Radiological X-ray dosimetry with single crystal CVD diamond detectors

Pulsed X-ray measurements have been carried out by using new single crystal epitaxial CVD diamond samples about 100 Am thick grown by microwave CVD in Roma Tor Vergata Laboratories on a 300 Am thick, low cost, HPHT diamond substrate. Both sandwich arranged and surface interdigitated contacts were used for the detectors in order to compare their performances. A standard X-ray radiological apparatus was used with maximum X-ray energies from 50 to 120 keV. Delivered doses were in the range between 0 and 50 mGy, with pulse duration times between 0.01 and 0.5 s were obtained either by using different time-integrated mAs products or, at a fixed value of mAs, by using different values of the bias voltage of X-ray generator. The linearity of the dose signal Q given by the integrated current with respect to dose recorded by ionization chamber D was checked by evaluating dose linearity index, i.e. the exponent in the equation Q=ADD. The values of D were very close to 1 (between 1.02 and 1.07) in the case of a fixed mAs product, while it was around 0.8 at fixed voltage in the range 50–120 kV. The response time of the detector as deduced from the tail of the pulse was between 15 and 20 ms. The reproducibility was very good among different series of measurements, with no memory or priming effect. These results suggest a strong and actually real possibility for diamond detectors to be used as solid state ionization chambers in radiology and for diagnostic purposes.