Harvey Gould

Slowing and cooling molecules and neutral atoms by time-varying electric-field gradients

A method of slowing, accelerating, cooling, and bunching molecules and neutral atoms using time-varying electric-field gradients is demonstrated with cesium atoms in a fountain. The effects are measured and found to be in agreement with our calculations. Time-varying electric-field-gradient slowing and cooling is applicable to atoms that have large dipole polarizabilities, including atoms that are not amenable to laser slowing and cooling, to Rydberg atoms, and to molecules, especially polar molecules with large electric dipole moments. The possible applications of this method include slowing and cooling thermal beams of atoms and molecules, launching cold atoms from a trap into a fountain, and measuring atomic dipole polarizabilities.

Relativistic Heavy-Ion-Atom Collisions

Publisher Summary This chapter reviews the atomic collisions of very heavy ions at relativistic velocities. The use of relativistic heavy ions permits several experimental simplifications. For example, the main source of error in x-ray-producing cross-section measurements at low velocities is the beam intensity normalization, determined either by beam current integration or Rutherford scattering normalization. With relativistic heavy ions, the cross sections are often very large thus making it possible to count every incident ion with ≈100% efficiency using surface barrier or scintillator detectors. An active collimation system can be used to measure x-ray cross sections using relativistic heavy ions, which can pass through several grams/cm of matter. Furthermore, relativistic, very high- Z atoms present special opportunities for atomic structure experiments because any atom in the periodic table can be stripped to few-electron or even bare ions. Relativistic and quantum-electrodynamics (QED) effects can then be examined in systems where they are very large, can be experimentally isolated, and where precise and unambiguous calculations can be performed. The understanding of relativistic ions allows, for the first time, the formulation of an ab initio theory of ions in matter incorporating excited-state effects.

Charge changing cross sections of relativistic uranium

We report equilibrium charge state distributions of uranium at energies of 962 MeV/nucleon, 437 MeV/nucleon and 200 MeV/nucleon in low Z and high Z targets and the cross sections for U/sup 92 +/ reversible U/sup 91 +/ and U/sup 91 +/ reversible U/sup 90 +/ at 962 MeV/nucleon and 437 MeV/nucleon. Equilibrium thickness Cu targets produce approx. = 5% bare U/sup 92 +/ at 200 MeV/nucleon and 85% U/sup 92 +/ at 962 MeV/nucleon. 7 references, 5 figures.

Tests of quantum electrodynamics in few-electron very high-Z ions

This article discusses our measurement of the Lamb shift in heliumlike uranium and outlines future tests of QED using few-electron very high atomic number (Z) ions. Our recently reported Lamb shift value of 70.4 (8.3) eV for the one-electron Lamb shift in uranium is in agreement with the theoretical value of 75.3 (0.4) eV. The experimental value was extracted from a beam-foil time-of-flight measurement of the 54.4 (3.4) ps lifetime of the 1s2p1/2 3P0 state of helium-like uranium.

Spectroscopy of one- and two-electron uranium

The spectra from n = 2 → n = 1 transitions of hydrogen-like and helium-like uranium have been observed. Possible experiments to study quantum electrodynamics in these systems are discussed.

Multiple ionization and capture in relativistic heavy-ion atom collisions

Abstract We show that in relativistic heavy-ion collisions the independent electron model can be used to predict cross sections for multiple inner-shell ionization and capture in a single collision. Charge distributions of 82- to 200-MeV/amu Xe and 105- to 955-MeV/amu U ion beams emerging from thin solid targets were used to obtain single- and multiple-electron stripping and capture cross sections. The probabilities of stripping electrons from the K, L, or M shells were calculated using the semiclassical approximation and Dirac hydrogenic wave functions. For capture, a simplified model for electron capture was used. The data generally agree with theory.

Electron impact ionization of U88+−U91+

We channeled 405 MeV/nucleon uranium ions in Si single crystals to determine the electron impact ionization cross sections for hydrogenlike‐berylliumlike uranium ions by 222 keV electrons. Our cross sections are 3.9, 11.0, 16.0, and 31.0 barns (+100%,−50%) respectively, for ionizing 1s, 1s2, 2s, and 2s2 electrons. Our 1s and 1s2 results disagree with present theory; our 2s and 2s2 results are not accurate enough to distinguish between theories.

A new experimental limit on the electric dipole moment of the electron

We describe a search for the electric dipole moment de of the electron, carried out with 205Tl atoms in the ground state. The experiment makes use of the separated‐oscillating‐field magnetic‐resonance method, laser state selection, fluorescence detection, and two counter‐propagating atomic beams. Very careful attention is paid to systematic effects. The result for the atomic electric dipole moment is da=(1.6±5.0)×10−24 e cm. If we assume the theoretical ratio da/de=−600, this yields de=(−2.7±8.3)×10−27 e cm.

New experiments on few‐electron very heavy atoms

New experiments, to test quantum electrodynamics (QED) in strong Coulomb fields and to study atomic collisions at ultra relativistic energies, are proposed. A 0.1% measurement of the 2 2P1/2–2 2S1/2 splitting in lithiumlike uranium (Z=92) and the 2 3P0–2 3S1 splitting in heliumlike uranium is proposed as a sub 1% test of the Lamb shift in a strong Coulomb field. Measurements of the hyperfine splitting of hydrogenlike uranium are proposed as a test of the QED contribution to the magnetic moment of an electron bound in a strong Coulomb field. Measurements of capture cross sections for ultra‐relativistic very heavy nuclei are proposed to look for the capture of electrons from pair production.