DEPENDENCE OF THE TSEE RESPONSE OF BEO THIN-FILMS ON PHOTON ENERGY AND COMPOSITION OF COVER MATERIALS

The TSEE response (thermally stimulated exoelectron emission) of BeO t hin films to photon irradiations at constant H(0.07) has been determin ed over the photon energy range from 15 keV to 1.25 MeV. The detectors were covered with different plastic foils of an effective atomic numb er varying between 6.7 and 9.7 and a thickness of 7 mg.cm-2 irradiated on a 30 x 30 x 15 cm3 PMMA slab phantom. The values of H(0.07) were c alculated from air kerma with the aid of published conversion coeffici ents. The response curves obtained demonstrate that the BeO layer of t he detectors behaves like a Bragg-Gray detector at photon energies abo ve 30 keV. Between 30-40 keV the response is strongly dependent on the composition of the cover material. At about 100 keV the low atomic nu mber of the detector substrate causes undersensitivity.