Gerda background calculation (Preliminary) INR, ITEP, DUBNA, MPIK

Background from inner tank envelope All dimensions are taken from the Letter of Intend (fig.17)

Method of calculation.

Calculation has been done by direct simulation of gamma transportation The calculation has been done for set up of the 252 detectors (2 kg each), taking into account the anti coincidences. The correspondence between index of the single detector and set up one has been found for different thickness’ and equal ~5,6 for liquid nitrogen .

The background is registered in the energy region 1800-2300 keV. The background is approximately flat in this region.

Input data Cu activity 25E-6 Bq/kg of Th-232 Fe activity 20E-3 Bq/kg of Th-232 Internal tank diameter 1885 mm Liquid Nitrogen Background index for single detector with 2 kg mass (cpy/kg.Kev) Cu Fe (Neck) Center 50 см below the Center Е-4 1.2Е-4 1.1Е-4 2Е-5 Conclusion: 1.

The background index 1E-3 is guarantied 2.

The position of 50 см below the Center does the background from Fe Neck negligible

Background of single detector from external gamma .

1. All construction elements of the detector are taken into account.

2. The Detector is place by 50 cm below the center.

3. Intensity of the 2.615 MeV gamma line is 0.0625 /cm2.c with isotropic distribution. This intensity corresponds the index background of unshielded detector (2 KG) – 13000 (The experimental number 12000) according to the program calculation.

Background index of single defector Thickness of the water Cylindrical part of the tank Upper spherical part of the tank (without lead shoulders) Low flat part of the tank Open neck 0 10.3

1.0

13.0

50 0.9

0.12

0.15

1.1Е-2 1.1Е-2 100 9Е-2 1.4Е-2 1.7Е-2 1.1Е-2 150 8.2Е-3 1.3Е-3 1.4Е-3 1.1Е-2 200 7.7Е-4 1.1Е-4 2Е-4 1.1Е-2

2 1 10 1 0,1 0,01 1E-3 1E-4 1E-5 1E-6 0 3 50 100 150 200 S,water thickness, cm 250 300 1 – Cylindrical part 2 - Upper spherical part 3 – Bottom part

Background of single detector for the completely filled water tank. The thickness of the water in cylindrical part is 300 cm, upper and bottom parts are 200 cm.

The number for cylindrical part with 300 cm was obtained by extrapolation data for 200 cm Cylindrical part Upper spherical part Bottom flat part Open Neck Neck with 10 cm Pb Neck with 15 cm Pb 6.6Е-6 1.1Е-4 2Е-4 1.1Е-2 1.1Е-4 1.1Е-5 Background index for single detector with 2 kG mass (cpy/kg.Kev) Center 50 см below the Center Cu Е-4 1.2Е-4 Fe (Neck) 1.1Е-4 2Е-5

Conclusions: 1.

The water thickness in cylindrical part guarantees the background index ~1E-5 2.

The 7 cm of Pb in the bottom part is desirable to have the background index ~1E-5 3.

The background index ~1E-4 is achievable without any lead shoulders in the upper part. The 6 cm of Pb is desirable in the upper part to have the background index ~1E-5 4.

The Neck must be shielded by 15 cm of Pb.

5.

The background of the set up from 252 detector with anticoincidence (7 layers with 36 detectors in each layer) is 5 times less.

6.

To have background index ~1E-5 from Cu tank the liquid Ar is required.

The program is ready now for other configuration calculations.

The time of calculations is 30 times less in comparing with JAUNT-4.