Comparison of Transfer-to-Continuum and Eikonal Models of Projectile Fragmentation Reactions

Spectroscopic properties of nuclei are accessible with projectile fragmentation reactions, but approximations made in the reaction theory can limit the accuracy of the determinations. We examine here two models that have rather different approximations for the nucleon wave function, the target interaction, and the treatment of the finite duration of the reaction. The nucleon-target interaction is treated differently in the eikonal and the transfer-to-continuum model, but the differences are more significant for light targets. We propose a new parameterization with that in mind. We also propose a new formula to calculate the amplitude that combines the better treatment of the wave function in the eikonal model with the better treatment of the target interaction in the transfer-to-continuum model.Comment: 21 pages, latex file including 3 tables. 5 figures. Submitted to Phys. Rev.

Unbound exotic nuclei studied by transfer to the continuum reactions

In this paper we show that the theory of transfer reactions from bound to continuum states is well suited to extract structure information from data obtained by performing "spectroscopy in the continuum". The low energy unbound states of nuclei such as $^{10}$Li and $^{5}$He can be analyzed and the neutron-core interaction, necessary to describe the corresponding borromean nuclei $^{11}$Li and $^{6}$He can be determined in a semi-phenomenological way. An application to the study of $^{10}$Li is then discussed and it is shown that the scattering length for s-states at threshold can be obtained from the ratio of experimental and theoretical cross sections. The scattering single particle states of the system n+$^{9}$Li are obtained in a potential model. The corresponding S-matrix is used to calculate the transfer cross section as a function of the neutron continuum energy with respect to $^{9}$Li. Three different reactions are calculated $^{9}Li(d,p)^{10}Li$, $^{9}Li(^{9}Be,^{8}Be)^{10}Li$, $^{9}Li(^{13}C,^{12}C)^{10}Li$, to check the sensitivity of the results to the target used and in particular to the transfer matching conditions. Thus the sensitivity of the structure information extracted from experimental data on the reaction mechanism is assessed.Comment: 21 pages, 5 ps figures, accepted for publication on Nucl. Phys.

10^{10}Li spectrum from 11^{11}Li fragmentation

A recently developed time dependent model for the excitation of a nucleon from a bound state to a continuum resonant state in the system n+core is applied to the study of the population of the low energy continuum of the unbound $^{10}$Li system obtained from $^{11}$Li fragmentation. Comparison of the model results to new data from the GSI laboratory suggests that the reaction mechanism is dominated by final state effects rather than by the sudden process, but for the population of the l=0 virtual state, in which case the two mechanisms give almost identical results. There is also, for the first time, a clear evidence for the population of a d$_{5/2}$ resonance in $^{10}$Li.Comment: 15 pages, 4 figures, 3 tables. Accepted for publication in Nucl.Phys.

Initial State Dependence of the Breakup of Weakly Bound Carbon Isotopes

The one-neutron nuclear breakup from the Carbon isotopes $^{19}$C and $^{17}$C, is calculated as an example of application of the theory of transfer to the continuum reactions in the formulation which includes spin coupling. The effect of the energy sharing between the parallel and transverse neutron momentum distributions is taken into account thus resulting in a theory which is more general than sudden eikonal approaches. Both effects are necessary to understand properly the breakup from not too weakly bound $l_i>1$ orbitals. Breakup which leaves the core into an excited state below particle threshold is also considered. The core-target interaction is treated in the smooth cut-off approximation. By comparing to presently available experimental data we show how to make some hypothesis on the quantum numbers and occupancy of the neutron initial state. Possible ambiguities in the interpretation of inclusive cross sections are discussed.Comment: 22 RevTeX pages,3 ps figures. Phys. Rev. C, accepte

Unbound exotic nuclei studied by projectile fragmentation

We call "projectile fragmentation" of neutron halo nuclei the elastic breakup (diffraction) reaction, when the observable studied is the neutron-core relative energy spectrum. This observable has been measured in relation to the Coulomb breakup on heavy target and recently also on light targets. Such data enlighten the effect of the neutron final state interaction with the core of origin. Projectile fragmentation is studied here by a time dependent model for the excitation of a nucleon from a bound state to a continuum resonant state in a neutron-core complex potential which acts as a final state interaction. The final state is described by an optical model S-matrix so that both resonant and non resonant states of any continuum energy can be studied as well as deeply bound initial states. It turns out that due to the coupling between the initial and final states, the neutron-core free particle phase shifts are modified, in the exit channel, by an additional phase. Some typical numerical calculations for the relevant observables are presented and compared to experimental data. It is suggest that the excitation energy spectra of an unbound nucleus might reflect the structure of the parent nucleus from whose fragmentation they are obtained.Comment: Proceedings of the 11th Conference on Problems in Theoretican Nuclear Physics, Cortona, Italy, 2006. World Scientifi

Particle-particle random phase approximation applied to Beryllium isotopes

This work is dedicated to the study of even-even 8-14 Be isotopes using the particle-particle Random Phase Approximation that accounts for two-body correlations in the core nucleus. A better description of energies and two-particle amplitudes is obtained in comparison with models assuming a neutron closed-shell (or subshell) core. A Wood-Saxon potential corrected by a phenomenological particle-vibration coupling term has been used for the neutron-core interaction and the D1S Gogny force for the neutron-neutron interaction. Calculated ground state properties as well as excited state ones are discussed and compared to experimental data. In particular, results suggest the same 2s_1/2-1p_1/2 shell inversion in 13Be as in 11Be.Comment: to appear in Phys. Rev.

Scientific community and civil protection synergy during the Stromboli 2002-03 eruption

The eruption of Stromboli 2002-03, thanks to its complex scenario (flank instability, tsunami, necessity to rapidly upgrade monitoring networks) has provided an important opportunity to verify the response of the national system of civil protection to volcanic emergencies. In particular, it has tested and validated the model of collaboration, in use by Italian law, between the Department of Civil Protection and the National Institute of Geophysics and Volcanology. This synergy has enabled a better understanding and ability to tackle the eruptive crisis from its first stages, as well as implement monitoring systems both dependably and swiftly. In this work, the numerous first monitoring tasks carried out during the critical initial stages of the eruption are described, and the activities and planned action are reported over the course of the eruption that has made Stromboli one of the best monitored volcanoes not only in Italy but throughout the world

New data from borehole strainmeters to infer lava fountain sources (Etna 2011-2012)

In January 2011 eruptive activity resumed at Etna producing a new phase with frequent lava fountain episodes until April 2012. In November 2011, the first two borehole strainmeters were installed, which detected negative strain changes (~ 0.15 - 0.8 strain) during the paroxysmal events. A Finite Element Model was set up to estimate accurately the tilt and volumetric strain, taking into account the real profile of the volcano and the elastic medium heterogeneity. The numerical computations indicated an elongated depressurizing source located at 0 km b.s.l., which underwent a volume change of ~2 x 106 m3 which is the most of the magma volume erupted while a smaller remaining part is accommodated by the magma compressibility. This shallow source cannot accumulate large magma volumes and, thus, favours short term periodic eruptive events with a fairly constant balance between the refilling and the erupted magma

Knowledge of HIV infection, risk perception, and sexual behaviour of undergraduates. May female medical students act as peer educators?

This paper is aimed to verify whether the knowledge and beliefs of female medical freshmen about HIV infection, their personal risk perception, and their sexual behaviour differs from their female peers, in view of the possibility of female medical student-based peer education. A purposive, theoretical quota sampling method was used to recruit the target population. A self-administered anonymous questionnaire was delivered to both female medical and non medical freshmen during March 2004 (n = 266: 124 medical students and 142 non medical students) in Catania (Sicily). The data were analysed for the whole sample and for the two groups of students individually. The Chi-square test was used to compare data from the two groups of students. Results showed that knowledge and risk perception about HIV infection were higher for medical students when compared with non medical students. Moreover, a lower rate of sexually active medical students and a higher rate of condom use was found among them. Since female medical students seem more sensitive to risk perception and aware of healthier lifestyles, they could be useful in peer sexual education and appropriate prevention programmes against HIV infection

Coulomb and nuclear breakup effects in the single neutron removal reaction 197Au(17C,16C gamma)X

We analyze the recently obtained new data on the partial cross sections and parallel momentum distributions for transitions to ground as well as excited states of the 16C core, in the one-neutron removal reaction 197Au(17C,16C gamma)X at the beam energy of 61 MeV/nucleon. The Coulomb and nuclear breakup components of the one-neutron removal cross sections have been calculated within a finite range distorted wave Born approximation theory and an eikonal model, respectively. The nuclear contributions dominate the partial cross sections for the core excited states. By adding the nuclear and Coulomb cross sections together, a reasonable agreement is obtained with the data for these states. The shapes of the experimental parallel momentum distributions of the core states are described well by the theory.Comment: Revtex format, two figures included, to appear in Phys. Rev. C. (Rapid communications