A. Moroni

Position sensitive and Bragg curve spectroscopy detector system

Abstract A heavy ion gas detector system consisting of a Bragg-curve spectroscopy ionization chamber for particle identification and a multiwire proportional chamber as position sensitive fast trigger device is described. The Bragg IC has been tested with several beams up to Z = 36 to investigate some aspects of the BCS method. Results are reported on energy resolution and linearity, Z resolving power and mass sensitivity. The energy resolution is well below 1%. The Bragg-peak amplitude is fairly independent of the energy in a wide energy range and single elements are identified up to Z = 38 with a resolving power Z / ΔZ − 50-80. Isotope identification by range measurement is limited by the straggling in the ionization process and the mass resolving power is M / ΔM ∼ 20–26 for S and Si isotopes. The MWPC allows subnanosecond time resolution and position identification along the in-plane coordinate within ±0.5 mm.

Evidence of the spectator role of unpaired nucleons of the target nucleus in (p, α) reactions

In this paper the spectra ofα particles emitted in (p, α) reactions induced by ∼24 MeV protons on adjacent target nuclei, onemagic, with a magic neutron or proton shell and the othernear magic, with one more nucleon outside the shell, are measured and compared.The nuclei investigated are90, 91Zr,122Sn,123Sb,142, 143, 144Nd,208Pb and209Bi. The weak population of low energy levels of the residual nucleus from thenear magic target nucleus and the excitation of homologous states in the residual nuclei from neighbouringmagic andnear magic target nuclei convincingly prove that in most of the cases the unpaired nucleon outside the magic shell acts as a spectator in the process.The implications of these experimental findings are discussed.

Hybrid low-noise charge preamplifiers for heavy-ion detectors

Abstract The characteristics of hybrid low-noise general-purpose preamplifiers are described. The basic performances are reported. They have been used in connection with ionization chambers, large-area Si detectors and photodiodes.

Comparison of the BGO and CsI(Tl) energy resolutions for p and α

Abstract Energy resolution and linearity of a BGO-photodiode have been measured for 20–40 MeV p and 14–25 MeV α. Comparisons are made to BGO and CsI(Tl) read by photomultipliers.

A remotely controlled four-channel spectroscopy amplifier

Abstract A four channel spectroscopy amplifier is described where coarse and fine amplification gains can be remotely adjusted using high speed CAENET serial line controllers.

Pion induced fission

Fissilities induced by the absorption ofπ− at rest in nuclei ranging from rare earth region to Uranium are evaluated by means of the Exciton Model. The theoretical results satisfactorily reproduce the experimental findings provided the ratioaf/an is greater than unity and equal to 1.1.

Discrete γ-rays in the reactions of 143 MeV32S with58Ni

The reactions induced by 143 MeV32S on58Ni have been studied detecting discrete γ-rays in coincidence with projectile-like fragments (PLF). Information on PLF excitation probability and sequential decay of target-like fragments (TLF) has been obtained. For the28Si+62Zn outgoing channel at small energy loss (¦Q¦<20 MeV), both PLF and TLF data indicate that thermal equilibrium is not attained. The hypothesis of an equal excitation energy partition between the two reaction fragments does not describe properly experimental TLF data. A dependence of PLF excitation probability on the outgoing channel is found for the two final channels32S+58Ni and28Si+62Zn. The values of the spin alignment parameterPzz, derived for PLF and TLF from measurements ofγ-rays anisotropy, are in disagreement with the expectations of the transport theory for dissipative collisions.

Simple observables sensitive to the transition from sequential decay to simultaneous break-up of nuclear systems

SummaryThe relative velocities and relative angles between massive fragments emitted in heavy-ion nuclear reactions have been studied as a tool to discriminate between two extreme break-up mechanisms in the intermediate energy regime. Considering a chain of sequential decays and a simultaneous break-up of an excited nuclear system, we show that the behaviour of the event distribution in the space of relative velocities and angles depends on the fragmentation mechanism, indicating the possibility of observing the transition from the binary-decay mechanism to the simultaneous cracking of nuclear systems.

A VME pressure control system for gas-filled detectors

Abstract A gas pressure regulation system has been constructed for a large number of gas-filled detectors operating with flowing gas. The system uses commercial valves and sensors and is controlled by a CPU operating in a VME environment. The pressure operating values are set through the console. Other useful parameters such as temperature and bias voltage are controlled. Pressure irregularities due to temperature changes are compensated. The performances of the system are satisfactory.

Bragg-curve spectroscopy at high rates

Abstract The performance of a Bragg ionization chamber has been investigated as a function of the counting rate with ≈ 5 MeV/amu 32 S beams: up to ≈ 20 kHz the energy resolution is below 0.9% and the Z resolving power is more than 50.