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本文描述了两种用于测量医用β敷贴器表面剂量率的外推电离室的设计原理、结构、性能和实验结果。一种的收集极和保护环块用喷涂小于０．０５ｍｍ的石墨层的聚苯乙烯材料做成；另一种的收集极和保护环块是由石墨块作成的分立的同心体。两种外推室的极间距行程均为０－１０ｍｍ，槽沟宽度均小于０．３ｍｍ，入射窗用７ｍｇ·ｃｍ－２厚度的铝化聚脂膜加聚脂膜构成；均能方便地更换（不同尺寸和材料）收集极和调节极间距。前一种在几十Ｇｙ照射后一小时，即可恢复到正常本底水平；后一种在几十Ｇｙ照射后，立即恢复到正常本底水平；解决了测量大剂量时克服“记忆效应”的难题
This article describes two design principles, structures, performance, and experimental results of two extrapolation ionization chambers designed to measure the dose rate of a medical beta applicator. One collector and guard ring block is made of a polystyrene material sprayed with a graphite layer of less than 0.05 mm; the other collector and guard ring block is a discrete concentric body made of graphite blocks. Polarization distance between the two types of extrapolation room are 0-10mm, groove width is less than 0.3mm, the incident window with 7mgcm-2 thickness of the aluminum-based polyester film and polyester film composition can be easily replaced (Different sizes and materials) collector and adjust the pole pitch. The former returns to its normal background level one hour after exposure to tens of Gy; the latter regains its normal background level immediately after exposure to tens of Gy; and overcomes the problem of “memory effect” The problem