cosmic rays plus interaction with neutrons from fission and (α,n) reactions interaction with cosmic muons and neutrons direct activation

Transcription

1 cosmic rays interaction with cosmic muons and neutrons direct activation plus interaction with neutrons from fission and (α,n) reactions

2 cosmogenic production rates in Cu at sea level radionuclide halflife production rate (saturation activity) [µbq/kg] cosmogenic exposed unexposed estimated* 56 Co d 230 ± Co d 1800 ± M. Laubenstein, G. Heusser, Appl. Radiat. Isot. 67 (2009) Cebrian et al., Astrop. Phys.33 (2010) Co d 1650 ± Co 5.27 y 2100 ± 190 < Mn d 828 ± Fe 44.5 d 118 ± Sc d 53 ± V d 110 ± 40 primordial 226 Ra (U) 1600 y < 35 < Th (Th) 1.91 y < 20 < K 1.277x10 9 y < 120 < 110

3 Cosmic ray induced isotopes in stainless steel (FeCrNiMo) measured for GERDA Steel sample 7 Be 54 Mn activity [mbq/kg] cosmogenic radionuclide 58 Co 56 Co 46 Sc 48 V M. Laubenstein, G. Heusser, Appl. Radiat. Isot. 67 (2009) T 1/2 Production channels 53.3 d spallation d 56 Fe(n,p2n) (µ -,ν2n) 70.9 d 60 Ni(n,p2n) (µ -,ν2n) 58 Ni(n,p) 77.3 d 58 Ni(n,p2n) (µ -,ν2n) 83.8 d 48 Ti(n,p2n) (µ -,ν2n) spallation on Fe 16.0 d 50 Cr(n,p2n) (µ -,ν2n) spallation on Fe G ± ± ±0.11 G ± ± ± ± ±0.07 G ± ± ±0.11 G4 9.6± ± ± ±0.13 G5 4.8± ± ± ± ± ±0.09 irradiation time at sea level: all other isotopes 200 d are compatible 600 d with saturation G6 13.6± ± ± ±0.12 G ± ± ± ±0.13 P.Rate sea level 4.5± ± ± ± ± ±0.04 [(10 3 sec) -1 kg -1 ] G2 exposed for 314 d

4 background level at shallow depth ANG2 LNGS, no shield Heidelberg Moscow β Cs 207 Bi 60 Co 40 K U Th reached at Heidelberg GeMPI plus continuous contribution of Ge intrinsic cosmogenics 0νββ 60 Co difference besides higher radiopurity due to: insufficient veto, neutron and muon activation with longer life time than the blocking time and interaction of delayed neutrons

5 depth dependence of background inducing muons and neutrons

6 muonic bremsstrahlung [ counts per channel and day] Fe or Pb iron no veto lead no veto lead with veto energy [kev]

7 47.7 s T 1/2 = 0.5 s 20.4 msec background of Pb/Cu and veto shielded Gedetectors at sea level and at shallow depth n-induced lines (in Geβ - and β + decays result not in a line) surface lab W. Preusse, PhD thesis TU Freiberg at MPI-K low level lab veto active at 15 mwe production rate still dominated by neutrons

8 muon intensity versus depth J. A. Formaggio, C. J. Martoff, Annu. Rev. Nucl. Part. Sci : neutrino-induced muons

9 plated out 222 Rn and 220 Rn progenies [ counts per channel and minute] energy [kev]

10 222 Rn protection of BOREXINO 40 Bq/m Rn 1.2 Bq/m 3 85 Kr 1 mbq/m 3 39 Ar solar 7 Be ν ν+e - ν+e - 70 µbq/m Rn 100 nbq/m 3 39 Ar/ 85 Kr develop methods to detect noble gas radionuclides and 226 Ra (via 222 Rn) at the µbq level provide nitrogen for scintillator purification at the required level

11 222 Rn diffusion, solubility and permeability Material description Diffusion coeff. D [10-10 cm 2 /s] Solubility coeff. S Permeability P [10-8 cm 2 /s] Diffusion length d e [mm] Polyamid supronyl Plexi Kalrez Teflon Butyl rubber Rubber soft Natural rubber PU hard PU soft PVC hard PVC soft Apiezon M grease Silicon grease PE Polyethylene PU Polyurethane PVC Polyvinylchloride d e = (D/λ Rn ) -2 MPI-K and Krakow

12 222 Rn ( 226 Ra) emanation data Material Sample Rn emanation [mbq/m²] Polyurethan 90 Shore 1 O-ring, 8.4 mm * 715 mm, 0.06 m², 150 g < 0.42 Polyurethan 70 Shore 5 flat gasket discs, 0.27 m² < 0.29 Butyl rubber 65 5 O-rings, 8.4 mm * 715 mm, 0.3 m², 791 g 13 ± 1 Butyl rubber 65 GD 3 flat gasket discs, 0.16 m² 59 ± 3 Butyl rubber 65 GD O-ring, 4 mm * 16 cm < 30 Viton 1 O-ring, 8.4 mm * 715 mm, 0.06 m² 322 ± 8 Viton GF, Batch O-rings, 3.3 mm * 38 mm, m², 23.6 g 75 ± 4 Silicon rubber 10 O-rings, 2.7 mm * 57 mm, m², 16g 196 ± 4 Teflon-coated silicon rubber 10 O-rings, 3..5 mm * 57 mm, m², 16g 11 ± 2 Teflon foil Foil, 28,5 m² < PCTFE Material for valve seat < 0.32 Kalrez O-ring 7 ± 2 Nitril 190 ± 10 Gylon flat gasket disc, m², 11.8 g 207 ± 4 Busto 1 flat gasket disc 1750 ± 40 MPI-K

13 Ar and Kr from different sources Nitrogen plant of BOREXINO activity in nitrogen [µbq/kg] nitrogen sample 39 Ar a) 85 Kr a) 222 Rn b) regular purity charcoal purified Charcoal purified liq.extr. < 0.3 Linde Worms (7.0) SOL Mantua (7.0) Westfalen Hörstel (6.0) required air ~1.1x10 4 ~1.2x10 6 ~1x10 7 a) measured by rare-gas MS; 1 ppm Ar = 1.19 µbq/kg; 1 ppt Kr = 1.03µBq/kg b) measured by concentration and proportional counting SOL LN 2 MPIK never empty the storage tank completely

14 rare gas activity in the atmosphere [m -3 ] at 15 C and 1 bar radionuclide 222 Rn 85 Kr 81 Kr 39 Ar 42 Ar/ 42 K halflife 3.82 d 10.7 y 2.3 E5 y 269 y 32.9y/12.36d decay mode α β - ε β - β - decay energy [MeV] /3.525 concentration ~ 15 Bq a) ~ 1 Bq b) 2 µbq c) ~ 18 mbq d) 0.5 µbq e) main source emanation nuclear cosmogenic cosmogenic cosmogenic from soil reprocessing elem. vol. air conc. [%] ~1x x x a) strongly variable b) BFS for northern hemisphere c) Collon P. et al. NIM B123 (1997)127 d) Loosli H.H. EPSL 63(1983)51 e) Barabash A.S.: Proc Int. workshop on techniques and application of Xenon detectors, Tokyo 2001, WS 2002

15 localized contamination of HDM detectors by Monte Carlo simulations 4 HD-M detectors in one shield Contamination of Cu [µbq/kg] 226 Ra (U) 228 Th (Th) 40 K Cryostat of ANG1 168 ± 8 84 ± ± 61 Cryostat of ANG2 Cryostat of ANG3 Cryostat of ANG4 Cryostat of ANG5 measured by GeMPI 91 ± ± ± ± ± 3 84 ± 5 87 ± 4 26 ± ± ± ± ± Monte Carlo simul. Ch. Doerr,Uni HD 2002 surface contamination also 70 % of the CUROCINO background is interpreted as surface contamination

16 naked Ge-crystals deployed in liquid nitrogen cooling medium, insulator and shield against external radiation conventional detector crystal gladding one out of several reduction of contact and gladding material: about factor 7000 in mass, 200 in surface not enough space at LNGS for full shielding by liquid N 2 /Ar

17 conclusions Ge gamma spectroscopy is very essential to screen materials for rare event experiments further sensitivity improvements are necessary and feasible underground storage and production will become more necessary more studies on properties and behaviour of 210 Po are required surface contamination needs more attention good approach: 210 Po plate out studies, as done at Krakow and Ra supported Rn emanation studies advice design your low background experiment with plenty safety margins, since there are always surprises and contributions from unexpected sources (double braces) do trust Monte Carlo simulations only as far, as verification in each allows