基于β射线技术测量PM_(2.5)的准确性研究

Exploration of PM_(2.5) measuring accuracy based on β-ray measure technology

为了实现对PM_(2.5)细颗粒物浓度的准确测量,分析了影响准确测量PM_(2.5)浓度的因素。β射线测量PM_(2.5)准确性的关键在于质量吸收系数的确定,其大小直接影响最终PM_(2.5)浓度的计算。通过试验证明决定质量吸收系数大小的四大因数为β射线穿过的多层滤膜的物理分布结构、射线源能量、射线源到滤膜的距离及滤膜的密度,被透射介质的厚度及滤膜的质量对质量吸收系数没有影响。利用标准膜对仪器的精度进行了校正,对量程进行了标定。

This paper is aimed at finding an approach to accurate measurement of the concentration of PM_（2.5）. As is known,PM_（2.5）has been a serious pollution problem for China,but it is hard to be measured accurately,especially under the complicated environment. In order to accurately measure the concentration PM_（2.5）,first of all,we have to study the measuring theory here in this paper,that is,the β-ray theory,or,more precisely speaking,theβ-ray attenuating theory,which can satisfy the index law perfectly. So there is a formula that can help to calculate the emission of PM_（2.5）concentration. From the formula,it can be seen that the key to the accurate measurement of β-ray is to determine the mass-absorption coefficient μmand mass thickness of dm. Thus,the formula involves two important parameters,the units of dmare g / cm2,which can be worked out by the formula： dm= ρL = m /（ πr2）; whilst the units of μmare cm2/ g is an experimental parameter,which is what this paper has to be concerned about most and accounts for what it can affect and how to be affected by. It is just for its importance that,we have,first of all,analyzed what can affect the said μm. And,secondly,we have to analyze how it can be affected. It is just for this purpose that we have established an experimental system which includes the natural radioactive element C14 and the band multiplier detector. What is more,it is just by using the system that the distance between the radioactive source and the detector can be easily changed. Furthermore,it is only by changing the said distance that it is possible for us to be able to analyze whether the energy of β-ray can affectμm. And,by changing the thickness L of the filters and the quality m of the filters that we can find out whether L or m can affectμm. And,finally,through the aforementioned experiment,we have confirmed the four factors that can determine the mass-absorption coefficient,namely： the physical structure of the penetrated filter by β-ray,the energy of β-ray,the distance between βsource and the filter,as well as the density of the filter. But,unfortunately,nothing has been found to contribute to the mass-absorption coefficient by changing the thickness of the penetrated filter,neither to the change of the quality of the filter. All in all,it can be concluded that,when we adopted the standard-filters in the system to test and examine whether the machine is equal to the weight,it can be found that the standard-filters may have different weights based on the measuring range of the machine,which can help us to work out the weight of the filters that are needed.