J.B. Viano

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.

Fast subcritical hybrid reactors for energy production: evolution of physical parameters and induced radiotoxicities

Abstract We have performed detailed Monte Carlo simulations of different subcritical fast hybrid reactor fuel configurations leading to the possible use of these devices as energy generators. The method is based on the coupling between a validated neutron transport code and a mathematical solution of the equations describing the time evolution of the neutron spectrum and mean cross-section during the reactor operation. We have optimized the geometrical and operational characteristics of reactors based on 232 Th / 233 U and nat U/Pu oxide fuels and simulated their operation over 20 fuel cycles (200 years of energy generation). Quantitative results are presented for the inventories, waste production and induced radiotoxicities under alternative scenarios of fuel reprocessing. The possible paths to start a fuel cycle based on thorium are studied, identifying the use of highly enriched uranium or plutonium from PWR spent fuel as options to start a fuel cycle which tends asymptotically towards 232 Th / 233 U . The comparison between the simulated hybrid systems and the existing PWR reactors indicate significant reductions of the total radiotoxicity for fuel cycles based on thorium and fuel reprocessing which include the minor actinides, as well as plutonium and uranium separation.

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.

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.

Fragmentation and massive transfer in (semi)peripheral collisions via the 35A MeV system

Peripheral and (semi)peripheral collisions of with at 35A MeV have been studied in the environment of the -detector AMPHORA. These classes of collisions were selected by using as a trigger (Z = 3 - 11) fragments detected in the vicinity of the grazing angle with energies higher than the ones corresponding to half the velocity of the beam. The inclusive data indicate the clear signature of projectile fragmentation. An analysis of momentum distributions leads to values of in agreement with the fragmentation model of Goldhaber. The fragment data (momentum distribution widths and isotopic yields) are also satisfactorily described by the cluster model of Friedman. Exclusive data are focused on measurements involving fragments emitted at forward angles in coincidence with a light charged particle (LCP) emitted at backward angles (and at forward angles or not). Analysis of their associated LCP multiplicities is consistent with a massive transfer mechanism via a two-body final state. Comparison with the predictions of a statistical model code (CASCADE) reveals an energy and angular momentum deposition in the target-like nuclei at values up to 2A MeV and respectively involving a significant emission of pre-equilibrium particles at an early stage of these (semi)peripheral collisions.