Tritium: tracing the hydrological cycle Tritium – the radioactive hydrogen isotope: A multi-porpose environmental tracer for the hydrological cycle helis helium isotopes studies Br emen Jürgen Sültenfuß [email protected] Institut für Umweltphysik Abt. Ozeanographie
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Tritium: tracing the hydrological cycle
Tritium – the radioactive hydrogen isotope: A multi-porpose environmental tracer for thehydrological cycle
helishelium isotopes studiesBremen
Jürgen Sültenfuß [email protected]
Institut für UmweltphysikAbt. Ozeanographie
Tritium: tracing the hydrological cycle
• fundamentals of tritium– properties of tritium– origin and distribution of tritium
• studies & applications– atmospheric circulation– water vapor transport– ocean circulation– groundwater dating– river discharge– lake ventilation– …
helishelium isotopes studiesBremen
Jürgen Sültenfuß [email protected]
Institut für UmweltphysikAbt. Ozeanographie
Tritium decay:
33H → H → 33He + He + ββββ- + νννν + E Emax = 18.6 KeV (very low)
half-life t1/2 = 12.32 yrλλλλ = 0.0563 yr-1 = 1.79 10-9 s-1
NICE:
t1/2 just right to study environmentalanual & decadal variations
decay product 3He - a stable noble gas (no chemical reactions)
if trapped in compartment: mother-daughter pair
OriginOrigin and and abundanceabundance of of tritiumtritium
NaturalNatural tritiumtritium::CosmicCosmic raysrays in in atmosphereatmosphere: : 1414N(n,N(n,33H)H)1212CC
Rapid Rapid reactionreaction to HTO to HTO →→ waterwater cyclecycle →→ precipitaionprecipitaion
SubsurfaceSubsurface productionproduction 66Li(n, Li(n, αααα))33H H
specificspecific activityactivity: Bq/kg : Bq/kg oror forfor tritiumtritium in form of HTO:in form of HTO:
1 TU (1 TU (tritiumtritium unitunit) = 3H/1H = 10) = 3H/1H = 10--1818
= 0.118 Bq/kg =1.11 10= 0.118 Bq/kg =1.11 10--1616 mol/kg = 6.68 10mol/kg = 6.68 1077 atomsatoms/kg /kg
Natural global tritum inventory
Steady state: production = decay PA = λN
Mean production rate: P = 0.28 atoms/cm2 s-1
Area of the Earth: A = 5.1 1018 cm2
Decay constant: λ = 0.0563 yr-1
→ amount of natural tritium = 1.3 kmol = 4kg
compare to global water mass: 1.4 1021 kg H2O = 1.6 1020 kg H
VeryVery lowlow productionproduction → → veryvery lowlow concentrationconcentration::ActivityActivity in in surfacesurface waterwater ~ 10TU ~ 10~ 10TU ~ 10--1515 mol/kgmol/kg
Cosmogenic production – latidute dependence
Charged particles in cosmic radiationare deflected by the geomagnetic field:
Fluxes and production largest near poles
0-10°: 0.12 60-90°: 0.6
other radio isotopes produced byspallation in the atmosphere
Anthropogenic Tritiumextreme large tritium production by hydrogen bomb testsend 50ies and early 60ies
mainly released to stratosphere in northern hemisphere
Bomb tests
Precipitation data: IAEA GNIP North America and Europeform Fritz & Clarke 1997
Bomb tests conduced in Northern Hemisphere
Tritium deposited in stratosphere: Time scale for inter hemispheric air mass exchange in stratosphere: ~ 2 yr
precipitation concentrationIAEA, GNIP
form Fritz & Clarke 1997
Stratospheric tritium concentration:
Mean life time for water vapour: 5.4 yr
from Ehhalt et al. 2002
Ottawa, 45°N, 75°W, 116m asl, CanadaValentia, 52°N, 10°W, 0m asl, IrelandHarare 18°S 31°E, 1500m asl SimbabweKaitoke 42°S, 175°E, 0m asl New Zealand
Tritium in the troposphere:
Mean life time for water ~ 4 weeks
Decline displays general structure
Ocean acts as global sink: max T <<< precipitation
Continental effect
1:1
Weiss et al. 1979
Marine water vapour
Continental water vapour
mean ridge of the alps
Minimum <3.4TU
Minimum >4.5TU
Minimum >4TU
Austria
Atlantic vs. Mediterranian
Umweltbundesamt Österreich 2005
Water vapour in polar regions: Greenland
black: Summit 72°Nred: Eureka 80°Nblue: Mould Bay 76°N
Fourre et al. 2006
partly reconstructed from ice cores
Fourre et al. 2006
Water vapour in polar regions: Antarctica
partly reconstructed from ice cores
Concentrations decline towards coast
substantial tropospheric-stratospheric water vapour ex change
marine or continental precipitation?
tritium in snow cover in the Weddell Sea
tritium records from river run-off:
comparing to precipitation concentration⇒ age spectrum
Esser 1980
0 1000 2000 3000 4000 5000
distance [km]
WOCE A9 19°S Tritium [TU]
-6000
-5000
-4000
-3000
-2000
-1000
0
dept
h [m
]
0
0.01
0.02
0.03
0.04
0.05
0.06
0.08
0.1
0.2
0.4
0.6
0.8
1North Atlantic Deep WaterTmax ~0.04TU
SouthAmerica
Africa
tracing water masses in the oceantritium in the South Atlantic
1TU = 13H/1018 H = 0.12 Bq/kg
Tmax ~1TU
Combining tritium with its decay product:33H → H → 33He + He + ββββ-if 3He is trapped ⇒ dating tool
τ = / ln 2t1/2 . ln (1 + / T
3He* )
Application:- oceanography- limnology- hydrogeology
3He - tritium - age in the Mediterranian:
exploring change of ocean circulation
0 500 1000 1500 2000
Distance [km]
M5 Helium/Tritium age [years]
-4000
-3000
-2000
-1000
0
Pre
s [d
bar]
780
779
778
777
773
761
760
759
758
756
751
723
725
730
734
739
740
741
743
1987
0 500 1000 1500 2000
Distance [km]
M31 Helium/Tritium age [years]
-4000
-3000
-2000
-1000
0
Pre
s [d
bar]
7 8 9 10 26 32 46 53 56 57 72 75 74
10.00 15.00 20.00 25.00 30.00 35.0030.00
35.00
40.00
1995
0 500 1000 1500
Distance [km]
M44 Helium/Tritium age [years]
-4000
-3000
-2000
-1000
0
Dep
th [m
]
306
305
303
300
295
294
292
291
290
289
251
265
247
239
238
237
236
219
217
10.00 15.00 20.00 25.00 30.00 35.0030.00
32.00
34.00
36.00
38.00
40.00
42.00
1999
stagnant: water just gets olderno steady state
3He - tritium - age in a groundwater system:exploring transit times
verify modells, date contaminations, study chemical reaction rates (O2, pharmaceuticals,…)
ditch
Industrial tritium:<1013 Bq per nuclear power plant/yr<1015 Bq nuclear reprocesing plant (Sellafield, La Hague)
heavy water reactorcommerial use: gaseous tritium light sourceused for military equipment, exit signs, watches, keyring pendant,…worldwide total production <1 kg
Summary:
tritium reservoirs: natural 4kgH-bombs 700kgcommercial use 1kg
converted to HTO ⇒ part of hydrological cycle ⇒ ocean acts as sink
precipitation: latitude dependent (increase towards poles)
continental effect: re-evaporation of tritium-rich water from continents ⇔ ocean as sink
seasonal variation: seasonality of stratosphere - troposphere exchange
atmosphere: water vapour residence time:
5yr stratosphere ⇔ ~4 weeks tropospherepathways & exchange between reservoirs:
N⇔S stratosphere ⇔ troposphere
Applications of tritium
marker of younger water in ocean, lakes and groundwaterstudy dynamics
combining with decay product:quantitative dating in ocean, lakes and groundwater
precipitation distribution: atmosphere dynamics
(much more in chemistry, biology, medicine)
Attention needed in the future for
locally elevated tritium concentrations
tritium release from nuclear power plants, reprocessing plants and industry
large amount of tritium will be needed for fusion reactor (10kg/unit)
BfG, 2006
BfG, 2006
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