Diamond Detectors for Ionizing Radiation - HEPHY

CHAPTER 6. CHARACTERIZATION 34
140
120
100
Pedestal and Calibration Pulse
Entries 1000
Constant 121.6
Mean 465.0
Sigma 3.192
80
60
40
20
0
440 460 480 500 520 540 560
cal_261197_0136_ped.hist
120
100
Entries 1000
Constant 120.5
Mean 535.9
Sigma 3.198
80
60
40
20
0
440 460 480 500 520 540 560
cal_261197_0153_cal.hist
Figure 6.7: Pedestal and calibration measured histograms with Gaussian ts applied.
height histograms. The left gure corresponds to a sample with low collection distance,
where pedestal and signal parts cannot be separated. On the contrary, the right histogram
is of a high quality sample, where separation is easier.
Neglecting any noise contributions, we would expect a Dirac delta needle at the
pedestal position plus a Landau distribution. Taking the electronic noise into account,
we have to convolute the spectrum with a Gaussian distribution, having a width as
observed from the pedestal contribution, resulting in
H F =[(pedestal) + L(signal)] G()=G(pedestal;)+L(signal) G() : (6.5)
This model is illustrated by g. 6.9.
However, as CVD diamond has a columnar structure in the growth direction and also
considerable lateral inhomogeneities (see section 5.1.1), the spectrum does not exactly
follow this shape. In fact, a superposition of various Landau distributions occurs, yielding
a broader shape. Therefore, we convolute the signal related to the Landau part in eq. 6.5
with a Gaussian distribution with a greater than that of the pedestal.
Thus, the nal t model is
| {z }
pedestal
H F = G(pedestal;)
+ L(signal) G( L )
| {z }
signal
with L > : (6.6)
The solid lines in g. 6.8 show the t results with this function. When the pedestal mean
and , which are known from pedestal runs, are kept constant and reasonable initial