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

22

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

33

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,

44

Energy spectrum of double-beta decays

2β2ν

2β0ν

E/Qee

dN/d

(E/Q

ee) [

a.u.

]E.g. 76Ge Qee = 2039 keV

55

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]

66

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

7

• 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

88

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-

99

GERDA espectrum before the unblinding (June 2013)

T1/2 = 269 yQ = 565 keV

2νββ

1010

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

1111

Cold Dark Matter – The DarkSide ExperimentWIMP

Two-phase Liquid Argon TPC

1212

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.

13

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

14

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).

1515

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.

1616

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/

1717

Neutrinoless double beta decay

Energetically forbiddenβ decay

Allowed double-β decay

1818

Neutrinoless double beta decay

22

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

1919

The GERDA Experiment @ LNGS

1400 m ~ 3.500 m.w.e.

shielding against muons

LNGSAssergi