^(252)Cf(D_2O)中子源实验室中子散射的模拟及验证

Simulation and verification of neutron scattering at ^(252)Cf(D_2O) neutron laboratory

为了准确刻度中子剂量当量仪的性能参数以及验证中子剂量当量仪设计的准确性,在252Cf(D2O)源实验室进行实验校准之前,先采用MCNP5分别模拟分析实验室中空气、墙壁以及石蜡桶对探头中子计数的影响。模拟实验表明,在理想条件下,随着源与探头距离的增大,中子计数率越来越小;空气对中子计数的影响呈先增加后减小再增加的趋势,中子散射率不超过10%,且距离越近,空气散射的中子对探头计数的影响越小;当探头与源距离260cm左右时,石蜡桶对探头计数的影响最小,达到1%;墙壁对中子计数的影响随着探头与源距离增大而逐渐增大,当探头与源距离为360cm时,墙壁散射的中子是源中子计数的2倍;当源与探头距离为175cm时,空气、墙壁以及石蜡桶对源中子的散射最小,测量数据最精确。并通过实验与模拟数据对比表明,源与探头距离在125–300cm之间,计数率误差不超过30%,符合中子剂量测量的技术要求,从而验证了此中子剂量当量仪设计的准确性。

Background： Although the measurement of neutron dose equivalent was initiated several decades ago, the accuracy of the measurement is not high enough due to the dosimeter＇s sensitivity and fiuence response. Purpose： The aim of this work is to accurately scale the performance parameters and insure the design accuracy of neutron dose equivalent instrument. Methods： MCNP5 was used for simulation analysis of the impact of air, walls, and paraffin in the laboratory respectively on the barrels of neutron counting before experiment. Results： The experimental results show that under ideal conditions, the neutron counting rate decreased with the increase of distance between the source and probe. The air impact on neutron count was up at first and then became weakened, but tended to be strengthened again finally. The neutron scattering rate was less than 10%. And the shorter the distance was, the weaker became air scattering neutrons impact on probe counting. When the probe and the source distance reached 260 cm, the influence of the paraffin barrels was the weakest, which was 1%. The influence of the wall on the neutron count increased with the source-probe distance. When the probe and the source distance was 360 cm, the neutron scattering from the wall was 2 times of that from the source. When the source and the probe distance was 175 cm, all of influences to the neutron scattering reached the minimum, and the measurement data tended to be the most accurate. Conclusion： Through the comparison between experimental and theoretical data, the error of the count rate is less than 30% when the source and the probe distance is between 125-300 cm, confirming with the requirements of the neutron dose measurement technology, which verifies the accuracy of the neutron dose equivalent instrument design.