Fundamental Studies on Radiation Thickness Gage (IV)
Experimental Analysis of Statistic Errors
1970 Volume 19 Issue 3 Pages 123-128
Details
1970 Volume 19 Issue 3 Pages 123-128
In last report, part (III), of this study, a formula for calculating the optimum radiaton intensity for the detection of small changes in thickness was induced. The formula includes some important factors such as the pulse height spectrum induced in the radiation detector and absorption characteristics of samples. These two factors are discussed minutely in this report.
The pulse height spectrum was investigated with β-rays from 90Y-90Sr. The β-rays were measured by silicon semiconductor radiation detectors of two different types, i.e. planer type and Li ion drift type. The reason why these two types were picked out is that these two solid state ionization detectors are considered to be similar in the function to the gas ionization chamber. The results are as follows; the shape of spectrum is obviously deformed with the change in thickness of the depletion layer, and the mean value ‹q›, standard deviation σq of the spectrum, and their ratio ‹q›/σq increase along with thickness of the depletion layer. In view of this result, it is hoped that the increasing air pressure in the ionization air chamber will decrease the statistical error of the output. The error, however, scarcely changes. When β-rays decrease by penetrating some absorber, the shape of spectrum changes little, and the same thing is observed with the ionization air chamber.
As to the absorption characteristics, the experimental results shown in the part (I) of this study is used. The absorption curves develope various shapes. They can be classified into three types, and are approximated by each formula.
Finally, the optimum intensity of radiation is calculated with some examples by putting these results into the formula.
