K. Bailey

One million year old groundwater in the Sahara revealed by krypton‐81 and chlorine‐36

Measurements of 81 Kr/Kr in deep groundwater from the Nubian Aquifer (Egypt) were performed by a new laser-based atom-counting method. 81 Kr ages range from ∼2 × 10 5 to ∼1 x 10 6 yr, correlate with 36 Cl/Cl ratios, and are consistent with lateral flow of groundwater from a recharge area near the Uweinat Uplift in SW Egypt. Low δ 2 H values of the 81 Kr-dated groundwater reveal a recurrent Atlantic moisture source during Pleistocene pluvial periods. These results indicate that the 81 Kr method for dating old groundwater is robust and such measurements can now be applied to a wide range of hydrolugic problems.

Laser Spectroscopic Determination of the ^6He Nuclear Charge Radius

We have performed precision laser spectroscopy on individual 6He (t(1/2)=0.8 s) atoms confined and cooled in a magneto-optical trap, and measured the isotope shift between 6He and 4He to be 43 194.772+/-0.056 MHz for the 2(3)S1-3(3)P2 transition. Based on this measurement and atomic theory, the nuclear charge radius of 6He is determined for the first time in a method independent of nuclear models to be 2.054+/-0.014 fm. The result is compared with the values predicted by a number of nuclear structure calculations and tests their ability to characterize this loosely bound halo nucleus.

Nuclear charge radius of 8He.

The root-mean-square (rms) nuclear charge radius of 8He, the most neutron-rich of all particle-stable nuclei, has been determined for the first time to be 1.93(3) fm. In addition, the rms charge radius of 6He was measured to be 2.068(11) fm, in excellent agreement with a previous result. The significant reduction in charge radius from 6He to 8He is an indication of the change in the correlations of the excess neutrons and is consistent with the 8He neutron halo structure. The experiment was based on laser spectroscopy of individual helium atoms cooled and confined in a magneto-optical trap. Charge radii were extracted from the measured isotope shifts with the help of precision atomic theory calculations.

Laser trapping of 225Ra and 226Ra with repumping by room-temperature blackbody radiation.

We have demonstrated Zeeman slowing and capture of neutral 225Ra and 226Ra atoms in a magneto-optical trap. The intercombination transition 1S0-->3P1 is the only quasicycling transition in radium and was used for laser-cooling and trapping. Repumping along the 3D1-->1P1 transition extended the lifetime of the trap from milliseconds to seconds. Room-temperature blackbody radiation was demonstrated to provide repumping from the metastable 3P0 level. We measured the isotope shift and hyperfine splittings on the 3D1-->1P1 transition with the laser-cooled atoms, and set a limit on the lifetime of the 3D1 level based on the measured blackbody repumping rate. Laser-cooled and trapped radium is an attractive system for studying fundamental symmetries.

Beam of metastable krypton atoms extracted from a rf-driven discharge

A rf-driven discharge is used to produce a beam of metastable krypton atoms at the 5s(3/2)2 level with an angular flux density of 4×1014 s−1 sr−1 and most probable velocity of 290 m/s, while consuming 7×1016 krypton atoms/s. When operated in a gas-recirculation mode, the source consumes 2×1015 krypton atoms/s with the same atomic-beam output.

39Ar detection at the 10(-16) isotopic abundance level with atom trap trace analysis.

Atom trap trace analysis, a laser-based atom counting method, has been applied to analyze atmospheric 39Ar (half-life=269  yr), a cosmogenic isotope with an isotopic abundance of 8×10(-16). In addition to the superior selectivity demonstrated in this work, the counting rate and efficiency of atom trap trace analysis have been improved by 2 orders of magnitude over prior results. The significant applications of this new analytical capability lie in radioisotope dating of ice and water samples and in the development of dark matter detectors.

Counting individual 41Ca atoms with a magneto-optical trap

Atom trap trace analysis, a novel method based upon laser trapping and cooling, is used to count individual atoms of 41Ca present in biomedical samples with isotopic abundance levels between 10(-8) and 10(-10). The method is calibrated against resonance ionization mass spectrometry, demonstrating good agreement between the two methods. The present system has a counting efficiency of 2x10(-7). Within 1 h of observation time, its 3-sigma detection limit on the isotopic abundance of 41Ca reaches 4.5x10(-10).

ATTA – A new method of ultrasensitive isotope trace analysis

Abstract A new method of ultrasensitive isotope trace analysis has been developed. This method, based on the technique of laser manipulation of neutral atoms, has been used to count individual 85Kr and 81Kr atoms present in a natural krypton gas sample with isotopic abundances in the range of 10−11 and 10−13, respectively. This method is free of contamination from other isotopes and elements and can be applied to various different isotope tracers for a wide range of applications. The demonstrated detection efficiency is 1×10−7. System improvements could increase the efficiency by many orders of magnitude.

An atom trap system for practical 81Kr dating

81Kr (t1/2=2.3×105 yr, 81Kr/Kr∼6×10−13) is a long-lived cosmogenic isotope, which is ideal for dating old groundwater and ice in the age range of 50,000 years to 1 million years. Here, we describe the apparatus and performance of an atom-counting system for practical 81Kr dating. This system is based upon the atom trap trace analysis method that was first demonstrated in 1999. Since then, significant improvements have been made to increase the system efficiency and to reduce the required krypton sample size. For a modern krypton gas sample of 100 μl STP, which contains 1.2×106 81Kr atoms, the system can accumulate approximately 240 81Kr counts in 20 h, thereby reaching a counting efficiency of 2×10−4. Detailed studies have been conducted to characterize the performance of this system. This system has been calibrated with a low-level counting method and has been used for 81Kr dating of ancient groundwater from the Nubian Aquifer (Egypt). It can also be used to measure the isotopic abundance of a fission-pr...

Improved limit on the Ra 225 electric dipole moment

Michael Bishof, ∗ Richard H. Parker, 1, † Kevin G. Bailey, John P. Greene, Roy J. Holt, Mukut R. Kalita, 3, ‡ Wolfgang Korsch, Nathan D. Lemke, § Zheng-Tian Lu, 1, ¶ Peter Mueller, Thomas P. O’Connor, Jaideep T. Singh, and Matthew R. Dietrich Physics Division, Argonne National Laboratory, Argonne, Illinois 60439, USA Department of Physics and Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506, USA National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA (Dated: June 16, 2016)