一、引言 利用大面积或中等面积的探测器测量放射性强度或表面放射性污染时,一定要对仪器进行适当的刻度,以定出探测器的探测效率或仪表总换算系数。探测效率与很多因素有关,原则上应当用与待测样品相同的核素制成的大面积(面积与探测器窗相同)校准源,在实际测量条件下进行刻度。这在实际上很难做到。因为制作各种核素的不同尺寸的大面积校准源(或参考源)成本很高,又不易做得均匀,准确确定其放射性(强度或单位时间向2π方向出射粒子数)也较复杂。而小面积或点状校准源却比较容易制备,成本也 I. INTRODUCTION When using large or medium area detectors to measure radioactive intensity or surface radioactive contamination, the instrument must be properly calibrated to determine the detector’s detection efficiency or total instrument conversion factor. Detection efficiency depends on many factors. In principle, a large area (same area as the detector window) calibration source made of the same sample as the sample to be measured should be calibrated under the actual measurement conditions. This is actually hard to do. Because large-area calibration sources (or reference sources) of different sizes for producing various nuclides are costly and difficult to be evenly distributed, accurate determination of their radioactivity (intensity or number of emitted particles in 2π direction per unit time) is also complicated. The small area or point calibration source is relatively easy to prepare, the cost is also