Diamond Detectors for Ionizing Radiation - HEPHY

CHAPTER 6. CHARACTERIZATION 35
300
250
200
Low Quality Diamond Pulse Height Spectrum
ID
Entries
Mean
RMS
8
4999
475.4
13.74
0. / 235
P1 0.8000
P2 475.0
P3 3700.
P4 900.0
P5 463.7
P6 4.249
P7 4.900
120
100
80
High Quality Diamond Pulse Height Spectrum
ID
Entries
Mean
RMS
8
5000
510.5
37.93
338.4 / 235
P1 6.573
P2 495.1
P3 4723.
P4 149.3
P5 440.2
P6 4.300
P7 16.74
150
60
100
40
50
20
0
440 460 480 500 520 540
u3_011297_1523_447v.hist
0
400 450 500 550 600 650 700
74p2_201197_2336_600v.hist
Figure 6.8: Typical diamond pulse height spectra. The histogram to the right shows a high
d c sample, where pedestal and signal are clearly separated, which is not the case in the left
histogram of a low d c diamond. The solid line shows the applied t function (see text below).
Pedestal + Ideal Signal
(Landau)
Noise
(Gauss)
Measured Spectrum
Figure 6.9: A model for tting histograms.
values are given, the t also works with low quality diamonds, as shown in the left plot
of g. 6.8.
After obtaining the t parameters, the question of the mean signal remains. As discussed
in section 4.2, the ideal Landau distribution does not have a mean value. The
Landau t, however, provides a weight, which corresponds to the area below the curve.
With the mean value and the area below the Gaussian pedestal t curve, which are also
resulting from the t, the pedestal contribution can be subtracted from the mean value
of the measured histogram, resulting in a signal mean. Finally, we obtain the charge
collection distance by multiplying the dierence between signal and pedestal means with
the calibration constant (C cal ),
d c = C cal
area(signal)+area(pedestal)
area(signal)
!
(mean(H) , mean(pedestal)) : (6.7)
For diamonds with reasonable pedestal separation (right histogram in g. 6.8), it is