Gamma Decay. Radioactive Decay Alpha Decay Radioactive Decay Alpha Decay Beta Decay.
Double Beta Decay With 20-ton Metal Loaded Scintillators A Detector for DUSEL?
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Double Beta Decay With 20-ton Metal Loaded
ScintillatorsA Detector for DUSEL?
Frank CalapricePrinceton University
Aldo IanniLNGS
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The Borexino Detector
• 14C ~ 3 x 10-18
• U/Th <10-17
• 85Kr ~ 0.35 cpd/ton• Cleanliness level 25
MIL-STD 1246C
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General Idea (Similar to SNO+)
• Use radiopurity MEASURED in the Borexino detector
• Use preliminary data on Nd-loaded LS based on PC
Goal:1. Search for double beta decay with a 20ton-
scale high purity LS detector2. SNO+ proposal is for 1000 ton LS.
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Basic working assumptions:
1. T1/2 = 7 x 1018 yr
2. 50 meV neutrino mass (inverted hierarchy)• T
1/2 = 1.2 x 1025 yr
3. Photon yield = 12000 / MeV (PC liquid scintillator)4. QE = 0.35 (new high QE PMTs)5. Coverage = 0.856. Low radioactivity PMTs: ~ 30 mBq/PMT
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The Detector: basic idea
FM
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Backgrounds:
• PMTs + Steel Sphere ~ 40 Bq• 208Tl from nylon (<1ppt in Th) :
– 0.861 MeV + 2.614 MeV ’s 12% BR– need to define FM– Radiopurity of nylon can be measured in CTF at ppt
level or below.
• Intrinsic Th in Scintillator:– Borexino 10-17 g/g gives ~ 1 c/yr around peak
• Th coming with Nd ??? – Required ~ 10-15 gTh/gNd
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1-kton SNO+ vs 20-ton scale detector:
1kton 20ton
Nd concentration 0.1%* 1%*
Nd mass nat. [kg] 1000 195
150Nd [kg] 56 12
Light yield [pe/MeV]
~400** ~700**
* Light absorption by Nd limits concentration**For comparison both detectors are assumed to have 50% PMT coverage.
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Nd concentration 10 g/l 20 g/l 32 g/l
Relative light yield to pure LS
0.7 0.6 0.5
150Nd mass
[kg]
10.9 21.9 35.0
Resolution
FWHM [%]
2.54 2.77 3.05
Rate 2 [Bq] 0.14 0.28 0.45
Rate 0 [c/yr] 2.5 5.1 8.1
S / B in
[Q -1,Q+1]
1.4 2.5 4.0
Natural abundance, 50 meV neutrino, 20-ton FM:
i) 1 c/yr from nylon, ii) 1 c/yr from internal Th, iii) << 1 c/yr externalii) Muon-induced activities above 3 MeV are short-lived and vetoed
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Nd concentration 10 g/l 20 g/l 32 g/l
150Nd mass
[kg]
98 195 313
Rate 0 [c/yr] 1 2 3
S / B in
[Q -1,Q+1]
0.4 0.5 1.2*
50% 150Nd enrichment, 10 meV neutrino, 20-ton:
•In 5 years the uncertainty in the measurement is 35%
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Breakdown of costs:
Item Cost [$M]*
Nd 0.2
WT + SSS 2.0
PMTs 5.0
Nylon Vessel 1.0
Electronics 5.0
LS (solvent) 0.1
solute 0.1
Enrichment 1.0
Total ~15•Add $3M for new purification system if LNGS system is not used.
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Roadmap:• Measure radiopurity of nylon with present CTF• Preliminary tests of light propagation and energy
resolution in small test chamber (~5 m3).• Rebuild CTF with Stainless Steel Sphere
– Study Nd-loaded LS• Light propagation• Radiopurity• Energy resolution
• Search for double beta decay at 50 meV sensitivity with CTF system.
• Build larger (~50 ton LS?) system with optimum resolution/background for 10 meV at DUSEL?
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