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 in measurements of gamma dose in mixed gamma-neutron fields, in high energy bremsstrahlung and soft X-ray fields. It is shown that a kovar cap should be avoided for dosimetry applications in the presence of strong thermal neutron fluences. In regions of strong electronic disequilibrium the “bare” or unencapsulated MOSFET is a unique tool for surface dose measurements and Monte Carlo model validation. For depths where electronic equilibrium exists (i.e. x>depth of D_max) the MOSFET package is not critical. For low energy X-ray fields the energy dependence of the dose enhancement factor (DEF) will differ depending upon whether the irradiation is performed in free air geometry or on the surface of a phantom