LArGe setups
Simulation of LArGe setup at MPIKSimulation of LArGe integrated in the MaGe
frameworkSimplified toy-
geometryGoal: complete
simulation of the scintillation photons
understand better shadowing effects and optimize the detector
packing
Possibly, understand and derive optical properties of interest (e.g. reflectivity of Ge
crystals), that are poorly known in the UV
LAr scintillation: large yield (40,000 ph/MeV) but in the UV
(128 nm)
PMT
crystal
reflector and WLS
tank
Optical physicsGeant4 (and then MaGe) is able to produce & track optical photons (e.g. from scintillation or Cerenkov)
Processes into the game:
• scintillation in LAr
• Cerenkov in LAr
• boundary and surface effects
• absorption in bulk materials
• Rayleigh scattering
• wavelenght shifting
The optical properties of materials and of surfaces (e.g. refraction index, absorption length) must be implemented
often unknown (or poorly known) in UV
Refraction index of LAr
Properties of all interfaces (reflectivity,
absorbance)
Absorption length of LAr
Rayleigh length of LAr
Emission spectrum of VM2000 (measured @MPIK)
and QE
Properties of LAr
Data kindly provided by ICARUS people
Absorption length in LAr not known ICARUS does not see effect in one semi-module, so L 1 or a few meters
Rayleigh scattering
length
20 cm at 128 nm
Wavelength (nm)
Rayle
igh length
(m
)
LAr refraction
index
1.5 at 128 nm
1.25 at visible
Wavelength (nm)
Refr
act
ion index
Output from the simulation
Frequency spectrum of
photons at the PM (to be
convoluted with QE!)
The ratio between the LAr peak and the optical part depends on the WLS QE: critical parameter
Scintillation yield 40,000 ph/MeV
Ar peak
VM2000 emission
Cerenkov spectrum
34 p.e. (60%
WLS QE)
Measurement with collimated 57CoLArGe setup irradiated with external collimated 57Co source
Measurement:
Drawback: the simulation is very slow (a few seconds
per 122-keV event)
From measurement: 122 keV correspond to 24.5 p.e.
Simulation of 122 keV line: (PMT QE included)
46 p.e. (80%
WLS QE)
LArGe set-up at Gran Sasso
Number of crystals columns and plans tunable by macro
( interfaced with the general Gerda geometry tools)
Available in MaGe and ready for physics
studies
The geometry for the LArGe set-up at Gran Sasso has been implemented in
MaGeIt includes the shielding
layers, the cryo-liquid and the Ge crystals
Optimization for Phase I
Gerda geometry in MaGe
Description of the Gerda setup including shielding
(water tank, Cu tank, liquid Nitrogen), crystals array
and kapton cables
Gerda geometry
top -vetowater tank
lead shieldingcryo
vessel
neck
Ge array Tunable by macro
Crystal packingA 3x3 crystal array will be
used for Phase I.
The supporting structures are under definition and
must be optimized
Monte Carlo to study close vs. loose packing.
Close packing: anti-coincidence more effective, but higher total
rate (crystals “see” the supporting structures of
neighbours)
2 parameters to play with:
column gap
column distance
( Munich group for Phase II)
depends on contamination and on its position
Crystal packing: 60Co contaminationPosition #1: 60Co 1 cm above the center of one of the crystals of the
middle planeStrategy: run MaGe with different column gap and column distance, see the
probability to find energy deposition in 2.0 2.1 MeV
Total
Anticoincidence
With anti-coincidence: dvertical 4 cm (plateau), dhorizontal as small as
possibleTotal rate: crystals as fas as possible
pro
bab
ility
per
deca
y
pro
bab
ility
per
deca
y
Crystal packing: 60Co contaminationPosition #2: 60Co 1 cm above the corner of one of the crystals of the
middle plane
Total
With anti-coincidence: dvertical 4 cm (plateau), dhorizontal 2 cm (plateau)
Total rate: crystals as fas as possible
pro
bab
ility
per
deca
y
Anticoincidence
pro
bab
ility
per
deca
y
Probability is weakly sensitive to the horizontal distance (more sensitive to
vertical distance)
Crystal packing: 208Tl contaminationPosition #1: 208Tl 1 cm above the center of one of
the crystals of the middle plane
Total
Anticoincidence
With anti-coincidence: close packing preferable
pro
bab
ility
per
deca
y
pro
bab
ility
per
deca
y
Total rate always decreases with crystal distance. With anti-coincidence, the optimal distance depends on source &
locationNext step: introduce the Phase I supporting structures geometry in MaGe
Radon contamination in the water
Energy (MeV)
Simulated 800M 214Bi decays uniformly in the water tank
Energy (MeV)
2 cts in 1 MeV
Background index < 10-2 R [cts/kg keV y] (95% CL)222Rn rate in Bq/m3
For 25 mBq/m3 < 2-3 · 10-4 cts/kg keV y (95% CL)For 5 mBq/m3 < 5 · 10-5 cts/kg keV y (95% CL)
The status of MaGe• MaGe is currently manteined and debugged jointly with the Majorana people. The code in the CVS is regularly tagged
• An official release, i.e. a stable MaGe version intended for “users” rather than for “developers” is going to be completed
• The physics capability has been extended to include the generation and tracking of optical photons
• An interface to the MUSUN generator for cosmic ray muons has been included (to be committed in CVS)
• New geometries and new i/o schemes have been added to handle the new Gerda test stands (at Munich, MPIK and GS)
• Validation studies with test-stand data are ongoing
• Together with Majorana people, we placed the request for MaGe dedicated talk (or a poster) to the Organizers of the next TAUP Conference
• Already used for physics studies and ready for others
Measurement with collimated 57Co
Measurement with collimated 57Co