Diamond x- ray dosimeters

The interest in the use of diamond as radiation dosimeter stems principally from its tissue equivalence. The atomic number of diamond (Z=6) matches that of the biological tissue being exposed to high energy photon radiation (the effective number of human tissue is 7.42 for muscle and 5.92 for fat), therefore the energy deposited by any beam of radiation for unit of mass will be virtually the same for tissue and for diamond. This fact makes diamond detectors more suitable than any other solid state dosimeter, e.g. the commonly used silicon diodes, for photon energies below 200 keV where the absorbed energy depends at least from the fourth power of the atomic number. Other attractive properties of diamond as dosimeter are that it is chemically stable, non toxic, mechanically robust and relatively insensitive to radiation damage. Diamond detectors can be fabricated with small volumes (of the order of 1 mm3 ) and then can be considered for in vivo dose measurements. As a consequence, diamond is particularly suitable for accurate dose measurements in small radiation fields such as in stereotactic radiosurgical beams where ion chambers are inappropriate because of their poor spatial resolution and their sensitivity to lateral electronic disequilibrium. Furthermore, diamond is an extremely versatile material and its dosimetric properties can be exploiting as a thermoluminescence (TL) or thermoconductive (TSC) dosimeter, as a solid state ionisation chamber (IC) and as a radiophotoluminescence detector. So far, commercial diamond detectors are fabricated by natural gems. The main drawbacks of these dosimeters are the high cost and long waiting time [4], due to the severe selection of gems with suitably quality, and the poor reproducibility overall in the case of TL dosimeters. However, the recent availability of synthetic samples, grown under controlled conditions both by the High Pressure-High Temperature (HPHT) and Chemical Vapour Deposition (CVD) techniques make in perspective possible a widespread application of diamond in medical radiation dosimetry.