1. New methodologies and techniques for 234 Th analysis Future Applications of 234 Th in Aquatic Ecosystems Woods Hole, August 2004

2. Talk outline Classical techniques New developments Marine vs Fresh water Alternative approaches, Automation Calculation of deficiency Outlook

3. followed by ion exchange separation Bhat et al., 1969Anderson and Fleer, 1982 alfa 230 Th beta 234 Th filtration Ion exchange plating Fe(OH) 3 precipitation U/Th separation 230 Th spike digestion Fe(OH) 3 precipitation Diss Part

4. Moore and Reid, 1973 Isotope ratios Bacon and Anderson, 1982 234 Th yield tracer MnO 2 impregnated fibre acrylic polypropylene

5. In-situ pumps Two cartridges Mann et al., 1984 in series Livingston and Cochran, 1987all Th,Ra,Ac, transuranics Ashing leaching Efficiency = 1 – MnB ____ MnA

6. Soxhlet leaching Hanfland et al.

7. Non-destructive techniques Buesseler et al., 1992 MnO 2 impregnated acrylic fibre Gamma detector efficiency (63 keV) Melt/ crush 5.3 % Gamma count < 1 % ash 16.1 % Gamma branching ratio: 63 keV93 keV 3.8 %5.4 %

8. techniqueFe(OH) 3 precipitation ion exchange MnO 2 cartridges ion exchange MnO 2 cartridges non-destructive gamma counting referencesBhat et al., 1969 Anderson and Fleer, 1982 Moore and Reid, 1973 Mann et al., 1984 Livingston and Cochran 1987 Buesseler et al., 1992 +++ reliable well-defined no interferences Spin-off of multi-tracer studies No chemical treatments - - - lengthy procedure, digestion and ion- exchange on board (1988 Polarstern) Large volumes Ship time ashing /leaching Needs same cartridge efficiency Large volumes Ship time Needs same cartridge efficiency 234 Th techniques by 1992

9. Beta counting 234 Th filtration MnO 2 precipitation U/Th separation no spike no digestion second filtrationDiss Part Mn 7+ + Mn 2+  MnO 2 MnO 2 precipitation direct beta counting 2MnO 4 - + 3Mn 2+ + 2H 2 O  5MnO 2 + 4H + RvdL & Moore, 1999

10. SD 3.2 % SD 2.4 % Precision Deep-water calibration of 20-L method

11. accuracy On-board Duplicate 20-L samples, acidified and stored 6 months before analysis Surface water samples

12. Small-volume techniques 20-L is too much for a Rosette cast Counting statistics are not limiting Reduction to 5, 4 and 2 liter versions

13. processSample size (kg) Counting techniqueSD (%) 1-  counting error N NELHA-600m Mn ppt20direct beta9.82.618 Mn ppt2direct beta5.63.44 Mn cart550gamma10.93.57 Fe ppt20direct beta15.53.96 Fe ppt20Chemistry-beta5.14.12 HOT-3500m Mn ppt2direct beta7.43.026 Southern Ocean >250m Mn ppt20direct beta3.21.110 Mn ppt5direct beta3.21.918 Comparison of techniques for total 234 Th Buesseler et al., 2001

14. 10-L Fe(OH) 3 ppt 229 Th + 232 Th Coppola et al., 2002 4-L MnO 2 ppt 230 Th + 229 Th Pike et al. 2004 Savoye et al. 2004 Return of the yield tracer Pike et al. 2004 uncorrected yield-corrected

15. Small-volume techniques Still to be worked out: RvdL & Moore 1999 20-L Buesseler et al. 2001 5-L Benitez- Nelson et al. 2001 2-L Pike et al., 2004 4-L MnO 2 concentration (mg/L) 10.20.10.25 reaction time (hour) 818-1212

16. Problems specific to direct beta measurements High self-absorption of thick sources Interference by other beta emitters

17. Beta detector source with self-absorption I(L) = I(0). (1-e -  L )/  L 0 L Z (cm) absorber 30 mg/cm 2 I(L) = I(0). e -  L absorber I = I(0) Correction required for variable  L But:  ( 234 Th) >>  ( 234m Pa) __ > eliminate  234 Th betas correct only for  ( 234m Pa) 238 U 234 Th 234m Pa 234 U 0.27 MeV 2.19 MeV   Thick beta sources

18. Beta detector source with self-absorption absorber 30 mg/cm 2 Decayed source with self-absorption absorber 30 mg/cm 2 Step 1: measure filter Step 2: repeat after decay Step 3: measure spike Decayed source with self-absorption Beta detector Step 4: measure  L by sample always use absorber to stop weak betas Determination of self-absorption coefficient  Thick filter measuring procedure

19. SPIKES Th-232U-238U-235 2.3 MeV 2.1 MeV 2.3 MeV 1.0 MeV 3.3 MeV 1.1 MeV 1.4 MeV 6.8 MeV 1.4 MeV alfa beta Beta energies > 1.0 MeV Low Medium High Decay modeParticle reactivity 2.3 MeV 0.27 MeV Interference by other betas

20. Interference of 226 Ra daughters Benitez-Nelson et al., 2001 recount after 234 Th decay background in open ocean samples approx. 4% 222 Rn vented from counter

21. Low 234 Th High particle loads – thick filters No equilibrium at depth Other interferences ( 232 Th series) Humics, Colloids MnO 2 ppt /direct beta method of limited value Coastal and fresh waters

22. 200-L method for fresh water Waples et al., 2003 Interference of other Th isotopes Total Th beta count Th-234 Th-230 + Th-232 Th-228 Th-229

23. Cerenkov radiation Cerenkov threshold for betas : 0.256 MeV 225 photons are produced for every cm When v > c_nc_n

25. Cerenkov photons produced E max (MeV) Activity (Bq m -3 ) Max # of photons per electron 234 Th0.27412 234m Pa2.2741238 40 K1.3112000130 214 Bi3.27up to 3.3368 Probability distribution of # of photons produced per decay of 40 K

26. Separation of 40 K and 234 Th by photon number Coincidence counting 0 # of photons 15 200 0 234 Th 40 K 40 K x 3 countrate (cpm) Distribution of # of photons per event  Too low optical yield

27. Moore, 1990 Ideas for automation

28. 2004 automation AWI and ISITEC

29. Claudia asked: What is the best way to convert these measurements into integrated 234 Th deficiencies? Can we assess and reduce the uncertainty in making this conversion? Integrated deficiency Discussion initiated by Moran et al., 2003

30. Integrated deficiency 1. Depth of integration Bottom of mixed layer? Depth of equilibrium? Depth of sediment trap? Depth of export calculation 2. Integration method Sampling integration (yo-yo) Trapezoidal integration

31. Current best methods DeficiencyParticulate Open Ocean Small-volume ev. Spike automation Large-volume-filtration + gamma 20-L + beta (note interferences) size-fractionation + Fresh water200-L, Waples et al., 2003 coastalDepends on salinity, particle loads, humics

32. summary Direct beta counting simplifies 234 Th analysis in seawater for better precision: yield measurement at home Thick sources: corrections required for self absorption Fresh waters and sediment samples: large contribution from other beta emitters

33. Outlook Surface waters: Continuous transects in surface waters on ships of opportunity High-resolution profiles should allow to make full budget in water column + surface sediment Parallel collection of size-fractionated particulate fraction for determination of X/ 234 Th ratio in exported material

35. IDtypeprocessSample size (kg) Counting technique SD (%) 1-  counting error N NELHA-600m 20-LfiltrateMn ppt20direct beta-up7.32.817 20-LfiltrateMn ppt20direct beta-down7.02.820 2-LfiltrateMn ppt2direct beta5.33.98 Fe pptfiltrateFe ppt20direct beta13.84.93 20-LtotalMn ppt20direct beta9.82.618 2-LtotalMn ppt2direct beta5.63.44 Mn carttotalMn cart550gamma10.93.57 Fe ppttotalFe ppt20direct beta15.53.96 Fe ppttotalFe ppt20Chemistry-beta5.14.12 Particles> 1 umNuclepore20direct beta21.44.818 Particles> 1 umNuclepore20Chemistry-beta7.94.23 HOT-3500m 2-LTotalMn ppt2direct beta7.43.026 Southern Ocean >250m 20-LTotalMn ppt20direct beta3.21.110 5-LTotalMn ppt5direct beta3.21.918

37. Trapezoidal integration

38. Other beta emitters E max (MeV) 234 Th0.27 234m Pa2.27 214 Pb1.02 214 Bi3.27 210 Pb0.06 210 Bi1.16 238 U series 235 U series 232 Th series E max (MeV) 231 Th0.39 227 Ac0.045 211 Pb1.37 211 Bi6.75 E max (MeV) 228 Ra0.05 228 Ac2.13 212 Pb0.57 212 Bi2.25

39.  = v/c cos  = 1/  n Cerenkov radiation

40. Coincidence counting set-up