A. Lleres

Investigation of the performance of CsI(Tl) for charged particle identification by pulse-shape analysis

We have studied the possibility of particle discrimination by pulse-shape analysis in CsI(Tl) scintillator. In order to investigate the limitations of that process we have analysed the time response of the scintillator for different ions at various energies. It is found that for energies lower than 200 MeV the identification is limited to charges Z < 4. This work also gives an understanding of these limitations.

The particle detector array AMPHORA

Abstract A 4π-multidetector consisting of 140 CsI(Tl) detectors has been designed and built to be used for detecting and identifying either light charged particles (with a detection threshold of about 0.4 MeV/nucleon) and neutrons or light heavy ions and light charged particles, in the range of energies available at SARA (from 10 to 40 MeV/nucleon). The choice of the scintillator material is discussed and a description of the mechanical and electronic design is given. First experimental results obtained with this device are presented.

Cross talk and diaphony in neutron detectors

Abstract A neutron which enters a detector can be scattered into a neighbouring detector. If the neutron is registered in each detector the effect will be calle

Using the combination Csl(TI) and photodiode for identification and energy measurement of light particles

Abstract The two gated method is used with a CsI(Tl)+photodiode combination for the identification and the energy measurement of light particles.

Dynamical aspects of intermediate mass fragment emission in the reaction of 32S + Ag at 3 A-MeV

Abstract The emission of intermediate mass fragments (IMFs) has been studied using the 4π array, AMPHORA. The energy spectra, the angular distributions, the multiplicities, and the charge distributions are studied inclusively as well as in coincidence with projectile-like fragments (PLFs) and other fragments. The low-energy component of the inclusive fragment spectra can be reproduced by a statistical binary decay code GEMINI, although the calculated absolute cross sections are an order of magnitude smaller than the experimental IMF cross sections. At intermediate angles the fragments are dominated by IMFs with Z ≤ 10 both for inclusive and coincidence events and the energy spectra of the fragments show hard components which cannot be explained as statistical emission. For this non-equilibrium component strong azimuthal angular correlations are observed in IMF-PLF and IMF-IMF coincidence events. Both the energy spectra and the azimuthal angular correlations of the non-equilibrium component are well reproduced by an extended classical dynamical model.

Gas chambers for identification of charged particles in 4π systems

Abstract Gas ionization chambers of a special shape adapted for 4π detector systems are presented. Different anode wire configurations are discussed for three working gases: Ar + methane(10%), isobutane, and tetrafluoromethane.

Testing the level density of A ∼ 100 hot nuclei from evaporative charged-particle spectra

Abstract Alpha particles and protons emitted in the 32S + 74Ge reaction at E = 160, 210, 259, 335 and 435 MeV were measured in coincidence with evaporation residues. The average inverse level-density parameter 〈 K 〉 for hot evaporation residues with A ∼ 100 was obtained by comparing the slope of the charged-particle spectra with the predictions from a full statistical model calculation. Spectral shapes are well reproduced by calculations using the standard values 〈K〉 = 7.5 MeV , except for alpha particles at the highest bombarding energy, which corresponds to an excitation energy ϵ = 2.2 MeV/nucleon . The present results are compared with other experimental investigations in the A ∼ 100 and A ∼ 160 regions and with predictions from theoretical models. Difficulties in extracting the nuclear temperature from the slope of the particle spectra for A ∼ 100 are discussed.

Transfer and break-up reactions in the 30 A · MeV22Ne + 93Nb system

Abstract Peripheral interactions of the 22 Ne + 93 Nb system at 30 A· MeV incident energy have been investigated using the forward 48 CsI scintillators of the AMPHORA multidetector array for the detection of light charged particles at forward angles. In addition fragments have been identified near the grazing angle in 4 Si-CsI telescopes. It is found that the transfer probability remains large at this intermediate energy. The stripping of one or two nucleons from the projectile to the target and the pick-up of one nucleon have been clearly observed. Binary quasi-projectile break-up events involving emission of one α are dominant. Dissociation of the projectile into up to five products has also been observed. The production of fragments is deduced to result mainly from sequential decay of the primary fragments rather than from a direct break-up process. The yields of fragments, except for the lightest ones, have been reproduced in the framework of a random-walk model.

Effect of the detector response on measurements performed with heavy-ion 4π detectors

Abstract We discuss the effect of geometrical efficiency and detection energy thresholds of a typical heavy-ion 4π detector (AMPHORA at the ISN) on measurements at energies near 35 MeV/nucleon. The study is based on simulation data generated by two different models: a microscopic interaction code which describes central as well as peripheral collisions, and a statistical code that describes the emission of pre-equilibrium nucleons followed by evaporation from an equilibrated incomplete-fusion system. Two reactions are studied, 32 S+ 27 Al at 37.5 MeV/nucleon and 40 Ca+ 40 Ca at 35 MeV/nucleon. We have investigated the effect of the incomplete (and selective) detection of the charged particles on several variables (parallel momentum, multiplicities, charge distribution), momentum distribution variables and moments of the event-by-event charge distribution. The results show that the response of the detector severely distorts the variable distributions and that a selection is required to obtain a set of data that represents the original ensemble. Total detected charge ( Z P + Z T ) selection can give, depending on the system, an acceptable representation of some of the variables in central and semi-peripheral reactions but the effect of the detector depends strongly on the kinematics of the studied reaction. The optimum application of this selection appears to be associated to relatively light systems studied under conditions of inverse kinematics.

Gaseous ΔE-type phoswiches

Results are presented on the use of gaseous xenon as the ΔE stage of a phoswich scintillator detector. The timing characteristics of the xenon detector have been investigated and found to be suitable as either the fast or the slow component of a phoswich detector depending on the operating pressure of the xenon. A xenon-CsI(Tl) and a xenon-plastic phoswich have been built and tested. The xenon-plastic detector is expected to be more suitable for high energies. In addition to the ease of obtaining various thicknesses by adjusting the pressure, the excellent uniformity of a gaseous ΔE can provide an improved identification of heavy ions.