AGATA, Technical Proposal for an Advanced Gamma Tracking Array for the European Gamma Spectroscopy Community

International audienceAn Advanced GAmma-ray Tracking Array, AGATA, is proposed for high-resolution γ-ray spectroscopy with exotic beams. AGATA will employ highly segmented Ge detectors as well as fully digital electronics and relies on newly developed pulse-shape analysis and tracking methods. The array is being designed in a way that it provides optimal properties for nuclear structure experiments in a wide range of beam velocities (from stopped to v/c ≈ 50%), almost independent of beam quality and background conditions. Selectivity and sensitivity of AGATA will be superior to any existing γ-array by several orders of magnitude. Hence, it will be for a long time a rich source for nuclear structure physics providing the means for new discoveries and opening challenging new perspectives. This document is the initial proposal sent to the European Commission to obtain the necessary funds for the project

DSAM lifetime measurements for the chiral pair in 194Tl

Most important for the identification of chiral symmetry in atomic nuclei is to establish a pair of bands that are near-degenerate in energy, but also in B(M1) and B(E2) transition probabilities. Dedicated lifetime measurements were performed for four bands of 194Tl, including the pair of four-quasiparticle chiral bands with close near-degeneracy, considered as a prime candidate for best chiral symmetry pair. The lifetime measurements confirm the excellent near-degeneracy in this pair and indicate that a third band may be involved in the chiral symmetry scenario

Coexistence of 'alpha+ 208Pb' cluster structures and single-particle excitations in 212Po

Excited states in 212Po have been populated by alpha transfer using the 208Pb(18O,14C) reaction at 85MeV beam energy and studied with the EUROBALL IV gamma multidetector array. The level scheme has been extended up to ~ 3.2 MeV excitation energy from the triple gamma coincidence data. Spin and parity values of most of the observed states have been assigned from the gamma angular distributions and gamma -gamma angular correlations. Several gamma lines with E(gamma) < 1 MeV have been found to be shifted by the Doppler effect, allowing for the measurements of the associated lifetimes by the DSAM method. The values, found in the range [0.1-0.6] ps, lead to very enhanced E1 transitions. All the emitting states, which have non-natural parity values, are discussed in terms of alpha-208Pb structure. They are in the same excitation-energy range as the states issued from shell-model configurations.Comment: 21 pages, 19 figures, corrected typos, revised arguments in Sect. III

Investigation of gamma-ray fold distributions in N <= 82 Gd, Eu and Sm nuclei: Observation of a double-humped fold distribution

Cross-sections and gamma-ray fold distributions have been measured for the 97Mo+51V, 100Mo+48Ti and 114Cd+36S reactions at energies of 238, 215 and 182 MeV of the 51V, 48Ti and 36S projectiles, respectively. For the 97Mo(51V, alpha2n)142Eu reaction channel a double-humped fold distribution has been observed. This fold distribution can only be understand if an incomplete-fusion reaction mechanism associated with the alpha-particle emission is assumed. The 97Mo(51V, alpha n 143Eu reaction channel represents an incomplete-fusion reaction channel as well and its single-humped fold distribution can be described on the same footing as that of the alpha2n channel. The fold distributions associated with xn and pxn channels can be explained assuming complete-fusion reactions. For the calculations in terms of an incomplete-fusion reaction mechanism a narrow angular momentum window, ranging from ~ 68 to 82 physics planck's constant has been assumed for the 97Mo(51V, alphan) and alpha2n reaction channels. The complete-fusion reaction mechanism is considered to be negligible in this angular-momentum range

The shears mechanism in 142^{142}Gd in the Skyrme-Hartree-Fock method with the tilted-axis cranking model

We report on the first Skyrme--Hartree--Fock calculations with the tilted-axis cranking in the context of magnetic rotation. The mean field symmetries, differences between phenomenological and self-consistent methods and the generation of shears-like structures in the mean field are discussed. Significant role of the time-odd spin--spin effective interaction is pointed out. We reproduce the shears mechanism, but quantitative agreement with experiment is rather poor. It may have to do with too large core polarization, lack of pairing correlations or properties of the Skyrme force