Atom Trap, Krypton-81, and Saharan Water

Western Desert, Egypt

• 81Kr dating

• Earlier Methods

• Atom Trap Trace Analysis (ATTA)

• Nubian Aquifer, Egypt

Supported by DOE, Office of Nuclear PhysicsNSF, Division of Earth Sciences

• Widely applied

• Limited to 50 kyr or younger

14N

14C14CO214CO

Cosmicneutrons

Radio-Carbon Dating

Willard Frank LibbyUniversity of Chicago

1960 Nobel Prize in ChemistryArnold & Libby, Science (1949)

14C (t1/2 = 5730yr, I.A.= 1×10-12)

• Polar Ice as a natural archivetemperatureprecipitationgas compositionvolcanic eruptionsolar variability...

• Number of 81Kr atoms in 1 liter of :Air → 20,000

Water → 1,000Ice → 1,000

83Kr, 82Kr...

81Kr

Cosmicp, n

81Kr

Radio-Krypton Dating81Kr (t1/2 = 230kyr, I.A.= 6×10-13)

Low-Level Decay Counting (LLC)

83 10Count Time 100 hrEfficiencyLifetime 330 kyr

−= = = ×

81Kr (230 kyr) activity: 0.1 dpm/l Kr 85Kr (10.7 yr) activity: 3×104 dpm/l Kr

X-ray @ 13.5 keV2 liters of krypton, 100 hours

Loosli & OeschgerEPSL (1969)

Proportionalcounter

Low-levellead

85Kr in the Atmosphere

• Nuclear non-proliferation – Monitor fuel re-processing activities;• Nuclear safety – Monitor leaks from nuclear fuel containers.

Von Hippel, Albright, Levi Sci. Am. (Sept., 1985)

(t1/2 = 11 yr, I.A.= 1×10-11)

Charge and mass measurements• Particle identification based on energy loss• Stripping eliminates molecular isobars• Negative ion tricks eliminates atomic isobars

Accelerator Mass Spectrometry (AMS)

14N vs. 14C

Science (1977): R.A. Muller / Nelson et al. / Bennett et al.

R.A. Muller, Physics Today Advantages of atom counting:• Fast, Sensitive; AMS / LLC = 105 (14C)• Not bothered by decay background

- -

National Superconducting Cyclotron LaboratoryMichigan State University

Full stripping at high energy (~ 4 GeV) for isobar separation: 81Kr36+ vs. 81Br35+.

Accelerator Mass Spectrometry of Kr-81Kutschera et al., NIM B (1994); Collon et al., NIM B (1997)

P. Collon et al., Earth Planet Sci. Lett. 182, 103 (2000)

Watson Creek (4.02 ± 0.51) × 105 yrOodnadatta (3.54 ± 0.50) × 105 yrDuck Hole (2.87 ± 0.38) × 105 yrRaspberry Creek (2.25 ± 0.42) × 105 yr

The Great Artesian Basin

First 81Kr-Dating of Old Groundwater

16,000 litersof water

0.5 ccSTP Kr~ 2 × 106 81Kr

56 81Kr countsin 9 hours

Chemitry AMS

AMS Counting Efficiency ~ 3 × 10-5

Laser Methods Based on Isotope Shifts

1s5--2p9 811nm Laser Frequency (MHz)0-713-997 -130 87

82 84 86 Kr-81 83 8580Kr-78Isotope shift due to the change in nuclear mass, charge radii and moments

Hypothetical

10-16

10-14

10-12

10-10

10-8

10-6

10-4

10-2

100

Pho

ton

Sca

tterin

g R

ate

(rel

.)

-150 -100 -50 0 50 100 150

Laser Frequency (MHz)

Kr-83

Kr-81Kr-85

Reality

10-16

10-14

10-12

10-10

10-8

10-6

10-4

10-2

100

Pho

ton

Sca

tterin

g Rat

e (rel

.)

-150 -100 -50 0 50 100 150

Laser Frequency (MHz)

Kr-83

Kr-81Kr-85

Photon Burst Spectroscopy

10-25

10-20

10-15

10-10

10-5

Pho

ton

Sca

tterin

g Rat

e (rel

.)

-150 -100 -50 0 50 100 150

Laser Frequency (MHz)

Kr-81Kr-83

Kr-85

One-photon probability

Four-photon probability

Greenlees et al., Opt. Commun. (1977); Balykin et al., JETP Lett. (1977)

Magneto-Optical Trap (MOT)

MOT Advantages• Long observation time -- 100 ms;• High capture rate -- 109-1012 s-1; • Narrow linewidth -- Doppler broadening negligible;• Spatial confinement -- trap size < 1 mm;• Storage -- separation of loading and detection.

Krypton Atom Level Diagram

5p[5/2]3

5s[3/2]2

4p6 Ground-level

Metastable τ ≈ 40 sec811 nm

10 eVelectron collision

0 . 0 0 . 5 1 . 0 1 . 5 2 . 0 2 . 5

0

5

1 0

1 5

2 0

2 5

B a c k g r o u n d

O n e A t o m 8 1 K r

Phot

on S

catte

ring

Rat

e (k

Hz)

T i m e ( s e c )

<Single atom signal> = 1600 counts<Background> = 340 ± 30 counts

0 1 2 3 4 5

0

5

1 0

1 5

2 08 1 K r

Phot

on S

catt.

Rat

e (k

Hz)

T i m e ( m i n . )

0 5 1 0 1 5 2 0 2 5

0

5

1 0

1 5

2 0

2 5

O n e A t o m

B a c k g r o u n d

8 3 K r

Fluo

resc

ence

(kH

z)

T i m e ( s e c )

Single Atom Detection

- 1 0 0 0 - 8 0 0 - 6 0 0 - 4 0 0 - 2 0 0 0 2 0 00 . 0

0 . 1

0 . 2

0 . 3

8 4 K r

8 1 K r 8 5 K r

8 6 K r8 2 K r

7 8 K r

8 0 K r 8 3 K r

Tr

ap F

luo.

(arb

. uni

t)

0 . 0

0 . 2

0 . 4

0 . 6

0 . 8

1 . 0

8 3 K r

Trap

Flu

o.(a

rb. u

nits

)

- 1 5 0 - 1 2 0 - 9 0 - 6 0 - 3 0 0 3 0 6 0 9 005

1 01 52 02 53 03 5

( 0 . 5 h r s . )

8 5 K r

8 1 K r ( 3 h r s . )

Ato

m C

ount

s

F r e q u e n c y O f f s e t ( M H z )

Counting 81Kr and 85Kr

Calibration: ATTA vs. Low-Level CountingDu et al., Geophys. Res. Lett. (2003)

ATTA at Argonne, LLC at Bern

Present Status of ATTA-2:

• Selectivity requirement: Done;

• Efficiency requirements: Practical, but far from perfection.

ATTA-1: Chen et al., Science (1999)ATTA-2: Du et al., Geophys. Res. Lett. (2003)

Atom Trap Trace Analysis (ATTA)

10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 1Efficiency

107 106 105 104 103 102 10 1Water or Ice

Sample Size (L)

GroundwaterPolar Ice

ATTA-11999

ATTA-22003

LLC1969

AMS1997

Nubian Aquifer

• Area ~ 2 x 106 km2

• Volume ~ 5 x 104 km3

• 500 years of Nile discharge

• Age ~ 105 years

First Applications: Nubian Aquifer, Egypt

Expedition Team

Argonne National Laboratory: Z.-T. Lu, M. SultanUniversity of Bern: R. Purtschert, R. LorenzoUniversity of Illinois: N. Sturchio

Ain Shams University: A. El Bedawy, Y. Dawood, B. El Kaliouby, A. Mohammed

Egyptian Geological Survey: Z. El Alfy, Radwan

One Million Years of Nubian Aquifer Groundwater History

333±44 kyr

212±42 kyr

391±46 kyr

488±45 kyr

678±75 kyr

0.60.21.0 Myr+

−

Sturchio et al., Geophys. Res. Lett. (2004)

• Groundwater at six sites dated;• Flow direction and speed measured;• Source determined.

Uweinat Uplift

81Kr Dating: From Dream to Practice

10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 1Efficiency

107 106 105 104 103 102 10 1Water or Ice

Sample Size (L)

GroundwaterPolar Ice

LLC1969

AMS1997

ATTA-I1999

ATTA-II2003

ATTA-III2008 ?

Kr-ATTA version 3.0Incremental improvements:

Cool Kr* source to 150 K;More laser power;Longer transverse cooling.

Kr-ATTA version 4.0Optical production of Kr*

124 nm + 819 nm Young et al., J. Phys. B (2002)

215 nm + 215 nmWendt et al.

5s[3/2]0

2

4p6

Ground

Metastable

5p[3/2]2

124 nm

5s[3/2]01

819 nm

215 nm

215 nm

ATTA-IV?

Argonne Atom Trappers

Argonne Atom TrapperYun DingKevin BaileyZheng-Tian LuPeter MuellerTom O’Connor

ATTA CollaboratorsNeil Sturchio – Univ Illinois ChicagoAndrew Davis – Univ of ChicagoShuiming Hu – USTC, ChinaRoland Purtschert – Univ of BernLinda Young & Bob Dunford - Argonne