[en] The transition of a physical system from one phase to another is familiar from everyday life. Water, for example, can be a solid (ice), a liquid or a gas (steam), and a change in temperature causes one phase to transmute into another. Phase transitions in atomic nuclei are more complicated - but a new modelling method could soon change that. The point at which a phase transition occurs is called the critical point and is dear to every physicist's heart. The fascination with systems at the critical point stems from the fact that a small change in one parameter, such as temperature, can trigger spectacular changes in the other properties. Indeed, it is this discontinuity in the properties at the critical point that makes phase transitions so challenging to describe. Phase transitions arguably play an even more important role in the world of quantum mechanics. In the case of nuclei, the numbers of neutrons, N, and protons, Z, act as a control parameter in the same way that temperature affects water. Physicists can study variations in the shape of the nucleus as a function of N and Z, paying particular interest to those regions where the shape changes most rapidly. These regions are the equivalent of the critical points in a standard phase diagram. In many examples in macroscopic and condensed-matter physics, it is easy to draw a phase diagram because huge numbers of particles participate. But nuclei contain at most a few hundred nucleons - and this makes the analysis of nuclear phase transitions more difficult. Now Franceso Iachello at Yale University in the US has proposed a method based on nuclear symmetries that might lead to a framework to deal with nuclei at, or around, critical points. Moreover, Rick Casten and Victor Zamfir, also at Yale, have shown convincing evidence that the properties predicted by Iachello's model are approximately observed in a samarium isotope (Phys. Rev. Lett. 2001 87 052502; 052503). In the August issue of Physics World, Piet Van Isacker of the GANIL laboratory, France, explores the new method for modelling the often complicated transitions in nuclear phase diagrams. (U.K.)

[en] We carry out a simple analysis of (n+3)-dimensional gravity in the context of recent work on 'large' supplementary dimensions and deduce a formula for the expected compactification radius for the n additional dimensions in the universe, as a function of the Planck and the electro-weak scales. We argue that the correspondingly modified gravitational force gives rise to effects that might be within the detection range of dedicated neutron experiments. A scattering analysis of the corresponding modified gravitational forces suggests that slow neutron scattering off atomic nuclei with null spin may provide an experimental test for these ideas

[en] The interrelation between the octupole phonon and the low-lying proton-neutron mixed-symmetry quadrupole phonon in near-spherical nuclei is investigated. The one-phonon states decay by collective E3 and E2 transitions to the ground state and by relatively strong E1 and M1 transitions to the isoscalar 2⁺₁ state. We apply the proton-neutron version of the interacting boson model including quadrupole and octupole bosons ( sdf -IBM-2). Two F -spin symmetric dynamical symmetry limits of the model, namely the vibrational and the γ -unstable ones, are considered. We derive analytical formulae for excitation energies as well as B(E1) , B(M1) , B(E2) and B(E3) values for a number of transitions between low-lying states

[en] Lifetimes of excited states in ²¹¹At were measured using the electronic γ-γ fast timing technique. The nucleus of interested was populated in a ²⁰⁸Pb(⁶Li,3n)²¹¹At fusion-evaporation reaction at the the 10 MV Tandem accelerator at the Institute for Nuclear Physics, University of Cologne. The lifetimes of the 17/2₁^-, 23/2₁^- states were determined for the first time. The experimental results are compared to two shell model calculations, one using the modified Kuo-Herling interaction and the other using an empirical interaction for 3 particles in a single j=9/2 shell.

[en] We investigate the modifications of the gravitational force in the context of recent work on large supplementary dimensions and deduce a formula for the expected compactification radius for the n additional dimensions in the universe, as a function of the Planck and the electro-weak scales. We argue that the correspondingly modified gravitational force gives rise to effects that, although very small, might be within the detection range of dedicated neutron scattering experiments. We discuss the characteristics of an experimental setup to observe these effects

[en] It has been suggested that there might be an inherent limit to the accuracy with which nuclear masses can be calculated, chaotic motion inside the atomic nucleus being responsible for this lack of predictability. However, a thorough application of a set of parameter-free relationships among neighboring nuclei, known as the Garvey-Kelson relations, to an up-to-date compilation of more than 2500 nuclear masses allows to set an upper bound for the proposed chaotical component, which turns out to be almost an order of magnitude smaller than previously suggested. This is good news for astrophysicists attempting to understand the processes that fuel the stars

[en] The matrix-coherent state approach in the IBM with configuration mixing is used to describe the geometry of neutron-deficient Pt isotopes. Employing a parameter set for all isotopes determined previously, it is found that the lowest minimum goes from spherical to oblate and finally acquires a prolate shape when approaching the mid-shell Pt isotopes