摘要:

Correlation studies of inelastic electron scattering from simple atoms are discussed, largely from an experimental viewpoint with the aim of complementing the contributions of Andersen and Bartschat in these proceedings. After a brief review of experimental advances over the last twenty-five years, major developments over the last four years are highlighted. These include excitation of higher angular-momentum states of helium, excitation of atomic hydrogen, and extension of the electron-photon correlation method to study production of excited-state ions. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59360

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We have measured the center of mass motion of the three massive Coulomb-interacting particlesH+,H−,H+in the continuum. Starting with excitedH3+we have experimentally studied the dissociation of this three-body system by determining the final-state energy sharing configurations and mutualH+,H+correlation angles. Each measured triple dissociation event was mapped onto a Dalitz Plot that elucidated the various dynamic processes. In addition to the direct dissociation of excitedH3+into three Coulomb-interacting particles, we have identified intermediate compound states that decay into the observed final-state channel. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59361

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Substantial progress has occurred during the last decade to develop improved methods for determining atomic polarizabilities. We review work that has been done on ground states as well as the study of Stark shifts of transitions to excited states that have been made with a precision of parts in104.Measurements done on alkali atoms have yielded significantly more accurate data than previously available, stringently testing atomic theory. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59362

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Today a variety of powerful techniques exist for direct mass measurements of unstable isotopes. This paper gives an overview of the most modern approaches, which enable us to investigate with high accuracy nuclear binding energies in regions very far from the valley of &bgr;-stability. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59363

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The new muon storage ring at Brookhaven is intended to measure the anomalous magnetic momenta&mgr;of the muon to sub ppm accuracy. A preliminary run in 1997 gavea&mgr;=1&hthinsp;165&hthinsp;925(15)×10−9in agreement with previous CERN measurements. The principles of the experiment and numerous detailed improvements are described. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59364

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The amount of187Osin meteorites resulting from beta decay of the long-lived187Renuclide has been used as a measure of the time span of nucleosynthesis in our galaxy. During the galactic history, however, the rhenium atoms can be “astrated” several times into newly forming stars, where they are stripped of most or all of their electrons. An experiment conducted at the ion storage ring ESR at Darmstadt showed that for bare187Reions, the lifetime is shortened by more thannine orders of magnitude. This observation strongly suggests that theeffectivelifetime of187Reduring the galactic evolution might differ significantly from the lifetime of neutral187Re.Furthermore, it enables a recalibration of the rhenium aeon clock in the framework of chemical-evolution models of our galaxy. Based on this new calibration, a preliminary lower limit of12×109&hthinsp;yrfor the age of our galaxy has been derived, which is, a fortiori, also a lower limit for the age of the universe. In combination with the Hubble constant, this limit provides narrow constraints for actual cosmological models. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59378

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

When comet Hyakutake (C/1996 B2) encountered Earth in March 1996 at a minimum distance of only 15 million kilometers (40 times the distance of the moon), x-ray and extreme ultraviolet emission was discovered for the first time from a comet. The observations were performed with the astronomy satellites ROSAT and EUVE. A systematic search for x-rays from comets in archival data, obtained during the ROSAT all-sky survey in 1990/91, resulted in the discovery of x-ray emission from four additional comets. They were detected at seven occasions in total, when they were optically 300 to 30&hthinsp;000 times fainter than Hyakutake. These findings indicated that comets represent a new class of celestial x-ray sources. Subsequent detections of x-ray emission from additional comets with the satellites ROSAT, EUVE, and BeppoSAX confirmed this conclusion. The x-ray observations have obviously revealed the presence of a process in comets which had escaped attention until recently. This process is most likely charge exchange between highly charged heavy ions in the solar wind and cometary neutrals. The solar wind, a stream of particles continuously emitted from the sun with ≈ 400 km s−1, consists predominantly of protons, electrons, and alpha particles, but contains also a small fraction (≈0.1&percent;) of highly charged heavier ions, such asC6+,O6+,Ne8+,Si9+,Fe11+.When these ions capture electrons from the cometary gas, they attain highly excited states and radiate a large fraction of their excitation energy in the extreme ultraviolet and x-ray part of the spectrum. Charge exchange reproduces the intensity, the morphology and the spectrum of the observed x-ray emission from comets very well. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59379

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Dramatic changes can be expected within the next few years in science that depends on synchrotron radiation today. An analysis of available data on short-pulse, high-intensity x-ray and electron sources indicate possibilities for imminent developments with x-ray free-electron lasers (driven primarily by the high energy physics community), and with table-top femtosecond x-ray sources based on laser-induced plasmas and wakefield acceleration. New sources could generate femtosecond x-ray pulses with as much as 12 orders of magnitude increase in peak brilliance and power over third-generation synchrotron storage rings. Such developments would create revolutionary new research opportunities in condensed matter physics, biology and medicine. Some of the possibilities are discussed here. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59365

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

This talk examines two distinct cases in strong optical fields where electron correlation plays an important role in the dynamics. In the first example, strong coupling in a two-electron-like system is manifested as an intensity-dependent splitting in the ionized electron energy distribution. This two-electron phenomenon (dubbed continuum-continuum Autler-Townes effect) is analogous to a strongly coupled two-level, one-electron atom but raises some intriguing questions regarding the exact nature of electron-electron correlation. The second case examines the evidence for two-electron ionization in the strong-field tunneling limit. Although our ability to describe the one-electron dynamics has obtained a quantitative level of understanding, a description of the two (multiple) electron ionization remains unclear. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59366

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We describe the Recollision Model of high-harmonic generation, in which electrons escape from atomic Coulomb binding in intense laser fields by tunneling, are ponderomotively accelerated, and recollide on return to the parent ionic core. High harmonics are generated by Bremsstrahlung, modulated by the coherent periodic nature of the tunneling process. Harmonic plateaux involve the time-dependent dipole induced by the returning wave packets. We show how atomic wave packets are generated and manipulated by strong laser driving fields, and link the recollision to nonsequential ionization. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59367

出版商:AIP    

年代:1999

数据来源: AIP