Diamond Detectors for Ionizing Radiation - HEPHY

Chapter 2
Introduction
Diamond is a material with a set of very unique characteristics. It is mainly known as
a gem, but also for its hardness. There is a third property that is not so well known;
diamond shows extremely high thermal conductivity while it is electrically insulating.
Besides that, diamond has the reputation of being radiation hard since the 1950s, but
only recently this has been examined systematically using modern irradiation facilities.
One eld of future applications of CVD (chemical vapor deposition) diamond could be
particle detection in high energy physics experiments, where fast, radiation-hard detectors
are required.
The goal of the RD42 collaboration is the development of tracking detectors 1 made of
CVD diamond for the LHC. The group is involved in both the ATLAS (A Toroidal LHC
Apparatus) and the CMS (Compact Muon Solenoid) experiments, which are projected
for the LHC. As I am aliated with CMS, I will give a short description of the possible
utilization of diamond there.
Fig. 2.1 shows the complete CMS experiment. Only the pink cylinder in the very
center is the solid state tracking detector, containing strip and pixel detectors. While the
strip detectors will be denitely made of silicon, the material for the pixel detectors could
be either silicon or diamond.
The reason for this diamond option is the extreme radiation in the vertex environment.
Present standard silicon detectors are operable up to a uence of approximately
10 14 particles cm ,2 [2]. With this uence, the radiation defects do no longer allow meaningful
measurements. The total uences of photons, neutrons and charged hadrons expected
in the CMS experiment over the scheduled 10 years of LHC operation is shown in g. 2.2.
z is the distance from the vertex along the beam axis, while the parameter is the radius
from the beam axis.
Two permanent pixel layers are planned at radii of 7 and 11 cm and a third one at
r = 4cm only for the low luminosity period in the beginning of LHC operation. The
photon and neutron uences are silicon-compliant. The charged hadrons, however, most
of which are pions with a momentum below 1 GeV c ,1 , are a challenge, which can be
accomplished with diamond detectors.
1 position-sensitive detectors with good spatial resolution
6