A. A. Stefanini

The pulsed beam facility at the 3 MV Van de Graaff accelerator in Florence: Overview and examples of applications

Abstract An electrostatic chopper has been installed at the KN 3000 accelerator in Florence to obtain short beam pulses with a number of particles per pulse whose average value can be chosen by varying the current intensity at the deflector plates input. Beam pulses can be obtained containing an average number of particles per pulse from less than one to thousands. The transmitted beam pulses can be as short as 200 ps FWHM, at a repetition rate up to about 100 kHz. Among the many applications of the facility, the direct measurement of energy loss and straggling of protons in Kapton and aluminium is reported. In this measurement, the facility has been tuned for transmission of mainly single-proton pulses; the beam energy is directly measured downstream with a good energy-resolution detector, without and with absorbers in front. In general, measurements of this kind can be directed both to study the basic processes of charged particles interactions in materials, or more practically to obtain the effective values of energy parameters useful in many IBA applications, avoiding the need to rely on simulations or theoretical estimates. Also briefly described is an application to Si-detector testing. In this case, the facility has been tuned for transmission of pulses containing many hundreds of protons of energy E p =2.5 MeV and the detector is directly exposed to the pulses. Spectra containing equally spaced peaks at energies multiple of E p are obtained and the response linearity of the detector plus electronics system can thus be checked.

A new approach to the kinematic coincidence method in heavy ion reactions

A new approach to the kinematic coincidence method (KCM) is proposed, which makes use of the whole kinematic information of heavy ion experiments in a self-consistent way. It takes advantage of the overdetermination of the measurement yielding not only solutions for the primary masses of the fragments, but also “improved values” for their velocity vectors. A statistical variable, Δν, indicates to what extent the secondary quantities violate the kinematics of the reaction. The ability of the present approach to reproduce the primary quantities of a binary or ternary reaction is compared with that of older approaches on the basis of realistic Monte Carlo simulations. The background of incompletely detected events of higher multiplicity can be effectively subtracted using the results of the present analysis.

Results on two-, three-, and four-body events from the100Mo+100Mo and120Sn+120Sn collisions aroundE/A=20 MeV

Events with 2, 3 and 4 heavy-fragments (A≧20) have been detected in the reactions100Mo+100Mo atE/A =18.7, 23.7 MeV and120Sn+120Sn atE/A=18.4 MeV. The experiments were performed with an array of 12 detectors which together covered a large fraction of the forward hemisphere and allowed a high detection efficiency for these events. Masses and energies of all fragments have been reconstructed by means of an improved version of the kinematic coincidence method. The probabilitiesP3 andP4 of producing 3- and 4-body events were found to depend mainly on the dissipated energy rather than on the bombarding energy, thus indicating that their origin lies more in the decay properties of the excited fragments than in the dynamics of the interaction. Emission of light particles from the composite system is shown to become more relevant with increasing bombarding energy and may explain the drop of theP3 andP4 curves at high energy losses. Small deviations of theP3 andP4 curves at 23.7A · MeV from those at lower bombarding energies were used to estimate the amount of a possible pre-equilibrium light particle emission as a function of impact parameter.

Analysis of the sequential fission observed in collisions of100Mo +100Mo and120Sn +120Sn around 20 AMeV

Events with 2, 3 and 4 heavy fragments (A≥20) detected in the reactions100Mo +100Mo at 18.7, 23.7 A·MeV and120Sn +120Sn at 18.4 A·MeV were analyzed by means of an improved version of the kinematic coincidence method. The phase-space distributions prove that 3- (and possibly 4-) body events predominantly originate from a two-step mechanism and are compatible with the hypothesis of a binary deep-inelastic interaction followed by the further fissionlike decay of one (or both) of the primary fragments. The characteristics of the fission step — mass asymmetry, relative velocity, in-plane and out-of-plane angles — have been reconstructed for the 3-body events and indications are found that nonequilibrium effects at the end of the deep-inelastic phase may influence the fissionlike decay.

PULSE HEIGHT DEFECT OF ENERGETIC HEAVY IONS IN ION-IMPLANTED SI DETECTORS

Abstract The pulse height defect in ion-implanted silicon detectors for elastically scattered 93 Nb, 100 Mo, 116 Sn, 120 Sn and 129 Xe ions, at energies ranging from about 4 to 25 A MeV has been measured. The results are compared with two widely used parametrizations taken from the literature.

Response of ion implanted silicon detectors to fully stopped Au ions of 11.5 A MeV impinging along crystallographic directions

Abstract The kinetic energy of Au ions at 11.5 A MeV fully stopped in thick ion-implanted silicon detectors has been measured. The energy deposit presents features (peak broadening and splitting) which depend on the orientation of the impinging particle with respect to the silicon crystal axes and can be attributed to partial channeling. Implications of the observed effects on precise energy measurements of heavy ions are discussed.

Particle and light fragment emission in peripheral heavy ion collisions at Fermi energies

A systematic investigation of the average multiplicities of light charged particles and intermediate mass fragments emitted in peripheral and semiperipheral collisions is presented as a function of the beam energy, violence of the collision, and mass of the system. The data have been collected with the FIASCO setup in the reactions

Energy measurement and fragment identification using digital signals from partially depleted Si detectors

^{93}\mathrm{Nb}+^{93}\mathrm{Nb}

Yrast states in the doubly-odd nucleus100Tc

at

Electromagnetic decay of the 6+ isomer of102Rh

(17,23,30,38)A