Energy and angular momentum sharing in dissipative collisions

Primary and secondary masses of heavy reaction products have been deduced from kinematics and E-ToF measurements, respectively, for the direct and reverse collisions of 93Nb and 116Sn at 25 AMeV. Light charged particles have also been measured in coincidence with the heavy fragments. Direct experimental evidence of the correlation of energy-sharing with net mass transfer has been found using the information from both the heavy fragments and the light charged particles. The ratio of Hydrogen and Helium multiplicities points to a further correlation of angular momentum sharing with net mass transfer.Comment: 21 pages, 20 figures. Submitted to European Physics Journal

Monitoring Of 14 Mev Neutrons

Long-lived fission products and minor actinides produced in nuclear power plants are the most radiotoxic nuclear wastes. They can be transmuted into stable nuclei or into nuclei with shorter lifetime thanks to the so-called Accelerator Driven Systems (ADS), consisting of the coupling of an intense high energy proton beam, a spallation target and a sub-critical reactor core. For safety reasons, an on-line and robust measurement of the reactivity during loading and power operation is mandatory. The investigation of the relationship between the current of the accelerator and the power level (or neutron flux) of the reactor appears to be powerful, any change in reactivity being accessible through the measurement of the current and the flux. Such a relationship will be studied in an experiment to be performed at the YALINA facility (JIPNR Sosny - Belarus) in the framework of the EUROTRANS IP (6$^{th}$ FP). At this installation, 14 MeV neutrons are produced in T(d,n)$^{4}$He reactions by a deuteron beam impinging on a TiT target. Due to the tritium consumption over time, the intensity of the deuteron beam cannot be used for the monitoring of the neutron beam. The source neutron yield itself has to be accessed. This contribution describes the performance of a three-element silicon telescope dedicate

Limitation of energy deposition in classical N body dynamics

Energy transfers in collisions between classical clusters are studied with Classical N Body Dynamics calculations for different entrance channels. It is shown that the energy per particle transferred to thermalised classical clusters does not exceed the energy of the least bound particle in the cluster in its ``ground state''. This limitation is observed during the whole time of the collision, except for the heaviest system.Comment: 13 pages, 15 figures, 1 tabl

Dynamical effects in multifragmentation at intermediate energies

The fragmentation of the quasi-projectile is studied with the INDRA multidetector for different colliding systems and incident energies in the Fermi energy range. Different experimental observations show that a large part of the fragmentation is not compatible with the statistical fragmentation of a fully equilibrated nucleus. The study of internal correlations is a powerful tool, especially to evidence entrance channel effects. These effects have to be included in the theoretical descriptions of nuclear multifragmentation.Comment: 13 pages, 26 figures, submitted to Physical Review

Angular momentum sharing in dissipative collisions

Light charged particles emitted by the projectile-like fragment were measured in the direct and reverse collision of $^{93}$Nb and $^{116}$Sn at 25 AMeV. The experimental multiplicities of Hydrogen and Helium particles as a function of the primary mass of the emitting fragment show evidence for a correlation with net mass transfer. The ratio of Hydrogen and Helium multiplicities points to a dependence of the angular momentum sharing on the net mass transfer.Comment: 8 pages, 2 figure

Correlations in Nuclear Arrhenius-Type Plots

Arrhenius-type plots for multifragmentation process, defined as the transverse energy dependence of the single-fragment emission-probability, -ln(p_{b}) vs 1/sqrt(E_{t}), have been studied by examining the relationship of the parameters p_{b} and E_{t} to the intermediate-mass fragment multiplicity . The linearity of these plots reflects the correlation of the fragment multiplicity with the transverse energy. These plots may not provide thermal scaling information about fragment production as previously suggested.Comment: 12 pages, Latex, 3 Postscript figures include

Evidence for Spinodal Decomposition in Nuclear Multifragmentation

Multifragmentation of a ``fused system'' was observed for central collisions between 32 MeV/nucleon 129Xe and natSn. Most of the resulting charged products were well identified thanks to the high performances of the INDRA 4pi array. Experimental higher-order charge correlations for fragments show a weak but non ambiguous enhancement of events with nearly equal-sized fragments. Supported by dynamical calculations in which spinodal decomposition is simulated, this observed enhancement is interpreted as a ``fossil'' signal of spinodal instabilities in finite nuclear systems.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Letter

Response of CsI(Tl) scintillators over a large range in energy and atomic number of ions (Part I): recombination and delta -- electrons

A simple formalism describing the light response of CsI(Tl) to heavy ions, which quantifies the luminescence and the quenching in terms of the competition between radiative transitions following the carrier trapping at the Tl activator sites and the electron-hole recombination, is proposed. The effect of the delta rays on the scintillation efficiency is for the first time quantitatively included in a fully consistent way. The light output expression depends on four parameters determined by a procedure of global fit to experimental data.Comment: 28 pages, 6 figures, submitted to Nucl. Inst. Meth.

A Novel Fast Neutron Detector For Nuclear Data Measurements

International audienceAccelerator 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