the F-score of U-chip to the place of U slice is the response value of this detector. In this paper, the responses of two highly sensitive and low-sensitivity ionization chambers are simulated respectively. The theoretical calculations are carried out at several single energy points. The results are shown in Tables 1 and 2. It is calculated that at 2.5 MeV monoenergetic neutron field, the influence of self-absorption of U-slice is about 0.6%, and the structure of the detector and the scattering of air are about 5%. It can be seen from the table that the influence of the detector itself on the scattering of neutrons is greater at low energy points and less at high energy of 14.8 MeV.