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This is a presentation given to UNC-Chapel Hill Department of Physics Nuclear Seminar in Nov 2005. It describes the results of an experiment designed to reduce coincidence summing in gamma-ray spectra aimed at future experiments in nuclear astrophysics.
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Reduction of Coincidence Summing in -raySpectra Using a Clover Detector
Peter Bertone
Department of Physics and AstronomyUniversity of North Carolina
Nuclear Seminar14 November 2005
What is Coincidence Summing?
Beam
Detector "Can"
Target HPGe
Figure : LENA Target/Detector Geometry
What is Coincidence Summing?
278
6176
6793
7278
0
7/2+
3/2+
3/2
1/2
-504
14N + p
JpiEx(keV )Ep(keV )
7556 1/2+
5183 1/2+
Figure : Partial Level Diagram for 15O
What is Coincidence Summing?
SFactor
(keV
barns)
0 100 200 300 400
1e-0
21e
-01
1e+0
01e
+01
1e+0
2LUNA1LUNA2LENAMunster
Ecm(keV )
Figure : 14N(p, )15O Ground State Transition
Imbriani, et al., arXiv:nucl-ex/0509005 v1, 1 Sep 2005Runkle, et al., Phys. Rev. Lett. 94, 082503 (2005)Formicola, et al., Phys. Lett. B 591 (2004)Schroder, et al., Nuc. Phys. A467 (1987)
Clover DetectorsClose Packed Crystal Geometry
Each crystal is nominally 50 mm diameter by 80 mm long.
Clover Detectors
Clover Detectors
Some Terminology
I HPGe or Germanium: The large volume single crystal detectorat LENA.
I Hit Multiplicity-1 : Category of incoming -ray events thatdeposit all of their energy in one crystal.
I Hit Multiplicity-2 : Category of incoming -ray events thatdeposit their energy in any two crystals, e.g.:1) One -ray enters the detector and its deposited energy isshared among two crystals.2) Two -rays simultaneously enter via two different crystalsand each crystal absorbs the full energy of each -ray.3) And so on . . .
I Likewise for Hit Multiplicity-3 and Hit Multiplicity-4.
Some Terminology
I HPGe or Germanium: The large volume single crystal detectorat LENA.
I Hit Multiplicity-1 : Category of incoming -ray events thatdeposit all of their energy in one crystal.
I Hit Multiplicity-2 : Category of incoming -ray events thatdeposit their energy in any two crystals, e.g.:1) One -ray enters the detector and its deposited energy isshared among two crystals.2) Two -rays simultaneously enter via two different crystalsand each crystal absorbs the full energy of each -ray.3) And so on . . .
I Likewise for Hit Multiplicity-3 and Hit Multiplicity-4.
Some Terminology
I HPGe or Germanium: The large volume single crystal detectorat LENA.
I Hit Multiplicity-1 : Category of incoming -ray events thatdeposit all of their energy in one crystal.
I Hit Multiplicity-2 : Category of incoming -ray events thatdeposit their energy in any two crystals, e.g.:1) One -ray enters the detector and its deposited energy isshared among two crystals.2) Two -rays simultaneously enter via two different crystalsand each crystal absorbs the full energy of each -ray.3) And so on . . .
I Likewise for Hit Multiplicity-3 and Hit Multiplicity-4.
Some Terminology
I HPGe or Germanium: The large volume single crystal detectorat LENA.
I Hit Multiplicity-1 : Category of incoming -ray events thatdeposit all of their energy in one crystal.
I Hit Multiplicity-2 : Category of incoming -ray events thatdeposit their energy in any two crystals, e.g.:1) One -ray enters the detector and its deposited energy isshared among two crystals.2) Two -rays simultaneously enter via two different crystalsand each crystal absorbs the full energy of each -ray.3) And so on . . .
I Likewise for Hit Multiplicity-3 and Hit Multiplicity-4.
More TerminologyClover Operating Modes
I Direct Mode: The four clover crystals are operatedindependently. The total spectrum is the channel sum of theindividual crystal spectra. The total efficiency is the sum ofthe four crystal efficiencies.
I Add-Back Mode: Incoming -ray events are sorted by hitmultiplicity. Events with hit multiplicity > 1 are summed inenergy across the crystals involved. The total spectrum is thechannel sum of the four hit multiplicity spectra. The totalefficiency is the direct mode efficiency plus an add-back factor.
More TerminologyClover Operating Modes
I Direct Mode: The four clover crystals are operatedindependently. The total spectrum is the channel sum of theindividual crystal spectra. The total efficiency is the sum ofthe four crystal efficiencies.
I Add-Back Mode: Incoming -ray events are sorted by hitmultiplicity. Events with hit multiplicity > 1 are summed inenergy across the crystals involved. The total spectrum is thechannel sum of the four hit multiplicity spectra. The totalefficiency is the direct mode efficiency plus an add-back factor.
Clover DetectorsInteractions Cartoon
Figure : Clover Crystals Front View
Clover Detectors and Coincidence Summing
I Direct mode should greatly reduce summing by dividingdetector material into multiple units each with smaller solidangle, but . . .
I Since each unit (crystal) acts independently, events whichdeposit energy into more than one crystal will not produce afull energy peak thereby degrading overall efficiency comparedto that of a single crystal of comparable volume.
I We can gain back this efficiency with the add-back modewhereby we sum in energy coincident events occurring in twoor more crystals, wait a minute . . .
I This just reintroduces coincidence summing of transitions.
I Is there some way to use the add-back mode to enhanceefficiency while also using the granularity of the cloverdetector to reduce coincidence summing?
Clover Detectors and Coincidence Summing
I Direct mode should greatly reduce summing by dividingdetector material into multiple units each with smaller solidangle, but . . .
I Since each unit (crystal) acts independently, events whichdeposit energy into more than one crystal will not produce afull energy peak thereby degrading overall efficiency comparedto that of a single crystal of comparable volume.
I We can gain back this efficiency with the add-back modewhereby we sum in energy coincident events occurring in twoor more crystals, wait a minute . . .
I This just reintroduces coincidence summing of transitions.
I Is there some way to use the add-back mode to enhanceefficiency while also using the granularity of the cloverdetector to reduce coincidence summing?
Clover Detectors and Coincidence Summing
I Direct mode should greatly reduce summing by dividingdetector material into multiple units each with smaller solidangle, but . . .
I Since each unit (crystal) acts independently, events whichdeposit energy into more than one crystal will not produce afull energy peak thereby degrading overall efficiency comparedto that of a single crystal of comparable volume.
I We can gain back this efficiency with the add-back modewhereby we sum in energy coincident events occurring in twoor more crystals, wait a minute . . .
I This just reintroduces coincidence summing of transitions.
I Is there some way to use the add-back mode to enhanceefficiency while also using the granularity of the cloverdetector to reduce coincidence summing?
Clover Detectors and Coincidence Summing
I Direct mode should greatly reduce summing by dividingdetector material into multiple units each with smaller solidangle, but . . .
I Since each unit (crystal) acts independently, events whichdeposit energy into more than one crystal will not produce afull energy peak thereby degrading overall efficiency comparedto that of a single crystal of comparable volume.
I We can gain back this efficiency with the add-back modewhereby we sum in energy coincident events occurring in twoor more crystals, wait a minute . . .
I This just reintroduces coincidence summing of transitions.
I Is there some way to use the add-back mode to enhanceefficiency while also using the granularity of the cloverdetector to reduce coincidence summing?
Clover Detectors and Coincidence Summing
I Direct mode should greatly reduce summing by dividingdetector material into multiple units each with smaller solidangle, but . . .
I Since each unit (crystal) acts independently, events whichdeposit energy into more than one crystal will not produce afull energy peak thereby degrading overall efficiency comparedto that of a single crystal of comparable volume.
I We can gain back this efficiency with the add-back modewhereby we sum in energy coincident events occurring in twoor more crystals, wait a minute . . .
I This just reintroduces coincidence summing of transitions.
I Is there some way to use the add-back mode to enhanceefficiency while also using the granularity of the cloverdetector to reduce coincidence summing?
Gated Add-Back Operating Mode
Yes there is.
Well use the add-back mode and construct rejection gates aroundthe transitions that sum-in to the transition we want the measure.
Source Test Procedure
I Collect data with same 60Co source on both the HPGe andthe Clover detector for the same amount of time and in thesame geometry.
I Compare efficiencies and coincidence summing for each Cloveroperating mode to the HPGe.
HPGe Spectrum for 60Co
500 1000 1500 2000 2500 3000
050
0015
000
2500
035
000
Channel
Coun
ts
Clover Crystal #1 Spectrum for 60Co
200 400 600 800 1000 1200 1400
050
0010
000
1500
020
000
Channel
Coun
ts
Direct ModeBlue: HPGeRed: Clover Direct Mode
Sep 25, 2005 10:03:19 PMRun 0File: narrow-gate-sort-rebinned+Ge - File: 20050918-60Co-Ge-CFD11-4hr - HPGe1, 10, 1, 1
1220 1240 1260 1280 1300 1320 13400
2000
4000
6000
8000
10000
Channels
Co
un
ts
60Co sum peak and 208Tl peak. BLUE = Ge; RED = Clover 4-way direct mode.
Clover Hit Multiplicity-1 Spectrum for 60Co
Clover Hit Multiplicity-2 Spectrum for 60Co
0 500 1000 1500 2000 2500 3000
020
040
060
080
010
00
Energy (keV)
Coun
ts
Clover Hit Multiplicity-3 Spectrum for 60Co
0 500 1000 1500 2000 2500 3000
05
1015
Energy (keV)
Coun
ts
Clover Total Add-Back Spectrum for 60Co
Clover Gated Hit Multiplicity-2 Spectrum for 60Co
0 500 1000 1500 2000 2500 3000
020
040
060
080
010
00
Energy (keV)
Coun
ts
Clover Total Gated Add-Back Spectrum for 60Co
Gated Add-Back ModeBlue: HPGeLight Blue: Clover Add-BackRed: Clover Gated Add-Back Sep 25, 2005 10:14:31 PMRun 0
File: narrow-gate-sort-rebinned+Ge - File: 20050918-60Co-Ge-CFD11-4hr - HPGe1, 19, 1, 1, 15
1220 1240 1260 1280 1300 1320 13400
2000
4000
6000
8000
10000
Channels
Co
un
ts
60Co sum peak and 208Tl peak; BLUE = Ge; LIGHT BLUE = Clover add-back mode; RED = Clover gated add-back mode
Preliminary Results
Operating Efficiency Summing ReductionMode Relative to HPGe Ratio Factor
HPGe 4.90% Direct 90.4% 0.71% 6.90Add-Back 86.4% 3.00% 1.63Gated Add-Back 85.4% 0.71% 6.904way Anti-Coinc 70.6% 0.68% 7.208way Anti-Coinc 49.7% 0.40% 12.25
Conclusions
I Detector granularity does significantly reduce coincidencesumming (no surprise).
I We have successfully implemented the add-back mode withthe clover detector.
I We have also successfully developed an operating mode usingrejection gating that preserves the efficiency gains of theadd-back mode while also preserving the level of coincidencesumming suppression seen in direct mode.
I Using this technique we therefore should be able tosignificantly improve upon the current data for the14N(p, )15O ground state transition and consequently thestellar reaction rate.
Conclusions
I Detector granularity does significantly reduce coincidencesumming (no surprise).
I We have successfully implemented the add-back mode withthe clover detector.
I We have also successfully developed an operating mode usingrejection gating that preserves the efficiency gains of theadd-back mode while also preserving the level of coincidencesumming suppression seen in direct mode.
I Using this technique we therefore should be able tosignificantly improve upon the current data for the14N(p, )15O ground state transition and consequently thestellar reaction rate.
Conclusions
I Detector granularity does significantly reduce coincidencesumming (no surprise).
I We have successfully implemented the add-back mode withthe clover detector.
I We have also successfully developed an operating mode usingrejection gating that preserves the efficiency gains of theadd-back mode while also preserving the level of coincidencesumming suppression seen in direct mode.
I Using this technique we therefore should be able tosignificantly improve upon the current data for the14N(p, )15O ground state transition and consequently thestellar reaction rate.
Conclusions
I Detector granularity does significantly reduce coincidencesumming (no surprise).
I We have successfully implemented the add-back mode withthe clover detector.
I We have also successfully developed an operating mode usingrejection gating that preserves the efficiency gains of theadd-back mode while also preserving the level of coincidencesumming suppression seen in direct mode.
I Using this technique we therefore should be able tosignificantly improve upon the current data for the14N(p, )15O ground state transition and consequently thestellar reaction rate.
Next Steps
I Repeat tests with actual reaction to verify results at higher-ray energies.
I Remeasure the ground state transition for 14N(p, )15O.
I Write tome. Graduate.
Next Steps
I Repeat tests with actual reaction to verify results at higher-ray energies.
I Remeasure the ground state transition for 14N(p, )15O.
I Write tome. Graduate.
Next Steps
I Repeat tests with actual reaction to verify results at higher-ray energies.
I Remeasure the ground state transition for 14N(p, )15O.
I Write tome. Graduate.
Thanks for your attention.
Acknowledgments:
I Art Champagne
I Christian Iliadis
I Werner Tornow
I Chris Fox
I Richard Longland
I Joe Newton
I Eliza Osenbaugh-Stewart
I Anton Tonchev
I Claudio Ugalde