progress on a gaseous xe detector for double beta decay (exo)
DESCRIPTION
Progress on a Gaseous Xe detector for Double Beta Decay (EXO). David Sinclair Xenon Detector Workshop Berkeley, 2009. EXO Gas participants. The Full EXO collaboration is participating in both the liquid detector (EXO200) and the Gas phase detector. - PowerPoint PPT PresentationTRANSCRIPT
Progress on a Gaseous Xe detector for Double Beta Decay (EXO)
David Sinclair
Xenon Detector Workshop
Berkeley, 2009
EXO Gas participants
The Full EXO collaboration is participating in both the liquid detector (EXO200) and the Gas phase detector.
Main gas phase activity focused at Alabama, Bern, Carleton, Laurentian, Moscow, Stanford
Objective – Based on the results of EXO200, and the demonstrated performance of liquid and gas detectors, decide on the optimal configuration for a detector at the ton (1-10) scale for neutrino-lsss double beta decay
Incentive for the gas phase approach Track information – Factor of 25 reduction in
background at Gottard experiment from the identification of 2 Bragg peaks
Excellent multisite identification Possibly improved energy resolution Different possible techniques for barium
tagging
Fundamental Questions
What are the performance characteristics of an optimized detector Energy resolution Tracking Backgrounds Ba tagging
Original Concepts
Look at incremental improvements to the Gottard detector
Gas TPC with micromegas gain stage Identify Ba with laser tag in high pressure gas
as suggested in Danilov et al.
Anode PadsMicro-megas
WLS BarElectrode
For 200 kg, 10 bar, box is 1.5 m on a side
Possible concept for a gas double beta counter
Xe GasIsobutaneTEA
. . . . . . . .
. . . . . . . .PMT
Lasers
Grids
Problems with original Concept Ba is produced as Ba++ Ba++ is (probably) stable in pure Xe
(demonstrated in Ar) Additives that would convert Ba++ to Ba+ will
probably capture Ba+ Any quench gas is likely to destroy Ba ion Quench gas kills the scintillation light The laser scheme does not work in high
pressure (but can be probably be modified)
New Concept
Use a gas of pure Xe (or possibly a Xe-Ne mix)
Use electroluminescence for gain Nygren has pointed out the advantages for energy
resolution Only scheme that works in pure gas
Drift Ba++ ion to a nozzle where it is extracted into vacuum and identified
Possible Concept for an electroluminescence readout with moderate tracking
Design copied from Fermilab RICH counter
CH4
Xe
Electroluminescence Demonstration EL is a well studied technique in noble gases
and mixed noble gases EL is preferred over electron proportional
counters for gamma ray detectors In Ne + Xe all of the light comes out at the Xe
scintillation wavelength (175 nm) for admixtures of >1% Xe
We are constructing a detector to establish performance of EL for this application
August 31, 2009 Matt Bowcock 11
Present chamber design
Chamber Design Features
Operation from vacuum to 10 bar Contain 1 MeV electrons above 1 bar Light readouts at both ends Anode gives tracking information Cathode end gives energy signal Probably use a teflon cylinder to improve light
collection and give electrical insulation for field cage Trigger on scintillation to give full 3d images and
location
Chamber status
Chamber is in final design phase Fabrication start in new year Vacuum systems out for tender Process systems in design Aim for completion next summer
Barium Tagging – a new concept Try to extract the Ba++ ion from the high
pressure gas Based on techniques used by radioactive
beam facilities Inspiration came from work of a student M.
Facina
Leuven Radioactive Beam Source
Extraction Concept – A working Example
Leuven Experiment – making 71Ni Beams Produce spallation of uranium target with
protons Stop fragments in Ar gas at 0.5 b Flow Ar out orifice Ionize Ni using lasers at the orifice Accelerate ions through 40 kV and mass
analyze selecting M=71 Measure gammas from accepted ions
Marius Facina PhD Thesis
Conclusions from Facina’s Data Ba++ is formed in the spallation/stopping
process Ba++ ions are stable in Ar (~second) Ba++ ions can be trapped using the SPIG
and released with ‘high’ efficiency
Barium Identification
Because of the complexity of the electron tracks in Ba, it will be hard to determine exactly where the Ba is produced.
We have some volume within which it will be contained.
Transport that ‘volume’ to the edge of the detector
Stretch and squeeze it using field gradient into a long pipe
Barium Identification (Cont)
At end of pipe have an orifice leading to evacuated region
Trap ions as they leave the gas using a Sextupole Ion Trap (SPIG)
Once the ion is in vacuum, use conventional techniques to identify it (eg Wein filter + quadrupole MS or TOF + rigidity or ….
Can also change charge state and look for laser fluorescence
The Xe ions will be left behind
Ba++ and Xe+ Mobilities in Xe
0
0.2
0.4
0.6
0.8
1
0 50 100 150 200 250
E/N
Mo
bili
ty
Xe+
Ba++
Ba++ mobilities calculated by Larry Viehland
Can we use this?
RIB facilities use He or Ar an ~0.5 b We want to raise the pressure to ~10 b We need to use Xe (or possibly Xe-Ne) However, Ba++ ions are preformed so we
can use electric fields to guide them to the nozzle
New nozzle concept
Most RIB facilities are using conducting nozzles
Thus field terminates on the nozzle Development on insulated, multi-hole nozzles
(Ross Willoughby, ChemSpace) Allows the velocity to reach sonic prior to
fields reaching conductors Higher efficiencies claimed Small holes lead to smaller gas flows
Expansion of Gas through multi-hole nozzle
Detailed image. Holes are 50 m diameter and about 1 mm longElectric field is maintained within the channelGreen => v ~ 0.8 sonic
Program for Ba Tagging in Gas Facility under design at Stanford to test the
concepts. Similar to the extraction systems at RIB
facilities except we are exploring the use of cryopumping to protect Xe
Workshop being arranged 21-24 March at Stanford
Progress on EL detection
Progress has been made in 3 areas: Demonstration of resolution of EL for alphas Tests of CsI cathodes Engineering work on the large detector
CsI Photocathode Tests
Can we produce CsI cathodes Can we make stable cathodes What are the constraints (eg exposure to air)
that we will have to work with
Schematic of the CsI test chamberSchematic of the CsI test chamber
CH4
(~20torr)
CsI coated pad
Grid/mesh
Quartz window
Xe gas (760torr)
Am sourceFirst:- Only look at the scintillation light in Xenon
Upgrade:- Add a high field region on the Xenon side to create electroluminescence
EXO Week, 08/31/09 C. Hägemann
Want to convince ourselves that the CsI concept will work in the large gaseous protoype
Data acquisition and analysis
• Xe signal to trigger
EXO Week, 08/31/09 C. Hägemann
Xe grid signal
CsI signal
Histogram peak pulse height of the CsI signal
• Non-gaussian shape of the distribution due to distributions of photons on the readout pad with respect to the track angle (can’t cut on track angle currently)
• Record the mean and sigma of the distribution
Data acquisition and analysis
• Xe signal to trigger
EXO Week, 08/31/09 C. Hägemann
Xe grid signal
CsI signal
Histogram peak pulse height of the CsI signal
• Non-gaussian shape of the distribution due to distributions of photons on the readout pad with respect to the track angle (can’t cut on track angle currently)
• Record the mean and sigma of the distribution
Using Tquartz=90%
1. Reproducibility of CsI Coating1. Reproducibility of CsI Coating• Compare runs with different CsI coatings – differ in exposure time to air
• Longest exposure shows large
decrease in pulse height
• Second and third coatings very
very similar in their response
Need to minimize exposure to air!!!<30 minutes is currently not possible
EXO Week, 08/31/09 C. Hägemann
VCsI = 700V, VXe = 350VPCH4 = 30.1torr
2h exposure30min30min
3. CsI Stability over time3. CsI Stability over time
EXO Week, 08/31/09 C. Hägemann
Event #Signal constant over days
Summary/ConclusionsSummary/Conclusions
• Confident that we can reproduce CsI coating
• Heating of the readout pad needed to improve QE after exposure to air (either need to heat the pad or minimize exposure)
• Seem to be able to achieve ~20% QE, but need to verify with EL signals
• Response is stable over time no flow seems to be needed can live with other materials than SS, macor, peek
• Upgrade to be installed in the next 2 weeks (if mesh design works) Larger Signals Determine and cut on track direction Test new grid holder design
EXO Week, 08/31/09 C. Hägemann