Development of Measurement Technique of Fast Neutron Flux with Nuclear Emulsion in the Underground Laboratory

核乳剂是一种高灵敏度的照相胶片，用于探测带电粒子的三维轨迹。用核乳剂测量快中子的原理是检测中子反冲的质子。然而，被伽马射线散射的电子轨迹也记录在核乳剂中。这些电子径迹是快中子测量的主要背景。通过在溴化银晶体中加入微量的铑来控制其灵敏度，从而开发出一种新型的核乳剂，并获得了良好的电子背景抑制性能。这种新型乳剂可用于地下实验中快中子通量的测量。

Nuclear emulsion is high sensitive photographic film used for detection of three-dimensional trajectory of charged particles. The principle of the measurement of fast neutron with nuclear emulsion is the detection of proton recoiled by neutron. However, electron tracks scattered by gamma rays are also recorded in the nuclear emulsion. These electron tracks are major background for fast neutron measurement. We developed new nuclear emulsion by adding a tiny amount of the rhodium into the silver bromide crystals in order to control the sensitivity and achieved high performance of electron background rejection. We can use this new emulsion to measure fast neutron flux in the underground experiment.