1. Proposal for high sensitive measurements of 238 U and 232 Th with NAA Ezio Previtali INFN Sez. Milano Milano-Bicocca University ILIAS: JRA1 3rd General Meeting Paris 14th February 2006

2. Approaches in Low Contamination measurements Bulk measurements:  rays spectroscopy with HPGe ICP-MS (Inductive Coupled Plasma – Mass Spectroscopy) NAA (Neutron Activation Analysis)...... What is considered Low Contamination? For future 0  decay experiments we consider for some materials: 232 Th < 10 -12 g/g (< 10 mBq/kg) 238 U < 10 -12 g/g (< 50 mBq/kg) Surface measurements: Cryogenic detectors Surface barrier detectors LA-MS (Laser Ablation – Mass Spectroscopy) Large area gas ionization chamber...... Intermediate measurements: Radon emanation from surfaces.....

3. Bulk Contamination  rays spectroscopy HPGe Neutron Activation Analysis mainly on solidssolids and liquids sensitivity on daughterssensitivity on primordial huge amount of materials few tens of kg moderate amount of materials few tens of g long running time measurement few months medium running time measurement few weeks well established techniquetechnique under development complementary approach

4. NAA status report Borexino: very sensitive measurements on liquids (scintillators and water) 238 U 232 Th sensitivity for scintillator<9.4 10 -17 g/g<2.4 10 -15 g/g sensitivity for nylon2.1 10 -12 g/g5.1 10 -12 g/g Majorana: measurements on electroformed copper request sensitivity for 232 Th 10 -14 g/g results (??) CUORE measurements on copper and lead shields measurements on small parts of CUORE detector

5. NAA on copper (September 2005) NAA for copper measurements:  the plan is to measure 232 Th contamination with high sensitivity  selected sample is a small bar of 9 g (Outokumpu)  1 week irradiation @ TRIGA reactor of Pavia  3 weeks stored in the irradiation channel for reduce the activity  after 1 month  activity was 100  Sv/h!!!  measurement was done in Pavia and Milano (single and coincidence) Limit on 232 Th (1  : <10 -10 g/g Our goal is: <10 -12 g/g

6. NAA on copper (January 2006) New irradiation started before Christmas:  dedicated to measure 232 Th contamination with high sensitivity  selected sample is 18x8 bars of 1.1 g (Outokumpu) total copper mass is 162.5 g  20 hours irradiation @ TRIGA reactor of Pavia (15-12-05)  28 days stored in the irradiation channel for reduce the activity  preliminary measurements on “solid sample” was done in Pavia gamma ray spectroscopy with HPGe (12-01-06) total activity 200  Sv/h Limit on 232 Th (1  ): <8.5 10 -12 g/g we need to chemically separate copper samples to reduce activity

7. NAA on copper (Febbruary 2006) Chemical treatment for the previous samples:  dedicated to measure 232 Th contamination with high sensitivity  separation was done with a chemical “column”) we plan to reduce the activity reducing low Z elements  activity of the separated samples 1  Sv/h strong reduction of Cu and Co sources efficiency on 232 Th larger than 96%  preliminary measurements on “diluted sample” was done in Pavia gamma ray spectroscopy with HPGe (03-02-06) Limit on 232 Th (1  ): < 9 10 -13 g/g we need to further separate copper samples

8. NAA on copper (future) During next weeks:  Copper sample will be chemically dissolved again: Nitric acid will be used for dissolve samples Fluoridric acid will be added to increase migration in solution  Various separation methods will be tested Chemical precipitation Extraction of actinides using organic compounds Separation in chemical “columns”  High sensitivity radioactive measurements on extracted solutions Preliminary test in Pavia using a standard HPGe (30% int. efficiency) Final measurements in Milan using a well HPGe (65% int. effiiciency) Coincidence measurements with 2 HPGe detectors is planned Future developments: Optimization of the samples preparation Selection of chemical procedure with evaluation of efficiency 238 U chain analysis...........

9. NAA copper byproduct h ~ 4.7 mm d ~ 5.8 mm mtmt msms (1  m) ~ 900 10 -8 Bq/cm 2  1.1 10 -9 g/g for 1  m depth  1.3 10 -12 g/g volume Actually our sensitivity on 232 Th contamination on surfaces is: < 10 -8 Bq/cm 2 for 1  m depth With a specific chemical treatment we can strongly improve this limits

10. NAA on lead Using NAA we try to analyze different types of lead: Roman Plumbum Standard (used in Pavia reactor) Procedure will be the same as copper: Preparation of samples Irradiation at TRIGA reactor Preliminary analysis with HPGe spectroscopy Chemical treatments for select actinides Measurement of solutions  In <5 days

11. NAA on lead preliminary results Limits on concentration in g/g 232 Th 238 U Roman lead (9.2g)<5.7 10 -10 <1.0 10 -9 Plumbum lead (11.5g)<5.6 10 -10 <7.0 10 -9 Standard lead (4.1g)<2.9 10 -10 <2.7 10 -9 Sensitivity limitation comes to: presence of some contaminants in samples (..Sb) irradiation procedure needed for 238 U analysis Chemical treatments of samples will be start soon

12. NAA on some materials For small mass samples it is difficult to obtain the necessary limits We measure some small samples to evaluate the contamination NAA:[ppt] 232 Th 238 U Epoxy glue< 200< 800 Si chips< 50<170 High Vacuum Grease< 5 10 4 < 10 3...... Other materials will be measured soon......

13. Teflon puzzle NAA:[ppt] 232 Th 238 U  Berkeley I 70  Berkeley II300<200  Milano I140<150  Milano II150078  Milano III235<90  Gerda310060 HPGe: [ppt]  LNGS<40<30 Bolometers: [ppt]  TeO 2 <630<380 232 Th results are compatible with ~ 100 ppt contamination for a broken chain (??)

14. NAA working activity People involved: A. Borio, A. Salvini LENA and University of Pavia M. Clemenza*, E. Previtali University of Milano-Bicocca and INFN Milano *actually under contract with Zaragoza University Formal agreement between: University of Milano-Bicocca University of Pavia LENA Laboratory INFN for R&D on high sensitivity NAA Now we pay half price for the use of the TRIGA reactor!!!!

15. NAA working activity During next months: a better definition of chemical treatments optimization of the sample preparation improvement in spectroscopy Limits for 232 Th for copper (and possibly for lead) < 10 -13 g/g Program definition for other elements: 238 U, K,......, Ra Improvement in coincidence methods Test of electrodeposition technique for  activated measurements

16. What we ask to JRA1? We need support for the NAA R&D program 2 years program It is necessary to have more man power: a fellowship contract can help very much For chemical treatments some consumable are necessary: Acids, Organic com.,...~6 k€ Vials, baker,...~5 k€ Resins,...~7 k€ Reactor cost for irradiation: ~18 k€ For short living nuclide a new semiautomatic system is needed Cask container~20 k€ Semiautomatic system~20 k€ Electrodeposition system: ~12 k€ “Hot” laboratory (for high activity samples)...........??? Travel expenses: ~10 k€

17. What we ask to JRA1? For future: NAA included in FP7 activity in collaboration with other groups