低气压高分辨裂变电离室研制

Design on Grid Ionization Chamber with Low Gas Pressure and High Resolution for Fission Fragments Measurement

为开展裂变独立产额测量,研制了一个带有Si3N4入射窗的低气压、纵向型屏栅电离室.通过Garfield++程序模拟计算气体的性质参数,确定了电离室的工作气体为异丁烷,最佳约化场强为3~6 V/(133 cm · Pa).通过 Geant4程序计算得到裂变碎片的射程与工作气压的关系,确定了该电离室的工作气压为 35 Torr(1 Torr= 133.329 Pa).用自转移252Cf裂变源对电离塞进行测试,得到自发裂变碎片的脉冲幅度谱,峰谷比为2.7,能量分辨率好于1%,满足裂变碎片测量的要求.

For measuring the fission fragments independent yields,an axial grid Ionization chamber(GIC)with a thin Si3N4 entrance window was developed which works at low gas pressure condition.The construction of this Ionization chamber is described.The Garfield++code was used to calculate the transport properties of electrons in gas mixtures,the iC4H10 is chosen to work in the GIC and the optimal reduced electric field is 3~6 V/(133 cm-Pa).Under different gas pressure,the range of fission fragments were calculated through Geant4 code,and the favorable gas pressure is 35 Torr.The Ionization chamber was first tested with spontaneous fission products from a self-transfer 252 Cf source,and from the pulse height spectrum,the peak-to-valley ratio of the light fission fragments is 2.7,the energy resolution is better than 1%.