1. May 6, 2006Henderson Dusel Capstone Meeting Low Background Counting A Facility Wish List for the New Underground Laboratory F. Calaprice

2. Henderson Dusel Capstone Meeting Low Background Experiments Dark Matter Searches Double Beta Decay Solar neutrinos Other –Radioactivity dating –Nuclear inspections

3. Henderson Dusel Capstone Meeting Typical Background Problems Cosmic ray muons Muon-induced neutrons & radioactivity Radon & A=210 Pb-Bi-Po daughters Atmospheric radioactive rare gas atoms – 222 Rn & daughters; 39 Ar, 85 Kr. Gamma and neutron emission from materials Radon emanation from materials

4. Henderson Dusel Capstone Meeting What would we like to have? Gamma detectors with sensitivity of < 1  Bq/kg Alpha & beta detectors for surface radioactivity – 210 Pb, 210 Po, etc. 39 Ar, 85 Kr detectors for gasses 222 Rn emanation detectors Low-radon fabrication clean room High purity water –De-ionized and stripped of 222 Rn, 39 Ar, 85 Kr. High purity nitrogen (low 222 Rn, 39 Ar, 85 Kr) Facilities for precision cleaning –Hot high-purity detergents, acids, rinse water (much!)

5. Henderson Dusel Capstone Meeting IGe Gamma Detectors Ge Max Planck Institute Heidelberg GeMPI-1 1997 –2.2 kg Ge-crystal –Materials in its construction carefully scanned for  -rays –Radon suppression with air lock for inserting samples –Sealed chamber with N 2 overpressure –Large samples (~15 liter) Used to select materials for Borexino and Gerda – 238 U (12  Bq/kg); 232 Th (4  Bq/kg); 40 K (31  Bq/kg) GeMPI-2 installed in LNGS- lower backgrounds

6. Henderson Dusel Capstone Meeting

9. Borexino CTF as  -Detector Liquid scintillator in water tank –Liq.Scint:Highest purity material known (~nBq/kg) Energy resolution adequate for gamma spectroscopy. High detection efficiency 4  Small sample (~2-10 liters) Sensitivity: 238 U, 232 Th: ~1  Bq/kg, or better –Current Ge detectors limited to ~10  Bq/kg

10. Henderson Dusel Capstone Meeting

11. Gamma Sensitivity of CTF

12. Henderson Dusel Capstone Meeting Detection of Radioactive Rare Gasses in CTF: 39 Ar 39 Ar is produced by cosmic rays in the atmosphere: ~ 1 mBq/kg (Ar) 39 Ar is used for dating water/ice (t 1/2 = 260 y ensitivity is limited by backgrounds Direct counting has been used on gas samples –Direct counting is limited to ~1/10 atmospheric Accelerator mass spectrometry has been developed at ANL. –Detection is limited to ~ 1/10 the atmospheric

13. Henderson Dusel Capstone Meeting Sensitivity of CTF to 39 Ar Rare gasses have high solubility in liquid scintillator: ~ 1% by mass. I000 kg of liquid scintillator would have 10 kg of argon dissolved in it. Count rate would be ~ 10 mBq. CTF background is ~ 10  Bq/ton Extend dating to 10 half-lives: ~ 2000 yr.

14. Henderson Dusel Capstone Meeting Argon in oceans and lakes Ocean and lake water in contact with the atmosphere has ~ 0.5 atm-cc argon dissolved in one liter of water. –Disintegration rate/liter of water: 0.075 c/d Currently, argon is removed from > 1000 liters of water by stripping. Typical count rater per sample is 75 c/d. In small scintillator sample with < 1c/d background an improvement of current methods by x10 should be “easy”.

15. Henderson Dusel Capstone Meeting Summary Low background counting will be crucial for upcoming experiments. –This is especially true for double beta decay experiments if other background suppression methods such as Ba detection in EXO do not work. Current gamma detector technology can be used but development of more sensitive detectors is essential. Dedicated space for new detectors such as CTF should be planned. Big resources needed. This is not a simple job.