Kossert Karsten, Nähle Ole J, Carles Agustín Grau
Physikalisch-Technische Bundesanstalt, Braunschweig, Germany.
Appl Radiat Isot. 2011 Sep;69(9):1246-50. doi: 10.1016/j.apradiso.2011.03.046. Epub 2011 Apr 9.
The Physikalisch-Technische Bundesanstalt (PTB) investigated the low-energy beta emitter (241)Pu within the scope of an international key comparison on the activity concentration of the same solution. The activity concentration was measured by means of liquid scintillation counters with two and three photomultiplier tubes (PMT). The counting efficiencies were determined with two established techniques, which are based on a free parameter model. The free parameter is determined via (3)H-efficiency tracing in systems with two PMTs, or it is derived from the triple-to-double coincidence ratio (TDCR) in a system with three PMTs. Both methods require an accurate computation of the beta emission spectrum of the first-forbidden (non-unique) transition. In this work, the experimental outcome of a recent measurement from Loidl et al. (2010) with cryogenic magnetic calorimeters was used to determine a shape-factor function. The computed beta spectrum is in good agreement with the measured data when the shape-factor function C(W)=1-1.9582W+0.96078 W(2) and an end-point energy E(β,max)=21.6 keV are used. The activity concentrations determined with the two methods agree well when using the new shape-factor function, whereas a considerable discrepancy is found when assuming C(W)=1, as for an allowed beta transition. Consequently, the difference between the efficiency tracing method and the TDCR method, as observed by other researchers, could be resolved.
德国物理技术研究院（PTB）在关于同一种溶液活度浓度的国际关键比对范围内，对低能β发射体（241）Pu进行了研究。活度浓度通过配备两个和三个光电倍增管（PMT）的液体闪烁计数器进行测量。计数效率采用两种既定技术测定，这两种技术均基于自由参数模型。在配备两个PMT的系统中，通过（3）H效率追踪确定自由参数；在配备三个PMT的系统中，则从三重符合与二重符合比（TDCR）推导自由参数。这两种方法都需要精确计算第一禁戒（非唯一）跃迁的β发射谱。在这项工作中，利用洛伊德尔等人（2010年）近期使用低温磁热计进行测量的实验结果来确定形状因子函数。当使用形状因子函数C（W） = 1 - 1.9582W + 0.96078W²以及端点能量E（β,max） = 21.6 keV时，计算得到的β谱与测量数据吻合良好。使用新的形状因子函数时，用这两种方法确定的活度浓度吻合良好；而当假设C（W） = 1（如同允许的β跃迁那样）时，则发现存在相当大的差异。因此，其他研究人员所观察到的效率追踪法与TDCR法之间的差异得以解决。
