中子活化分析参量化的进一步研究——Ⅱ.堆快中子阈反应干扰的参量法校正

FURTHE.R STUDY ON PARAMETERIZATION OF REACTOR NAA Ⅱ.PARAMETERIZED CORRECTIONS FOR THRESHOLD REACTION INTERFERENCES INDUCED BY REACTOR FAST NEUTRONS

在文献[1]中作者建议了裂变干扰校正的Ik_0法。堆中子活化分析中的另一重要干扰是堆快中子引起的阈反应干扰。鉴于此类干扰的日益增长的重要性和使用“干扰标准”进行相对比较法校正的困难,本工作以多个阈探测器证实了我院重水反应堆典型的重水反射层孔道和2号水平孔道跑兔位置的快中子通量(E_n>4MeV)具有近似的初级裂变谱。在此基础上,建议了在常规分析的长照射中以T_i片作快通量分布的初级裂变谱性质检验和“即时”快通量监测器,进行阈反应干扰的参量法校正;对2号孔道的短照射,本工作得到的φ_f/φ_s=0.70％,在定期核对的基础上,可直接用于阈反应干扰的计算扣除。

In the last paper,Ik0, method was proposed for fission interference corrections. Another important kind of interferences in reactor NAA is due to threshold reaction induced by reactor fast neutrons. In view of the increasing importance of this kind of interferences, and difficulties encountered in using the relative comparison method, a parameterized method has been introduced.Typical channels in heavy v/ater reflector and No. 2 horizontal channel of Heavy Water Research Reactor in our institute have been shown to have fast neutron energy distributions(E>4 MeV) close to primary fission neutron spectrum, by using multi-threshold detectors. On this basis, Ti foil is used as an ''instant fast neutron flux monitor'' in parameterized corrections for threshold reaction interferences in our long irradiations. Constant values of (φ)/(φ)s=0.70±0.02% have been obtained for No.2 rabbit channel.This value can be directly used for threshold reaction interference correction in our short irradiations.