Sl. Cavallaro

Vanishing spin alignment: Experimental indication of a triaxial {sup 28}Si+{sup 28}Si nuclear molecule

Fragment-fragment-{gamma} coincidences have been measured for {sup 28}Si+{sup 28}Si at an energy corresponding to the population of a conjectured resonance in {sup 56}Ni. Fragment angular distributions as well as {gamma}-ray angular correlations indicate that the spin orientations of the outgoing fragments are perpendicular to the orbital angular momentum. This differs from the {sup 24}Mg+{sup 24}Mg and the {sup 12}C+{sup 12}C resonances, and suggests two oblate {sup 28}Si nuclei interacting in an equator-to-equator molecular configuration. {copyright} {ital 1999} {ital The American Physical Society}

Heavy ions detection by using BaF2 crystals coupled to thin plastic scintillator

Abstract By coupling a thin fast NE102A plastic scintillator to a BaF2 crystal, we have been able to detect and identify simultaneously light charged particles and heavy ions from Z = 1 to Z = 18. Time-of-flight information is used to separate Z = 1 isotopes and to distinguish fission fragments from other reaction products.

Li7+p interaction and excited states of Be8

Abstract The Li7+p interaction has been extensively studied and its various products analysed. The results confirm the presence of the well known levels of Be8 at 2.9, 17.63 and 18.15 MeV and give clear evidence for the existence of the discussed 7.56 MeV level. Three new levels of Be8 have been discovered at the energies 13.91, 17.9 and 18.0 MeV. Widths, angular momenta, parities and isobaric spins of several levels have been determined Some anomalies of the Li7+p interaction, previously observed by others, are explained.

Timing performances and edge effects of detectors worked from 6-in. silicon slices

Abstract Prototypes of new passivated implanted planar silicon detectors, obtained for the first time from 6 in. silicon slices, have been tested. The time and energy resolutions have been studied as a function of the type and energy of the detected particles, in order to test the performances of these detectors for time of flight measurements in the Chimera project. Some problems arising from edge effects observed in double-pad detectors have been solved by using a guard ring.

Plasma effects for heavy ions in implanted silicon detectors

Abstract Plasma effects for heavy ions in implanted silicon detectors have been investigated for different detector characteristics as a function of type and energy of the detected particles. A new approach is presented and used to reproduce the effect of the plasma delay in the timing performances. The results are in good agreement with the present data and with previous measurements found in the literature.

Determination of sidefeeding intensity by γ-γ coincidence data analysis

Abstract A method has been developed to determine sidefeeding intensities of residual nuclei produced in heavy ion fusion reactions by means of the analysis of γ-γ coincidence data. In order to take into account the angular correlation effects, the calculations based on the directional correlation from oriented states (DCO) are employed to acquire the angular correlation functions by fitting the experimental DCO ratios from the γ-γ coincidence data. A typical example is given for the determination of sidefeeding intensities of 53 Mn which is produced in the 30 Si( 28 Si, αp) 53 Mn reaction channel with a low cross section and many other open channels. This method is found to be not only very successful but also necessary for cases where disturbing outgoing channels, contaminations and background problems make the single γ-spectrum rather complex.

Calibrating the CsI(Tl) detectors of the GARFIELD apparatus

The energy and charge dependence of the light output of the CsI(Tl) detectors of the GARFIELD apparatus has been investigated for heavy ions with 5pZp16 in the energy range from 2.2 to 8:3 A MeV: The results have been compared to an analytical expression successfully used in previous calibration procedures at higher energies, and a rather good agreement was obtained between measured and calculated quantities. The resulting parameter set was successfully applied to another set of experimental data. The overall result demonstrates the validity of the above mentioned calibration procedure in a wide range of incident ion energies and masses. r 2002 Elsevier Science B.V. All rights reserved. PACS: 29.40.Mc

Evaporation decay following the32S+24,25,26Mg fusion reactions

SummaryThe evaporation residue cross-sections are measured for all the outgoing channels of the32S+24,25,26Mg fusion reaction leading to the formation of56Ni,57Ni,58Ni compound nuclei in the range ofElab=(90÷175) MeV. The identification in bothA andZ is carried out by means of the in-beam γ-ray detection. Suppression of any long-lived γ radioactivity has been done by means of a beam chopper automatically controlled by the acquisition system. Correction for12C and16O impurities of the targets and of the beam is also applied. Comparison with statistical model calculation is performed through individual residue excitation functions, summed channel cross-sections and nucleon and α multiplicities. The general behaviour and the main features of the data are well accounted by the model, when a standard set of parameters is used. Due to the limitation of the angular momentum occurring in the entrance channel, a reduction of the α emission probability and consequently a favoured nucleon emission is observed, related to the decreasing angular momentum of the compounds.RiassuntoSono misurate le sezioni durto dei residui di evaporazione per tutti i canali uscenti delle reazioni di fusione:32S+24,25,26Mg, nellintervallo di energie incidentiElab=(90÷175) MeV. La identificazione dei residui, inA e inZ, è fatta tramite la rivelazione dei γ in beam. La soppressione di qualunque radioattività γ a vita media lunga viene effettuata attraverso un beam chopper automaticamente controllato dal sistema di acquisizione. La correzione per impurezze di12C e/o16O presenti nel fascio e/o nel bersaglio viene anche applicata. Il confronto con le previsioni del modello statistico viene effettuato attraverso le funzioni di eccitazione del singolo canale, le sezioni durto dei canali sommati a parità di molteplicità e le molteplicità di nucleoni e di particelle α. Il comportamento globale e le caratteristiche principali sono ben riprodotte dal modello, anche se nessuna variazione dei parametri viene effettuata. In seguito alle limitazioni del momento angolare nel canale di ingresso e con riferimento al processo di fusione-evaporazione, viene osservata una riduzione della probabilità di emissione α (e conseguentemente una emissione favorita di nucleoni) connessa con il diminuito momento angolare del nucleo opposto.

The Chimera Facility at LNS

CHIMERA is a 4π detector for charged particles whose construction at LNS is in progress and is coming at end. The main features, some performances and the status of the project is presented.

Production of heavy fragments in the reaction

Heavy fragments of mass approximately 150u are observed in the reaction 40Ar(44 and 77 A.MeV) + 232Th. At 27 A.MeV the yield of heavy fragments is small. The data indicate that the heavy products are formed at high excitation and are accompanied by two intermediate mass fragments, IMF. Boltzmann-Nordheim-Vlasov calculations give a good description and interpret the IMF emission as arising from the overlapping nuclear zone.