How do I use an exposure chart?
How do I use an exposure chart?
While it may be possible to gradually build up a store of information which can be consulted in day-to-day work, it is better to make use of good exposure charts. This system has many advantages to offer, particularly when it comes to choosing the most suitable working method. Apart from saving time, it gives a guarantee of efficiency and moreover does away with, or reduces to an acceptable extent, the need for trial exposures on jobs which are a little outside the normal routine.
Different X-ray tubes can in practice give quite different results, even though they may be of the same type. Even a different cable length between the control panel and the tube may be of influence. Therefore, an exposure chart for each individual X-ray set should be drawn up. This is an excellent way to become familiar with the equipment, while time and money put into this work will be amply repaid at a later stage.
Exposure charts for gamma-ray examination are drawn up in a similar way as described above.
Figure 5-9 shows one for a Cobalt60 source. A specially designed slide-rule can also be used, since there is no need to consider individual radiation spectra as for X-ray tubes. Figure 6-9 shows a similar exposure chart for an Iridium192 source.
