关键词: 射线衰减规律, 质量吸收系数, 混相密度, 测量精度

Abstract: Several methods of improving measurement precision, other than traditional methods such as adopting a high activity ray source and prolonging sampling time, are presented. The attenuation law of the ray was discussed, and an amended mass absorption coefficient (m￠m) was suggested to make convenient use of this law. m￠m was almost independent of the ray intensity when the ray intensity was more than 100 Bq, but decreased evidently when the response frequency of the measurement system was low and the ray intensity was high, especially when the ray intensity was less than 100 Bq. Therefore, the response frequency and the ray intensity should be as high as possible to improve the measurement precision. It was found that m￠m did not depend on the object's thickness but on the location where the object was placed between the ray source and the detector. It can be concluded that in any cases, the closer the object to the detector, the less the m￠m. It was also found that the effect of object's location on m￠m was related to the area through which rays are entered to the detector, and this effect increased with the increase of the detector area. This is more evident when the object is near the detector or the ray source. The GTS-2000 measurement system was developed and used to measure not only ray intensity but also ray spectrum. By the aid of the ray spectrum obtained by GTS-2000, the gain of the measurement system could be easily adjusted to an optimum value and the up-threshold and down-threshold values of the single-energy rays could be easily selected before ray intensity was measured.

Key words: ray attenuation law, mass absorption coefficient, mixture density, measurement precision