G. Viesti

Temperatures, barriers, and level densities of highly excited nuclei with A ≈ 160☆

Abstract From coincidence measurements between heavy residues, light particles, and γ -rays, the excitation excitation energy dependence of the temperatures, barriers, and nuclear level density parameters for nuclei with A ≈ 160 has been determined. The temperature increases with excitation energy in the range of 100 to 400 MeV consistently with a nuclear level density parameter a increasing from essentially a = A /8 to a = A /13. The emission barrier is lower than predicted by either spin dependent or temperature dependent theoretical calculations.

Measurement of 14 MeV neutron-induced prompt gamma-ray spectra from 15 elements found in cargo containers

Within the EURopean Illicit TRAfficking Countermeasures Kit (EURITRACK) project, the gamma-ray spectra produced in a series of materials by 14-MeV tagged-neutron beams have been collected in the inspection portal equipped with large volume NaI(Tl) detectors, in order to build a database of signatures for various elements: C, N, O, Na, Al, Si, Cl, K, Ca, Cr, Fe, Ni, Cu, Zn, Pb. The measured spectra have been compared with prediction from Monte Carlo simulations to verify the consistency of the relevant nuclear data inputs. This library of measured 14-MeV neutron-induced gamma-ray spectra is currently used in a data processing algorithm to unfold the energy spectra of the transported goods into elementary contributions, thus allowing material identification.

The EXPLODET project: advanced nuclear techniques for humanitarian demining

Thermal neutron activation and fast neutron scattering are known to be a useful tool to detect hidden explosives which present an elevated concentration of nitrogen and peculiar elemental ratio for light elements (C, N, O). Such characteristics can be suitably optimized to detect the small amount of explosives contained in anti-personnel mines (APM) disseminated in former war theatres. We report here on a research program aimed at defining a conceptual design of a field operated system for APM detection based on neutron induced reactions. ( 1999 Elsevier Science B.V. All rights reserved.

The response of a CsI(Tl) scintillator with photodiode readout to light particles and heavy ions

Abstract The response of a small (1 cm3) CsI(Tl) crystal coupled to a silicon photodiode to light particles and heavy ions has been investigated using proton, alpha and oxygen beams in the energy range 10–25 MeV/n. Pulse-height resolution of 1.2 and 2.9% [fwhm] have been measured for 98 MeV 4He and 278 MeV 16O. The use of CsI(Tl)-photodiode assembly in nuclear physics experiments with intermediate energy heavy-ions beams is envisaged

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.

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.

CsI(Tl)-photodiode detectors for γ-ray spectroscopy

Abstract We report on the performances of CsI(Tl)-photodiode detectors for γ-ray spectroscopy applications. Light output yield and energy resolution have been measured for different crystals and read-out configurations.

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.

Cross sections and mean angular momenta for 64Ni + 92,96Zr fusion near and below the Coulomb barrier

Abstract Fusion cross sections and mean angular momenta have been measured for 64 Ni + 92,96 Zr around the Coulomb barrier. The results are presented and systematically compared with the predictions of a schematic coupled-channel model, demonstrating the need of more refined calculations including higher-order coupling effects, and/or other degrees of freedom, beyond the usual inelastic and quasi-elastic transfer channels.

The light output and the detection efficiency of the liquid scintillator EJ-309

The light output response and the neutron and gamma-ray detection efficiency are determined for liquid scintillator EJ-309. The light output function is compared to those of previous studies. Experimental efficiency results are compared to predictions from GEANT4, MCNPX and PENELOPE Monte Carlo simulations. The differences associated with the use of different light output functions are discussed.