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Ultra-low background gamma spectrometry

Ultra-low background gamma spectrometry. Pia Loaiza. Laboratoire Souterrain de Modane. 2 nd LSM-Extension Workshop, Valfréjus, 16 October 2009. n. . Shielding. close mat. Det. U,Th,K (n, , ). e -. Sources of radioactive background. External gamma radiation, neutrons

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Ultra-low background gamma spectrometry

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  1. Ultra-low background gamma spectrometry Pia Loaiza Laboratoire Souterrain de Modane 2nd LSM-Extension Workshop, Valfréjus, 16 October 2009

  2. n  Shielding close mat. Det. U,Th,K (n,,) e- Sources of radioactive background • External gamma radiation, • neutrons • Rn and its progenies • Radioimpurities in shielding • materials • Radioimpurities in materials • close to detectors • Contaminants in detector itself Rn Need material screening Pia Loaiza, 2nd LSM-Extension Workshop,Valfréjus, October 16th, 2009

  3. Mass spectrometry, Neutron Activation Analysis, Alpha-spectrometry 238U decay chain Gamma emitters Sub-chains Pia Loaiza, 2nd LSM-Extension Workshop,Valfréjus, October 16th, 2009

  4. 232Th decay chain Mass spectrometry, NAA, Alpha spectrometry NA: typical limits,Th: some ppb Gamma emitters Sub-chains Pia Loaiza, 2nd LSM-Extension Workshop,Valfréjus, October 16th, 2009

  5. Ge spectrometry Best limits 226Ra, 228Th : 20 Bq/kg for measurement time 100 days and 125 kg of Cu • R = resolution • = efficiency I = intensity of the line M = sample mass t = time of measurement Backg. R Detection Limit   . I. M. t COAXIAL WELL PLANAR high resolution at low energies high efficiency high sample mass The choice depends on what we want to measure For all types: To improve sensitivity  BACKGROUND REDUCTION Pia Loaiza, 2nd LSM-Extension Workshop,Valfréjus, October 16th, 2009

  6. neutron  210Bi (210Pb) DET. - e- 511 keV Pb Rn e- e+ Background components in Ge spectrometry deep underground • External gamma radiation (up to • 2.6 MeV 208Tl) • neutrons from fission and (,n) reactions • Rn and its progenies • Radioimpurities in the shielding materials • Radioimpurities in cryostat Mass = 140 kg Mass = 1125 kg 2.6 MeV MOST IMPORTANT : MATERIAL SELECTION Done in iterative steps Pia Loaiza, 2nd LSM-Extension Workshop,Valfréjus, October 16th, 2009

  7. Which sensitivities for the future experiments? EURECA: • Present  rejection factor ~ 105 • According to simulations: ~105 evts/year in 10 keV<E<50 keV in 1000 kg • of Ge from Cu 226Ra, 228Th : 20 Bq/kg SuperNEMO 40 mBq/kg in 214Bi 3 mBq/kg in 228Th needed for PMTS The necessary sensitivity levels are reached, but time-consuming measurements needed need more detectors further reduce background? Pia Loaiza, 2nd LSM-Extension Workshop,Valfréjus, October 16th, 2009

  8. Measurement of 208Tl and 214Bi concentration in foil-sources and other thin materials Goal : measurement of 10 m2 of foil-sources (40 mg/cm2) in 1 month with sensibility : Volume concentrations : 208Tl < 2 Bq/kg & 214Bi < 10 Bq/kg Detection of the BiPo cascade :  + delayed  b- a Experiment-specific radioctivity measurements Example: the BiPo detector for SuperNEMO Plastic scintillateurs Source foil Pia Loaiza, 2nd LSM-Extension Workshop,Valfréjus, October 16th, 2009

  9. Conclusions Gamma-spectrometry: non destructive technique of measurement of low radioactivities Sensibilities needed for future experiments are reached Need probably a large number of detectors AND detector-specific methods Pia Loaiza, 2nd LSM-Extension Workshop,Valfréjus, October 16th, 2009

  10. Copper: FROM G. HEUSSER NOSV quality 99.9975% (1-4 ppm O2) 97-99 % + 2000 ppm O2 +... Ni: % IN ORE < !-2 ppm Co: about 5 ppm < 1 ppm 40K: 7.5  1.0 mBq/kg < 0.088 mBq/kg 226Ra: 1.8  0.4 mBq/kg < 0.020 mBq/kg 228Th: < 0.44 mBq/kg < 0.023 mBq/kg Aluminium PHP: 40K 1.1 + 0.2 – 0.1 mBq/kg 226Ra 0.270.19 mBq/kg 228Ra < 0.11 mBq/kg 228Th 1.4  0.2 mBq/kg Stainless steel: (From G. Heusser): 40K 17+/-3 mBq/kg 1.8+/-6 mBq/kg 226Ra < 1 mBq/kg 0.6+/-0.2 mBq/kg 228Ra 228Th < 1 mBg/kg 0.2+/-0.1 mBq/kg 60Co 12+/-5 mBq/kg 18+/-1 mBq/kg Pia Loaiza, 2nd LSM-Extension Workshop,Valfréjus, October 16th, 2009

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