JRA2 - IDEA Integrated Double-beta

Transcription

1 Dresden, 6th ILIAS general meeting 167th February 2009 JRA2 - IDEA Integrated Double-beta beta-decay European Activities Summary of 5 year activity Andrea Giuliani University of Insubria, Como, and INFN Milano-Bicocca, Italy Outline Status of DBD in Europe Presentation of the IDEA tasks scientific issues advancements and results Conclusions

2 Characteristics of the European research in DBD High sensitivity best results in the world m ee < ~0.5 ev ( 76 Ge, 130 Te, 100 Mo) Innovative techniques Complementarity Excellent prospects low-temperature calorimeters Bare Ge diodes dipped in liquid nitrogen/argon New semiconductor technology (CdTe) source detector + source detector techniques multi-isotope testing 76 Ge 82 Se 100 Mo 116 Cd 130 Te 150 Nd 48 Ca can be studied with high sensitivity techniques in hands can extend sensitivity to m ee down to mev

3 Laboratories and institutions participating to IDEA EU institutions (11 countries) 1. Bordeaux (F) 2. Caen (F) 3. Firenze (I) 4. Gif sur Yvette (F) 5. Heidelberg (D) 6. Como (I) 7. Jyväskylä (SF) 8. Leiden (NL) 9. Gran Sasso (I) 10. Legnaro (I) 11. Milano (I) 12. Orsay (F) 13. Strasbourg (F) 14. Tübingen (D) 15. Zaragoza (E) 16. Praha(Cz) 17. Bratislava(Sk) 18. London (UK) 19. IRMM, Geel (B) Non-EU institutions JINR (Russia) Idaho National Engineering and Environmental Laboratory (USA) ITEP (Russia) Mount Holyoke College (Usa) Saga University (Japan)

4 IDEA: presentation and role of the tasks B1 - Cosmogenic induced activity B2 - Underground crystal growth B3 - Rejection of surface radioactivity background control B4 - Ge diodes in liquid nitrogen sensitivity to M ββ ~ G 1/2 1 1 bδe M nucl (I.A.) 1/2 MT 1/4 P1-82 Se project P2-150 Nd project promising nuclides I1 - Isotope enrichment

5 Meetings, scientific programs and web page Biannual general meetings All presentations at the meeting can be downloaded from the WEB site

6 I1 - Isotope enrichment: the physics case With the significant exception of 130 Te (CUORICINO and CUORE experiments), all the interesting isotopes have a low natural abundance Isotopic abundance (%) % 5.6 % 0 48 Ca 76 Ge 82 Se 96 Zr 100 Mo 116 Cd 130 Te 136 Xe 150 Nd Enrichment is a crucial step for almost all the significant experiments

7 I1 - Isotope enrichment: overview Original objectives: Production of 82 Se Study on the production of 150 Nd with the novel techniques (plasma / laser separation) (particularly interesting in case of success of task 150 Nd project) Feasibility study on the enrichment of Ca in 48 Ca Enrichment of Cd in 116 Cd and of Te in 130 Te Supply of the European Bank of Pure Isotopes with the nuclides produced Comments: only the first point is well defined not enough resources for all the points selection in favour of the first two items selection depending on programs in NW and on results from other tasks

8 I1 - Isotope enrichment: work done 3.5 kg of enriched Se was procured: 1+1 kg from ITEP (Kurchatov, Moscow) in the first part of the project, up to 2006 serious pollution in 106 Ru 1.5 kg from French company Chemgas (in contact with a production plant in Tomsk, Russia) in the last part of the project Two techniques for Nd enrichment under study: 1. plasma -based isotope separator (ICR technique) [versatile] 2. laser-based isotope separator (AVLIS technique) [dedicated] A program for an enriched Nd bolometer was outlined Preparation of a full isotope table reporting the technical and practical information

9 1 st kilogram Sample (mbq/kg) 82 Se powder Mass (kg) Selenium from ITEP Measurement of radio-element traces Time(h) 40 K 60 Co 137 Cs 238 U 235 U 226 Ra 228 Th 228 Ra 106 Ru < ± ± ± ± 5 < ± ± 5 24 ± 3 2 nd kilogram Sample (mbq/k) Mass (kg) Time(h) 40 K 60 Co 137 Cs 238 U 235 U 226 Ra 228 Th 228 Ra 106 Ru 82 Se powder ± ± 0.3 < ± ± ± ± ± 1 16 ± Ra and 228 Th give the 208 Tl contamination 2 mbq/kg is a factor 1000 too high for a source of SuperNEMO 226 Ra gives the 214 Bi contamination more precise measurements would be useful 108 Ru is a beta emitter of Q ~ 3 MeV so pollution is catastrophic! purification!

10 New producers for Selenium Initially, very important contact with ECP (Electro-Chemical Plant, Svetlana), Zelenogorsk (Siberia) Easier collaboration with this factory today 40 kg of enriched 76 Ge for GERDA experiment Possibility of 2 kg of 82 Se in this facility (IN2P3 ownership) Enrichment of 100 kg of 82 Se is possible in 3 years at ECP cost: ~ 50 k / kg May 11th, 2007 arrival of 1.5 kg of enriched Selenium 82 In 2007, tender for the production of further 1.5 kg of enriched Se Now 3.5 from kg Tomsk of via enriched Chemgas Se are available Surprise A new company entered the game: The French Chemgas, selling Se produced at Tomsk, Russia 1.5 kg of enriched Se was purchased from Chemgas (lower price) No sign of Ru pollution! detailed analysis in progress

11 P1 82 Se project: the physics case 82 Se is very interesting because: 1. Favorable NME 2. High Q-value: 2995 kev 3. Low 2ν-rate NEMO 3 results: 9.6 x y one order of magnitude slower than 100 Mo ideal for a low energy resolution NEMO-like experiment 2ν 0ν

12 P1 82 Se project: overview General purpose of this task is to put the bases for a zero-background experiment with the tracking technique using the isotope 82 Se,a nd to explore the bolometer option. Original objectives : Chemical and physical purification of the 82 Se produced in Task I1. R&D activity is required for the implementation of the purification procedure and for the measurement of the low radioctivity level required (diagnostic challenge) Realisation of the 82 Se source for tracking experiments Feasibility study of a bolometric experiment based on 82 Se Comment: well defined, low risk task (at least for the non-bolometric part)

13 Sample (mbq/kg) Masse (g) P1-82 Se project: purification Purification of natural Selenium at INL, Idaho Measurement time (h) 40 K 60 Co 137 Cs 226 Ra 228 Ra 228 Th natural Se ± 31 < ± ± 2 13 ± 2 11 ± 2 Purified natural Se < 20 < ± 0.4 < 0.9 < 2.4 < 1.6 reduction Factor > > 51 > 5.4 > 6.9 Conclusions : 226 Ra gives the 214 Bi contamination - the chemical purification gives a factor greater than 50 - the level to be measured needs a more precise measurement 228 Ra and 228 Th give the 208 Tl contamination so : - the chemical purification gives a factor greater than 6 - the level to be measured needs a more precise measurement

14 P1-82 Se project: purification from Ru Purification at INL of intentionally contaminated natural selenium with Ru

15 P1-82 Se project: physical purification All purification techniques are very successful, but the real level of purity is by far below the detection limits of Ge detectors

16 P1-82 Se project: diagnostic Both in 238 U and 232 Th chains, there are sequences (Bi-Po): Bi Po Pb β prompt α delayed that can be used for diagnostic at the sensitivity level of 2 μbq/kg ( 208 Tl) and 10 μbq/kg ( 214 Bi) e - Scintillator + PMT In principle, a very useful tool Tracking for diagnostic a delay (wire chamber) for CUORE experiments (high sensitivity in the detection of surface radioactivity) Source foil (40 mg/cm 2 ) Shield radon, neutron,g

17 P2 150 Nd project: the physics case 150 Nd is potentially an excellent candidate for 0ν-DBD search 1. much faster that any other nucides but new theoretical efforts are necessary (deformation) 2. very high Q-value bolometric technique would be ideal for a high sensitive search Half life range for inverted hierarchy Tuebingen et al. g A =1.25 and r 0 =1.1fm 150 Nd 100 Mo 82 Se 116 Cd 130 Te 136 Xe 76 Ge T 1/2 x10 26 y

18 P2 150 Nd project: overview This task is devoted to the investigation, realisation, and test of Nd-based bolometers. Original objectives: Test on the feasibility of NdF 3 and NdGaO 3 bolometers (requires substantial R&D work) and study of other Nd compounds Development and test of small scale Nd-based bolometers Study of the background in Nd-based bolometers, in case of success in the previous items Comments: high risk task nobody knows if a Nd-based bolometer can work results affect selection of isotopes in task Isotope Enrichment

19 P2-150 Nd project: status Several Nd-based bolometers were realized and tested. The final analysis of their performance was released in NdGaO 3 detectors 30x30x30 mm 10x10x10 mm Cooling down curves

20 P2-150 Nd project: status The NdGaO 3 detector responds to thermal excitations injected by a heater, but not to equivalent energies delivered by elementary particles 1.3 MeV heater pulse Possible explanation of this fact is that elementary particles, unlike Joule heating injections, produce excitations (e-h pairs before and ballistic phonons after) which couple to the nuclear spin system of the crystals, whose specific heat is huge This effect should disappear in a pure 150 Nd crystal, since the nuclear spin is due to the odd A isotopes 143 Nd (12.2 %) and 145 Nd (8.3 %) Three steps program: 1. find, rent or purchase ~ 50 g Nd enriched as much as possible in 150 Nd 2. grow a crystal with this isotopic pure material 3. operate the crystal as a bolometer

21 P2-150 Nd project: change of the objectives Since there are strong indications that Nd-based bolometers cannot work at the level required for a DBD experiment, an amendment was prepared in February 2006 in order to replan the activity of this task in the following three years. From annex 1 - milestones and deliverables X X X Already achieved The Nd project program is changed into a plan for the development of scintillating bolometers for high-q value Scintillating candidates Proposed amendments bolometers including DBD promising candidates ( 100 Mo, 116 Cd) and related technical reports Technical drawing of CUORE detector including a section based on scintillating bolometers Update of CUORE proposal to include a section based on scintillating bolometers

22 P2 Scintillating bolometer: the physics case Promising isotopes were tested with the bolometric technique, combining heat read-out with light read-out to control the alpha background normally, promising isotopes have high Q-value, in a region with very low gamma radioactivity but where alpha background could spoil the sensitivity in a bolometric detector Gamma background spectrum collected underground

23 P2 Scintillating bolometer: results Different scintillating crystals (CdWO 4, CaF 2, CaMoO 4, SrMoO 4, PbMoO 4, ZnSe) were tested successfully and with some of them excellent results were obtained (for example CdWO 4 and ZnSe). β/γ Heater 180 W α Stefano Pirro s talk - tomorrow Highlight on scintillating bolometers α

24 B1 Cosmogenic induced activity: the physics case Exposure to cosmic rays of Ge and TeO 2 crystals can produce radioactive isotopes that in principle could spoil the sensitivity of next generation experiments like GERDA and CUORE Example: 60 Co counts/kev 10 4 MC simulation β γ 1 γ 2 Q ββ Q ββ 76 Ge 130 Te γ1 + γ energy (MeV)

25 B1 Cosmogenic induced activity: overview In the source=detector approach, an important part of the intrinsic background is due to cosmogenic activation of the detector Original objectives : Development and upgrade of the cosmogenic activation codes New experiments based Very on irradiation successful of Ge and task TeO 2 with samples with high energy protons at acceleratorsmany extensions of the Analysis of the irradiation results to check/upgrade activation codes initial program Comments: well defined, low risk task

26 B1 Cosmogenic induced activity: results Various activation experiments performed during the last years with Te, Ge, Cu, Nd and NaI targets Estimates of activation yields based on various codes Production rates of relevant isotopes for activation by cosmic rays at sea level and by neutrons underground have been estimated, initially in Te and Ge, and then in Se, Mo and Nd.

27 Cosmogenic activation of Te (formation of Co-60) Initial problem: cosmic activation in Te may require underground crystal growth (COSMO model prediction) COSMO predicted a high production cross section of 60 Co in Te for proton irradiation 1,E+02 between 1 3 GeV (σ 10 mb) 1,E+01 1,E+00 sigma (mb) 1,E-01 1,E-02 1,E-03 Disagreement with YIELDX calculations and measurement at Berkelety and at CERN (σ 1 mb) 1,E-04 1,E Co production in nat Te energy (MeV) Silberberg &Tsao (YIELDX) measurement Berkeley measurement CERN GEANT4 modified COSMO Sensitivity of CUORE to 130 Te DBD is not jeopardized by cosmogenic 60 Co in crystals and YIELDX calculations are in good agreement with measurements

28 B2 Underground crystal growth: the physics case and overview The most direct way to eliminate Cosmogenic Induced Activity is to grow crystals underground and in any case in radio-clean conditions Original objectives: Crystallization of TeO 2 in radio-clean conditions, by eliminating radioactivity coming from crucibles and other elements (see 190 Pt problem) Feasibility study of underground Ge crystallization Feasibility study of underground TeO 2 crystallization Comments: strong connection with Cosmogenic Induced Activity task it is unlikely that funds are enough for test crystallization plants

29 B2 - Underground Crystal Growth TeO 2 section Initially, double purpose Get rid of 190 Pt contamination in TeO 2 crystal Study and design of underground growth plant Czochralski technique is being studied in addition to the traditional Bridgmann technique (less important crucible interference is foreseen) Experimental studies on cross sections have proved that the cosmogenic activation giving 60 Co is at least one order of magnitude less important than foreseen No underground growth is required

30 B2 - Underground Crystal Growth: CZ growth Contac with two crystal companies in the US to explore the possibility to grow crystals with the CZ method. The traditional provider (SICCAS, Shanghai, China) does not use and does not intend to implement the CZ method. TeO 2 crystal production facilities contacted in USA Company: Integrated Photonics Inc. (IPI), Hillsborough NJ Company: Crystal Technology Inc. (CTI), Palo Alto CA One 3x3x3 cm 3 crystal was purchased and successfully tested as a bolometer in LNGS Four 5x5x5 cm 3 crystals (a complete CUORE single module) were delivered and tested in CUORE-like configuration

31 Comparison between CTI and SICCAS crystals CTI SICCAS Huge Po contamination The project was abandoned

32 B2 - Underground Crystal Growth Present goal for TeO 2 The research objectives were once again redirected Realization of a protocol for TeO 2 crystal growth in SICCAS in view of the CUORE mass production Material 238 U [g/g] 232 Th [g/g] 210 Pb [Bq/kg] 40 K [Bq/kg] 60 Co [Bq/kg] Nat. Pt [g/g] 190 Pt [Bq/kg] Te Metal Acids Water Other liquids TeO 2 powder TeO 2 as-grown crystals TeO 2 ready-to-use crystal

33 B2 - Underground Crystal Growth Test of the CUORE production in SICCAS The first 60 crystals of the CUORE production have been grown according with the specifications set in this task The surface treatment of the crystals was made directly in China, following a procedure developed at LNGS A test of 4 crystals is underway in LNGS Bulk contamination is deducible from internal alphas Assuming secular equilibrium (preliminary): 238 U (3.8 +/- 0.9)x10-14 g/g 232 Th < 8.3x10-14 g/g Within requirements

34 210 Po under control: a few tens of counts / hour

35 B2 - Underground Crystal Growth: Ge section The initial purpose of realizing a full underground production of Ge-diodes was abandoned because it showed to be: - economically prohibitive - not really necessary The new objective has been to set up a cycle including production in a commercial growth plant and a quick underground storage in the IRMM underground laboratory

36 B2 location of critical labs/companies IRMM HADES UMICOR CANBERRA ~ 10 km

37 B3 Rejection of surface radioactivity: the physics case The backgorund in CUORICINO is due to degraded alpha s and beta s which release only a part of their energy in the detector (surface contamination) TeO 2 TeO 2 Cu 214 Bi Limiting factor for 60 Co p.u. 208 Tl CUORE Cuoricino background

38 B3 Rejection of surface radioactivity: overview In bolometric detectors, the radioactivity of the materials facing the crystals is presently the most dangerous contribution to the background Original objectives : Implementation of various surface analysis methods Implementation of various surface cleaning procedures Realisation of surface sensitive prototype bolometers (SSB) Development of CUORE-like modules with foreseen reduction of surface radioactivity by a factor between 10 and 100 with respect to present CUORICINO modules Comment: very critical task: the CUORE success depends on the success of this task

39 B3 - Rejection of surface radioactivity: SSB Development of prototypes with active shields + = Comparison of signals between main and auxiliary bolometers identify the particles originated at the surfaces

40 CUORE-size four-detector module was realized and tested (with Si and TeO 2 slabs) Good results, but not conclusive: Slab contamination Only partial cover of the surface Nice surprise Slab (surface) signal can be recognized thanks to the temporal structure of the pulse read by the main absorber thermistor (PSA)

41 Decay time (main absorber thermistor) as a pulse-origin indicator Decay time detector without slabs Energy detector with slabs Surface events anomalous events

42 B3 - Rejection of surface radioactivity: plasma cleaning Laser ablation in conjunction to HR-ICPMS was proved to be a powerful method for surface activity diagnostic Plasma cleaning is under tests. Receipt for cleaning: several ingredients T Mechanical barrel polishing by Tumbling E Removal of ~100 micron by Electropolishing C Removal of ~ tenths of microns by Chemical Etching M Removal of few microns by Magnetron Sputtering in UHV I Removal on nanometric scale by Ion Beam Cleaning in UHV CUORICINO: T + C CUORE: T + E + C + M + (I )

43 B3 - Rejection of surface radioactivity: Polyethilene sheet Every Cu structure is covered with 7 layers of polyethylene sheet, 12 μm thick, total thickness ~ 85 μm. Reduction of a factor 2 is obtained Extrapolated to CUORE structure: ~ c/kev kg y Is residual radioactivity due to surface contamination of plastic sheet itself? Is there an unknown component without surface origin? Gran Sasso cleaning Polyethilene sheet CUORICINO Bkg 3-4 MeV Pt (count / kev kg y) 0.16 ± ± ± 0.01

44 Final comparison among two Cu cleaning methods and polyethilene shields Scheme of the 3-tower test

45 B4 Operation of Ge diodes in liquid nitrogen: the physics case LN2 and LAr can work at the same time as coolant and as shielding materials (passive and active) for Ge diodes

46 B4 Operation of Ge diodes in liquid nitrogen: overview Original objectives: Study of adsorption materials, especially for 222 Rn, 85 Kr and other potential contaminants like cosmogenic 7 Be. Upgrade of the potential of the existing nitrogen (gas) purification plant (which is housed in LNGS) in order to serve a large self-shielding liquid nitrogen tank Test operation of Ge diodes in purified nitrogen Extend to Argon the purification method Comment: task connected to a fast moving field: possibly, substantial changes of the program and of its realization rate (may be faster)

47 Absorber selection A selection of adsorbers for LN2 and LAr purification was performed, based on the theoretical and experimental studies. This has enabled to design a purification system based on activated carbons Adsorber N H [mol/pa/kg] Molecular sieves 5Å/10Å (Roth) Hydrophobic zeolite, BEA-type, 5.3Å, Si/Al 200 (Südchemie) Hydrophobic zeolite, MFI-type, 6.6Å, Si/Al 75 (Zeochem) only very small purification effect observed 4 ± 1 (6 ± 1) ± 1 (6 ± 2) 10-3 Synthetic carbon CarboAct 1 ± 1 (6 ± 2) 10-2 Synth. carbon CarboTech C38/2 8 ± 2 (2 ± 1) 10-2 Charcoal Cloth FM ± 3 (3 ± 1) 10-2 Carbosieve SIII 2 ± 1 (8 ± 1) 10-2

48 Extension to LAr Liquid and gas phase adsorption have been systematically investigated. Conceptual design of the nitrogen purification plant was presented, based on CarboAct (adsorber) and working in the liquid phase. Argon shielding, initially the back-up solution, will be adopted in GERDA due to the better shielding properties, necessary after the decision in favor of a stainless steel dewar. Measurement of Rn concentration in Ar Sample No. Description C Rn at the measurement time [mbq/m 3 ] C Rn at the filling time [mbq/m 3 ] 1 Westfalen A.G., Ar class ± 0.2 > 8 2 Westfalen A.G, Ar class ± Westfalen A.G, Ar class ± ± Westfalen A.G, Ar class ± ± Air Liquide, Ar class 5.0 <

49 Purification tests show that 1 kg of CarboAct is able to reduce the radon concentration in liquid argon by a factor of about 170. This means that for GERDA we would need a trap containing at least 2 kg of charcoal The target for GERDA is 1 μbq/m 3 This amount may be significantly reduced if we combine purification with argon storage in clean containers. Studies on the delivery chains show that these tanks are available. Purification plant scheme Pump El. valve (level control) Experiment LN 2 Particle filter Flow/mass meter AC El. valve (level control)

50 LAr purification plant and its integration in GERDA

51 Summary of the achieved results and impact N4 + JRA2 (IDEA) funded in ILIAS (6FP) ~ 0.35 M ~ 1.1 M Isotope enrichment procurement of ~ 4 kg of pure 82 Se Important test of this isotope and its purity for supernemo for some of these activities, new null technology or scarce funds for the enrichment (ICR, AVLIS) from the national funding agencies Increase of sensitivity control surface radioactivity in CUORE large liquid impact nitrogen on the and sensitivities argon shields for GERDA of present study and of cosmogenics future experiments (simulation and experiments) clean crystallization techniques New detectors for promising isotopes Nd- and Se-based calorimeters Scintillating bolometers Occasions for the theorists to meet and discuss

52 The activity in IDEA would have not been possible without the work of: Serge Jullian Dominique Lalanne Stefano Pirro Susana Cebrian Maura Pavan Julio Morales Silvia Capelli Marisa Pedretti Stefan Schoenert who have coordinated the scientific work in their tasks and helped me in preparing the programs and the reports