D. Fabris

Light output of EJ228 scintillation neutron detectors.

The light output of neutron detectors based on the plastic scintillator EJ228 is studied as a function of neutron energy using a time tagged (252)Cf source. Calibration of the light output scale is performed by fitting the experimental distribution of Compton scattering events of photons from a (22)Na source with a response function obtained by Gaussian smearing of the predicted line-shape. The light output curve as well as the pulse height resolution for the EJ228 scintillators is very close (within 5%) to those recently reported for NE213 type organic liquid scintillators.

Effects of soil moisture on the detection of buried explosives by radiative neutron capture

Abstract The effect of soil moisture on the sensitivity for detecting buried landmines by neutron capture reactions has been experimentally investigated. An explosive simulant melamine sample has been placed at different depths in soil having different water contents. In dry soil it is found that the decrease of counting rate by increasing the depth follows the decrease of the average solid angles. In the case of soil with higher water content, an extra yield of prompt gamma-rays following thermal neutron capture in nitrogen is evidenced due to the extra moderation provided by the presence of additional hydrogen nuclei.

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.

The parallel grid avalanche counter

Abstract Prototypes of parallel grid avalanche counter (PGAC) to be used as transmission time detector in heavy ion experiments, have been studied. The PGACs timing properties were investigated using α-particles and fission fragments as a function of the electrodes grid mesh. Standard parallel plate avalanche counters have been used for comparisons sake. Time resolution δt = 200−300ps (fwhm) was obtained using 45 lines per inch mesh grid electrodes with fission fragments.

Experimental optimisation of a moderated 252Cf source for land mine detection

Abstract A moderated 252 Cf source to be used for the detection of buried land mines has been experimentally characterised. The moderating structure was obtained by using an inner sphere of Pb embedded in a high-density polyethylene (HDPe) brick assembly. The number of capture events in a Cd sample placed outside the structure was used, by varying the dimensions of the brick assembly, to determine the best moderator geometry. Furthermore, the detection of land mines by neutron capture reaction on nitrogen nuclei contained in the explosive was simulated by in field measurements placing the Cd sample at different depths in the soil. The obtained results are compared with predictions from Monte Carlo calculations.

The ALICE Silicon Pixel Detector: readiness for the first proton beam

The Silicon Pixel Detector (SPD) is the innermost element of the ALICE Inner Tracking System (ITS). The SPD consists of two barrel layers of hybrid silicon pixels surrounding the beam pipe with a total of ≈ 107 pixel cells. The SPD features a very low material budget, a 99.9% efficient bidimensional digital response, a 12 μm spatial precision in the bending plane (r) and a prompt signal as input to the L0 trigger. The SPD commissioning in the ALICE experimental area is well advanced and it includes calibration runs with internal pulse and cosmic ray runs. In this contribution the commissioning of the SPD is reviewed and the first results from runs with cosmic rays and circulating proton beams are presented.

A compact gas detector for heavy ion identification

Abstract A prototype ionization chamber coupled to a parallel grid avalanche counter, working in the same gas volume has been built. Subnanosecond time resolution and δE / E ∼ 1% have been obtained with 5.48 MeV α-particles.

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.