INTEGRAL SPECTROMETER
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Report about the Scientific ACS Delta-EM Measurements
Robert Georgii, Andreas von Kienlin, Cornelia Wunderer
Issue No.:0
Revision No.:-
Document No.: SPI-MPE-RP-12-28
Issue Date:
Revision Date:-
Distribution List
Name
Organisation Dist. Name
Organisation
V. Schönfelder
G. Lichti
R. Georgii
M. Ertl
H. Schenkl
H. Scheuerle
G. Vedrenne
P. Mandrou
H. Gehrke
MPE
MPE
MPE
MPE
MPE
DARA
CESR
CESR
DSS
P. von Ballmoos
N. Geraud-Liria
M.-A. Clair
E. Hinglais
P. Koutsikides
Ph. Durouchoux
B. Cordier
P. Leleux
F. Sanchez
CESR
CNES
CNES
CNES
CNES
CEA
CEA
G. Skinner
B. Teegarden
P. Caraveo
J. Matteson
Univ. of Birmingham
x
x
x
x
x
x
x
x
1
University of Louvain
University of Valencia
GSFC
IFCTR
UCSD
Dist
x
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1.
PURPOSE ........................................................................................................... 3
2.
APPLICABLE DOCUMENTS ............................................................................. 3
3.
THE TEMPERATURE TESTS AT MPE .............................................................. 4
3.1.
Functional tests – Spectra.................................................................................................................. 4
3.2.
The processing time ........................................................................................................................... 4
4.
THE TESTS IN TOULOUSE ............................................................................. 10
APPENDIX: THE NUCLEAR DECAY SCHEMES ................................................... 11
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1. Purpose
The measurements for the EM scientific tests have been performed 1998 at DSS and are
described in the document RD1. The tests described here are a part of this EM-test of the
ACS, but had to be performed separately. Their main purpose was to obtain the temperature
and energy dependence of the processing time of the total ACS measurement chain. They
again had to be divided in two parts:


The chain from the BGO-crystal to the output of the FEE was measured during a campaign at the MPE. For this set-up the whole operating temperature range for 3 FEEs with
2 BGO-modules was measured.
The complete chain from the BGO-crystal to the output of the VCU was tested on SPIEM level in Toulouse. Here only measurements at room temperature could be performed.
Furthermore some functional tests of the FEEs were obtained on this level as well.
2. Refernce documents
RD1
RD2
Report about the ACS-EM Measurements
The temperature dependence of the ACS
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SPI-MPE-RP-12-26
SPI-MPE-TN-1-15
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3. The temperature tests at MPE
3.1. Functional tests – Spectra
In order to assure the correct function of the FEEs and the BGO-crystal modules spectra
were taken with the energy-stepping method described in the RD1.
3.2. The processing time
The DFEE needs information about the total processing times and jitters of the ACS veto signals after an interaction of an event in any of the BGO crystals, in order to set the anticoincidence window correctly with respect to the Ge-events. This window has to incorporate



temperature effects, therefore the processing time and jitter has to be known over the
whole temperature range,
energy effects, mainly at lower energies, where the jitter due to the photoelectron statistics
is large and
effects, which are due to different performance of the electronic elements used in each
FEE.
3.2.1. The test set-up
The overall physical processing time was measured with the set-up, shown in Figure 1.
A Time-to-Amplitude Converter (TAC-2043) and a Multi-Channel Analyser (MCA) of the
type Inspector with the acquisition program Genie 2K_V1.1, both from Canberra were used to
acquire the timing spectrum. The Signals from 3 different tagged sources (241Am, 22Na, and
60
Co) were used as the start signals and the veto from the ACS was taken as the stop signal.
The decay schemata for the tagged sources are shown in the Appendix, Figure 1-3.
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22
PMT
Na

BGO
Dual Gate
LeCroy 222
F
E
E
Start
gate width
0.5 s
TTL Del
In
Range
100x50 ns
In
Gate
Coarse 100
Fine 0
Out
Start
gate width
1 s
Out
Stop
Start
Canberra
2043
Time-ToAmplitude
Converter
TPHC
Del
Resolving time
32 ns
A
&
B
Timing Filter
Ampflifier 2110
MCA
Out
ORTEC 414A
Fast Coincidence
Figure 1: The electronic set-up for measuring timing spectra using tagged radioactive sources
(22Na as an example).
For all 3 source identical cable lengths, electronic modules and set-ups of the MCA
were used, allowing for an easier comparison of the results. Using a variable delay from the
Gate & Delay 416A from Ortec the time calibration in Figure 2 was determined.
For obtaining absolute processing times, the influence of the cable length and electronics has to be included as well. These times have been measured with a scope yielding the following equation:
Real processing time = measured processing time + 38 ns
Since this value is equal for all 3 sources and an additional unknown delay due to the
opto-coupler in the FEE-UT-1 would have to be added, this correction was neglected in the
following evaluation.
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Figure 2: The time calibration of the TAC-2043 from Canberra for a setting of 100 x 50 ns.
The detection chain was mounted in a clima chamber for varying the ambient temperature in the operational temperature range from –10o C to +50o C. In order to measure the effects on the BGO-crystal and the FEE only, the tagged source was mounted outside the
chamber. The radiation was observed though a window in the chamber. For 241Am a different
set-up to be chosen. For this isotope the tagged source had to be within the climate chamber,
because otherwise all the 59 keV -photons would have been absorbed. Furthermore, due to
the low activity of the source unrealistic long measurement times would have been needed.
3.2.2. The results of the low energy measurements with 241Am
On FEE-level, i.e. the FEE was commanded with the FEE-Unit Tester (FEE-UT-1), 3
FEEs (EM3-5, EM4-6 and EM5-7) and 2 BGO-modules (EM2-4, EM2-5) were tested for obtaining the processing times and jitters. This gives an idea of differences due to individual
FEEs and BGO crystal combinations. 241Am was used to get an impression of the behaviour
of the jitter at low energies. A typical time spectrum is shown in Figure 3.
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Figure 3: A typical time spectrum with the 241Am tagged source.
In order to account for the temperature effects, the temperature range from 5o C to 30o C
was tested. This limitation came from the fact that the tagged source was mounted within the
clima chamber and could not be cooled down further or heated up higher. The settings of all
FEEs were equal, the event trigger was set to 6 and the energy triggers to 1. The HV was
adapted to each PMT pair. The results are shown in Figure 4 and 5.
Zusammenfassung Delay G,H,K
Figure 4: Processing times for different FEEs and BGO-crystals in the EM in dependence of
the temperature.
Zusammenfassung Jitter G,H,K
Figure 5: Jitters for different FEEs and BGO-crystals in the EM in dependence of the temperature.
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There are several effects observed:


For all FEEs the processing time is getting larger with rising temperatures.
There is a significant spread of the processing times due to different FEEs (especially for
FEE5-7).

The spread of the processing time due to different crystals is not larger than due to different FEEs.
The jitters are nearly temperature independent, but have a spread due to different FEEs,
whereas different crystals play a less important role.

The first point seems to come from ???
Point 2 and 3 can be adjusted via the veto delay, but only in a limited range and for a
certain temperature. The last point comes from the fact that the jitter depends on the quotient
of the BGO light decay constant and the light yield. Since both parameters show an opposite
temperature behaviour the influence of the temperature on the time jitters is small in the temperature range considered here (see part 3.1 of AD2).
3.2.3. The measurements with 60Co
For higher energies a 60Co tagged source was used. Additionally to the dependencies,
which were already measured for the 241Am source, the event-trigger threshold was varied
between level 6 and 15. The results for these measurements are shown in Figure 6 and 7.
Zusammenfassung Delay M,N
Figure 6: Processing times for different FEEs and BGO-crystals in the EM in dependence of
the temperature and event-trigger.
Zusammenfassung Jitter M,N
Figure 7: Jitters for different FEEs and BGO-crystals in the EM in dependence of the temperature and event-trigger.
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Here again are some trends visible:




The processing time gets larger for higher temperatures.
The spread in the processing times is larger for different event-trigger thresholds than for
individual FEEs. Furthermore is the spread in the processing times between the different
FEE smaller than during the 241Am measurements.
The jitter is much smaller than for the low energy measurements.
The jitter becomes a little bit smaller for higher temperatures.
Again the first point comes from
The second point is due to the fact that
The third is related to the much higher energies of the -rays from
60
Co compared to
241
those from Am, thus reducing the statistical single photon jitter dramatically. The last point
may be due to the reduction of the light decay time with rising temperature, which reduces the
statistical jitter further. This is contrary to the results for 241Am, where the jitter was nearly
temperature independent, which might be a hint, that for this case the jitter is mainly due to
the decay of the intermediate level with 67 ns life time.
3.2.4. Processing time in dependence of the energy
Additionally a tagged 22Na source was used for getting more information about the energy dependency of the processing time. The result of these measurements is shown in Figure
8 and 9.
Zusammenfassung Delay L 1,K,M 12,14,16,18
Figure 8: The energy dependency of the processing time for the 3 tagged sources.
Zusammenfassung Jitter L 1,K,M 12,14,16,18
Figure 8: The energy dependency of the jitter for the 3 tagged sources.
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3. The tests in Toulouse
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Appendix: The nuclear decay schemes
Figure 1: The decay scheme for 22Na. The tagged signal for the 511 keV and the 1274.5 keV
-rays is derived from the -decay.
Figure 2: The decay scheme for
60
Co. The tagged signal for the 1173.2 keV and the 1332.5
keV -rays is derived from the -decay.
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Figure 3: The partial decay scheme for 241Am. The tagged signal for the 59.6 keV and the ray is derived from the -decay. The signal is in the mean delayed by 67 ns, the
live time of the 59.6 keV 5/2- level of the daughter 237Np nucleus.
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