Study of short-lived silver isotopes with a laser ion source

The continuum part of the⁶Li (a,a)⁶Li (1.47–2.47 MeV) scattering data at E_a=50 MeV are extracted in two discretized bins. Coupled-channel calculations are carried out coupling the 1⁺ ground state of⁶Li with both the resonant, 3⁺ ₁ state, and two non-resonant continuum states. The discretized continuum of the⁶Li (p,p)⁶Li (1.75–3.25 MeV) scattering data at E_p=65 MeV are also analysed on the same footing. In both the cases the effect of coupling is found to be minimal.     

Unambiguous identification of three beta-decaying isomers in 70Cu

Using resonant laser ionization, beta-decay studies, and for the first time mass measurements, three beta-decaying states have been unambiguously identified in 70Cu. A mass excess of -62 976.1(1.6) keV and a half-life of 44.5(2) s for the (6-) ground state have been determined. The level energies of the (3-) isomer at 101.1(3) keV with T(1/2)=33(2) s and the 1+ isomer at 242.4(3) keV with T(1/2)=6.6(2) s are confirmed by high-precision mass measurements. The low-lying levels of 70Cu populated in the decay of 70Ni and in transfer reactions compare well with large-scale shell-model calculations, and the wave functions appear to be dominated by one proton-one neutron configurations outside the closed Z=28 shell and N=40 subshell. This does not apply to the 1+ state at 1980 keV which exhibits a particular feeding and deexcitation pattern not reproduced by the shell-model calculations.     

An Inverse Finite Element Method for Pure and Binary Solidification Problems

A 2D axisymmetric formulation for the solution of a directional solidification problem using an inverse finite-element method (IFEM) is presented. An algorithm developed by A. N. Alexandrou (Int. J. Numer. Methods Eng.28, 2383, 1989) has been modified and extended to include more general boundary conditions. The latter includes the explicit presence of an ampoule (with a complex shape) that contains the solid and the melt from which it is growing. Heat transfer between the ampoule and the external environment, time-dependent thermal boundary conditions, nonmonotonic temperature distributions, and species diffusion in the melt and crystal are also taken into account. Thus, our extended formulation encompasses a wider class of solidification problems than previous IFEM methods. Numerical experiments that illustrate the suitability of the extended IFEM are presented. In particular, we present a simulation of the directional solidification of zinc cadmium telluride using boundary conditions corresponding to an actual experiment scenario.     

Electromagnetic moments and nuclear charge radii for neutron-deficient Tb isotopes and the deformation jump nearZ=64,N=90

Optical isotope shifts and hyperfine structures of the^{147–153,155,157,159} Tb isotopes have been measured by the resonance ionization spectroscopy method. Nuclear moments and changes in nuclear charge radiiΔ 〈r ²〉 have been deduced. The “jump” inΔ 〈r ²〉 atN=88–90 has been revealed. It is compared with the relevant data for nuclei with other proton numbers.     

Atomic lines isotope shifts of short-lived radioactive Eu studied by high-sensitive laser resonance photoionization method in “on-line” experiments with proton beams

In “on-line” experiments the isotope shifts (IS) of ^141–144Eu have been measured at the mass-separator output. The overall detection efficiency of Eu atoms is equal to 3 x 10^-4. The accuracy of IS measurement is ±70 MHz and determined by laser linewidth.     

Ground state of a bound polaron with a weak electron-phonon interaction

With the use of the integral representation of the Coulomb Green's function (3) the exact expression for the polaron shift of the ground state of the bound electron in the second order perturbation theory is obtained (5).     

New states in heavy Cd isotopes and evidence for weakening of the N = 82 shell structure

A chemically selective laser ion source has been used in a β-decay study of heavy Ag isotopes into even-even Cd nuclides. Gamma-spectroscopic techniques in time-resolving event-by-event and multiscaling modes have permitted the identification of the first 2⁺ and 4⁺ levels in ¹²⁶Cd₇₈, ¹²⁸Cd₈₀, and tentatively the 2⁺ state in ¹³⁰Cd₈₂. From a comparison of these new states in ₄₈Cd with the E(2⁺) and E(4⁺)/E(2⁺) level systematics of ₄₆Pd and ₅₂Te isotopes and several recent model predictions, possible evidence for a weakening of the spherical N = 82 neutron-shell below double-magic ¹³²Sn is obtained. Received: 13 July 2000 / Accepted: 12 October 2000     

The ISOLDE laser ion source for exotic nuclei

At the ISOLDE on line mass separator a system of copper vapor lasers and dye lasers serves for resonant ionization of atoms inside a hot cavity attached to the target. Radioactive ion beams of Yb, Ag, Mn, Ni, Zn, Be, Cu, Cd and Sn were produced with the Resonance Ionization Laser Ion Source (RILIS). Two and three step excitation schemes are used, providing an ionization efficiency of about 10%. Thanks to the use of the RILIS it became possible to ionize beryllium efficiently at ISOLDE, and all particle stable Be isotopes could be separated for the first time. Separation of Ag and Cu nuclear isomers was achieved in the ion source by appropriate tuning of the laser wavelength. New isotopes of Ag, Mn, Zn, Cd and Sn were found, including the r process “waiting point” nucleus ¹²⁹Ag. This revised version was published online in August 2006 with corrections to the Cover Date.     

Laser ionization in β decay studies of Zn and Mn nuclei

Resonance ionization laser ion source (RILIS) technique has been used in the β-decay studies of ⁵⁹Mn and ⁵⁸Zn. The importance of the RILIS for production of these elements is discussed. The properties of the low-lying levels of the studied nuclei are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of the neutron deficient 182–190Pb isotopes by simultaneous atomic- and nuclear-spectroscopy

Mean-square charge radii and magnetic moments have been measured for the neutron deficient lead isotopes, ^182–190Pb. The measurement was performed at the ISOLDE online mass separator, using the in-source resonance ionization spectroscopy technique. The wavelength of the first excitation step for the resonance ionization laser ion source (RILIS) was scanned over the resonance(s) whilst the α- and γ-ray spectra from the decay of the Pb isotopes were recorded as a function of the wavelength. The isotope shift and, in the case of odd-A isotopes, the hyperfine splitting were deduced. The rms-charge radii of the very neutron deficient Pb isotopes follow the smooth trend of the heavier isotopes. This finding indicates a spherical shape for the lead ground states at the neutron mid-shell (N = 104), where the excitation energy of the oblate 0⁺ state in the even isotopes reaches its minimum.