Diamond Detectors for Ionizing Radiation - HEPHY

CHAPTER 7. RADIATION HARDNESS 43
events [ ]
45
40
35
30
25
20
15
10
5
0
DB74-P1, D = 611 µm
0 5000 10000
collected charge signal [e]
Figure 7.5: The pumped state signal distribution of a CVD diamond sample before and after
receiving a pion uence of 1:1 10 15 particles cm ,2 .
an exponential decay, and additionally, there is a constant factor of approximately 2,
independent on the uence. The reasons for the excess factor are currently unknown.
One irradiation experiment was performed each autumn from 1994 to 1997. It was
found that the state of all samples was conserved over one year without irradiation, letting
the pic continue at the end value of the previous year in all cases. During the intervals,
the samples were characterized as well as pumped and depumped. Thus, for the excess
factor, we can exclude short-term eects such as activation.
7.3.2 Electron Irradiation
In 1995, an irradiation was performed with 2:2 MeV electrons from a Van de Graaf accelerator
at the Societe AERIAL in Strasbourg, France [35]. The CVD diamond samples
absorbed a uence of up to 1 MGy (= 100 MRad), while no decrease in the charge collection
distance could be observed, as shown in g. 7.7.
7.3.3 Photon Irradiation
An irradiation experiment with 1:2 MeV photons emitted by a 60 Co source was carried
out at the Argonne National Laboratory in 1993 [36]. The bias voltage during irradiation
was resulting in an electric eld strength of 0:2Vm ,1 .
In g. 7.8, the collection distance is shown normalized to the unpumped value before
irradiation vs. the photon uence. The rst four points were obtained with electrons
from a 90 Sr source and correspond to the pumping process, which saturates at a few 10 Gy.