Transcript Document 7321094

Double Beta Decay With
20-ton Metal Loaded
Scintillators
A Detector for DUSEL?
Frank Calaprice
Princeton University
Aldo Ianni
LNGS
The Borexino Detector
• 14C ~ 3 x 10-18
• U/Th <10-17
• 85Kr ~ 0.35 cpd/ton
• Cleanliness level 25
MIL-STD 1246C
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 20tonscale high purity LS detector
2. SNO+ proposal is for 1000 ton LS.
Basic working assumptions:
1. T21/2 = 7 x 1018 yr
2. 50 meV neutrino mass (inverted hierarchy)
•
3.
4.
5.
6.
T1/2 = 1.2 x 1025 yr
Photon yield = 12000 / MeV (PC liquid scintillator)
QE = 0.35 (new high QE PMTs)
Coverage = 0.85
Low radioactivity PMTs: ~ 30 mBq/PMT
The Detector: basic idea
FM
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
1-kton SNO+ vs 20-ton scale detector:
1kton
20ton
Nd concentration
0.1%*
1%*
Nd mass nat. [kg]
1000
195
56
12
~400**
~700**
150Nd
[kg]
Light yield
[pe/MeV]
* Light absorption by Nd limits concentration
**For comparison both detectors are assumed to
have 50% PMT coverage.
Natural abundance, 50 meV neutrino, 20-ton FM:
Nd concentration
10 g/l
20 g/l
32 g/l
Relative light yield
to pure LS
0.7
0.6
0.5
mass
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
150Nd
[kg]
i)
ii)
1 c/yr from nylon, ii) 1 c/yr from internal Th, iii) << 1 c/yr external
Muon-induced activities above 3 MeV are short-lived and vetoed
50% 150Nd enrichment, 10 meV neutrino, 20-ton:
Nd concentration
150Nd
mass
10 g/l
20 g/l
32 g/l
98
195
313
1
2
3
0.4
0.5
1.2*
[kg]
Rate 0 [c/yr]
S / B in
[Q -1,Q+1]
•In 5 years the uncertainty in the measurement is 35%
Breakdown of costs:
Item
Nd
WT + SSS
PMTs
Nylon Vessel
Electronics
LS (solvent)
solute
Enrichment
Total
Cost [$M]*
0.2
2.0
5.0
1.0
5.0
0.1
0.1
1.0
~15
•Add $3M for new purification system if LNGS
system is not used.
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?