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