August 2001

"Low-energy positron dynamics in polyatomic gases"

西村 民男（University of Rome）

Time/Date: 14:00, Friday, August 10, 2001

Place: Meeting Room 624-626 at 6th Floor RIKEN Main Building

"平行電磁場中の Rydberg 原子"

数納 広哉（Kansas State University）

Time/Date: 15:00, Friday, August 10, 2001

Place: Meeting Room 624-626 at 6th Floor RIKEN Main Building

（Abstract）　This PhD work has been done under the direction of Ronald McCarroll at the Laboratoire de Dynamique des Ions, Atomes et Molecules (DIAM) of the Universite Pierre et Marie Curie (Paris VI) in Paris and in collaboration with Tasko P. Grozdanov at the Institute of Physics in Belgrade.

The subject of this work concerns the study of Rydberg atoms in parallel electric and magnetic fields. We are mainly interested in the strong field case, that is beyond the perturbation regime and the beyond the classical ionization threshold.

We develop a non perturbative calculation method by combining the discrete variable representation (DVR) and the complex coordinate method with the Lanczos algorithm. Our method allows us to calculate the resonances associated with ''circular'' Rydberg states of maximum angular momentum. Combining our method with a continued-fraction representation of the Green function, we were able to calculate directly photoionization cross sections. Our method is also applied to the case of field-free atoms. Our results are in very good agreement with experimental results and theoretical prediction obtained by previous methods.

We also study the discrete photoabsorption spectrum of atoms below the classical ionization threshold by using a combination of the DVR and the filter diagonalization.

"Low energy alkali collisions with ground and excited state Rb, investigated using MOTRIMS"

Brett DePaola (Kansas State University)

Time/Date: 11:00, Thursday, August 16, 2001

Place: Meeting Room 624-626 at 6th Floor RIKEN Main Building

(abstract) Combining the technology of the Magneto Optical Trap (MOT) with that of COLd Target Recoil Ion Momentum Spectroscopy (COLTRIMS) allows one to study ion-atom collisions with unprecedented precision in scattering angle and final state determination. We use this technique to measure charge transfer from ground and excited state atoms in our Rb MOT. We further demonstrate the usefulness of the technique in the study of the dynamics of a MOT under the influence of an external perturbation.

"Ultra trace isotope determination in environmental, bio-medical and fundamental research by high resolution laser-mass spectrometry"

Klaus D.A. Wendt (Johannes Gutenberg-Universitat)

Time/Date: 13:30, Thursday, August 16, 2001

Place: Meeting Room 624-626 at 6th Floor RIKEN Main Building

(abstract) The precise determination of relative abundances for ultra rare isotopes in the range below 10^-9 of the dominant isotope of an element is a challenge to the experimentalist. Depending on the origin and the production mechanism of the individual trace isotope, the investigations either lead to refined insight into fundamental processes, e.g. in radiodating or cosmochemistry, are important for environmental protection or become useful in bio-medical tracer studies. Prerequisites for these investigations are high isotopic selectivity, rather complete isobaric suppression and good overall efficiency. For this purpose High-resolution Laser-Resonance Ionization Mass Spectrometry with multi step continuous wave laser excitation and ionization at a quadrupole mass spectrometer has been developed as a compact and reliable experimental method, being somewhat complementary to the technique of Accelerator Mass Spectrometry. Measurements with highest isotopic selectivity concern the isotopes 90Sr and 41Ca while further studies have been performed in Gd and Pu. In all cases extensive atomic spectroscopic investigations as well as analytical studies relevant for environmental, cosmochemical and bio-medical ultratrace determination were carried out and are discussed.

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