Improvement of the dosimetric properties of chemical-vapor-deposited diamond films by neutron irradiation

The performance of chemical-vapor-deposited (CVD) diamond films as on-line dosimeters has been substantially improved after irradiation with fast neutrons up to a fluence of 5x10(14) n/cm(2). This is correlated to a decrease of more than one order of magnitude in the concentration of deep levels with activation energy in the range 0.9-1.4 eV, as observed by thermally stimulated current and photoinduced current transient spectroscopy. As a consequence, a fast and reproducible dynamic response is observed during irradiation with a 6 MV photon beam from linear accelerator and with a Co-60 source. A quasilinear dependence of the current on the dose rate is obtained in the range of interest for clinical applications (0.1-10 Gy/min). The resulting sensitivity is definitely higher than that of standard ionization chambers, and compares favorably with those of standard silicon dosimeters and of best-quality natural and CVD diamond devices. (C) 2002 American Institute of Physics.