Behaviour of. 222 Rn. and its daughters in liquid nitrogen. GERDA Collaboration Meeting Jagellonian University,, Kraków 2008

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1 Behaviour of Rn 222 Rn and its daughters in liquid nitrogen Marcin Wójcik,, Nikodem Frodyma,, Krzysztof Pelczar GERDA Collaboration Meeting Jagellonian University,, Kraków

2 Problems and Questions Rn as a time-dependent background source in e.g. the GERDA experiment Rn and Rn-daughters location in cryostat with liquid gas Rn partition between liquid and gas phase Behaviour of Rn and its daughters in LN 2 in electric field 2

3 222 Rn and its daughters 226 Ra 214 Pb 210 Pb 206 Pb α T 1/2 = 1622 y E = 4.8 MeV β T 1/2 = 26.8 m E m = 0.7 MeV β T 1/2 = 22.3 y E m = 0.06 MeV Stable 222 Rn 214 Bi 210 Bi α T 1/2 = 3.8 d E = 5.5 MeV β T 1/2 = 19.8 m E m = 1.5 MeV β T 1/2 = 5.0 d E m = 1.2 MeV 218 Po 214 Po 210 Po α T 1/2 = 3.1 m E = 6.0 MeV α T 1/2 = 164 µs E = 7.7 MeV α T 1/2 = d E = 5.3 MeV 3

4 222 Rn and its daughters α α 222 Rn 218 Po 214 Pb 214 Bi 214 Po β β in gas: in liquid: + +? 4

5 GERDA model of the detector 5

6 Rn dissolving in LN 2 6

7 Free evaporation of LN 2 with Rn 7

8 Free evaporation of LN 2 with Rn 8

9 Free evaporation of LN 2 with Rn 9

10 Free evaporation of LN 2 with Rn count rate [counts/min] :00:00 6:00:00 12:00:00 18:00:00 24:00:00 time [hh:mm:ss] 10

11 Free evaporation of LN 2 with Rn 16 count rate [counts/min] Fit parameters (y = ax +b) a = 7.6E-5 ± 2.3E-5 cpm/m b = ± cpm :00:00 150:00:00 156:00:00 162:00:00 168:00:00 time [hh:mm:ss] 11

12 Free evaporation of LN 2 with Rn 1000 count rate [counts/m] :30:00 309:30:00 315:30:00 321:30:00 327:30:00 time [hh:mm:ss] 0,1 12

13 Rn count rate growth after LN 2 evaporation 13

14 Measurement of the Rn concentration in LN 2 14

15 Rn concentration in liquid and gaseous nitrogen 15

16 Variable heating inside the Dewar 16

17 Variable heating inside the Dewar 17

18 Rn-daughters deposition on stainless steel plates (SSP) and alfa-spectrometry SSP placed in different posotions and under different conditions: Liquid nitrogen Gaseous nitrogen High voltage applied Long and short exposition time SSP in N 2 gas SSP in liquid N

19 alfa-spectrometer 19

20 alfa-spectrometer 214 Po T 1/2 = 1188 s 218 Po T 1/2 = 186 s 20

21 High voltage influence on counts of 214 Po 21

22 Counts of 214 Po and 218 Po vs applied voltage negative voltage LN 2 22

23 Counts of 214 Po and 218 Po vs applied voltage positive voltage LN 2 23

24 Rn (and daughters) concentration growth in time (with 2000V applied) LN 2 24

25 Plans for further measurements Germanium plates Liquid argon Dynamics simulations 25

26 Preliminary conclusions Large part of Rn is dissolved in LN 2 The Rn concentration in evaporated gas is lower than in liquid gas and depends on the evaporating rate (heating power) High voltage forces Rn to concentrate around the SSP The polarity of HV is not meaningless The concentration of Rn depends on time of SSP exposure Open questions Mechanism of Rn and Rn daughters concentration 26

27 Behaviour of Rn 222 Rn and its daughters in liquid nitrogen Marcin Wójcik,, Nikodem Frodyma,, Krzysztof Pelczar GERDA Collaboration Meeting Jagellonian University,, Kraków

28 Temperature inside the dewar (top and bottom, after N 2 evaporation) 28

29 Temperature difference between top and bottom wall of the dewar (after nitrogen evaporated) 29

30 Rn concentration growth (after LN2 evaporated) with constant flow rate 30