M. Lunardon

The EURITRACK project: development of a tagged neutron inspection system for cargo containers

The EURopean Illicit TRAfficing Countermeasures Kit project is part of the 6th European Union Framework Program, and aims at developing a neutron inspection system for detecting threat materials (explosives, drugs, etc.) in cargo containers. Neutron interaction in the container produces specific gamma-rays used to determine the chemical composition of the inspected material. An associated particle sealed tube neutron generator is developed to allow precise location of the interaction point by direction and time-of-flight measurements of the neutrons tagged by alpha-particles. The EURITRACK project consists in developing: a transportable deuterium-tritium neutron generator including a position sensitive alpha detector (8×8 matrix of YAP:Ce crystals coupled to a multi-anode photomultiplier), fast neutron and gamma-ray detectors, front-end electronics to perform coincidence and spectroscopic measurements, and an integrated software which manages neutron generator and detectors positioning, data acquisition and analysis. Hardware components have been developed and tested by the consortium partners. Current status of this work and provisional performances of the system assessed by Monte Carlo calculations are presented.

The 8/spl pi/LP project: A 4/spl pi/ light charged particle detection array at LNL

A 4/spl pi/ detection system sensitive to light charged particles is being developed at the Laboratori Nazionali di Legnaro (LNL) for the study of the reaction mechanisms produced in heavy ion collisions at energies up to 20 AMeV. The 8/spl pi/LP apparatus is a telescope assembly characterized by large solid angle (90% of 4/spl pi/) and high granularity (262 modules). Particle identification at low energy is obtained by combining /spl Delta/E-E, TOF and PSD techniques. Each telescope is made of a 300 /spl mu/m passivated silicon detector and a 15 mm (or 5 mm) CsI(Tl) crystal with photodiode readout. Thresholds for particle identification range from 1 MeV for protons and 3 MeV for alpha particles to about 2-3 AMeV for C ions. A low-cost trigger and readout bus system has been developed to cope with the large number of parameters and the high counting rate. The system will be fully operational for experiments in the summer of 1997.

Rotational quenching of the N = 72 shell gap and the role of the νi132 intruder orbital in 132Nd

Abstract Rotational structures in 132Nd have been investigated via the 104 Pd ( 32 S ,2p2n) reaction at 160 MeV. Four highly-deformed bands have been observed, out of which three have been linked to the normal-deformed states. Two of them are signature partners. A mixing at high spin is observed between levels of one highly-deformed band and the ground-state band allowing for an unambiguous assignment of the spins and parity of that band. The present data brings new evidence on the role of the N = 72 shell gap to the stabilization of the highly-deformed minimum in the A = 130 mass region and on the importance of the νi 13 2 intruder orbital in the structure of the highly-deformed bands.

The use of tagged 14 MeV neutron beams for the detection of illicit materials in land and sea transportation

A prototype of portable sealed neutron generator has been recently built to deliver 14 MeV neutron beams tagged by a YAP:Ce alpha-particle detector in order to produce simultaneously multiple neutron beams to irradiate complex samples. Preliminary tests performed at the Institute Ruder Boskovic on the detection of explosives and fissile materials in maritime containers are presented

Study of the Mo-Ba partition in 252Cf spontaneous fission

Abstract: Measurements of fission fragment yields and neutron multiplicities have been carried out for the Mo-Ba fragment pairs in the spontaneous fission of 252Cf, using the γ-ray spectroscopy technique to analyze γ-γ-γ coincidence data. Prompt γ -ray multiplicities were also measured as a function of the number of neutrons emitted in the fission process leading to the Mo-Ba partition. We do not observe the enhancement in the yields of events with high neutron emission multiplicity (νn > 7) that has been associated to a second fission mode leading to the production of hyperdeformed Ba fragments, as reported in some earlier studies. The average γ-ray multiplicity is found to be rather weakly dependent on the number of neutrons emitted in the fission process.

Alpha particle emission, incomplete fusion and population of high-spin states in the reaction 120 MeV 19F + 181Ta

Abstract The reaction 120 MeV 19 F + 181 Ta has been studied by charged particle-γ-ray coincidence techniques. An incomplete fusion component has been identified in coincidence with 192,191 Hg residues which are populated in the αxn channels. Evidence has been found that the feeding of high spin states in final residues is enhanced when the coincidence is required with alpha particles emitted at forward angles, where the incomplete fusion component dominates.

INFLUENCE OF THE ENTRANCE CHANNEL IN THE FUSION REACTION 318 MEV 74GE+74GE

Abstract Entrance channel effects in the fusion of heavy ions have been studied by using the 74Ge+74Ge reaction at 318 MeV. The population of the yrast superdeformed band in 144Gd shows an increase when compared with the results obtained in the more asymmetric 48Ti+100Mo reaction at 215 MeV. The relative yields of the different evaporation residues produced in the 74Ge+74Ge and in the 48Ti+100Mo reactions are very similar, with the exception of the 145,144Gd residual nuclei (3n and 4n decay channels) which are populated with a larger yield in the symmetric reaction. Statistical model calculations reproduce qualitatively such effect if a fission delay is explicitly taken into account. Effects related to fusion barrier fluctuations seem to be important in determining the spin distributions of the compound nucleus. The spectra of the high energy γ-rays emitted in the 74Ge+74Ge reaction have been measured as a function of the γ-ray multiplicity as well as in coincidence with selected evaporation residues. They are reproduced by standard statistical model calculations with GDR parameters taken from systematics, demonstrating that, in agreement with dynamical model prediction, the emission of γ-rays from the dinucleus formed in the earlier stage of the collision is unimportant.

Fission dynamics with the 4π detector 8πLP

A 4π light charged particle spectrometer, named 8πLP, is in operation at the Laboratori Nazionali di Legnaro (Italy) for the study of the reaction mechanisms produced in low-energy heavy-ion reactions. The spectrometer has recently been used in a study of fission dynamics that involves the detection of light charged particles in the fission and evaporation residue channel in a system of intermediate fissility, as well as in a study of multinucleon transfer to heavy target. Data on the system 240 MeV 32S + 100Mo are presented. Dynamical effects extracted as a consequence of the comparison of the data to the statistical model calculations are discussed.

CsI(Tl)-photodiode detectors for /spl gamma/-ray spectroscopy

We report on the performances of CsI(Tl)-photodiode detectors for /spl gamma/-ray spectroscopy applications. Photoelectron yield and energy resolution have been measured for different crystals and read-out configurations.

Excitation energy deposition in 209Bi(α,α′) reactions at 240 MeV

The excitation energy deposited in the reaction 209 Bi(α,α′) at 240 MeV has been determined using the TAMU Neutron Ball. The reconstructed average excitation energies as a function of the beam energy losses show that not all of the missing beam energy is usually deposited as thermal excitation in the target nucleus. Requiring an additional coincidence with a light charged particle or fission fragment leads to selection of a significant higher average excitation energy. This effect is extrapolated to explore results of previous GDR decay measurements in the case of a 208 Pb target.