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P Beller

Publications and source records attributed to P Beller.

6 recordsLinked to original sources
PubMed2006

First measurement of the linear polarization of radiative electron capture transitions.

For radiative electron capture into the K shell of bare uranium ions, a study of the polarization properties has been performed. For this purpose a position sensitive germanium detector has been used as an efficient Compton polarimeter. This enabled us to measure the degree of linear polarization by analyzing Compton scattering inside the detector and to determine the orientation of the polarization plane. Depending on the observation angle and the beam energy used, the radiation is found to be linearly polarized by up to 80%. In all cases studied, the plane of polarization coincides with the collision plane. The results will be discussed in the context of rigorous relativistic calculations, showing that relativistic effects tend to lead to a depolarization of the radiation emitted.

Journal Article↗
PubMed2005

Simultaneous measurement of beta- decay to bound and continuum electron states.

We report the first measurement of a ratio lambda(beta(b))/lambda(beta(c)) of bound-state ((lambda(beta(b))) and continuum-state (lambda(beta(c))) beta(-)-decay rates for the case of bare 207Tl81+ ions. These ions were produced at the GSI fragment separator FRS by projectile fragmentation of a 208Pb beam. After in-flight separation with the Brho-deltaE-Brho method, they were injected into the experimental storage-ring ESR at an energy of 400.5A MeV, stored, and electron cooled. The number of both the 207Tl81+ ions and their bound-state beta(-)-decay daughters, hydrogen-like 207Pb81+ ions, were measured as a function of storage time by recording their Schottky-noise intensities. The experimental result, lambda(beta(b))/lambda(beta(c)) = 0.188(18), is in very good agreement with the value of 0.171(1) obtained from theory employing spectra of allowed transitions.

Journal Article↗
PubMed2005

Quantum electrodynamics in strong electric fields: the ground-state Lamb shift in hydrogenlike uranium.

X-ray spectra following radiative recombination of free electrons with bare uranium ions (U92+) were measured at the electron cooler of the ESR storage ring. The most intense lines observed in the spectra can be attributed to the characteristic Lyman ground-state transitions and to the recombination of free electrons into the K shell of the ions. Our experiment was carried out by utilizing the deceleration technique which leads to a considerable reduction of the uncertainties associated with Doppler corrections. This, in combination with the 0 degree observation geometry, allowed us to determine the ground-state Lamb shift in hydrogenlike uranium (U91+) from the observed x-ray lines with an accuracy of 1%. The present result is about 3 times more precise than the most accurate value available up to now and provides the most stringent test of bound-state quantum electrodynamics for one-electron systems in the strong-field regime.

Journal Article↗
PubMed2004

Electron-electron interaction in strong electromagnetic fields: the two-electron contribution to the ground-state energy in He-like uranium.

Radiative recombination transitions into the ground state of cooled bare and hydrogenlike uranium ions were measured at the storage ring ESR. By comparing the corresponding x-ray centroid energies, this technique allows for a direct measurement of the electron-electron contribution to the ionization potential in the heaviest He-like ions. For the two-electron contribution to the ionization potential of He-like uranium we obtain a value of 2248+/-9 eV. This represents the most accurate determination of two-electron effects in the domain of high-Z He-like ions, and the accuracy reaches already the size of the specific two-electron radiative QED corrections.

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PubMedDate not supplied

Pathogenesis of degenerative joint disease produced by in vivo freezing of rabbit articular cartilage.

In vivo freezing of rabbit lateral femoral arterial cartilage with a cryoprobe produces an osteoarthritic-like condition in 12 months. Previous studies have established that the chondrocytes are killed by the freezing process. A loss of stainable mucopolysaccharide occurs. The collagen content of the lesional tissue does not change. The present study investigates the extracellular lysosomal enzyme content, collagen type (I or II), and histologic changes which produce chondrocyte cell clusters in the frozen tissue in response to freezing or articular cartilage. The results indicate that after the initial 30 days there is no significant rise in the extracellular lysosomal enzyme content of the experimental tissue compared with controls. Type II, or cartilage, collagen remains the major constituent of the lesional tissue. Histologic examination at six- to 12-month intervals suggests that chondrocyte clones are produced by invasion by the underlying viable subchondral bone. These results provide insight into the pathogenesis of degenerative joint disease and the rationale of treatment by the use of inhibitors of vascular invasion of articular cartilage.

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