Heavy Ion CVD-Diamond Detectors for R3B

CVD-diamond is a detector material with fast signals, high charge carrier mobility, smallest lattice constant, and large band-gap [1] resulting in radiation hardness, very good timing and high count rate capability. These properties make it an ideal material for heavy ion tracking and TOF detectors. Polycrystalline diamond is successfully used as detector material at GSI for some years at several experiments (HADES, FOPI,...). Especially for the R3B experiment where a minimum material budget around the target is essential, we carry on this development towards highly segmented, thin, large area (50× 50 mm) devices. First investigations were made with a new material from the IAF Fraunhofer Institute Freiburg. We have produced small test detectors of 10 × 10 mm area with different thicknesses ranging from 20 μm up to 100 μm and a segmentation of four strips in x and y direction on the front and the back side respectively. Leakage currents of typically 5 nA/cm are constant up to fields of 5 V/μm and increases by a factor of 10 between 5 7 V/μm. We applied a field of 3 V/μm. Basic tests were performed at the Munich Tandem accelerator using O and Li beams of 117 MeV and 48 MeV. The detectors were set up as a stack consisting of a diamond detector and a Si diode. After passing through the diamond detector the beam was stopped in the diode which provided a trigger and the residual energy signal. The detector efficiency was measured for a 50 μm thick diamond substrate. Using the Li beam and an energy cut of 20 % of the average signal, 98 % of all particles passing the diamond are recognized. This value is consistent with the segmentation gaps of 50 μm at a pitch of 2 mm.