Ibbott G S, Barnes J E, Hall G R, Hendee W R
Med Phys. 1975 Nov-Dec;2(6):328-30. doi: 10.1118/1.594202.
Ionization chambers often exhibit a stem effect, caused by interactions of radiation with air near the chamber end, or with dielectric in the chamber stem or cable. These interactions contribute to the apparent measured exposure. To determine the stem efffect for several common ionization chamber systems, exposures were measured with TLD capsules placed at the center of 60Co fields of various sizes. These exposure measurements then were repeated with various ionization chamber systems, including two Victoreen R meters (25- and 100-R chambers), a Capintec 192 dosimeter with a Farmer 0.6-cm3 probe, a PTW transit dose probe, and an EG and G IC-18 probe with a Keithley 610-B electrometer. From a comparison of TLD and ionization chamber measurements of the variation in exposure rate with field size, stem corrections for the different systems were determined within 1%.
电离室常常表现出一种“杆效应”，这是由辐射与电离室末端附近的空气、或者与电离室杆或电缆中的电介质相互作用所引起的。这些相互作用会对表观测量剂量产生影响。为了确定几种常见电离室系统的杆效应，使用热释光剂量计胶囊置于不同大小的钴-60射野中心来测量剂量。然后使用各种电离室系统重复这些剂量测量，这些系统包括两个 Victoreen R 剂量仪（25-R 和 100-R 电离室）、一个配有 Farmer 0.6 cm³ 探测器的 Capintec 192 剂量仪、一个 PTW 传输剂量探测器、以及一个配有 Keithley 610-B 静电计的 EG 和 G IC-18 探测器。通过比较热释光剂量计和电离室对剂量率随射野大小变化的测量结果，确定了不同系统的杆效应校正值，其误差在 1% 以内。
