P. Eudes

HINDAS A European Nuclear Data Program for Accelerator-Driven Systems

In the HINDAS program, nuclear data in the 20-2000 MeV range are evaluated by means of a combination of nuclear tmodels and well-selected intermediate- and high-energy experiments. A panoply of European accelerators is utilized to provide complete sets of experimental data for iron, lead and uranium over a large energy range. Nuclear model codes are being improved and validated against these new experimental data. This should result in enhanced ENDF-formatted data libraries up to 200 MeV, and cross sections for high-energy transport codes above 200 MeV. The impact of the new data libraries and high-energy models will be directly tested on some important parameters of an accelerator-driven system (ADS). Here, we report the recent progress of the various experimental and theoretical activities in HINDAS.

TEMPERATURE AND EXCITATION-ENERGY DETERMINATION IN PB-208+AU-197 REACTIONS AT 29 MEV/U

Abstract The violence of collisions induced by 208 Pb projectiles bombarding a 197 Au target at 29 MeV/u has been deduced by detecting the accompanying neutrons. With this filter, the temperature of the projectile-like fragments formed in very dissipative collisions has been extracted from the slope of the alpha-particle energy spectra. Temperatures of the order of 7 MeV are found, in very good agreement with the energy dissipations deduced from an energy balance assuming binary kinematics. The associated neutron multiplicities are well reproduced by a standard evaporation model, despite the dissociation into intermediate mass fragments observed in previous experiments. However, the measured temperatures exceed by a significant amount the limits predicted by theoretical calculations.

Hot-nuclei formation and decay: The Ar + Ag system at 50 and 70 MeVu

Abstract Hot-nuclei fusion properties have been studied for the Ar + Ag system at 50 and 70 MeV/u bombarding energy. The set up was very well suited to the analysis of sequential evaporation leading to an evaporation residue since the residue was detected in coincidence with all the corresponding light charged particles by use of a 4π- multidetector. An event by event analysis was performed in order to distinguish between particles evaporated from the fusion nucleus and others. It was possible to reconstruct the initial excitation energy of the fusion nucleus by adding the contributions of all the charged decay products and by estimating the neutron contribution. It was found that the excitation energy distributions obtained at 50 and 70 MeV/u were quite similar. Very large values are reached in both cases (∼ 600 MeV). This result means that the standard statistical decay observed at limited excitation is still observed for very hot nuclei. The corresponding temperatures were measured from the kinetic-energy spectra slopes. Slightly larger values were observed at 70 MeV/u. This result is consistent with a slightly smaller mass of the fusion nucleus obtained in this case. In a last aspect of the experiment where many particles events were analysed in the 4π set up, it turned out that the highest involved excitation energies can lead either to a multifragment emission, or to a standard sequential statistical decay.

Two-proton correlation function measured at very small relative momenta

Abstract Two-proton coincidences at very small relative momenta were measured in the reaction 129 Xe+ 48 Ti at 45 MeV/nucleon using the SPEG spectrometer at GANIL. From the experimental correlation function, a precise value of the lifetime τ 0 = (3.90±0.15) 10 −21 s is extracted. Applying three angular cuts on the correlation function, a signature of directional effects is observed and a value of the particle source velocity v s = (0.27±0.03)c is deduced in case of a sequential equilibrium emission.

Extended pulse shape discrimination capabilities using a CsI-BGO phoswich

Abstract An attractive concept of phoswich detector composed of CsI(Tl) and BGO crystals has been developed to detect and identify light charged isotopes up to Z = 3, with energies ranging from a few MeV/nucleon up to several hundred MeV/nucleon. This detector combines the phoswich technique with the intrinsic capabilities of pulse shape discrimination of the CsI(Tl).

INTERFEROMETRY MEASUREMENTS SELECTED BY NEUTRON CALORIMETRY

Abstract Two-proton correlation functions have been measured in the reaction 208 Pb+ 93 Nb at 29 MeV per nucleon at GANIL in the scattering chamber of ORION used as a neutron calorimeter. In the same experiment preequilibrium and equilibrium emissions are observed. Very strong effects are seen after centrality selection and directional cuts.

Cross Section Data and Kerma Coefficients at 95 MeV Neutrons for Medical Applications

Motivated by the need of data on neutron-induced reactions with biologically relevant materials, e.g., carbon and oxygen, we have constructed and installed the MEDLEY detector array at the neutron beam facility of the The Svedberg Laboratory in Uppsala. The central detection elements of MEDLEY are three-detector telescopes, consisting of two silicon detectors and a Csl crystal. To cover wide energy and angle ranges, we have mounted eight such telescopes at 20° intervals. We have used ΔE − ΔE − E techniques to obtain good particle identification for protons, deuterons, tritons, 3He and α particles over an energy range from a few MeV up to 100 MeV. To define the detector solid angle, plastic scintillators were employed to serve as active collimators. We have up to now measured double-differential cross sections of inclusive light-ion production induced by 95 MeV neutrons on carbon and oxygen. From these data production cross sections, as well as partial kerma coefficients, are being determined. We have found that especially the proton kerma coefficient for carbon is substantially larger than that of a recent evaluation, leading to a larger total kerma coefficient. The obtained data supports a trend observed for similar data at lower energies.

A Novel Fast Neutron Detector for Nuclear Data Measurements

Accelerator driven system will use a heavy element target such as lead. Many calculations are available to simulate high-energy spallation neutron induced reactions, but little data are available for comparison with the simulations. In order to constrain the simulation tools we have measured (n,Xn) double differential cross section on different targets at The Svedberg Laboratory, Uppsala, Sweden. For neutron energy above 40 MeV, we have developed a novel detector, CLODIA, based on proton recoil and drift chambers to determine neutron energy. CLODIA (Chamber for LOcalization with DrIft and Amplification) is able to track recoil protons with energy up to 90 MeV with spatial resolution of about one millimeter and a detection efficiency of 99% for each drift chamber. Using CLODIA coupled with the SCANDAL set-up, we have been able to measure double differential (n,Xn) cross section on lead and iron for incident neutron energy in the 40-95 MeV energy region.

SCANDAL - A Facility for Elastic Neutron Scattering Studies in the 50–130 MeV Range

Recently, a large number of applications involving high-energy (> 20 MeV) neutrons have become important. Examples are development of spallation sources, transmutation of nuclear waste, fast-neutron cancer therapy, as well as dose effects for airflight personnel and electronics failures due to cosmic-ray neutrons. Elastic neutron scattering plays a key role for the understanding of all these areas. The most important reason is that it allows a determination of the optical potential, which plays a decisive role in every microscopic calculation including neutrons in either the entrance or exit channel. In addition, the elastic cross section is also the largest of the individual partial cross sections contributing to the total cross section. A facility for detection of scattered neutrons in the energy interval 50–130 MeV, SCANDAL (SCAttered Nucleon Detection AssembLy), has recently been installed at the 20–180 MeV neutron beam facility of the The Svedberg Laboratory, Uppsala. It is primarily intended for studies of elastic neutron scattering, but can be used for the (n,p) t and (n,d) reaction experiments as well. The performance of the spectrometer is illustrated in measurements of the (n,p) and (n,n) reactions on 1H and 12 C at 96 MeV.