Muons crossing the detector (2)The contribution coming from neutrons and

hadronic showers is < 0.1 %. Due to the specific Gerda set-up:crystals surrounded by low-Z material (low n yield

from )water and nitrogen are effective neutron moderators

In the assumptions that all neutrons above threshold

give (n,n’) interaction, neutron signal is

conservatively < 10% of the EM signal (without any cut)

Spectrum of neutrons in the crystals from QGSP_BIC_ISO

physics list (good for -induced neutrons). Agreement with FLUKA within a factor

of 2 [Araujo et al. NIM A 545 (2005) 398]

Log(Energy/keV)

Events

/bin

/5.4

y

Q

(n,n’) thr

Integral: 1.4 n/kg

yAbove Q: 0.6 n/kg y

Thermal: 0.02 n/kg

y

distance from track (m)

Gerda water tank

radius

Muons interacting in the rock

Water and nitrogen are effective neutron moderators

Conservative estimate: the distance -n is <R> = 0.6 m (from LVD) good chances that neutrons in the

crystal are accompained by the primary in the water (veto is

effective!)

Estimate the contribution from high-energy neutrons produced in the surrounding rock by

cosmic ray ’sSpectrum and total flux (~ 300 n/m2y) from Wulandari et al., hep-ph/0401032 (2004) agrees with LDV

measurementsBackground: ~ 4 · 10-5 cts/keV

kg y(without any cut: can be further reduced by anti-coincidence)

19.1 EdE

dNn

LVD, hep-ex/9905047

Mu-induced activationMuon-induced interactions can create long-lived (> ms) unstable isotopes in the set-up materials with Q

> Q

Isotopes in LN2 (12B, 13N, 16N), copper (60Co, 62Cu) and water (16N, 14O, 12B, 6He, 13B) give contributions below 10-6 cts/keV kg y

Notice: 16N production rate in water is in good agreement with FLUKA (& data from SK) [hep-ph/0504227] good MC

cross-check

cannot be vetoed or shielded against

Isotopes in the crystals are relevant (detected with high-efficiency). From the MC 6· 10-5 cts/keV kg y

74Ga 8.1 m <0.08 ev/kg y

69Ge 39 h <0.05 ev/kg y

75Ga 2 m 0.09 ev/kg y 77Ge 11 h <0.02 ev/kg y

76Ga 33 s 0.06 ev/kg y 71Ge and 75Ge not dangerous

- a

nd

- ca

ptu

ren

captu

re,

in

ela

stic

Neutrons from fission and (,n)Neutrons from rock

radioactivity:flux: ~ 3.8 10-6 n/cm2

s

Ge ~ (40 cm)2 3.8 10-6 n/cm2s 0.0065 0.02

surface fluxLN2

suppression

vertical neutrons (?)

~ 0.2 neutrons/day 3 times higher than -induced flux

thermal component ( 77Ge)

If a neutron enters in the water, it does not get out!

Concern: neutrons channeling through the neck

No extensive simulation, only rough estimate

In water, flux reduced exponentially with <R> ~ 5 cmThen, 2 m of nitrogen suppress of a factor of 150(2 m of LAr: only a factor of

2!)

Specific MC needed

Materials & masses in Phase II set-up

Part Material Mass [g]

Crystal Germanium 2400 (per detector)

Holder CopperTeflon

31 (per holder)7 (per holder)

Cable CopperKaptonCopperNickelGoldAluminum

1.3 (per cable)0.8 (per cable)0.04 (per detector)0.04 (per detector)5.6·10-4 (per detector)8.2·10-4 (per detector)

Support strings Copper 10 (per string)

Electronics misc (mixture) 100 (per set)

Measured activities in materials Material Contamination

Copper (from LENS) ≤ 16 μBq/kg≤ 19 μBq/kg≤ 10 μBq/kg

Ra-226Th-228Co-60

Teflon ≤ 160 μBq/kg≤ 160 μBq/kg

Ra-226Th-228

Kapton ~ 2 mBq/kg [1] Ra-226, Th-228, Co-60

Enr. Germanium ≤ 0.1 μBq/kg≤ 0.1 μBq/kg145 atoms/kg40 atoms/kg0.63 μBq/surface0.13 μBq/surface

Ra-226Th-228Ge-68Co-60Pb-210Th-232

Electronics 10 mBq/kg [1] Ra-226, Th-228

[1] estimate!

Background estimationPart Bkg Rate

[10-3 cnts/kg/keV/y]Events

[cnts/y] [1]

Crystal U-238Th-232Co-60Ge-68Pb-210 (s)Th-232 (s)

0.250.050.031.530.130.17

0.250.050.031.550.130.17

Holder all (copper)all (Teflon)

0.120.17

0.120.17

Cables all (copper)all (Kapton)

0.021.31

0.021.34

Electronics all 23.65 23.84

Sum ~27 ~27

[1] 20 keV window

Plan for further studies in Munich

Pulse shape simulation and analysis first results show suppression ~4 at 90% signal efficiency for

photons

Ensemble tests based on MaGe and statistical analysis

Implementation of test-stands geometries into MaGe (for local MPI set-ups)

Neutron studies (-produced and from radioactivity)

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

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

avoid the work duplication for the common parts (generators, physics, materials, management)provide the complete simulation chain

more extensive validation with experimental datarunnable by script; flexible for experiment-specific implementation of geometry and output;

Generator, physics processes, material, management, etc.

mjgeometry mjio

gerdaiogerdageometry

Idea: collaboration of the two MC groups for the development of a common framework based on

Geant4

The MaGe framework

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)

Optimization of Cerenkov vetoAssumptions on Cerekov veto threshold: 120 MeV (~60 cm)

40 p.e. (0.5% cov + VM2000) 80 PMTs

Detailed Monte Carlo studies (Tuebingen and Dubna) with optical photons to optimize the placement of the PMTs

neck minimum GS coverage

Pb plate

shadow

Input angular

spectrum

cos

Optimization of Cerenkov veto (2)

Optical photons tracked within the MaGe framework. CPU-intensive but works ok. It also

works with LAr scintillation and WLS

top -veto

Water tank

“Pillbox”

“Ring”

VM2000

PMT

Configurations with 72 and 78 PMTs are

being explored.

Crytical regions:

neck and bottom of cryovessel