1. MaGe framework for Monte Carlo simulations MaGe is a Geant4-based Monte Carlo simulation package dedicated to experiments searching for 0 2  decay of 76 Ge (and low-background experiments in general). It is developed jointly by the Majorana and GERDA Monte Carlo groups avoids duplication of the work for the common parts of the simulations (generators, physics, materials, management) can provide the complete simulation chain (including pulse shape) can be run by script and is flexible for experiment- specific implementation of geometry and output allows a more extensive validation of the simulation with experimental data coming from both experiments  also Geant4 validation arXiv:0802.0860

2. MaGe/GERDA applications Top muon veto Neck Cryostat Water Water tank Detector array GERDA geometry in MaGe MaGe used for background and sensitivity studies in GERDA and for design optimization Description of the Gerda setup including shielding (water tank, stainless steel cryostat, copper lining, cryogenic liquid), crystals array and suspension system MaGe includes the whole simulation chain (generator, physics processes, material, management, etc.)

3. MaGe/GERDA applications MaGe used for the simulation of the main GERDA setup and of many GERDA-related test stands Siegfried 2 GDL test stand Gerda array Phase I detector

4. Muon-induced background e ± and  -rays from electromagnetic showers,  -rays from neutron inelastic interactions or captures Reduced by anticoincidence or segmentation (Phase II) and muon veto. Background reduction depends essentially on the veto efficiency only Production of long-lived unstable isotopes in the crystals or in the surrounding material  veto not effective Reduced by multiplicity or segmentation. Delayed coincidence cuts  Prompt background: Delayed background: 10 m

5. (Reduction by PS discrimination not considered!) Prompt muon-induced background Energy spectrum in the detectors Anti-coincidence: factor from 15 (Phase I) to 25 (Phase II) Segmentation: extra factor of two (Phase II) Cherenkov muon veto required ! With 70 8” PMTs and VM2000 foils a veto efficiency >95% for “dangerous” muons (those that can possibly give a fake signal) can be achieved  ~3·10 -5 counts/(keV kg y) crystal anticoincidence segmentation counts/(keV·kg·y) goal Energy (keV) Q  no cut (EM showers)

6. Isotopes production rate Isotope nucl/(kg·y)cts/(keV·kg·y) (no cuts) 74 Ga/ 75 Ga/ 76 Ga< 0.1< 4·10 -5 68 Ge0.085·10 -6 69 Ge1.85·10 -6 77 Ge/ 77m Ge0.511.1·10 -4 38 Cl46 day -1 3.3·10 -5 40 Cl2.7 day -1 4·10 -6 Actual background depends on: production rate, location and decay scheme. Isotopes produced in water and cryostat < 10 -6 cts/(keV·kg·y) 38 Cl and 40 Cl reduced below 10 -5 cts/(keV·kg·y) by segmentation cuts Main contribution from 77m Ge (thermal neutron capture, Q  =2.862 MeV, T 1/2 =53 s)  up to 10 -4 cts/(keV·kg·y) Background can be reduced by at least a factor of two by a dedicate time cut (taking into account: primary , prompt  -rays produced in capture and delayed  decay of 77m Ge)