γ射线衰减法测量混相密度

Improvement of γ-ray Attenuation Technology in Measuring Density of Multiphase Flow

对射线的衰减规律提出了一个修正的质量吸收系数μ'm.测量系统的响应频率偏低而射线强度又较大,或者射线强度较小时(＜100 Bq),射线强度将明显影响μ'm.待测物体离探头相对位置越近时,物体对射线的μ'm越小.物体在探头和射线源之间的中部(相对位置在20%～80%),位置对μ'm的影响较小.实验还发现μ'm几乎与物体的厚度和状态无关.采用GTS-2000系统既能测量射线强度,又能测量射线能谱,借助能谱可直观地选定单能峰值γ射线所在的上下阈值,有助于提高测量系统的稳定性.

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 (mm) was suggested to make convenient use of this law. mm 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 mm did not depend on the object抯 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 mm. It was also found that the effect of object抯 location on mm 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.