Effective moment of inertia in132Ce,134Nd and136Nd

The effective moment of inertiaI _eff ⁽²⁾ of¹³²Ce,¹³⁴Nd and¹³⁶Nd produced in⁴⁰Ar induced reactions has been deduced from continuumγ-ray spectra measured by sum spectrometer methods. Results concerning the deformation of these nuclei are obtained by comparison of the experimental data and calculations in the frame of a cranking Nilsson — Strutinsky model.     

Competing interactions, the renormalization group, and the isotropic-nematic phase transition

We discuss 2D systems with Ising symmetry and competing interactions at different scales. In the framework of the renormalization group, we study the effect of relevant quartic interactions. In addition to the usual constant interaction term, we analyze the effect of quadrupole interactions in the self-consistent Hartree approximation. We show that in the case of a repulsive quadrupole interaction, there is a first-order phase transition to a stripe phase in agreement with the well-known Brazovskii result. However, in the case of attractive quadrupole interactions there is an isotropic-nematic second-order transition with higher critical temperature.     

On lineγ-Ray emission following 30 MeV/A12C induced reactions on some medium-heavy targets

Preliminary results on residual nuclei production in 30 MeV/A¹²C interaction with medium heavy targets are presented. Gamma-ray spectroscopic techniques were used. Evidence for charge and angular momentum transfer is found.

     

Effective Maxwell equations for finite planar samples in QHE regime

Effective Maxwell equations for the mean quantum electromagnetic field in planar samples in QHE regime are investigated. Boundary conditions to be satisfied by the mean field intensities at the filamentary boundaries (edges) are determined. For ideal strictly 2D samples embedded in real 3D space, these constraints imply that the total filamentary charge at the boundaries (the free plus polarization terms) and current densities identically vanish at all times. In the static limit the exact quantization of the Hall resistance of samples of arbitrary form, directly follows from the boundary condition. The equations for the electromagnetic response in a neighborhood of the edge of a half-plane in QHE regime are solved. The system exhibits a weak diamagnetic response and inhomogeneous charge and current distributions develop in the sample.     

New measurement of exotic decay of 225Ac by 14C emission

The branching ratio of ²²⁵Ac decay by emission of ¹⁴C was remeasured under improved experimental conditions by using a radioactive source produced at the ISOLDE mass-separator at CERN and a nuclear track detector technique. The result, B = λ_14C/λ_α = (4.5±1.4)10^-12, is consistent with the anomalously high value obtained in the 1993 experiment, thus confirming the importance of nuclear-structure effects in this exotic decay. Received: 20 July 2001 / Accepted: 28 November 2001     

Low-level measurements of actinides and long-lived radionuclides in biological and environmental samples

This paper describes a radiochemical method for the determination of⁹⁹Tc in large volumes of rain, river and seawater. The procedure is based on the reduction of technetium to the +4 oxidation state with potassium disulfite in a slightly acidic medium, followed by iron hydroxide precipitation. After oxidation to the +7 oxidation state, the technetium fraction is purified with iron hydroxide and calcium carbonate precipitations. Technetium (+7) is extracted with TBP (xylene) in 3M H₂SO₄, back extracted in 2M NaOH or ammonia, and the electrodeposition is made in 2M NaOH or H₂SO₄/NH₄OH medium at pH 5–6. The radiochemical yield is determined by gamma counting of the 140 keV gamma ray from⁹⁹Tc^m.⁹⁹Tc is counted on an anti-coincidence shielded GM-gas flow counter. The purity of the⁹⁹Tc plated samples is checked by alpha and beta spectrometry using surface barrier detectors and by gamma spectrometry on Ge(HP) detector. The radiochemical yield of 50–150 l water samples is around 20–60%.     

High-spin yrast isomer in theN=83151Er nucleus

An highspin yrast isomer (T_1/2 ? 420ns, E>10.286 MeV, 67/2≤ I≤ 71/2) is observed in the¹⁵¹Er nucleus excited in the¹¹⁶ Sn+⁴⁰ Ca reaction, using the recoil shadow method.     

Possible shape-change observed at high spin in123Cs

The collective moment of inertia ? _band ⁽²⁾ of¹²³Cs produced in the¹¹⁵In+¹²C reaction at 80 MeV has been measured by gamma-gamma energy correlation techniques. The variations of ? _band ⁽²⁾ with the rotational frequency are compared to those of¹²²Xe and analysed in the frame of a cranked Nilsson-Strutinsky model. We conclude that the addition of one proton to the triaxial (γ?30°)¹²²Xe core gives a final prolate-type nucleus¹²³Cs withγ?0° above a rotational frequency?ω?0.55 MeV.