Transcript Document

Astroparticle Physics
at
Gran Sasso Underground Laboratory:
Borexino and geo-neutrino
Lino Miramonti – 7 Feb 2006 - Honolulu (Hawaii)
Lino Miramonti - 7 February 2006 - Honolulu Hawaii (USA)
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Astroparticle
Physics
Particle
physics
Astrophysics
Astroparticle
&
physics
Cosmology
Employs knowledges and techniques from particle physics in order to study
cosmological and astrophysical aspects.
Detects particles coming from space for particle physics studies.
Typical studies of astroparticle physics are:

Neutrino Physics (Solar, Supernova, Atmospherics,
Geoneutrinos, neutrinos from reactors and from accelerators, etc..)





Cosmic Ray Physics
Rare Processes (double beta decay, proton decay etc..)
Dark Matter (WIMP’s)
Gravitational Waves
Nuclear Physics (Cross section measurements of astrophysics
interest)

…….
Very little cross sections and/or very
rare processes of events means to
locate detector apparatus to the
shelter from cosmic radiation
Underground
Physics
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France
Commissariat a l’Energie Atomique,
Centre National de la Recherche Scientifique
Italy
Istituto Nazionale di Fisica Nucleare,
Istituto di Fotonica e Nanotecnologie Trento,
European Gravitational Observatory
Germany
Max Planck Institut für Kernphysik, Technische
Universität München,
Max Planck Institut für Physik Muenchen, Eberhardt,
Karls Universität Tubingen
Spain
Zaragoza University
UK
Sheffield University,
Glasgow University,
London University
Czech Rep
Czech Technical Univ. in Prague
Denmark
University of Southern Denmark
Netherland
Leiden University
Finland
University of Jyväskylä
Slovakia
Comenius University Bratislavia
Greece
Aristot University of Thessaloniki
Integrated
Large
Infrastructures
for
Astroparticle
Science
ILIAS is an initiative supported by the
European Union with the aim to
support
the
European
large
infrastructures operating in the
astroparticle physics sector.
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The ILIAS project is based on 3 groups of activities:
• Networking Activities
(N2) Deep Underground science laboratories
(N3) Direct dark matter detection
(N4) Search on double beta decay
(N5) Gravitational wave research
(N6) Theoretical astroparticle physics
• Joint Research Activities (R&D Projects)
(JRA1) Low background techniques for Deep Underground Science
(JRA2) Double beta decay European observatory
(JRA3) Study of thermal noise reduction in gravitational wave detectors
• Transnational Access Activities
(TA1) Access to the EU Deep Underground Laboratories
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JRA1 (Joint Research Activities 1)
Low background techniques for deep underground sciences (LBT-DUSL)
Objectives:
Background identification and measurement (intrinsic, induced, environmental)
Background rejection techniques (shielding, vetoes, discrimination)
Working packages
A vast R&D programme on the
improvement and implementation of
WP1:
Measurements of the backgrounds in the underground labs
ultra-low
background
techniques will be carried out
WP2:
Implementation of background MC simulation codes
cooperatively in the 5 European
Underground Laboratories.
WP3:
Ultra-low background techniques and facilities
WP4:
Radiopurity of materials and purification techniques
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http://www.lngs.infn.it/
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LNGS
LNGS permanent staff: 60 (physicists, technicians, administration)
Scientists involved in LNGS experiments: 700 from 24 countries
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3 main halls
A B C 100 x 18 m2 (h.20 m)
Operating
Institution
Istituto Nazionale di Fisica Nucleare
(INFN)
Location
Gran Sasso Tunnel (Abruzzi, Italy)
Excavation
1987
Underground area
3 halls A B C (100m x 18m x 20m) +
service tunnels
Depth
1400 m (3800 mwe)
Total volume
180000 m3
Surface
> 6000 m2
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Backgrounds & Facilities @ LNGS
Muon Flux
Residual muon flux
(6 order of magnitude lower than surface)
1.1 μ m-2 h-1
Neutron Flux
1.08 10-6 n cm-2 s-1
(0-0.05 eV)
1.84 10-6 n cm-2 s-1
(0.05 eV- 1 keV)
0.54 10-6 n cm-2 s-1
(1 keV-2.5 MeV)
0.32 10-6 n cm-2 s-1
(> 2.5 MeV)
Coming from
spontaneus fission (in particular from 238U)
and
(α,n) reaction on light elements in the rock
also µ-induced neutrons
Primordial Radionuclides
238U
232Th
K
6.8 ppm
Rock
(Hall A)
0.42 ppm
Rock
(Hall B)
0.66 ppm
Rock
(Hall C)
1.05 ppm
Concrete
All Halls
2.167 ppm
Rock
(Hall A)
0.062 ppm
Rock
(Hall B)
0.066 ppm
Rock
(Hall C)
0.656 ppm
Concrete
All Halls
160 ppm
Troublesome for anti-ν detection by
Cowan-Reines reaction!
Rock of Hall A is 10 times more radioactive in 238U than
Hall B and Hall C (and 30 times more radioactive in 232Th)
Rock
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FACILITY FOR LOW-LEVEL RADIOACTIVITY MEASUREMENTS
Present: 32 m2 on one floor in service tunnel
Future: 60 m2 distributed on three floors in hall A
HPGe Hall
(32 m2 floor)
Courtesy by Matthias.Laubenstein
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Completed experiments
Atm ν, Monopoles
Solar neutrinos
ββ
Dark Matter
MACRO
GALLEX / GNO
Heidelberg-Moscow
Mibeta
DAMA
(Streamer tubes + Liquid scintillators)
(~ 30 T Gallium radiochemical detector)
(~ 11 kg enriched 76Ge detectors)
(~ 7 kg Bolometers TeO2)
(~ 100 kg NaI detectors)
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Running experiments
ββ
Dark Matter
Supernova neutrinos
Nuclear astrophysics
Cuoricino
CRESST
LIBRA
HDMS / Genius-TF
LVD
LUNA
(~ 41 kg TeO2 crystals)
(Sapphire cryodetector & CaWO4 crystals (phonons+scintillation))
(~ 250 kg NaI crystals)
(Ge detector 73Ge enriched)
(Streamer tubes + Liquid scintillator)
(Accelerator)
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Under construction
CERN-GS beam ν
Solar Neutrinos
OPERA
ICARUS
Borexino
(Emulsion)
(~ 600 T Liquid Argon)
(~ 300 T Liquid scintillator)
Planned & proposed
ββ
Nuclear astrophysics
Gravitational waves
Dark matter
CUORE
GERDA
LUNA-III
LISA R&D
Liquid Xe / Liquid Ar
(~ 750 kg Te02)
(76Ge)
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The main goal of Borexino is the
measurement in real time of the low
energy component of solar neutrinos.
RADIOCHEMICAL
Integrated in energy and
time
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CHERENKOV
Less than 0.01% of the solar
neutrino flux is been measured in
real time.
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Borexino Collaboration
–
Italy (INFN & Universiy of Milano and Genova, Perugia Univ., LNGS)
–
USA (Princeton Univ., Virginia Tech.)
–
Russia (RRC KI, JINR, INP MSU, INP St. Petersburg)
–
Germany (Hiedelberg MPI, Munich Technical University)
–
France (College de France)
–
Hungary (Research Institute for Particle & Nuclear Physics)
–
Poland (Institute of Physics, Jaegollian University, Cracow)
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BOREXINO: subsystems
Borexino detector
Scintillator purification systems:
Water extraction
Vacuum distillation
Silicagel adsorption
Storage tanks: 300tons of PC
Control room
Counting room
CTF
DI Water plant
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Core of the detector: 300 tons of liquid
scintillator (PC+PPO) contained in a nylon
vessel of 8.5 m diameter. The thickness of
nylon is 125 µm.
1st shield: 1000 tons of ultra-pure buffer
liquid (pure PC) contained in a stainless steel
sphere of 13.7 m diameter (SSS).
2200 photomultiplier tubes pointing towards
the center to view the light emitted by the
scintillator.
2nd shield: 2400 tons of ultra-pure water
contained in a cylindrical dome.
200 photomultiplier tubes mounted on the
SSS pointing outwards to detect Cerenkov
light emitted in the water by muons.
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Eν = 862 keV (monochromatic)
7
ΦSSM = 4.8 · 109 ν s-1 cm2
Be  e  7Li  e
e
Recoil nuclear energy of the e-
x
Elastic Scattering
 x  e   x  e
  1044 cm2 (at 1 MeV )
expected rate (LMA hypothesis) is 35 counts/day in the 250-800 keV energy range
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18 m
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Cleen Room (on top of the
Water Tank) for the
insertions of lasers and
sources for calibrations.
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Cleen Room (on top of the Water
Tank) for the insertions of lasers
and sources for calibrations.
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CTF is a prototype of Borexino. Its main goal was to verify the capability to
reach the very low-levels of contamination needed for Borexino
100 PMTs
4 tons of scintillator
4.5m thickness of water shield
Muon-veto detector
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The CTF as a tool for tuning the
apparatus before filling
In this moment we use the CTF in order:
To asses the performances of the different BOREXINO sub-
systems.
To test the 14C content in the PC
To test the efficiency of the purification methods (Water
extraction, Vacuum distillation, Silicagel adsorption)
To test the cleanliness of the apparatus
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1. Natural radioactivity
2. Muon Induced reactions
3. Cosmogenic induced isotopes
4.
14C
5. Air contaminants: 222Rn, 85Kr, 39Ar
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Natural radioactivity
Primordial radioactivity: ( about 20 radioisotopes with half-life > Earth life)
between them:
238U and 232Th (α and β emitters)
40K (β emitter with end-point = 1.3 MeV)
•
Selection of materials
•
Surface treatment to avoid dust and particulate
•
Purification:
•
Water extraction,
•
Vacuum distillation,
•
Ultra filtration
•
Nitrogen sparging
•
Alpha/Beta Discrimination
•
Delayed Coincidence
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Typical Conc.
Borexino level
238U, 232Th
~ 1ppm in dust
~ 1ppb stainless steel
~ 1ppt IV nylon
~ 10-16g/g (PC)
~ 10-14g/g (water)
Knat
~ 1ppm in dust
< 10-13g/g (PC)
Purification of the Scintillator (with US Skids):
•Water extraction: Impurity with high solubility in aqueous
phase such as K and heavy metals in U Th chains.
•Vacuum distillation: Low volatility components such as metals
and dust particles.
•Ultra filtration: Particle dust.
•Nitrogen stripping: Nobles gases.
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The excitation of the scintillator depends on many factors
including the energy loss density – a large dE/dx
enhances the slow component of the decay curve
The ratio tail over total is expected to be greater for alpha
than for electrons
An efficiency for alpha identification of ~ 97% at 751 keV
with an associated beta misidentification of ~ 2.5%.
Tail/Total charge ratio
At low energies (300-600 keV) the alpha I dentification
efficiency range from 90 to 97 % with an associated beta
misidentification of ~ 10%.
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222Rn
α=5.49 MeV
218Po
α=6.02 MeV
214Pb
214Bi
214Po
α=7.69 MeV
T=163 µs
210Pb
210Bi
210Po
α=5.30 MeV
210Pb
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224Ra
α=5.68 MeV
220Rn
α=6.29 MeV
216Po
α=6.792 MeV
T=19.8 m
212Pb
α=6.04 MeV
212Bi
212Po
α=8.79 MeV
T=0.3 µs
208Tl
208Pb
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Muon Induced reactions
At LNGS we have 1.1 µ m2 h-1 with a <Eµ> = 320 GeV
A muon-veto system (The outer water shielding serves at the same time as water Cerenkov detector for
atmospheric muons) reduce this number by a factor 5000-10000
Interacting with 12C of the organic scintillator they give:
11Be
τ = 13.8 s
β-
7Be
τ = 53.3 d
β- EC
11C
τ = 20.4 m
β- EC
10C
τ = 19.3 s
β- EC
Ultrarelativistic
These elements having a τ > 1 s
is not possible to tag them
µ can produce n which after been captured by p give a 2.2 MeV γ ray:
n  p  d   (2.2 MeV )
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Cosmogenic induced isotopes
Theoretical sea-level Cosmic Ray Flux
(Latitude New York City ≈ LNGS)
During transportation, pseudocumene is
exposed to cosmic neutrons.
Pseudocumene is produced in Sardinia and the
voyage to LNGS take about one day.
During transportation cosmic neutrons interact
with 12C producing 7Be:
n C Be  X
12
7
Be-7 decays by electron capture to Li-7
and emits (with a 10.52% branching
fraction) a 478 keV gamma.
This line is a potential background in the
Borexino neutrino window.
7Be
is efficiently removed by distillation!
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14C
The reactions expected to contribute the most to
14C production in deep underground geological
formations are:
Typical Conc.
Borexino level
14C/ 12C
14C/ 12C
< 10-12
~ 10-18
The 14C content depend on the site of extraction. There is no possibility to eliminate this radionuclide,
the only thing we can do, is to test, in CTF, samples of pseudocumene before to transport it to LNGS.
Our threshold (at 250 keV) is due to the 14C!
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Regular N2
High Purity N2
LAK (Low Ar/Kr content) N2
Air contaminants: 222Rn, 85Kr, 39Ar
To reduce the effect of emanation we used only electroplisched stainless steel, applied orbital weldings .
85Kr
β emitter: Emax = 687 keV
(Eγ = 514 keV)
Half-life: 10.8 years
39Ar
β emitter: Emax = 565 keV
(no gamma)
Half-life: 269 years
Origin
Typical Conc.
(in air)
Borexino
level
10-100 Bq/m3
~ 70 Bq/m3 in PC
222Rn
238U
85Kr
Anthropogenic origin
(nuclear fue reprocessing)
1 Bq/m³
0.16 Bq/m3 in N2
39Ar
Cosmogenic production
11 mBq/m³
0.5 Bq/m3 in N2
chain
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N2 used to
sparge
scintillator
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Liquid Nitrogen (commercial quality 4.0, i.e. 99,99%) is delivered with a truck and stored on site in three
tanks of 6 m³. The tanks can be refilled without interrupting the nitrogen supply.
•For Standard Purity N2 the liquid nitrogen is simply evaporated. The gas passes through a heat
exchanger to keep it at constant temperature of ca. 15°C. The level of 222Rn is usually in the range of 0.1
– 0.2 mBq/m³ (STP).
•For the High Purity N2 the liquid nitrogen passes through a cryogenic adsorption trap ("LTA" = Low
Temperature Absorber), filled with 11.5 liters of activated carbon. (We use CarboAct F3/F4, which was
found to be very low in 226Ra (less than 0,3 mBq/kg)). For the evaporation we use an electrical evaporator
with only low surface. The level of 222Rn is usually is below 1 µBq/m³ (STP). The output can be up to
100 m³/h.
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Deionization Unit
Reverse Osmisis
Nitrogen Stripping
Ultra Filters
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Schematic of the scintillator purification system for CTF. The scintillator is either
water extracted, or vacuum distilled then filtered and stripped with nitrogen before
being returned to the scintillator containment vessel.
The purification system was constructed entirely of electropolished stainless steel,
quartz and teflon
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Installation of the US Skids
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Installation of the US Skids
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Earth emits a tiny heat flux with an
average value of
ΦH ~ 60 mW/m2
Integrating over the Earth surface:
HE ~ 30 TW
Detecting antineutrino
emitted by the
decay of radioactive isotopes
It is possible to study the
radiochemical composition of the Earth
Giving constrain on the heat generation within the Earth.
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238U 232Th 40K
The 235U chain contribution can be neglected
238
 12300
U
NA
A
Bq
g
T h  4000 Bq g
40
Bq
K
 30
g
( 40K  0.0118 % of natK)
232
12300

ln 2
1
2
Bq
MeV 

8 W
 51.7 MeV  1.6 10-13
  9.8 10
g
J 
g

238
U206 P b  8α  6e-  6 ν  51.7 MeV
e
232
T h208 P b  6α  4e-  4 ν  42.8 MeV
e
 40 K40 Ca  e   ν  1.32 MeV (89%)
e
 40

40
 K  e  Ar  νe  1.51MeV (11%)
Neutrinos
 (U )
e
Heat
ε(U)

ε(T h) 
ε(K)
9.5 10-8
2.7  10
-8
12
 3.6 10
W
g
W
g
W
g
 7.4  104
 (Th)  1.6  104
e
 ( K )

27
 ( K )

3 .3
e
e
12300
e
Bq

 6 e  7.4  104 e
g
gs
gs
e
gs
e
gs
(ε is the present
natural isotopic
abundance)
e
gs
Each element has a fixed ratio :
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Heat

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The best method to detect electron
antineutrino is the classic Cowan Reines
reaction of capture by proton in a liquid
scintillator:
e  p  n  e

E(e )  E( e )  Q  2mec2 (Q  1.8 MeV )
The electron antineutrino tag
is made possible by a
delayed coincidence of the
e+ and by a 2.2 MeV γ-ray
emitted by capture of the
neutron on a proton after a
delay of ~ 200 µs
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and 232Th chains have 4 β
with E > 1.8 MeV :
238U
Anti-neutrino from
40K
end.point
[Th-chain]
228Ac
< 2.08 MeV
[Th-chain]
212Bi
< 2.25 MeV
[U-chain]
234Pa
< 2.29 MeV
[U-chain]
214Bi
< 3.27 MeV
are under threshold!
The terrestrial antineutrino spectrum above 1.8 MeV has a
“2-component” shape.
high energy component coming solely from U chain and
low energy component coming with contributions from U + Th chains
This signature allows individual assay of U and Th abundance in the Earth
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KamLAND
Nature vol 436 july 20 2005
Experimental investigation of geologically
produced antineutrinos with KamLAND
Reactors
13C(α,n)16O
α’s are produced by 210Po that
created by the 210Pb (τ = 22.3 y)
210Pb
210Bi
210Po
α=5.30 MeV
210Pb
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Background from nuclear
No working nuclear plants in Italy
Reactors
The nearest are at about 700 km
Borexino
is located in the
Gran Sasso underground
laboratory (LNGS)
in the center of Italy:
42°N 14°E
Earth data from F. Mantovani et al., Phys. Rev. D 69 (2004) 013001
Calculated anti-νe flux at the Gran Sasso Laboratory
(106 cm-2 s-1)
U
Crust
3.3
Th
Mantle
0.95
Crust
3.0
Total (U+Th)
Reactor
BKG
Data from the
International Nuclear
Safety Center
(http://www.insc.anl.gov)
Mantle
0.77
8.0
0.39
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Background from Po-210
210Pb
C ( , n) O
13
16
concentration measured in the Counting Test Facility
 20
 Bq / ton
• 210Pb related background negligible
• Only significant source of background are nuclear reactors
• Accidental rate also negligible (< 10% of reactors background)
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The number expected events in Borexino
are:
events
6
yr
The background will be:
 19
events
yr
Predicted accuracy of about 30%
in 5 years of data taking
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