INTERNATIONAL PHD PROJECTS IN APPLIED NUCLEAR PHYSICS AND INNOVATIVE TECHNOLOGIES
This project is supported by the Foundation for Polish Science – MPD program, co-financed by the European Union within the European Regional Development Fund
Technologies for obtaining radio-pure materials;
methods of low radioactivity detection
Krzysztof Pelczar
M. Smoluchowski Institute of Physics
Jagiellonian University, Cracow
Symposium on applied nuclear physics
and innovative technologies, UJ, Kraków, 2013
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
2
Double beta decay
2νββ
Z , A  Z  2, A  2e
0νββ

 2 e
Allowed in SM and observed for
several isotopes with forbidden single
beta decay. Conserves lepton
number. Long half-lifetimes
(1019 ÷ 1021 y).
Z , A  Z  2, A  2e
Does not conserve lepton number
(ΔL=2). Possible if neutrinos are
Majorana particles. Expected
lifetimes > 1024 y.
3
Energy spectrum of double-beta decays
dN/d(E/Qee) [a.u.]
E.g. 76Ge Qee = 2039 keV
2β2ν
2β0ν
E/Qee
4
2β0ν limit on T01/2 depends on the background index BE
Without background
0
1/ 2
T
0
1/ 2
In the presence
of background BE
T
A
ε
T
NA
m
mmol
BE
δE
isotope abundance
registration efficiency
time of measurement [y]
Avogadro constant
m
 A ln 2 T
NA
mmol
ln 2 mT
 A
NA
mmol BE E
detector mass [kg]
molar mass of Ge [kg/mol]
background in Qee region [y-1keV-1kg-1]
energy resolution [keV]
5
The GERDA Experiment @ LNGS
Steel cryostat with
internal Cu shield
Clean room
Lock system
Array of bare
Ge-diodes
Water: γ,n shield
Cherenkov medium
for µ veto
High-purity liquid argon
(LAr) shield & coolant
Optional: active veto
6
Surprising 42K
•
•
•
•
•
•
β– decay with Q = 3525 keV
above 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
42K
7
Surprising 42K
Drifting in E-field
+
-
β- decays to 42K+
Charged 42K drifts towards the detector
42K β- decays (Q = 3525 keV, above Q )
ββ
possibly nearby the detector
42Ar
e-
+
Ar
e+
Ar
+
42K
O2 -
Germinate
recombination
µs
42K
β42K
β-
+
42K
Detector surface
e-
+
42Ar
42K
O2
Recombination on
electronegative impurities
s
min
TIME
h
8
GERDA espectrum before the unblinding (June 2013)
T1/2 = 269 y
Q = 565 keV
2νββ
9
Cold Dark Matter
•
•
•
Astronomical evidences (largescale 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
10
Cold Dark Matter – The DarkSide Experiment
WIMP
Two-phase Liquid Argon TPC
11
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.
12
DarkSide – Electrostatic Rn monitor
•
•
Simulations of 222Rn
daughters drift in
electric field to
optimize efficiency for
different carrier
gases
Design allowing for operation up
to 20 kV
13
DarkSide – Electrostatic Rn monitor
•
•
•
On-line monitoring of the 222Rn
content in the DarkSide cleanrooms (Rn-reduced air);
Recently completed;
Sensitivity ~0.5 mBq/m3
(250 atoms of Rn/m3).
14
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.
15
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/
16
Neutrinoless double beta decay
Energetically forbidden
β decay
Allowed double-β decay
17
Neutrinoless double beta decay
In theory:
1
2
 GQ  M mee
0
T1 2
2
mee 
U
2
ei
mi
i
G(Q) – Kinematic coefficient
|M|2 – Nuclear matrix element
<mee> – effective Majorana neutrino mass
T0ν1/2 will be determined experimentally
18
The GERDA Experiment @ LNGS
1400 m ~ 3.500 m.w.e.
shielding against muons
LNGS
Assergi
19