元素分离样品中丰中子同位素弱γ活性探测

Detection of Weak γ-Activities of Neutron-Rich Isotopesin Element-Separated Sample

ＭＰＧｅγ探测器的γ能量信号与４πＥβ探测器的β射线能损信号符合后再与ＢＧＯ探测的β＋衰变的正电子湮灭５１１ｋｅＶγ信号作反符合组成一种新的探测系统。该系统可使γ谱测量的康普顿本底下降约一个数量级。对缺中子同位素衰变γ射线的探测作强抑制的同时，丰中子同位素衰变γ射线的探测仍能保持相对单谱为（４６±３）％的高效率。使用该系统对已被合成的丰中子核素２０８Ｈｇ的半寿命进行了一次新的测定。所得新的２０８Ｈｇ半寿命测定值４１．５＋ｍｉｎ，与以往用放射化学母牛法给出的结果一致，测量误差有较大改进。

A new detection system was constructed by means of combination of a coincidence and an anticoincidence. The γ-ray energy signals detected by a HPGe detector were in coincidence with energy-loss signals of β rays detected by a 4 detector, then the coincidence output were in anticoincidence with the positron-annihilating 511 keV signals detected by a large BGO detector. This system may reduces the Compote background for spectrum measurement by about one order of magnitude. With strong suppression to the detection of the decaying rays from neutron-deficient isotopes, the detection of the decaying rays from neutron-rich isotopes can keep a higher efficiency of (46 ± 3)% compared to single-spectrum measurement. This system was used for determining the half-life of the neutron-rich isotope 208Hg. A new value of 41.5 min was obtained, which is in agreement with the earlier value obtained by radiochemical milking method, but the measurement error was substantially improved.