Technologies for obtaining radio-pure materials ; methods of low radio activity detection
description
Transcript of Technologies for obtaining radio-pure materials ; methods of low radio activity detection
INTERNATIONAL PHD PROJECTS IN APPLIED NUCLEAR PHYSICS AND INNOVATIVE TECHNOLOGIESThis project is supported by the Foundation for Polish Science – MPD program, co-financed by the European Union within the European Regional Development Fund
Symposium on applied nuclear physics and innovative technologies, UJ, Kraków, 2013
Technologies for obtaining radio-pure materials; methods of low radioactivity detection
Krzysztof PelczarM. Smoluchowski Institute of Physics
Jagiellonian University, Cracow
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Outline
• Physics beyond the Standard Model– Double-beta decay – The GERDA Experiment
• Surprising 42K• Ions in cryogenic liquids
– Cold Dark Matter – The DarkSide Experiment• Ubiquitous 222Rn• Electrostatic chamber for on-line gas monitoring
• Summary
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Double beta decay
eeAZAZ 22,2,
2νββ 0νββ
Allowed in SM and observed for several isotopes with forbidden single beta decay. Conserves lepton number. Long half-lifetimes(1019 ÷ 1021 y).
Does not conserve lepton number (ΔL=2). Possible if neutrinos are Majorana particles. Expected lifetimes > 1024 y.
eAZAZ 2,2,
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Energy spectrum of double-beta decays
2β2ν
2β0ν
E/Qee
dN/d
(E/Q
ee) [
a.u.
]E.g. 76Ge Qee = 2039 keV
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2β0ν limit on T01/2 depends on the background index BE
A
EEmol
NBmT
mAT
2ln0
2/1
Amol
NmmTAT 2ln0
2/1
In the presenceof background BE
Without background
A isotope abundanceε registration efficiencyT time of measurement [y]NA Avogadro constant
m detector mass [kg]mmol molar mass of Ge [kg/mol]BE background in Qee region [y-1keV-1kg-1]δE energy resolution [keV]
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The GERDA Experiment @ LNGS
High-purity liquid argon (LAr) shield & coolantOptional: active veto
Clean roomLock system
Steel cryostat with internal Cu shield
Array of bareGe-diodes
Water: γ,n shield Cherenkov medium
for µ veto
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• 42K β– decay with Q = 3525 keVabove Qee of 76Ge (2039 keV)
• Half life-time of 42Ar is 32.9 y• 42K half life-time is 12.36 h• If 42K decays on the surface of
detectors then background for 0νββ• 42K signature – 1525 keV γ line• GERDA proposal:
42Ar / natAr < 3 × 10-21 g/g(43 µBq/kg) homogenously distributed in the cryostat volume
Surprising 42K
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Surprising 42K
TIMEµs s min
Drifting in E-field
42K
Det
ecto
r sur
face42K
+
O2-
42K
+
42K
+
Germinaterecombination
Recombination onelectronegative impurities
e-
e-
O2
-
h
Ar+
Ar+
42K
+
42Ar β- decays to 42K+
Charged 42K drifts towards the detector42K β- decays (Q = 3525 keV, above Qββ)
possibly nearby the detector
β-
e-
42ArT 1/2
= 12 h
β-
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GERDA espectrum before the unblinding (June 2013)
T1/2 = 269 yQ = 565 keV
2νββ
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Cold Dark Matter
• Astronomical evidences (large-scale galaxy surveys and microwave background measurements) indicate that the majority of matter in the Universe is non-baryonic
• The “dark matter” is typically a factor of 10 times greater in total mass
• The nature of this non-baryonic component is unknown, but of fundamental importance to cosmology, astrophysics, and elementary particle physics
• One of the candidates are WIMPs – Weakly Interacting Massive Particles, possibly detectable through their collisions with ordinary nuclei, giving observable low-energy (<100 keV) nuclear recoils
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Cold Dark Matter – The DarkSide ExperimentWIMP
Two-phase Liquid Argon TPC
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Ubiquitous 222Rn
• 226Ra present in most of the construction materials;
• Gaseous 222Rn emanation dissolves into the cryoliquids;
• Ionized decay products are subject to electric field, induced in the cryoliquid (e.g. drift chambers);
• Energy released in alpha, beta and gamma decays in 226Ra decay chain are high;
• Natural intrinsic source of background in majority of the low background experiments.
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DarkSide – Electrostatic Rn monitor
• Design allowing for operation up to 20 kV
• Simulations of 222Rn daughters drift in electric field to optimize efficiency for different carrier gases
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DarkSide – Electrostatic Rn monitor
• On-line monitoring of the 222Rn content in the DarkSide clean-rooms (Rn-reduced air);
• Recently completed;• Sensitivity ~0.5 mBq/m3
(250 atoms of Rn/m3).
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Summary
• Ultra-low background experiments demand supreme purities of the construction materials and online monitoring;
• Technologies for obtaining highly radiopure materials rely on:– careful material selection;– understanding properties of the radio-impurities;– dedicated experiments focused only on the impurities;
• Material selection and online monitoring depend on the limitations of the activity detection techniques (minimum detectable activity), e.g.:– direct measurements of 42K in cryoliquids;– online monitoring of gases in drifting chambers (222Rn);
• Physical and chemical properties of radio-impurities need to be studied in sophisticated experiments due to their… low activities. We need to know:– diffusion coefficients;– chemical reactions;– neutralization time;– mobility etc.
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Backup slides & References
• ZDFK UJ: http://bryza.if.uj.edu.pl/• The GERDA Experiment: http://www.mpi-hd.mpg.de/gerda/• The DarkSide Experiment: http://darkside.lngs.infn.it/
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Neutrinoless double beta decay
Energetically forbiddenβ decay
Allowed double-β decay
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Neutrinoless double beta decay
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021
1eemMQG
T
iieiee mUm 2
In theory:
G(Q) – Kinematic coefficient|M|2 – Nuclear matrix element<mee> – effective Majorana neutrino mass
T0ν1/2 will be determined experimentally
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The GERDA Experiment @ LNGS
1400 m ~ 3.500 m.w.e.
shielding against muons
LNGSAssergi