1. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 Low-level techniques applied in experiments looking for rare events Germanium spectroscopy Grzegorz Zuzel Max Planck Institute for Nuclear Physics, Heidelberg, Germany Radon detection Mass spectrometry Conclusions Introduction

2. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 1. Introduction Low-level techniques: experimental techniques which allow to investigate very low activities of natural and artificially produced radio-isotopes. material screening (Ge spectroscopy, ICPMS, NA) surface screening ( , ,  spectroscopy) study of radioactive noble gases (emanation, diffusion) purification techniques (gases, liquids) background events rejection techniques modeling of background in experiments (Monte Carlo) Low-level techniques are “naturally” coupled with the experiments looking for rare events (detection of neutrinos, search for dark matter, search for 0ν2  decay, search for proton decay,...), where the backgrounds identification and reduction plays a key role. Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction

3. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 2. Germanium spectroscopy Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction Germanium spectroscopy is one of the most powerful techniques to identify γ-emmiters (U/Th chain, 40 K, 60 Co,...). excellent energy resolution (~ 2 keV) high purity detectors (low intrinsic background) In order to reach high sensitivity it is necessary: reduce backgrounds originating from external sources - active/passive shielding (underground localizations) - reduction of radon in the sample chamber assure (reasonably) large volumes of samples assure precise calculations/measurements of detection efficiencies Highly sensitive Ge spectroscopy is a perfect tool for material screening

4. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 2. Germanium spectroscopy Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction GeMPIs at GS (3800 m w.e.) GeMPI I operational since 1997 (MPIK) GeMPI II built in 2004 (MCavern) GeMPI III constructed in 2007 (MPIK/LNGS) Worlds most sensitive spectrometers GeMPI I: Crystall: 2.2 kg,  r = 102 % Bcg. Index (0.1-2.7 MeV): 6840 cts/kg/year Sample chamber: 15 l Sensitivity: ~10  Bq/kg

5. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 2. Germanium spectroscopy Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction Detectors at MPI-K: Dario, Bruno and Corrado Sensitivity: ~1 mBq/kg MPI-K LLL: 15 m w.e.

6. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 2. Germanium spectroscopy Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction Selected results: different materials 228 Th 226 Ra 40 K 210 Pb Copper≤ 0.012≤ 0.016≤ 0.088 Lead DowRun ≤ 0.022≤ 0.029 0.044  0.014(27  4)  10 3 Ancient lead≤ 0.072≤ 0.045≤ 0.27≤ 1300 Teflon 0.023  0.0150.021  0.0090.54  0.11 Kapton cable≤ 4 9  6130  60 Specific activities in [mBq/kg] G. Heusser et al.

7. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 2. Germanium spectroscopy Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction Selected results: steel for the GERDA cryostat (MPIK/LNGS)

8. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 3. Radon detection Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction Radon 222 Rn and its daughters form one of the most dangerous source of background in many experiments inert noble gas belongs to the 238 U chain (present in any material) high diffusion and permeability wide range of energy of emitted radiation (with the daughters) surface contaminations with radon daughters (heavy metals) broken equilibrium in the chain at 210 Pb level

9. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 3. Radon detection Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction Proportional counters Developed for the GALLEX/GNO experiment Hand-made at MPI-K (~ 1 cm 3 active volume) In case of 222 Rn only α-decays are detected 50 keV threshold - bcg: 0.1 – 2 cpd - total detection efficiency of ~ 1.5 Absolute detection limit ~ 30 µBq (15 atoms)

10. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 3. Radon detection Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction 222 Rn in gases (N 2 /Ar) - MoREx 222 Rn detection limit: ~0.5  Bq/m 3 (STP) [1 atom in 4 m 3 ] 222 Rn adsorption on activated carbon several AC traps available (MoREx/MoRExino) pre-concentration from 100 – 200 m 3 purification is possible (LTA) A combination of 222 Rn pre-concentration and low-background counting gives the most sensitive technique for radon detection in gases 222 Rn/ 226 Ra in water - STRAW 222 Rn detection limit: ~0.1 mBq/m 3 226 Ra detection limit: ~0.8 mBq/m 3 222 Rn extraction from 350 liters 222 Rn and 226 Ra measurements possible Great importance for B OREXINO, GERDA, EXO, XENON, XMASS, WARP, CLEAN, … Production rate: 100 m 3 /h 222 Rn ≤0.5  Bq/m 3 (STP)

11. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 3. Radon detection Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction 222 Rn emanation and diffusion Absolute sensitivity ~100  Bq [50 atoms] Blanks: 20 l  50  Bq 80 l  80  Bq Sensitivity ~ 10 -13 cm 2 /s

12. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 3. Radon detection Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction B OREXINO nylon foil 1 ppt U required (~12  Bq/kg for 226 Ra) D dry = 2x10 -12 cm 2 /s (d dry = 7  m) D wet = 1x10 -9 cm 2 /s (d wet = 270  m) A dry = A sf + 0.14  A bulk A wet = A sf +A bulk Separation of the bulk and surface 226 Ra conc. was possible through 222 Rn emanation Very sensitive technique: (C Ra ~ 10  Bq/kg) Bx IV foil: bulk ≤ 15  Bq/kg surface ≤ 0.8  Bq/m 2 total = (16  4)  Bq/kg (1.2 ppt U eqiv.)

13. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 3. Radon detection Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction Online 222 Rn monitoring: electrostatic chamber (J. Kiko) 222 Rn monitoring in gases Shape adopted to the electrical field Volume: 750 l Sensitivity goal: ~ 50  Bq/m 3

14. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 3. Radon detection Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction 222 Rn daughters on surfaces (M. Wojcik) Screening of 210 Po with an alpha spectrometer 50 mm Si-detector, bcg ~ 5  /d (1-10 MeV) sensitivity ~ 20 mBq/m 2 (100 mBq/kg, 210 Po) Screening of 210 Bi with a beta spectrometer 2  50 mm Si(Li)-detectors, bcg ~ 0.18/0.40 cpm sensitivity ~ 10 Bq/kg Screening of 210 Pb (46.6 keV line) with a gamma spectrometer 25 % - n-type HPGe detector with an active and a passive shield sensitivity ~ 20 Bq/kg Only small samples can be handled – artificial contamination needed: e.g. discs loaded with 222 Rn daughters Copper cleaning tests Etching removes most of 210 Pb and 210 Bi (> 98 %) but not 210 Po Electropolishing is more effective for all elements but proper conditions have to be found (e.g. 210 Po reduction from 30 up to 200) Etching: 1% H 2 SO 4 + 3% H 2 O 2 Electropolishing: 85 % H 3 PO 4 + 5 % 1-butanol

15. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 4. Mass spectrometry Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction Noble gas mass spectrometer Detection limits: Ar: 10 -9 cm 3 Kr: 10 -13 cm 3 VG 3600 magnetic sector field spectrometer. Used to investigate noble gases in the terrestial and extra- terrestial samples. Adopted to test the nitrogen purity and purification methods.

16. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 4. Mass spectrometry Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction Ar and Kr in nitrogen for the B OREXINO experiment (SOL) Requirements: 222 Rn: < 7  Bq/m 3 39 Ar: < 0.5  Bq/m 3 85 Kr: < 0.2  Bq/m 3 Ar: < 0.4 ppm Kr: < 0.1 ppt 222 Rn: 8  Bq/m 3 Results: Ar: 0.01 ppm Kr: 0.02 ppt

17. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 4. Mass spectrometry Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction Kr in nitrogen: purification tests

18. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 5. Conclusions Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction Low-level techniques have “natural” application in experiments looking for rare events. There is a long tradition and a lot of experience at MPI-K in this field (GALLEX/GNO, HDM, B OREXINO, GERDA). Several detectors and experimental methods were developed allowing measurements even at a single atoms level. Some of the developed/applied techniques are world-wide most sensitive (Ge spectroscopy, 222 Rn detection). The ”low-level sub-group” is a part of the new division of M. Lindner.

19. LAUNCH - Low-energy, Astroparticle Underground, Neutrino physics and Cosmology in Heidelberg, 21-23.03.2007 2. Germanium spectroscopy Germanium spectroscopy Radon detection Mass spectrometry Conclusions Introduction Comparison of different detectors Slide from M. Hult