Phillips H C, Sephton J P, Johansson L C, Dean J C J
National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, UK.
Appl Radiat Isot. 2012 Sep;70(9):2043-6. doi: 10.1016/j.apradiso.2012.02.039. Epub 2012 Apr 3.
The activity concentration of gaseous beta-emitting radionuclides such as (3)H, (85)Kr and, more recently, (11)C, is measured at NPL using a set of length-compensated proportional counters. The active gas is mixed with argon-methane (P-10) and passed to the counters. Adding gases to P-10 changes the mean ionisation energy, W, of the gas mixture. Estimation of the counting losses using the Monte Carlo model requires a knowledge of W. Unfortunately, only a limited amount of published data is available. This paper describes the initial experimental studies performed to enable the extension of the MC model based loss correction method to gases other than carbon dioxide in P-10. Preliminary measurements have been made to determine the W value for a gas mixture containing (85)Kr in nitrogen and P-10. The DC current through the counters is measured; the counters are also operated in the normal way with pulse amplifiers, discriminators and scalers. The value of W is derived from a knowledge of activity, counter current and mean beta energy.
使用一组长度补偿比例计数器在国家物理实验室测量气态β发射放射性核素如³H、⁸⁵Kr以及最近的¹¹C的活度浓度。活性气体与氩甲烷（P - 10）混合后通入计数器。向P - 10中添加气体会改变混合气体的平均电离能W。使用蒙特卡罗模型估算计数损失需要了解W值。不幸的是，公开数据有限。本文描述了为将基于蒙特卡罗模型的损失校正方法扩展到P - 10中除二氧化碳以外的气体而进行的初步实验研究。已进行初步测量以确定含氮和P - 10的混合气体中⁸⁵Kr的W值。测量通过计数器的直流电流；计数器也以正常方式与脉冲放大器、鉴别器和定标器一起运行。W值由活度、计数器电流和平均β能量推导得出。
