MOSFET DOSIMETERS - THE ROLE OF ENCAPSULATION ON DOSIMETRIC CHARACTERISTICS IN MIXED GAMMA-NEUTRON AND MEGAVOLTAGE X-RAY FIELDS

This paper is concerned with the role of the package of MOSFETs used i n measurements of gamma dose in mixed gamma-neutron fields, in high en ergy bremsstrahlung and soft X-ray fields. It is shown that a kovar ca p should be avoided for dosimetry applications in the presence of stro ng thermal neutron fluences. In regions of strong electronic disequili brium the 'bare' or unencapsulated MOSFET is a unique tool for surface dose measurements and Monte Carlo model validation. For depths where electronic equilibrium exists (ie. x > depth of D-max) the MOSFET pack age is not critical. For low energy X-ray fields the energy dependence of the dose enhancement factor (DEF) will differ depending upon wheth er the irradiation is performed in free air geometry or on the surface of a phantom.