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Message ID: 5346
Entry time: Fri Jul 26 13:48:41 2019
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| Author: |
Marlène, Faïrouz, Bertrand & Nicolas |
| ExpNbr: |
e768s |
| Type: |
BEAM |
| Category: |
General |
| Status: |
Fixed |
| Target-Source: |
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| Subject: |
G1 profiler & VAMOS efficiency |
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Factor of two between the profiler and VAMOS FP determination of incident beam is now understood.
Several effects were at work simultaneously and checked at 2 beam intensities (9e3 pps and 5e4 pps):
1. Profiler is using energy loss of the crossing beam particles to deduce the beam intensity. But the profiler was set to 15N instead of 15O.
We checked that for the same beam intensity of 15O the profiler gives 1.2e4 pps / 9e3 pps when tuned on 15N / 15O respectively. This amouts for 75% difference
2. Profiler tends to overestimate the real beam intensity by about 20% when compared to CATS1
Profiler / CATS1: 9e3 pps / 7.3e3 pps (81%)
Profiler / CATS1: 5e4 pps / 3.9e4 pps (78%)
3. VAMOS counting rates are lower than CATS1 by 20% which is consistent with the charge state distribution q(8+)/q(7+) = 80% calculated from LISE++
CATS1 / VAMOS: 7.5e3 pps / 5.8e3 pps (78%)
CATS1 / VAMOS: 3.9e4 pps / 3.0e4 pps (77%)
4. VAMOS PPAC efficiency was checked to be 100%: the PPAC logic signal is always present when triggerd by the drift chamber logic signal
Results:
By combining all previous factors and for 15O beam at the beginning of the experiment we obtain between the profiler and VAMOS FP a reduction factor of: 0.75 * 0.81 * 0.78 = 47%, CQFD!
Discussion:
This factor of two explains the difference we always observed when comparing estimated and measured g-ray yields. |