\alpha-decay spectroscopy of light odd-odd Bi isotopes - I: 188,190Bi nuclei

Detailed fine-structure -decay studies of ^188,190Bi were performed using the complete-fusion reactions of ^50,52Cr ions with a ¹⁴²Nd target at the velocity filter SHIP. The evaporation residues were separated in-flight and subsequently identified on the basis of recoil- , recoil- - /X-ray and excitation function measurements. Improved data on the -decay of ^188,190Bi were obtained and a number of new low-lying excited states in the daughters ^184,186Tl were observed. An intruder, presumably 10^- state was identified in ¹⁸⁴Tl, extending the systematics of such states in the odd-odd Tl nuclei beyond the neutron mid-shell at N = 104. Some technical aspects of experiment at recoil separators are also discussed.Received: 14 March 2003, Revised: 1 May 2003, Published online: 2 September 2003PACS: 23.60.+e decay - 27.70.+q - 27.80.+w C.D. OLeary: Present address: Department of Physics, University of York, York, UK.M.J. Taylor: Present address: Department of Physics and Astronomy, Rutgers Univesity, NJ, USA.L. Weissman: Present address: NSCL, Michigan State University, East Lansing, MI 48824-1321 USA.K. Heyde: Present address: EP-ISOLDE, CERN, CH-1211, Geneva 23, Switzerland.     

The light clock: Error and implications

The light clock (a photon undergoing successive reflections between two particle mirrors a fixed distance apart) has commonly been used as a theoretical confirmation of the special-relativistic slowing of clock rates. In order to obtain that result one must describe the clock photon in a system moving relatively to the clock. However, contradictory frequency transformations for the photon, as observed from the mirrors, are then predicted by relatively moving observers. A correct and consistent analysis utilizes the Lorentz-invariant relative velocity and distance between the mirrors. An invariant time period is also then involved; a parallel is drawn between it and the invariance of cosmic time for internal processes in distant systems. Considering that space-time and momentum-energy are described by conjugate 4-vectors, it is conjectured that a time transformation occurs only in association with a transformation of energy.     

Superposition in quantum and relativity physics—An interaction interpretation of special relativity theory: Part III

With the interaction interpretation, the Lorentz transformation of a system arises with selection from a superposition of its states in an observation-interaction. Integration of momentum states of a mass over all possible velocities gives the rest-mass energy. Static electrical and magnetic fields are not found to form such a superposition and are to be taken as irreducible elements. The external superposition consists of those states that are reached only by change of state of motion, whereas the internal superposition contains all the states available to an observer in a single inertial coordinate system. The conjecture is advanced that states of superposition may only be those related by space-time transformations (Lorentz transformations plus space inversion and charge conjugation). The continuum of external and internal superpositions is examined for various masses, and an argument for the unity of the super-positions is presented.     

Optical reflectivity of CdCr2Se4 single crystals in the visible and ultra-violet spectral region

The specular reflectivity of CdCr₂Se₄ single crystals has been measured within the spectral energy interval E = 0.5 ? 12.0 eV at room temperature. The spectral dependence of the real and imaginary part of the dielectric constant has been obtained from a Kramers-Kronig analysis of the experimental data. The observed optical transitions and the origin of the red-shifting band are discussed with respect to the semiempirical ionic model of the spinel structure, based on the recently reported increase of the structure parameter u of the spinel during cooling (Göbel, J. Magn. Magn. Mat. 3 (1976) 143). Contradicting results of the optical measurements in the region of the red-shifting edge may be attributed to the sensitivity of the parameter u on the internal stress.     

Reflectivity of Tm monochalcogenides: No evidence of valence fluctuations

The reflectivity of metallic TmS, TmSe and semiconducting TmTe has been measured between 0.03 eV and 12 eV and has been interpreted as 4fⁿ-4f^n?15d and p-d interband transitions and coupled plasmon modes.     

Electron correlation theories and their application to the study of simple reaction potential surfaces

This paper serves two purposes. The first is to describe an implementation of the coupled cluster theory with double substitutions (CCD ) previously developed by Cizek. The second is to apply this method and closely related fourth-order perturbation methods to some simple molecules and reaction potential surfaces. These studies show that CCD theory gives results close to those of a Møller-Plesset perturbation treatment to fourth order in the space of double and quadruple substitutions MP 4(DQ). Addition of contributions from single substitutions at fourth order makes little change in predicted relative energies. Preliminary results on the potential surfaces for 1,2-hydrogen shifts in C₂H₂, HCN, CH₂O, and N₂H₂ are discussed and compared with previous studies.     

Decay studies of N ≈ Z nuclei from 75Sr to 102Sn

Neutron deficient nuclei near ¹⁰⁰Sn have been produced by fragmentation of a 1 ^. AGeV ¹¹²Sn beam. The fragments were separated, identified and stopped in a highly segmented silicon strip detector stack. This detector measured the total energy of emitted β⁺-particles. γ-radiation was measured with surrounding detectors. The half-lives for many nuclides have been determined for the first time and give important information for the following topics: For the heaviest particle-stable odd-odd nuclei ⁹⁰Rh, ⁹⁴Ag and ⁹⁸In we observed for the first time fast β-decays, compatible with superallowed Fermi transitions and confirmed such decays for ⁷⁸Y, ⁸²Nb and ⁸⁶Tc. We have also observed long-lived T = 0 states in some of these nuclei. We measured the half-lives of all rp-process waiting-point nuclei from ⁸⁰Zr up to ^{92, 93}Pd. In addition we find the proton drip line nucleus ⁷⁷Y to decay dominantly via β-decay. To study the Gamov-Teller strength in the β-decay near the doubly magic ¹⁰⁰Sn we measured the half-life, β- and γ-spectrum of ¹⁰²Sn. We propose a level scheme for the daughter nuclide ¹⁰²In and deduce the Gamov-Teller strength (B _GT = 4.0±0.6). This is one of the largest values known. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: thomas.faestermann@ph.tum.de     

Inversion versus retention of configuration for nucleophilic substitution at vinylic carbon

A high-level computational study using CCSD, CCSD(T), and G2(+) levels of theory has shown that unactivated vinyl substrates such as vinyl chloride would afford gas phase, single-step halide exchange by a pure in-plane sigma-approach of the nucleophile to the backside of the C--Cl sigma bond. Geometry optimization by CCSD/6-31+G* and CCSD(T)/6-31+G* confirms the earlier findings of Glukhovtsev, Pross, and Radom that the S(N)2 reaction of Cl(-) with unactivated vinyl chloride in the gas phase occurs by a sigma attack. Complexation of vinyl chloride with Na(+) does not alter this in-plane sigma preference. However, moderately activated dihaloethylenes such as 1-chloro-1-fluoroethylene undergo gas-phase S(N)2 attack by the accepted pi-route where the nucleophile approaches perpendicular to the plane of the C==C. In the latter case a single-step pi pathway is preferred for the Cl(-) + H(2)C==CFCl reaction. This is the first definitive example at a high level of theory where a single-step pi nucleophilic vinylic substitution is preferred over a multistep mechanism in the gas phase. The activation barriers for these gas-phase single-step sigma- and pi-processes involving both naked anions and Na(+) complexes are, however, prohibitively high. Solvation and the presence of a counterion must play a dominant role in nucleophilic vinylic substitution reactions that proceed so readily in the condensed phase. In solution, nucleophilic vinylic substitution reactions involving electron-withdrawing groups on the carbon--carbon double bond (e.g., -CN, -CHO, and -NO(2)) would almost certainly proceed via a free discrete carbanionic intermediate in accord with experiment.     

Photoneutron cross sections for unstable neutron-rich oxygen isotopes.

The dipole response of stable and unstable neutron-rich oxygen nuclei of masses A = 17 to A = 22 has been investigated experimentally utilizing electromagnetic excitation in heavy-ion collisions at beam energies about 600 MeV/nucleon. A kinematically complete measurement of the neutron decay channel in inelastic scattering of the secondary beam projectiles from a Pb target was performed. Differential electromagnetic excitation cross sections d sigma/dE were derived up to 30 MeV excitation energy. In contrast to stable nuclei, the deduced dipole strength distribution appears to be strongly fragmented and systematically exhibits a considerable fraction of low-lying strength.     

Depopulation of the Jπ = 9- isomer in 180Ta to the Jπ = 1+ ground state by Coulomb excitation

In-beam Coulomb excitation of the exotic odd-odd nucleus ¹⁸⁰Ta has been studied by using a ¹³⁶Xe beam and a setup consisting of five EUROBALL CLUSTER detectors and the Darmstadt-Heidelberg Crystal Ball array. Spectroscopic information on the extremely rare ¹⁸⁰Ta is obtained from the comparison between an enriched (3.6±0.3% ¹⁸⁰Ta) and a natural tantalum target. Possible evidence for a depopulation from the long-lived high-spin J ^π = 9^- isomer to the short-lived J ^π = 1⁺ ground state is searched for by different methods. The decay of low-K bandheads, which are nanosecond isomers, towards the ground-state band can be demonstrated in delayed spectroscopy. A γγ coincidence analysis provides indications of K = 5 in-band transitions. Finally, when the Crystal Ball is used as an energy and γ multiplicity filter, signals of decay into the K = 0 band are observed. Received: 23 January 2001 / Accepted: 8 February 2001