Showing papers by "A. Bracco published in 2003"

Coupling a CLOVER detector array with the PRISMA magnetic spectrometer - Investigation of moderately neutron-rich nuclei populated by multinucleon transfer and deep inelastic collisions

Abstract: Following the commissioning of the PRISMA large-acceptance spectrometer, installed at the Laboratori Nazionali di Legnaro (LNL), an international nuclear-structure collaboration has started to develop a large $\gamma$ -ray setup to be installed in the target position of the spectrometer. The array is based on the EUROBALL composite CLOVER detectors. In this contribution the CLOVER detector array is described and its expected performance figures discussed. This new setup, by using the high-intensity heavy-ion beams provided by the LNL ALPI linac, will push the study of nuclear structure towards moderately neutron-rich nuclei by means of quasi-elastic and deep inelastic reactions.

In-beam γ-ray spectroscopy of 42 Ca

Abstract: High-spin states of the 42Ca nucleus, populated in the 68 MeV 18O + 30Si reaction, have been studied in a γ-γ-recoil coincidence experiment. The level scheme of 42Ca has been extended up to 13.7 MeV. An elaborate decay pattern with various paths, together with high-quality DCO and polarization information assigns spins and parities for almost all observed levels. The sequence of non-yrast positive-parity states is discussed and compared with highly deformed bands in 36Ar and 40Ca.

Collectivity and single-particle degrees of freedom

Abstract: Intruder rotational bands in 45 Sc and 45 Ti have been investigated up to the maximum aligned angular momentum by means of EUROBALL IV and the Recoil Filter Detector (RFD). The use of the RFD allowed for a reduction of the $\gamma$ -line Doppler broadening and, moreover, for a determination of very short level lifetimes. In the studied nuclei, the estimated deformation shows a gradual disappearance of the collectivity at the highest available spins.

Search for the Jacobi shape transition in light nuclei

Abstract: The γ-rays following the reaction 105 MeV 18 O+ 28 Si have been measured using the EU- ROBALL IV, HECTOR and EUCLIDES arrays in order to investigate the predicted Jacobi shape tran- sition. The high-energy γ-ray spectrum from the GDR decay indicates the presence of large deformations in the hot 46 Ti nucleus, in agreement with new theoretical calculations based on the rotating liquid-drop model. PACS. 24.30.Cz Giant Resonances - 21.60.Ev Collective models

The EUROBALL gamma ray detector array

Abstract: THE EUROBALL collaboration is a common effort of several European countries to provide a forefront experimental facility for nuclear structure research. Using composite germanium (Ge) counters, the EUROBALL detector is the prototype of a new generation of gamma-ray detector arrays that has set new limits to gamma-detector technology and provided a step forward both in basic research and in applications. As an example of application outside the nuclear physics domain we should mention the recent discovery by the NASA probe, Mars Odyssey, oflarge quantities of hydrogen that most probably is bound in water under the Mars surface. This evidence was obtained through neutron and gamma detection, the latter based on the EUROBALL detector technology (encapsulated \"(-ray detectors)-see Fig.1 [1]. The Euroball array consists of 239 Ge crystals geometrically arranged in order to cover 45 % of the total solid angle. Technical details are reported in ref. [2]. Installed at two of the main nuclear structure facilities in Europe, at LNL (Legnaro-Italy) and at IReS-Vivitron (Strasbourg-France), see fig. 2, it has allowed the investigation of atomic nuclei at extreme conditions of angular momentum values and ofproton/neutron ratios. This paper will give an overview of the research activities by selecting a number of examples. We, the authors, would like to dedicate this article to the memory of our IReS colleague and good friend Dr. lean-Pierre Vivien who has untimely and brutally passed away when this paper was under discussion.

Hunting grounds for Jacobi transitions and hyperdeformations

Abstract: Author(s): Herskind, B; Benzoni, G; Wilson, JN; Dossing, T; Hagemann, GB; Sletten, G; Ronn Hansen, C; Jensen, DR; Bracco, A; Camera, F; Leoni, S; Mason, P; Wieland, O; Maj, A; Brekiesz, M; Kmiecik, M; Hubel, H; Bringel, P; Neusser, A; Singh, AK; Diamond, RM; Clark, RM; Cromaz, M; Fallon, P; Gorgen, A; Lee, IY; Macchiavelli, AO; Ward, D; Hannachi, F; Korichi, A; Lopez-Martens, A; Byrski, T; Curien, D; Bednarczyk, P; Dudek, J; Amro, H; Ma, WC; Lisle, J; Odegard, S; Petrache, C; Petrache, D; Steinhardt, T; Thelen, O | Abstract: In recent attempts to search for exotic shapes, hyperdeformation (HD), and Jacobi transitions in Hf, Ba, Xe, Sn and Nd nuclei, ridge structures presumably originating from nuclei of very elongated shapes have been observed in 126Ba, with Gammasphere (GS) and in 126Xe, with Euroball-IV (EB-IV). After the promising results from GS, a second experiment in 126Ba followed at EB-IV, taking advantage of the use of the BGO Inner Ball (IB) for selecting the highest spins. The decay of the Giant Dipole Resonances (GDR) is also studied, and the analysis in progress. The Quasi-continuum transitions in the Jacobi region, show a significant decrease in energy for both 126Ba and 126Xe, compared to the Thomas-Fermi- and the LSD model predictions. Similar effects were recently found for other nuclei by Ward et al.

New Perspectives for Studies of Reaction Mechanisms at Low-Medium Energies

Abstract: PF Mastinu"),L Vannucci"), E Boscolo Marchi"), R Cherubini",A Moronib), A Braccob), F Camerab), B Millionb), 0 Wielandb), G Benzonib), S Leonib), A Airoldib), R Sacchib), E Galbuserab), A Giussanib), A0ttolenghib2'), E Gadiolib), F Ballarinib),A Maj"),M Brekieszc), M Kmiecik"), S Barhid), A Lanchaisd), M Brunod), M D'Agostinod), E Geraci d), G Vanninid), A Ordinee), G CasiniO, A NanniniO, M ChiariO,U Abbondanno"), PM Milazzo"),GV MargagliottF) and ABonaserah) a) Laboratori Nazionali di Legnaro, I N F N, Legnaro (Padova), Italy, b) I N F N and Dipartimento di Fisica dell'Universit6 di Milano, Milano, Italy c) The Niewodniczanski Institute of Nuclear Physics, Krakow Poland d) IN FN and Dipartimento di Fisica dell'Universit6 di Bologna, Bologna, Italy e) INFN Sezione di Napoli, Napoli, Italy # I N F N Sezione di Firenze, Firenze, Italy g) IN FN and Dipartimento di Fisica dell'Universit6 di Trieste, Trieste Italy h) Laboratori Nazionali del Sud, INFN Catania l) Universitii degli Studi di Pavia, Dipartimento di Fisica, Pavia, Italy

Search for the Jacobi shape transition in light nuclei

Abstract: The gamma-rays following the reaction 105 MeV 18O + 28Si have been measured using the EUROBALL IV, HECTOR and EUCLIDES arrays in order to investigate the predicted Jacobi shape transition. The high-energy gamma-ray spectrum from the GDR decay indicates a presence of large deformations in hot 46Ti nucleus, in agreement with new theoretical calculations based on the Rotating Liquid Drop model.

Rotational Damping And Compound Formation In Warm Rotating Nuclei

Abstract: The rotational damping width Γrot and the compound damping width Γcomp are two fundamental quantities that characterize rapidly rotating compound nuclei having finite thermal excitation energy. A two‐component structure in the strength function of consecutive E2 transitions reflects the two widths, and it causes characteristic features in the double and triple gamma‐ray spectra. We discuss a new method to extract experimentally values of Γrot and Γcomp. The first preliminary result of this method is presented.

Study of thermally excited nuclei through E1 and E2 decay from collective modes

Abstract: The nuclear system at the limit of excitation energy and angular momentum is here studied in the case of the superdeformed nucleus 143 Eu using $\gamma$ -spectroscopy techniques. The data are based on a EUROBALL experiment using the reaction 37 Cl + 110 Pd $\to^{143}$ Eu + 4n. The influence of thermal energy on superdeformed configurations is investigated through the analysis of the quasi-continuum spectra formed by E2 transitions among states of excited rotational bands with energy extending up to 4-5 MeV above the yrast line. In particular, the effective lifetimes of the discrete rotational bands forming ridge structures in $\gamma$ - $\gamma$ coincidence matrices is measured by a Doppler Shift Attenuation Method. The deduced quadrupole deformation of $Q_t \approx$ 10 eb indicates that the nucleus maintains its collectivity with increasing excitation energy, supporting the superdeformed character of the excited nuclear rotation. The obtained number of superdeformed discrete bands forming the ridge structures is found in good agreement with microscopic cranked shell model calculations including the decay-out process into the lower deformation minimum. In addition, the nuclear properties at higher excitation energies are investigated through the E1 $\gamma$ -decay of the giant dipole resonance (GDR). It is found that the intensity of the superdeformed yrast and excited bands increases by a factor of approximately 1.6 when a coincidence with a high-energy $\gamma$ -ray is required, showing the importance of the E1 cooling in the feeding mechanism of the superdeformed states.

New Perpspectives for Studies of Reaction Mechanisms at Low Medium Energies

Abstract: P.F. Mastinu"),L. Vannucci"), E. Boscolo Marchi"), R. Cherubini",A. Moronib), A. Braccob), F. Camerab), B. Millionb), 0. Wielandb), G. Benzonib), S. Leonib), A. Airoldib), R. Sacchib), E. Galbuserab), A. Giussanib), A.0ttolenghib2'), E. Gadiolib), F. Ballarinib),A. Maj"),M. Brekieszc), M. Kmiecik"), S. Barhid), A. Lanchaisd), M. Brunod), M. D'Agostinod), E. Geraci d), G. Vanninid), A. Ordinee), G. CasiniO, A. NanniniO, M. ChiariO,U. Abbondanno"), P.M. Milazzo"),G.V. MargagliottF) and A.Bonaserah) a) Laboratori Nazionali di Legnaro, I. N. F. N., Legnaro (Padova), Italy, b) I. N. F. N. and Dipartimento di Fisica dell'Universit6 di Milano, Milano, Italy c) The Niewodniczanski Institute of Nuclear Physics, Krakow. Poland d) I.N. F.N. and Dipartimento di Fisica dell'Universit6 di Bologna, Bologna, Italy e) I.N.F.N. Sezione di Napoli, Napoli, Italy # I. N. F. N. Sezione di Firenze, Firenze, Italy g) I.N. F.N. and Dipartimento di Fisica dell'Universit6 di Trieste, Trieste. Italy h) Laboratori Nazionali del Sud, I.N.F.N. Catania l) Universitii degli Studi di Pavia, Dipartimento di Fisica, Pavia, Italy