Gamma_spectrometry_in_deep_sea_water

Report
Gamma spectrometry in
deep sea water
Jose Busto
CPPM / 9 -11 - 2010
Concentrations of Natural Radionuclides in the sea
Half – life
Radionuclide
Single Long
Lived
U and Th
Chains
40
K
87Rb
129I
1.25 109 yr
4.7 1010 yr
1.7 107 yr
238U
4.9 109 yr
670
64
0.06
~3 – 0.2
… ,226Ra, 214Bi, 210Pb … 206Pb
232Th
1.4 1010yr
..., 228Ac,212Pb,
3H
Cosmogenic
Activity ( dpm / l)
7Be
14C
208Tl
0.005 - 0.05
… 208Pb
12.26 yr
53 d
5570 yr
0.036
0.05
0.2 - 0.3
Anthropogenic Radionuclides
137Cs, 60Co, 90
Sr, 3H, ….
Radioactivity in the marine environment
 1950’s
-> Water or sea floor measurements
=> mineral exploration
=> geological mapping
=> sediments transport
=> discharge and dump of radioactive wastes
=> radiation damage to optical fiber telephone cables.
=> …
 Single sample collection of water or sediments
===> Classical Radioanalytical methods
 Preconcentration
 Separation
 Long-term measurements




+
-
Alpha spectrometry
Gamma spectrometry
Neutron Activation Analysis
Mass spectrometry
Access to all radionuclide with very high sensibility
( -> < 10-12 g/g in 238U )
No continuous evaluation of radioactivity
 Towed detector systems
• Mapping large area
• Control time of measurement
• Gamma spectrometry (NaI)
 Autonomous in situ detectors
• Very high statistic time
• Evolution of radioactivity
• Gamma spectrometry (NaI, Ge)
Measure the radioactivity of the water
continuously in the ANTARES site
The case of 40K
40Ca
40K
--->
40Ar
+
(10.7 %)
g spectrometry
(NaI, Ge)
b-
+ e- + ne
e+ + ne
ne
(0.03 %)
EC
(10.67 %)
Cerenkov light
(ANTARES)
10.67 % EC
1312 keV b-
40Ca
40Ar
b+
(89.3 %)
40K
1460 keV
(89.3 %)
40K
continuous measurement with ANTARES
-2400 m
13.0 ± 0.5 Hz observed => 12 ± 4 Hz expected
40Ca
40K
Anti-neutrino
b-
Cerenkov
Project to measure gamma activity in ANTARES site
NaI g spectrometer in an standard ANTARES glass sphere
USB feed
HV + MCA
3’ x 3’ NaI cristal
17’ ANTARES glass sphere
3’ PM
FIT PC2 data acquisition ( 6W )
226Ra
spectrum
226Ra
214Pb
214Pb
214Pb
214Bi
214Bi
214Bi
40K
spectrum
226Ra
214Pb
40
214Bi
K
• Preliminary tests => Autonomy ~ 15 days
 Autonomy increase => suppression of hard disk
• Still to do
 inner background => Pb shielding (LSM)
 efficiency => MC v.s KCl dilute in water
A dream ?
Gamma spectrometry with Ge detectors
226Ra
Ge spectrum
Not a dream
Canberra
4 h operation with a single battery
Existing project in India cost for a continuous Ge spectrometer @ 500 m deep
Conclusion
 Many measurements of sea radioactivity.
 Long period in situ measurements never done (?).
 Installation of a preliminary continuous NaI gamma
spectrometer in the ANTARES site.
Possibility to perform continuous gamma spectrometry
with very high energy resolution ( Ge ).
Radioactivity from Salt
 Fraud control

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