A New Approach to Old Water: Atom-Trap Trace Analysis of Noble Gas Radionuclides N.C. S TURCHIO 1 *, R. Y OKOCHI 1,2 , Z.-T. L U 2,3 , R. P URTSCHERT 4 1 University of Illinois at Chicago, Chicago, IL 60607, USA 2 University of Chicago, Chicago, IL 60637, USA 3 Argonne National Laboratory, Argonne, IL 60439, USA 4 University of Bern, Switzerland
Noble gas radionuclides: Ideal tracers of residence time Half-life (yr) Abundance 81 Kr 229,000 10 -12 85 Kr 10.8 10 -11 39 Ar 296 10 -15 81 Kr, 39 Ar Well-mixed 85 Kr Solubility equilibrium 1.0 Isotopic Abundance 0.8 0.6 0.4 0.2 0.0 0 10 20 30 40 50 Time (Years)
Noble Gas Radionuclides vs. Other Tracers Half-life Atmospheric isotopic abundance Sources 85 Kr 10.8 yr 2x10 -11 Nuclear fuel reprocessing 39 Ar 269 yr 8x10 -16 Cosmic-ray induced reaction 81 Kr 229,000 yr 1x10 -12 Cosmic-ray induced reaction
Analytical Challenge of Noble Gas Radionuclides How do you find 1 atom in 10 15 atoms which all look very similar? Example: 39 Ar Argon Isotope Abundance Half-Life 36 0.003336 Stable 38 0.000629 Stable 8.1 x 10 -16 39 269 y 40 0.996 Stable
The Three Methods: LLC, AMS, and ATTA Low Level Counting (LLC) -3 1.0x10 background sample -4 8.0x10 Underground -4 6.0x10 35 meters cpm laboratory in below -4 4.0x10 Bern, ground Switzerland -4 2.0x10 0.0 0 20 40 60 80 100 120 140 channel no Detection Limit: ~4x10 -17 Sample Size: ~0.3-1L STP Ar (1-3 Tons H 2 O) Time: 8-60 days Limiting Factors: Variation of environmental background
The Three Methods: LLC, AMS, and ATTA Accelerator Mass Spectrometry (AMS) Detection Limit: ~4.3x10 -17 Sample Size: ~2mL STP Ar (2L H 2 O) Time: ~8 hours Limiting Factors: Accelerator based Background from 39 K Ph. Collon et al. / Nucl. Instr. and Meth. In Phys. Res. B 223 – 224 (2004) 428 – 434
The Three Methods: LLC, AMS, and ATTA Atom Trap Trace Analysis (ATTA) • Based on Selectivity of Magneto-Optical Trap (MOT) 4p[5/2] 3 • Long observation time -- 100 ms 811 nm • High loading rates -- 10 9 -10 12 s -1 for 38 Ar 4s[3/2] 2 • Narrow linewidth Metastable 11 eV electron • Spatial confinement -- trap size < 1 mm collision • Extremely high selectivity statistics limited 3p 6 Ground-level • Background from scattered laser light Chen et al. Science 286 , 1139 (1999)
Atom-Trap Trace Analysis (ATTA-2) @ 2003 Polar Ice Polar Ice Groundwater Groundwater Water or Ice Water or Ice Water or Ice Sample Size (L) Sample Size (L) Sample Size (L) 10 7 10 7 10 7 10 6 10 6 10 6 10 5 10 5 10 5 10 4 10 4 10 4 10 3 10 3 10 3 10 2 10 2 10 2 10 10 10 1 1 1 Efficiency Efficiency Efficiency 10 -8 10 -8 10 -8 10 -7 10 -7 10 -7 10 -6 10 -6 10 -6 10 -5 10 -5 10 -5 10 -4 10 -4 10 -4 10 -3 10 -3 10 -3 10 -2 10 -2 10 -2 10 -1 10 -1 10 -1 1 1 1 Only 1000 liters for LLC LLC ATTA-1 ATTA-1 AMS AMS ATTA-2 ATTA-2 ATTA-3 ATTA-3 81 Kr in groundwater ! 1969 1969 1999 1999 1997 1997 2003 2003 2008 (projected) 2008 (projected) ATTA-1: Chen et al., Science (1999) ATTA-2: Du et al., Geophys. Res. Lett. (2003)
Kr atom excitation and trapping scheme ( Chen et al., SCIENCE, 1999 ) 5p[5/2] 3 811 nm 5s[3/2] 2 Metastable t 40 sec 10 eV electron collision 4p 6 Ground-level Kr atom
Counting 81 Kr and 85 Kr with ATTA 86 Kr 82 Kr 0.3 Trap Fluo. (arb. unit) 80 Kr 83 Kr 84 Kr 0.2 78 Kr 0.1 81 Kr 85 Kr 0.0 -1000 -800 -600 -400 -200 0 200 Trap Fluo.(arb. units) 1.0 83 Kr 0.8 0.6 0.4 0.2 0.0 35 85 Kr 30 (0.5 hrs.) Atom Counts 25 20 81 Kr (3 hrs.) 15 10 5 0 -150 -120 -90 -60 -30 0 30 60 90 Frequency Offset (MHz)
Single Atom Detection! 25 83 Kr Fluorescence (kHz) 20 One Atom 15 10 Background 5 0 0 5 10 15 20 25 Time (sec) 25 Photon Scattering Rate (kHz) One Atom 81 Kr 20 15 10 Background 5 0 0.0 0.5 1.0 1.5 2.0 2.5 Time (sec) 81 Kr Photon Scatt. Rate (kHz) 20 15 10 5 0 0 1 2 3 4 5 Time (min.)
First application of ATTA in hydrology: Nubian Aquifer, Egypt (2003)
First application of ATTA in hydrology: Nubian Aquifer, Egypt (2003) 150 ) -15 100 Cl/Cl (x 10 Gum Horia El Zayat 12 Farafra 6 50 36 Baris(Aden) Bauti 1 Sherka 36 0 0 500 1000 1500 2000 81 Kr age (kyr) (Sturchio et al., GRL, 2004; Patterson et al., G 3 , 2005)
What’s new? ATTA-3!!! We’re 1000 1 there!!! 2 3 85 Kr measured (dpm/cc Kr) 4 5 10 100 6 7 8 9 10 1 1 10 100 1000 85 Kr Mixed (dpm/cc Kr) Polar Ice Polar Ice for 81 Kr: Groundwater Groundwater Water or Ice Water or Ice Water or Ice Sample Size (L) Sample Size (L) Sample Size (L) 10 7 10 7 10 7 10 6 10 6 10 6 10 5 10 5 10 5 10 4 10 4 10 4 10 3 10 3 10 3 10 2 10 2 10 2 10 10 10 1 1 1 Efficiency Efficiency Efficiency 10 -8 10 -8 10 -8 10 -7 10 -7 10 -7 10 -6 10 -6 10 -6 10 -5 10 -5 10 -5 10 -4 10 -4 10 -4 10 -3 10 -3 10 -3 10 -2 10 -2 10 -2 10 -1 10 -1 10 -1 1 1 1 LLC LLC ATTA-1 ATTA-1 AMS AMS ATTA-2 ATTA-2 ATTA-3 ATTA-3 1969 1969 1999 1999 1997 1997 2003 2003 2008 (projected) 2008 (projected)
Loading Rate Improvements in ATTA-3 2D Transverse CCD Focusing Cooling Zeeman Camera Slower Beam Discharge Chopper Source MOT Atomic Beam Stage ATTA II ATTA III Enhancement LN 2 pre-cooling N.A. x 2 x 2 Transverse Cooling 70 x 140 x 2 Sidebands in T.C. x 160 N.A. x 3 x 3 2D-MOT N.A. x 3 x 3 New Zeeman Slower x1000 x 3000 x 3 More Trapping Power N.A. x 1.5 x 1.5
What else is new? 39 Ar atom counting!!! 0.5mm 0.5mm
Single Atom Counting of 39 Ar I.A. = 0.064%
Experiment 1: Frequency Switching Results Laser Expect to Measured Detuning See 39 Ar ? (in 57 hrs) -20 MHz No 0 -6 MHz Yes 12 +10 MHz No 0
Experiment 2: 39 Ar in air and groundwater atmospheric Ar groundwater Ar 1 Jiang et al., PRL 106, 103001 (2011)
Summary o ATTA-3: enhancement of efficiency by a factor of 160 o Reduced sample size requirement (10-100 L of H 2 O) o Faster counting times o Improved precision (better than +/- 5%) o First 39 Ar measurement of Ar from groundwater o The next generation ATTA is here, opening opportunities for new and exciting applications (to be presented in future talks)
Recommend
More recommend
