Detectors Used in Health Physics

For the monitoring of personnel radiation exposures, measurement of radioactive contamination and surveying of laboratories and equipment, and for the detection of radionuclides incorporated in the human body, various detectors and instruments are used. The principles of operation of these detectors have been discussed in the previous sections of this chapter. 

Pocket ionization chambers are small enough to be worn like a ball-pen. They are charged by a temporary connection to a voltage source, and the residual charge after exposure is read on the scale of an electrometer fitted in the ionization chamber. Pocket ion chambers are not sensitive to a and low-energy f radiation. 

In certain crystals such as LiF or CaF2 containing Mn as impurity, the electrons and holes produced by nuclear radiation are trapped on the impurities. In this way energy is stored in the crystals. It can be released in the form of light by heating the crystals. This property of thermoluminescence can be used for radiation dosimetry. 

The crystals are heated electrically and the hght output is measured by means of an photomultiplier. In the ease of LiF(Mn) crystals the response is nearly independent of the energy in the range between about 30 keV and 3 MeV, and the effective atomic number of LiF is similar to that of soft tissue. On the other hand, Li(Mn) is only suitable for doses lOmrad, whereas CaF2(Mn) is sensitive down to %0.1 mrad. 

Contamination on the hands can be detected with Geiger Muller or proportional counters. For detection and measurement of air-borne contamination, filters may be used. The activity on the filters can be measured continuously by passing the filters througli a proportional counter. Radioactive contamination on laboratory benches, instruments or floors can be detected by the simple method of wiping the surface to be checked for contamination is wiped with a piece of filter paper, and the filter paper is measured with a suitable detector for a, p or y activity. 

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