Application of semiconductor elements for dosimetric purposes

The effect is described of the individual types of radiation with an energy greater than 100 keV on a semiconductor crystal from the point of view of permanent changes. Radiation defects in semiconductors resulting from ionization, elastic collisions and secondary collisions are shown. The differences between defects resulting from fast neutron and photon irradiation of silicon may be used in fast neutron dosimetry. Fast neutron-induced defects form clusters with a diameter of up to 0.05 μm. Diode sensitivity changes with Esup(1/3) in an energy range of 0.45 to 6 MeV; in a range of 0.45 to 14 MeV the diode may be considered equivalent to a biological tissue with an accuracy of about 20%. Crystal defects in silicon due to fast neutrons are not stable; with increasing temperature their stability decreases. The dependence is shown of Czechoslovak diodes on fast neutron fluence at a measuring current of 25 mA. The detection threshold of neutron doses is 0.05 Gy while the upper limit is 1O Gy. Diode sensitivity to gamma radiation is lower by more than 3 orders. Gamma doses may be determined using MOS transistors by e.g. measuring the shift of characteristics. MOS transistor (MH 2009) responses to gamma radiation doses (60Co) are shown. The silicon diode is advantageous in that it may be re-used after annealing. MOS transistors may be re-used for dosimetric purposes after annealing at 300 to 400 degC for over several hours. (J.P.)