Neutron damage of chemical vapour deposition diamond

Abstract

Many of the components of particle detectors for the next generation of high energy experiments need to be extremely radiation-hard if they are to continue to function for more than a few months. For example, in the first few year's operation of the large hadron collider, we expect about 10¹³ neutrons cm^-2 year^-1 1 cm from the beam pipe, with other particles causing about ten times as much additional damage. Diamond is being considered as both a detector material and perhaps as a structural component. We report on tests of chemical vapour deposition diamond films irradiated by 6*10¹⁴ neutrons cm^-2 of energy below 10 keV, plus (2.0+or-0.5)*10¹⁴ neutrons cm^-2 of energy above 10 keV peaking at about 1 MeV. The diamonds were metallized with titanium-gold contacts-strips on the front and a continuous electrode on the back. The leakage current (already extremely small) decreased by factors of about 50 as a result of the irradiation, both measured between adjacent strips and through the thickness of the samples. The detection efficiency of charged particles improved by 30-40% after irradiation. In addition, natural diamonds irradiated by 4*10¹⁴ neutrons cm^-2 showed very little optical absorption in the GR1 and ND1 bands (neutral and negative vacancy) corresponding to a concentration of vacancies of 4(+or-2)*10¹⁴ cm^-3.