Particle and radiation detectors based on diamond

CVD diamond is a remarkable material for the fabrication of particle and photon radiation detectors. The improvement of the electronic properties of the material has been under intensive investigations and led to the development of a few applications that are addressing specific industrial needs. In particular, we have used diamond layers for industrial applications where it exhibits attractive: characteristics as compared with other materials: e.g.. radiation and corrosion hardness for a-counters or high gamma-meters at high fluxes: high transparency to low energy X-rays for synchrotron beam line monitoring devices, etc. These specific properties can motivate the use of diamond even though the detection properties remain relatively poor. Indeed. one inherent problem with diamond is the presence of defect levels that are altering the detection characteristics. These are observed in all CVD materials but also in very high quality natural diamonds. They result in unstable responses and carrier losses. Also. it has been observed that high sensitivities may result from the progressive filling of deep levels, e.g. pumping effects, with a detrimental effect on the stability and the response time. Also. the polycrystalline nature is somewhat detrimental as it induces significant non-uniformities of the device response with respect to the position of interaction. We have investigated these features by imaging the response of CVD diamond using a micrometer size focused X-ray beam. The comparison with the grain structure showed that it has a strong influence on the field distribution. We present here recent developments studied at CEA in Saclay for the optimisation of the material with respect to the specific requirements of several applications. They include radiation hard counters: X-ray intensity, shape and beam position monitors, solar blind photodetectors. and high dose rate gamma-meters.