Search

A recent renascent interest in energetic proton-induced production of neutrons originates largely from the inception of projects for target stations of intense spallation neutron sources, like the planned European Spallation Source (ESS), accelerator-driven nuclear reactors, nuclear waste transmutation, and also from the application for radioactive beams. In the framework of such a neutron production, of major importance is the search for ways for the most efficient conversion of the primary beam energy into neutron production. Although the issue has been quite successfully addressed experimentally by varying the incident proton energy for various target materials and by covering a huge collection of different target geometries --providing an exhaustive matrix of benchmark data-- the ultimate challenge is to increase the predictive power of transport codes currently on the market. To scrutinize these codes, calculations of reaction cross-sections, hadronic interaction lengths, average neutron multiplicities, neutron multiplicity and energy distributions, and the development of hadronic showers are confronted with recent experimental data of the NESSI collaboration. Program packages like HERMES, LCS or MCNPX master the prevision of reaction cross-sections, hadronic interaction lengths, averaged neutron multiplicities and neutron multiplicity distributions in thick and thin targets for a wide spectrum of incident proton energies, geometrical shapes and materials of the target generally within less than 10% deviation, while production cross-section measurements for light charged particles on thin targets point out that appreciable distinctions exist within these models. [ABSTRACT FROM AUTHOR]

Events with 2, 3 and 4 heavy fragments (A≥20) detected in the reactionsMo +Mo at 18.7, 23.7 A·MeV andSn +Sn at 18.4 A·MeV were analyzed by means of an improved version of the kinematic coincidence method. The phase-space distributions prove that 3- (and possibly 4-) body events predominantly originate from a two-step mechanism and are compatible with the hypothesis of a binary deep-inelastic interaction followed by the further fissionlike decay of one (or both) of the primary fragments. The characteristics of the fission step - mass asymmetry, relative velocity, in-plane and out-of-plane angles - have been reconstructed for the 3-body events and indications are found that nonequilibrium effects at the end of the deep-inelastic phase may influence the fissionlike decay. [ABSTRACT FROM AUTHOR]

Events with 2, 3 and 4 heavy-fragments ( A≧20) have been detected in the reactionsMo+Mo at E/A =18.7, 23.7 MeV andSn+Sn at E/A=18.4 MeV. The experiments were performed with an array of 12 detectors which together covered a large fraction of the forward hemisphere and allowed a high detection efficiency for these events. Masses and energies of all fragments have been reconstructed by means of an improved version of the kinematic coincidence method. The probabilities P and P of producing 3- and 4-body events were found to depend mainly on the dissipated energy rather than on the bombarding energy, thus indicating that their origin lies more in the decay properties of the excited fragments than in the dynamics of the interaction. Emission of light particles from the composite system is shown to become more relevant with increasing bombarding energy and may explain the drop of the P and P curves at high energy losses. Small deviations of the P and P curves at 23.7 A · MeV from those at lower bombarding energies were used to estimate the amount of a possible pre-equilibrium light particle emission as a function of impact parameter. [ABSTRACT FROM AUTHOR]

The directional dependence of the measured correlationfunction of two particles emitted from an evaporative source is shown to offer a weak sensitivity to the source lifetime. From the agreement with evaporative calculations, one cannot rule out a sequential emission. [ABSTRACT FROM AUTHOR]

Atomic number and energy of fragments emitted in theKr+Nb reaction at 34.5 MeV/u have been measured in the angular range [4∘,14∘]. It is found that most of the detected fragments, particularly those with charge far from the projectile, have an almost constant velocity corresponding to 80-90 % of the projectile velocity. [ABSTRACT FROM AUTHOR]

By on-line mass separation and subsequent gamma and electron decay-spectroscopy at very low energy, two new isomers,Cs (T=6.3 ±0.3 seconds) andBa (T=1.9±0.2 seconds) have been identified. [ABSTRACT FROM AUTHOR]