A. O. Macchiavelli

Fusion of 16O + 144Sm at sub-barrier energies

Abstract Fusion cross sections have been measured for the system 16 O+ 144 Sm at bombarding energies in the range 63 MeV ⩽E lab ( 16 O )⩽72 MeV by observation of delayed X-rays emitted by the evaporation residues. Comparison of the present results for the magic nucleus 144 Sm with those already existing for the fusion of 16 O with other samarium isotopes shows that the enhancement of the cross sections at sub-barrier energies can be explained in terms of a one-dimensional barrier-penetration model that incorporates the quadrupole deformation parameter, s 2 . There is no need to invoke the neck degree of freedom.

Examination of nuclear measurement conditions in cold fusion experiments

The recent announcement of electrochemically induced nuclear fusion [1,2] has generated great interest and activity within the scientific community. In particular, there are several aspects related to the work of ref. 1 which are not fully understood and therefore deserve further investigation. One of them is the huge discrepancy between the amount of measured heat and the intensity of the supposedly accompanying nuclear radiation, namely neutrons and gamma rays. In view of the fact that the detection of nuclear radiation in the context of an electrochemical process is perhaps the most unequivocal fingerprint for the occurrence of fusion, we feel that a careful re-evaluation of the measurement conditions may be needed. In order to address this question, in the present paper we report on an attempt to observe this phenomenon and on the possible problems related to the detection techniques.

The high-spin structure of 100Rh☆

Abstract High-spin states of 100Rh have been populated with the reactions 99Ru(α, 2np) and 98Mo(6Li, 4n) and their γ-decay has been studied with Ge(Li) detectors in singles and coincidence. Angular and time distributions of the γ-rays were also measured. As a result 14 new levels spanning spins up to I = 16 built on the 5+, 4.5 min isomer at 107 keV have been established, and a half-life of T 1 2 = 120 ± 5 nsec has been determined for the 7+ state at 111.9 keV. The rotor-plus-two-quasiparticle model has been used to describe the observed level structure. The pn interaction is shown to be of negligible effect. On the other hand, the introduction of a soft core is essential. The application of the VMI model with the parameters extracted from the 98Ru core yields a remarkably good agreement. This is the first time that the anomalous VMI root ( I 0 has been applied to a doubly odd nucleus.

Improved beam-energy calibration technique for heavy-ion accelerators

Abstract A simple technique for beam energy calibration of heavy-ion accelerators is presented. A thin hydrogenous target was bombarded with 12C and 19F and the energies of the protons knocked out, elastically were measured at several angles using two detectors placed at equal angles on opposite sides of the beam. The use of these two detectors cancels the largest errors due to uncertainties in the angle and position at which the beam hits the target. An application of this energy calibration method to an electrostatic accelerator is described and the calibration constant of the analyzing magnet was obtained with an estimated error of 0.4%.

Measurement of inelastic-scattering cross sections in the 16O+28Si system to discriminate regular and chaotic regimes

A new experiment to measure differential cross sections as a function of the bombarding energy and scattering angle for the 16O + 28Si system in order to discriminate regular and chaotic regimes, was performed using the particle spectrometer CHICO combined with the multidetector array Gammasphere. In this contribution we summarize the characteristics of the method developed to analyze the experimental data and present the preliminary results.

Near-barrier transfer in16O +144, 154Sm

The production of nitrogen and carbon fragments in the reactions induced by16O on144Sm and154Sm targets was studied at two bombarding energies (65 MeV and 72 MeV) around the interaction barrier. The measured angular distributions exhibit the characteristic behaviour of direct transfer reactions, and theQ-value spectra are typically centered at the values predicted by kinematic selectivity. The comparison between fusion and charged-particle transfer cross sections shows that whereas fusion is the most important process at the highest bombarding energy, transfer reactions become comparable or even dominant (as in the144Sm case) at near-barrier energies. The different transfer probabilities observed for the two systems are analyzed in terms of nuclear deformation.

Scattering, fusion and transfer reactions in 16O + ASm at energies close to the Coulomb barrier

Abstract Recently measured scattering cross sections for the 16 O + 144 Sm system allow to extract a bare potential which is used in a global analysis of scattering, fusion and transfer experimental data for 16 O on different samarium isotopes at energies close to the Coulomb barrier. The analysis is done within the framework of an extension of a method based on the intrinsic-coordinate-dependent phase shifts and the equivalent-spheres formalisms which has been previously reported. Consistent fits are obtained for an important amount of data covering a wide range of target deformations, bombarding energies and scattering angles for different reaction channels. As a significant exception, the fusion excitation function for 144 Sm is overestimated.