Heavy Radiation Backgrounds in the LSBB · Heavy Radiation Backgrounds in the LSBB Tom Girard, Ana...
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Heavy Radiation Backgrounds in the LSBB Tom Girard, Ana Fernandes, Miguel Felizardo Advanced Detectors Group Centro de Física Nuclear Universidade de Lisboa
Transcript of Heavy Radiation Backgrounds in the LSBB · Heavy Radiation Backgrounds in the LSBB Tom Girard, Ana...
Heavy Radiation Backgroundsin theLSBB
Tom Girard, Ana Fernandes, Miguel Felizardo
Advanced Detectors GroupCentro de Física NuclearUniversidade de Lisboa
SIMPLE
gas
25 µm 1 mm
WIMP
superheated freon droplet
(i) E > Ec = 4πrc2γ/3ε
(ii) ∆E/∆x > Ec/arc
( Seitz : Phys. Fluids 1 (1979) 1 )
∆ E/ ∆ x ≥ 150 keV/µm
intrinsic BG rejection < 10-10
v-a-v
bolometers: 10-4,-5
xenon: 10-2
argon: 10-7,-8
• key feature: selective sensitivitytunable (P,T) double threshold device
The problem with rare event searches : S / B << 1
cosmogenics, radio-contaminants, ...
underground sitingφµ (surface) ~ 4 x 105 µ/hr
φµ (capsule) ~ 36 µ/hr
φµ (SG) ~ 105 µ/hr
but ....... you begin to see your mountain !
1260 n/hr
(0.4-4)x10-3 n/m2s-> 14 n/hr
( U/Th )
231Th227Ac
231Pr
223Fr
211Pb
219Rn
227Th
223Ra
215Po
207Tl
207Pb
232Th
228Ra
228Th
228Ac224Ra
208Pb
220Rn
216Po
212Pb
212Bi
212Po
208Tl
211Bi
235U14x109 y
α
α
α
α
α
α
α
α
7x108 y
α α
α
α
α
α
α
U / Th decay chainsα (α,n) spontaneous fission
Neutron shielding : low Z material (H, Li, B....
N(x) ~ N(0) e –x / λ
Common shielding materials :
� Concrete : ~ water
� Water : factor 5-10 reduction per 10 cm
� PE : ~ water
� Wood : factor 5-10 reduction per 20 cm
SIMPLE in GESA
Marine blue: 30-100 cm thick concrete
Cyan: 50-75 cm thick water(shield, pool)
Brown: 20 cm thick wood
Yellow: 1 cm thick steel
Grey: 50 thick concrete (floor)
alpha’s < 0.5 evt/kgd� ~4 x 10-3 evts/hr
232Th (Bq/kg) 238U (Bq/kg) 40K (Bq/kg)
LSBB 7.7 11 57
Canfranc-14m 60 30 880Canfranc-31m 8.5 4.5 37Canfranc-43m 23 9.8 43Canfranc-51m 76 31 680
GSasso ~8 ~83 --GSassso ~ 0 ~ 0 --
Modane ~ 10 ~ 10 --
shielding radio-assays
1 cm thick steel
30-100 cm thick concrete (± 4π)
232Th (Bq/kg) 238U (Bq/kg) 40K (Bq/kg)
LSBB 0.02 1.8 0.02
GESA MCNP simulations(schematic)
Figure 1. Room model with water shielding.Color code: yellow - water; blue - air;
magenta - concrete; green – SDDs.
(b) Top view
(a) Front view
Table 2. Simulation results.
File Sourcelocation
Sourcevolume
(103 cm3)
Shield’g F4 < 5 keV(x10-8)
F4 > 5 keV(x10-8)
bair Tank base 2961 No 81.9 ± 0.4% 10.4 ± 0.7%
bwat Yes 42.1 ± 0.2% 4.53 ± 0.5%
cair Ceiling andfloor
11216 No 65.8 ± 0.4% 8.49 ± 0.6%
cwat Yes 1.50E-1 ± 4% 6.00E-3 ±11%
fair End walls 320 No 12.3± 0.9% 1.41E-3 ±1.7%
fwat Yes 1.03E-3 ±22%
0
lair Side walls 10362 No 72.7± 0.4% 10.6 ± 0.6%
lwat Yes 7.60E-1 ± 2% 1.97E-2 ± 7%
concrete only: ~ 3000 evt /kgd
226Ra
222Rn
214Pb
218Po214Bi
214Po
210Pb
210Bi
210Po
206Pb
α
α
α α
1600 y
radon decayα, (α,n)
radon [ α , (α,n) ] : Cradon = 20 � 1500 α /m3s (seasonal)
Nα(x) ~ Nα(0) e – x / D
> Shielding : common materials
D (cm)
> concrete 6 – 80
> water 2
> plastics < 0.07
9cm H2O 4mm glass( 1000 α /m3s 11 α /m3s 0.04 α /m3s )
> Ventilation: air or N2 flow at 1 liter / hr
x ≥ 3D � “radon tight”
+ monitor’g
ventilation
shielding....
Instrumentation
6.3 6.4 6.5 6.6 6.7 6.8 6.9−3
−2
−1
0
1
2
3
Time [s]
Am
plitu
de [V
]
0 2000 4000 6000 8000 10000 12000 14000 16000−90
−80
−70
−60
−50
−40
−30
−20
−10
639.51 Hz
Frequency [Hz]
Pow
er [d
B]
0 2000 4000 6000 8000 10000 12000 14000 16000−90
−80
−70
−60
−50
−40
−30
−20
−10
3.44 kHz
Frequency [Hz]
Pow
er [d
B]
microleak FFT
0 500 1000 1500 2000−90
−80
−70
−60
−50
−40
−30
−20
−10
34.37 Hz
Frequency [Hz]
Pow
er [d
B]
fracture FFT
0 20 40 60 80 100−100
−95
−90
−85
−80
−75
−70
−65
−60
−55
−50
40.33 Hz
Frequency [Hz]
Pow
er [d
B]
trapped N2 gas FFT
MCE-200 microphone+
PGA2500 adaptive amplifiernucleation
event
SIMPLE measures ( 27/10/2009 – 05/02/2010 )
3.43 ± 0.51 ± 0.12 evt/kgd
consistent with diffusionof 15 Bq/m3 radon level
1.11 ± 0.28 ± 0.22 evt/kgd
consistent with MCNP1.09 ± 0.02 ± 0.07 evt/kgd
based on materials’radio-assays
450 500 550 600 650 700 750100
1000
10000
100000
Pow
er [u
W]
Frequency [Hz]
true event
103 µW
α
n
CONCLUSIONS
1. Neutron flux into GESA ~ 3000 evt / kgd
> mainly from concrete (rock shielding efficient)
> below health & safety standards (LSBB NOT a reactor ! )
> of possible concern to some experiments
> reduced to 1 evt / kgd in SIMPLE
2. Radon flux into GESA ~ 0.26 - 3.9 x 108 evts / kgd
> consistent with 15 Bq /m3 ( x10 < 102 measured – water flow?)
> sometimes above health & safety standards ( ~ 1/2 year)
> of possible concern to some experiments
> of concern to human activity...
> reduced to ~ 2.8 evt/ kgd
