露出線図のパラメータにはどのようなものがあるか？

What are different exposure chart parameters?

Codes for the inspection of welds and castings specify the maximum allowed radiation intensity, based on the type of material and the thickness of the object. Exposure charts are necessary to etablish the correct exposure value. A universal exposure graph or slide-rule can be used for radioactive sources, as these have a fixed natural radiation spectrum.

Fig. 1-9. Step wedge

The radiation spectrum of X-ray tubes varies with each tube, even if they are of the same type. This problem is easily solved by using a universal exposure chart for the specific type of tube, and then individualise it for each tube, the so-called “curve fitting”. The adaptation is normally limited to a zero-point correction, based on a few measured values obtained by trial. Sometimes the gradient of the exposure graph needs to be adjusted as well.

An exposure chart is produced by making a series of radiographs of a step wedge as illustrated in figure 1-9.

The radiation intensity level of most X-ray equipment is expressed by the amperage of the current through the X-ray tube, measured in milliampères (mA).
The exposure (radiation dose) is specified as the product of radiation intensity and exposure duration in mA.min. (intensity x time).

The exposure chart shows the relationship between the thickness of the object (in mm) and the exposure value (for X-ray tubes in kV and mA.min; for sources in GBq/h).