质谱法测定西安脉冲反应堆^(99)Tc嬗变率

Determination of ^(99)Tc Transmutation Rate in Xi'an Pulse Reactor by Mass Spectrometer

热堆是嬗变长寿命放射性裂变产物的有效途径之一。西安脉冲反应堆属于低中子通量热堆(满功率运行时热中子通量密度为4.5×10^(13)cm^(-2)·s^(-1)),利用该堆开展了6个裂变产物^(99)Tc靶的嬗变技术研究。经过6h满功率辐照,^(99)Tc辐照产物^(100)Ru在靶件中的含量接近10^(-6)水平,为测定^(99)Tc的嬗变率,采用高灵敏的质谱分析方法准确测量辐照产生的痕量^(100)Ru的量。为克服本底干扰和同质异位素的影响,采用单接收ICP—MS测量了未辐照前锝金属靶件中的杂质含量,采用^(99)Ru同位素稀释多接收电感耦合等离子体质谱技术测定了化学制样流程本底铷的含量,并对流程本底中Ru同位素比值进行了分析,最后采用同位素稀释质谱技术测量了6个辐照靶件^(100)Ru的含量。结果表明,嬗变率测量值的扩展不确定度好于1.5%。

Thermal reactor is an effective transmutation way of long-lived fission products. Transmutation of six fission product targets containing 99Tc was studied in Xi＇an Pulse Reactor, which is a low flux reactor with the thermal neutron flux density of about 4.5 × 1013 cm-2 s-1. After a 6-hour irradiation of effective full-power, the concentrations of 100 Ru as the transmutation product of 99 Tc in the targets were on the level of 10-5. In order to determine the 99Tc transmutation ratio, measurement of trace 100 Ru in the irradiated targets by highly sensitive mass spectrometer was conducted. But the mass spectrometry analysis of low-level l00Ru was interference by background and isobars. Firstly the amount of impurities in the targets was analyzed before irradiation, and then the Ru background including content and isotopic rates during the chemical preparation procedure were determined by 98Ru isotope dilution with MC-ICP-MS, at last the 100Ru amount of six irradiated targets was measured by isotope dilution mass spectrometry. Result shows that the expanded uncertainty of the result is better than 1.5 %.