M. Carson, University of Sheffield, UKDMC ILIAS-Valencia-April 15 2005 Gamma backgrounds, Gamma backgrounds, shielding and veto shielding and veto performance for dark performance for dark matter detectors matter detectors M. Carson, University of Sheffield
17
Embed
M. Carson, University of Sheffield, UKDMC ILIAS-Valencia-April 15 2005 Gamma backgrounds, shielding and veto performance for dark matter detectors M. Carson,
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
M. Carson, University of Sheffield, UKDMC
ILIAS-Valencia-April 15 2005
Gamma backgrounds, shielding Gamma backgrounds, shielding and veto performance for dark and veto performance for dark
matter detectorsmatter detectors
M. Carson, University of Sheffield
M. Carson, University of Sheffield, UKDMC
ILIAS-Valencia-April 15 2005
Sources of radioactivitySources of radioactivity
• Gammas/neutrons from Uranium and Thorium decay chains.
• Gammas from 60Co (1.17 MeV, 1.33 MeV) and 40K (1.46 MeV).
• Radon and 85Kr (in Xe).
• External sources: rock, laboratory …
• Internal sources: readout (PMTs), copper, steel, target …• Aim is to figure out the main contributions to background
signal in the target and develop techniques to remove them: shielding, active veto, muon veto …
M. Carson, University of Sheffield, UKDMC
ILIAS-Valencia-April 15 2005
Th chain decaysb1: with; b0: without Coulomb correction
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
25 1025 2025 3025 4025 5025 6025 7025 8025 9025
E (keV)
DN
(/5
0 k
eV b
in/d
ecay
)
a
b1
b0
g
c.e.
U chain decaysb1: with; b0: without Coulomb correction
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
25 1025 2025 3025 4025 5025 6025 7025 8025 9025
E (keV)
DN
(/5
0 k
eV b
in/d
ecay
)
a
b1
b0
g
c.e.
M. Carson, University of Sheffield, UKDMC
ILIAS-Valencia-April 15 2005
Radon and KrRadon and Kr• 222Rn from decay chain of 238U.
• Rn decay in air produces alpha, beta and gamma radiation. Detector vessel can shield against alpha and beta radiation but gammas may deposit energy in target.
• Beta decay of 214Pb and 214 Bi gives main contribution to gammas from Rn.
• In liquid Xenon, 85Kr beta-decay can also deposit energy in target.
M. Carson, University of Sheffield, UKDMC
ILIAS-Valencia-April 15 2005
Model detectorModel detector
250 kg liquid xenon
CH2
Pb
PMTs
Cu (1m diameter)
M. Carson, University of Sheffield, UKDMC
ILIAS-Valencia-April 15 2005
Contamination levelsContamination levels
U (ppb) Th (ppb) K Co60 (ppb)
PMT (R8778) 4 4 0.31 ppb 1.9×10-9
Cu Vessel 0.02 0.02 1 ppb N/A
NaCl 60 300 1300 ppm N/A
M. Carson, University of Sheffield, UKDMC
ILIAS-Valencia-April 15 2005
Model detectorModel detector
NaCl rock
M. Carson, University of Sheffield, UKDMC
ILIAS-Valencia-April 15 2005
Gammas from rockGammas from rock
• A is spectrum of gammas from rock (input). Total rate 0.09 cm -2 s-1.
• B, C, D, E after 5, 10, 20, 30 cm of lead shielding.
• F shows gamma spectrum after 20 cm Pb + 40 g cm-2 CH2.
M. Carson, University of Sheffield, UKDMC
ILIAS-Valencia-April 15 2005
Energy deposition in targetEnergy deposition in target
0.9 kg-1 day-1
0.03 kg-1 day-1
0.004 kg-1 day-1
0.00002 kg-1 day-1
+ 40 cm CH2
+ 40 cm CH2
2-10 keV 222Rn (10 Bq/m3)
PMTs
85Kr (5 ppb)
Copper vessel
10 cm Pb + 40 cm CH2
20 cm Pb + 40 cm CH2
M. Carson, University of Sheffield, UKDMC
ILIAS-Valencia-April 15 2005
Veto performanceVeto performance
• Detector is 250 kg of liquid Xe viewed by array of R8778 PMTs contained in copper vessel.
• Surrounded by CH2 veto in stainless steel container 0.5 cm thick.
• 10 cm lead shielding outside.
• Neutrons and gammas generated in copper vessel and propagated isotropically through the detector.
• Internal neutrons only, lead shielding reduces external neutron flux.