可燃毒物铒的辐照及其同位素热电离质谱法测定

铒(Er)是一种适用于轻水堆(LWR)的长效可燃毒物,Er_2O_3的堆内辐照是研究中子毒物Er辐照性能的基本手段。Er_2O_3在高通量工程试验堆(HFETR)中子注量率约为2×10~(14)/(cm~2·s)的辐照孔道中辐照91.3h。采用热电离质谱法(TIMS)测定辐照前、后样品中Er同位素丰度,跳峰模式测定6个Er同位素,低丰度~(162)Er由法拉第杯检测。测定时准确控制升温测量电流,将蒸发带和电离带电流控制在1 400、5 500mA以下,可减小~(168)Yb、~(170)Yb对~(168)Er、~(170)Er的同量异位素影响。结果表明,经中子辐照后~(166)Er、~(167)Er、~(168)Er同位素丰度变化较大,丰度变化与中子吸收截面大小密切相关。

Irradiation of Burnable Poison-Erbium and Its Isotopic Determination by TIMS

Erbium(Er) is a kind of long-term burnable poison which is suitable for lightwater reactor(LWR).The irradiation of Er2O3 is a basic means to study the performance of burnable absorber Er in the reactor.Er2O3 samples were irradiated in the irradiation channel (neutron fluence rate is about 2 × 1014/(cm2 · s)) of high flux engineering test reactor (HFETR) for 91.3 h.The Er isotopic abundances of irradiated samples were measured by thermal ionization mass spectrometry(TIMS).The peak jumping mode was applied to determine the 6 isotopes of Er,and the low abundance 162Er was detected by the Faraday cup.Isobaric interferences can be reduced by accurate control of heating current.Experiment shows that the isobaric interferences of 168Yb,170Yb were reduced when the evaporation filament current was below 1 400 mA and ionization filament current was below 5 500 mA.The measurement results show that the 166Er,167Er and 168Er isotopic abundance changes greatly after neutron irradiation,and the variation of abundance is closely related to the neutron absorption cross section.