Download EXO_Gas_David_Sinclair

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.
Possible concept for a gas double beta counter
Anode Pads
Micro-megas
Electrode
Xe Gas
Isobutane
TEA
WLS Bar
Lasers
Grids
. . . . . . . .
. . . . . . . .
For 200 kg, 10 bar, box is 1.5 m on a side
PMT
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
CH4
Xe
Design copied from Fermilab RICH counter
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
Present chamber design
August 31, 2009
Matt Bowcock
11
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
Extraction Concept – A working Example
Leuven Radioactive Beam Source
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
1
Ba++
Mobility
0.8
0.6
Xe+
0.4
0.2
0
0
50
150
100
200
E/N
Ba++ mobilities calculated by Larry Viehland
250
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 mm diameter and about 1 mm long
Electric field is maintained within the channel
Green => 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 chamber
Want to convince ourselves that the CsI concept will work in the large gaseous protoype
Am source
Xe gas (760torr)
Quartz window
First:
- Only look at the
scintillation light in Xenon
Upgrade:
- Add a high field region on
the Xenon side to create
electroluminescence
CH4 (~20torr)
Grid/mesh
CsI coated pad
EXO Week, 08/31/09
C. Hägemann
Data acquisition and analysis
• Xe signal to trigger
Histogram peak pulse height of the CsI
signal
Xe grid signal
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
EXO Week, 08/31/09
C. Hägemann
Data acquisition and analysis
• Xe signal to trigger
Histogram peak pulse height of the CsI
signal
Xe grid signal
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
EXO Week, 08/31/09
Using Tquartz=90%
C. Hägemann
1. Reproducibility of CsI Coating
• Compare runs with different CsI coatings – differ in exposure time to air
• Longest exposure shows large
decrease in pulse height
2h exposure
30min
30min
• Second and third coatings very
very similar in their response
Need to minimize exposure to air!!!
<30 minutes is currently not
possible
VCsI = 700V, VXe = 350V
PCH4 = 30.1torr
EXO Week, 08/31/09
C. Hägemann
3. CsI Stability over time
Signal constant over days
EXO Week, 08/31/09
Event #
C. Hägemann
Summary/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