Diamond Detectors for Ionizing Radiation - HEPHY

Chapter 9
Summary
The possible application of radiation detectors based on CVD diamond has been demonstrated.
Similar to semiconductor detectors such as silicon, the Bethe-Bloch and Landau
theories are ecient tools to describe the behavior of diamond detectors.
The polycrystalline structure of CVD diamond implies its inhomogeneity. A linear
model over the detector thickness describes the relationship between local and average
collection distances. This model satises experimental data. High quality CVD diamond
is obtained by removing material with poor charge collection properties from the substrate
side. The growth process has been successfully applied to grow large area detectors.
Excellent progress has been achieved over the past years by the RD42 collaboration.
The charge collection distance of diamond has been increased, now reaching 230 m (corresponding
to 8300 e) with a sample 432 m thick and slightly more with thicker samples.
A compact characterization station was built in Vienna, which has been successfully used
for pulse height measurements. Due to my contribution and optimization, it has a very
low noise gure (ENC = 270 e).
Moreover, I was involved in the pion irradiation of CVD diamond samples, which was
carried out by the HEPHY in the autumns of 1995, 1996 and 1997. I made essential
contributions in preparation, realization and data analysis including further studies such
as the calculation of electric eld distributions in diamond samples. In agreement with the
linear model we could show that diamond samples with higher initial collection distance
are more aected by irradiation than those with lower d c . Similar, we have demonstrated
that the upper (Landau) tail of the signal distribution suers more from radiation than
the low signal region, which remains almost unaected. This implies that the eciency
of applications with a moderate threshold (a few thousand electrons) will be less aected
by radiation than the mean value of the distribution.
Furthermore, the radiation hardness of diamond has been demonstrated for all major
particles. Simplifying the results of the irradiation experiments, diamond is expected to
survive a hadronic uence of at least 10 15 particles cm ,2 , corresponding to the projected
charged hadron uence at a radius of 7cm from the vertex in the LHC accelerator at
CERN over 10 years. This is ten times more than present silicon detectors allow.
Diamond micro-strip detectors were successfully tested with both slow (VA2) and
fast (SCT128AHC) electronics. With the best diamond sample available, most probable
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