Transcript Document

LArGe setups
Simulation of LArGe setup at MPIK
Simulation of LArGe integrated in the MaGe framework
Simplified toy-geometry
tank
Goal: complete simulation
of the scintillation photons
understand better shadowing
effects and optimize the
detector packing
PMT
reflector
and WLS
crystal
LAr scintillation: large yield (40,000
ph/MeV) but in the UV (128 nm)
Possibly, understand and derive
optical properties of interest
(e.g. reflectivity of Ge crystals),
that are poorly known in the UV
Optical physics
Geant4 (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
Refraction index of LAr
Properties of all
interfaces (reflectivity,
absorbance)
Absorption length of LAr
• Rayleigh scattering
Rayleigh length of LAr
• wavelenght shifting
Emission spectrum of VM2000
(measured @MPIK) and QE
The optical properties of materials and of surfaces (e.g.
refraction index, absorption length) must be implemented 
often unknown (or poorly known) in UV
Rayleigh
scattering
length
Refraction index
Rayleigh length (m)
Properties of LAr
LAr refraction
index
1.5 at 128 nm
1.25 at visible
20 cm at 128 nm
Wavelength (nm)
Wavelength (nm)
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
Output from the simulation
Ar
peak
VM2000
emission
Cerenkov
spectrum
The ratio between the LAr peak
and the optical part depends on
the WLS QE: critical parameter
Scintillation yield  40,000 ph/MeV
Frequency
spectrum of
photons at the PM
(to be convoluted
with QE!)
Measurement with collimated
LArGe setup irradiated with external collimated
Measurement:
Drawback: the simulation is
very slow (a few seconds per
122-keV event)
57Co
source
Simulation of 122 keV line:
(PMT QE included)
46 p.e.
(80%
WLS QE)
From measurement: 122 keV
correspond to 24.5 p.e.
57Co
34 p.e.
(60%
WLS QE)
LArGe set-up at Gran Sasso
The geometry for the LArGe
set-up at Gran Sasso has
been implemented in MaGe
It includes the shielding
layers, the cryo-liquid and
the Ge crystals
Number of crystals columns and
plans tunable by macro
( interfaced with the general
Gerda geometry tools)
Available in MaGe and
ready for physics studies
Optimization for
Phase I
Gerda geometry in MaGe
Gerda geometry
top m-veto
water tank
neck
cryo
vessel
lead
shielding
Ge array
Description of the Gerda
setup including shielding
(water tank, Cu tank, liquid
Nitrogen), crystals array and
kapton cables
Tunable by macro
column gap
Crystal packing
A 3x3 crystal array will be
used for Phase I.
The supporting structures are
under definition and must be
optimized
( Munich group for Phase II)
2 parameters to play with:
column
distance
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)
depends on contamination and on its position
Crystal packing:
60Co
contamination
Position #1: 60Co 1 cm above the center
of one of the crystals of the middle plane
Strategy: run MaGe with different column
gap and column distance, see the probability
to find energy deposition in 2.0  2.1 MeV
probability per decay
Total
probability per decay
Anticoincidence
With anti-coincidence: dvertical  4 cm
(plateau), dhorizontal  as small as possible
Total rate: crystals as fas as possible
Crystal packing:
60Co
contamination
Position #2: 60Co 1 cm above the corner
of one of the crystals of the middle plane
probability per decay
Total
probability per decay
Anticoincidence
With anti-coincidence: dvertical  4 cm
(plateau), dhorizontal  2 cm (plateau)
Total rate: crystals as fas as
possible
Probability is weakly sensitive to
the horizontal distance (more
sensitive to vertical distance)
Crystal packing:
208Tl
contamination
Anticoincidence
probability per decay
Total
probability per decay
Position #1: 208Tl 1 cm above the center of one of the
crystals of the middle plane
With anti-coincidence: close packing
preferable
Total rate always decreases with crystal distance. With anticoincidence, the optimal distance depends on source & location
Next step: introduce the Phase I supporting
structures geometry in MaGe
Radon contamination in the water
Simulated 800M 214Bi decays uniformly in the water tank
2 cts in 1 MeV
Energy (MeV)
Energy (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