L. Vannucci

Time-of-flight telescope for mass identification of heavy ions

SummaryA time-of-flight telescope, employing microchannel plate electron multipliers as start detector and a silicon surface barrier as stop detector, is presented. The measured intrinsic time resolution is 160 ps FWHM for262Cf α-particles and 235 ps FWHM for252Cf fission fragments selected in the energy rangeE = (79÷80) MeV. The contribution of each fragment mass is estimated to be 120 ps. The measured detection efficiencies are ≿95%, depending on ion masses.RiassuntoSi presenta un telescopio per tempi di volo, che impiega come rivelatore di start dei moltiplicatori di elettroni a placoa fotomolti plioatrice e un rivelatore a barriera di superficie al silieio come stop. La risoluzione temporale intrinseca è risultata essere di 160 ps FWHM per particelle alfa dal262Cf e 235 ps FWHM per quei frammenti di fissione del252Cf che hanno energia cinetica compresa fra 79 e 80 MeV. II contributo di ogni massa dei frammenti è stimato essere 120 ps. Le efficienze di rivelazione misurate sono ≿95%.РезюмеОписывается Временипролетный телескоп, использующий микроканальные пластинчатые электронные умножители как запускающий детектор и силиконовый детектор с поверхностным барьером как останавливающий детектор. Измеренное внутреннее временное разрешение составляет 160 ps FWHM для ачастиц252Cf и 235 ps PWHM для фрагментов деления252Cf, в области энергий E=(79/80)МэВ. Оценивается вклад каждого фрагмента, который составляет 120 ps. Измеренные эффективности детектирования оказываются 95%, в зависимости от массы ионов.

Experimental evidence of intermediate mechanisms in the 32S+59Co reaction

Abstract The fissionlike fragments resulting from the collisions of 32 S on 59 Co have been studied for different incident energies and emission angles. The mass distributions show a strong dependence on energy and angle which cannot be interpreted in terms of an asymmetric fission process. The TKEs released in the fragmentations turn out to be independent of fragment mass, emission angle and incident energy. These results can be interpreted as an evidence of the existence of mechanisms intermediate between fusion-fission and deep inelastic processes.

Intermediate mechanisms in fission-like fragmentation in the 32S + 59Co and 32S + 63Cu reactions

Abstract The fission-like fragmentation of the 32 S + 59 Co and 32 S + 63 Cu composite systems has been studied at incident energies E / A ≈ (4–5) MeV/nucleon. Mass, energy and angular distributions of the fission-like fragments were obtained from time-of-flight measurements. The mean total kinetic energies of the fragments are found to be fully relaxed, whereas a strong angular dependence is observed in the mass distributions. The data are interpreted in terms of a dynamical model based on the transport theory.

Three-body processes in the32S+45Sc reaction at 5.6 MeV/u

SummaryThe three-body channel in the32S+45Sc reaction has been studied at 5.6 MeV/u bombarding energy. Fragment-fragment coincidence measurements were performed using two ΔE(gas)-E(solid-state) detector telescopes. Data analysis indicates that three-body production results from a two-step binary process. The excitation energy partition between the fragments originating in the first reaction step is found to be compatible with the thermal-equilibrium limit.

Resonances in the32S+24Mg reaction

SummaryElastic and inelastic excitation functions have been measured for the32S+24Mg colliding system at incident energies from 110 to 137 MeV. Evidence has been found for a broad resonance (Γc.m.⋍2 MeV) atEinc=130 MeV, in both the elastic and the inelastic channels. The excitation energy of this resonance in the composite system56Ni corresponds very well to that observed in the28Si+28Si reaction.

Clustering in dissipative ternary processes induced in medium-mass systems

SummaryTernary reactions, induced by low energy collisions (E ≃ 6A MeV), have been studied in the32S+45Sc,76Ge,89Y,59Co,63Cu and19F+63Cu systems. Both, sequential binary decay and fast disassembly of the system have been observed. Clustering effects influence the system fragmentation.

Charge transfer in three-body reactions induced by low-energy heavy ions

The study of three-body channels in32S+45Sc,76Ge,89Y,59Co,63Cu and19F+63Cu reactions around 6 MeV·A evidenced the presence of two-step binary processes even at low bombarding energy. A fairly constant charge amount is found to be transferred from target to projectile, regardless of the system total mass and mass asymmetry.

The Ni+Ni Puzzle: Resonances in the Scattering of Medium Heavy Ions?

Excitation functions and angular distributions of 58Ni+58Ni and 58Ni+62Ni scattering have been measured at energies just above the Coulomb barrier. Evidence for structure in the angle-integrated excitation functions has been found. Attempts are presented to interpret these results, including the presence of resonant states.

Clustering states in the62Ni(58Ni,58Ni)62Ni reaction

Excitation function and angular distributions of the 62Ni(58Ni,58Ni)62Ni elastic scattering have been measured at incident 58Ni energies from 220.0 to 230.0 MeV in steps of 0.5 MeV. Evidence of two structures was found in the excitation function; a statistical analysis suggests a possible nuclear cluster quasi-molecular nature for these structures.

Search for quasi-molecular resonances in the 62 Ni( 32 S, 32 S) 62 Ni reaction

SummaryExcitation function and angular distributions of the62Ni(32S,32S)62Ni reaction were studied for incident32S energies ranging from 154 to 170 MeV. In spite of the current phenomenological models, predicting the presence of a resonant behaviour in this energy range, neither structures were observed in the elastic excitation function nor the presence of prominent single-wave states appeared in a statistical analysis of the angular distributions.