1. Isotope Hydrology: 3H/3He dating
Peter Schlosser, February 19, 2008

2. Syllabus Date Reading Lecture HW Prof Tu 1/22
Orientation, Principles of tracer applications
MS,PS
Th 1/24
Surface water hydrology 101 PS
Tu 1/29
Groundwater hydrology 101 Groundwater flow
HW1 MS
Th 1/31
Groundwater transport
Tu 2/5
Dyes, particles, ions, and other deliberate tracers
HW2
Th 2/7
Stable isotopes
Tu 2/12
 HW3
Th 2/14
  3H
Tu 2/19
3H/3He

3. Radiocarbon dating (14C)
Syllabus
Date
Reading
Lecture HW
 Prof
Th 2/21
Carbon Isotopes (14C, 13C) MS
Tu 2/26
Radiocarbon dating (14C)
 HW4
Th 2/28
 CFCs, SF6, SF5CF3 PS
Tu 3/4
85Kr, 39Ar
HW5
Th 3/6
Noble gases (incl Rn)
Tu 3/11
Noble gas thermometry

4. Transient Tracers
Tracers: trace substances of natural or anthropogenic origin (stable and radioactive isotopes; chemical compounds. Sometimes toxic or otherwise harmful (contaminants)
Transient tracers: ‘Dyes’ with known delivery rates to the environment (e.g., 3H, 3He, CFCs, 129I, SF6, 85Kr)
Radioactive clocks (e.g., 14C, 39Ar, 3H/3He)
Special sources (e.g., 18O, Ba, nutrients, Ra isotopes, Rn isotopes)
Deliberately released tracers (e.g., SF6, 3He)

5. 3He Radioactive daughter of 3H
1939: Luis Alvarez discovered an isotope of mass 3 and distinguished it from tritium. He noted that the isotope was the rare isotope of natural helium.
Mass: amu (HD/H3+: / amu)
Abundance in the atmosphere: 5.24 ppm * *10-6
(3He/4He)atm = * 10-6
Solubility of He in water: Ostwald coefficient: ca to 0.01
3He is less soluble than 4He: α ca for seawater at low temperatures
Low abundance requires sophisticated analytical methods for precise measurement.

6. 3H/3He method: motivation

7. Tritium/3He method

8. Tritium/3He method

9. Tritium/3He method

10. Tritium/3He method
Determination of 3H/3He age requires measurement of tritium and helium isotopes at time t. No knowledge of tritium and 3He concentrations at time t0; i.e., at time of isolation of water parcel, is needed.

11. Tritiogenic 3He in TU
R = [3He]/[4He]

12. Early 3H/3He literature
Early theoretical work by Tolstikhin and Kamensky,
Geochemical International, 6, 810 – 811, 1969

13. Basics of 3H/3He method

14. 3H/3He profiles
Adapted from Schlosser et al., 1988 (EPSL)

15. 3H/3He profiles
Adapted from Schlosser et al., 1989 (EPSL)

16. Separation of tritiogenic 3He
From Schlosser et al., 1989 (EPSL)

17. Separation of tritiogenic 3He
From Schlosser et al., 1989 (EPSL)

18. 3H/3He profiles
Adapted from Schlosser et al., 1989 (EPSL)

19. Future of 3H/3He method
From Schlosser et al., 1989 (EPSL)

20. Future of 3H/3He method
From Schlosser et al., 1989 (EPSL)

21. Future of 3H/3He method
From Schlosser et al., 1989 (EPSL)

22. 3He confinement
From Schlosser et al., 1989 (EPSL)

23. 3H/3He age: mixing
The 3H/3He age is non – linear with respect to mixing. It favors the age of the water component with the higher tritium concentration.
From Jenkins and Clarke, 1976 (DSR)

24. Summary
Combined tritium/3He can extend the utility of tritium as absolute time marker
They also can be used as a radioactive clock
Terrigenic helium can complicate the separation of tritiogenic 3He from the total measured helium. In many cases this problem can be solved by additional measurement of Ne
The 3H/3He age is an apparent age. It has to be interpreted with care to account for non – linearities introduced during mixing of two or more water masses
3H/3He can be used for another several decades to come before tritium will have decayed to a large degree and dispersion will have homogenized the 3He signal