NeuLAND - FAIR

counts
Time difference S2-S1 with cut on protons
time (ns)
350
300
250
200
150
100
50
0
12 13 14 15 16 17 18 19 20
time (ns)
T2-T1 vs. position S2
20
19
18
17
16
15
14
13
12
-150 -100 -50 0 50 100 150
position (cm)
Figure 3.1.: The measured time difference tS1 − tS2 of the two scintillator bars S1 and
S2 is shown in the upper panel. The Gaussian fit corresponds to a width of
σt = 176 ps. The two-dimensional plot in the lower panel shows this time
difference tS1 − tS2 as function of the position along the scintillator bar,
derived from xS2.
Here, in figure 3.2 we display the time difference spectrum with a condition on central
hits, thus neglecting the position dependence. In this case a Gaussian fit yields a width
of 125 ps which results in a time resolution of σt=88 ps for one single module.
In the following two parameters were varied. We used a different photomultiplier type
and varied the length of the bars. As read-out device we chose a similar, but more
economical 1 inch photomultiplier, i.e. R8619 from Hamamatsu. At the same time we
explored the effect of the length of the scintillator bars. We extended the 2 m long bars
each by attaching a 1 m long piece of the same cross section with optical grease. A
measurement, again with fast protons from a nuclear reaction, results in a width of the
30
9
8
7
6
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4
3
2
1
0