M. Morjean

The decay of primary products in binary highly damped 208Pb + 197Au collisions at 29 MeV/u☆

Abstract Events with fragment multiplicities up to eight have been detected with a large detector array in Pb + Au reactions at 29 MeV/u. All collisions show a binary character irrespective of a possible further disassembly of the two highly excited primary partners. For the most violent collisions, dissipative orbiting is observed as well as full energy damping corresponding to excitation energies as high as 6 MeV/u.

Hot nuclei in reactions induced by 475 MeV, 2 GeV 1H and 2 GeV 3He

Abstract Inclusive neutron multiplicity distributions have been measured for 475 MeV, 2 GeV proton- and 2 GeV 3 He-induced reactions on Ag, Au, Bi, U targets. There is general agreement between these multiplicity data and results of intranuclear cascade calculations. The results indicate a broad distribution of excitation energies with 10% of the events exceeding 500 MeV. For a thermalized nucleus this would translate into temperatures exceeding 5 MeV

Saturation of the thermal energy deposited in Au and Th nuclei by Ar projectiles between 27 and 77 MeV/u

Abstract Multiplicities of neutrons and light charged particles associated with central collisions have been measured in the energy range 27–77 MeV/u for the systems 40Ar+197Au, 232Th. The experiments demonstrate the occurrence of a saturation of the thermal energy deposited in the system around 650 MeV, corresponding to a constant internal temperature close to 5 MeV.

Approaching peripheral collisions in the reaction Ar+Au at 27.2 MeV/u by the associated neutron multiplicities☆

Abstract A 4π detector has been used to measure the neutron multiplicity associated with peripheral heavy ion reactions induced at 27.2 MeV/u. A strong correlation is observed between the number of emerging neutrons and the mass of the projectile-like-fragment. However, the large energy dissipation which is observed is still too small to support the idea of a pure massive transfer process.

Neck formation and decay in Pb + Au collisions at 29 MeV/u☆

Abstract Three fragment production has been studied in peripheral 208 Pb + 197 Au collisions at 29 MeV/u. The data suggests the formation and subsequent decay of necklike structures producing a small fragment emitted at mid-rapidity in between the two partners of a deep inelastic scattering. Data and trajectory calculations suggest also the existence of a competing process in which the neck is absorbed by one of the reactants, this latter decaying further by binary fission.

Complete energy damping in 29 MeV/nucleon Pb+Au two-body final-state reactions☆

Abstract Decay products emitted in highly dissipative Pb+Au reactions at 29 MeV/nucleon have been detected using a large area array. Multiplicities of fragments as large as 8 have been detected with a sizeable cross section. The m -fragment exit channels are fully compatible with the formation of a transient excited dinuclear system formed in damped collisions. The excitation energy function shows that fully damped collisions are achieved even for m = 2 indicating that heavy nuclei are able to sustain high excitation energy and end up as evaporation residues.

Nuclear disassembly time scales using space-time correlations

Abstract The lifetime, τ, with respect to multifragmentation of highly excited nuclei is deduced from the analysis of strongly damped Pb + Au collisions at 29 MeV/u. The method is based on the study of space-time correlations induced by “proximity” effects between fragments emitted by the two primary products of the reaction and gives the time between the reseparation of the two primary products and the subsequent multifragment decay of one partner. A lifetime significantly longer than the interaction time is found. It is compared with time scales corresponding to different types of dynamical instabilities which may be responsible for nuclear disassembly.

Long Fission Times of Super‐Heavy Compound Nuclei

The blocking technique in single crystals is a direct method to investigate the presence of long fission time components. With a lead beam impinging on a germanium single crystal, we tried to produce compound nuclei (CN) with atomic number Z = 114 at high excitation energy. Blocking patterns for reaction products are reconstructed with position sensitive detectors at 20 ° relative to the beam direction. The Z and the energies of all products are measured with DeltaE-E telescopes of the 4pi INDRA array, so that all reaction channels are unambiguously identified. With this setup, we can reach long fission times (>10−18 s) that can be associated with CN fissions. However, in contrast to previous experiments in which such long fission times could be measured for Z = 120 and 124, no hint of long lifetimes within our sensitivity limit for Z = 114 was observed, which may be due to the neutron deficiency of the formed isotopes.This paper generalizes the classification in a paper of Dimitrov and Penkov of Borel subalgebras of gl_infty. Root-reductive Lie algebras are direct limits of finite-dimensional reductive Lie algebras along inclusions preserving the root spaces with respect to nested Cartan subalgebras. A Borel subalgebra of a root-reductive Lie algebra is by definition a maximal locally solvable subalgebra. The main general result of this paper is that a Borel subalgebra of an infinite-dimensional indecomposable root-reductive Lie algebra is the simultaneous stabilizer of a certain type of generalized flag in each of the standard representations. For the three infinite-dimensional simple root-reductive Lie algebras more precise results are obtained. The map sending a maximal closed (isotropic) generalized flag in the standard representation to its stabilizer hits Borel subalgebras, yielding a bijection in the cases of sl_infty and sp_infty; in the case of so_infty the fibers are of size one and two. A description is given of a nice class of toral subalgebras contained in any Borel subalgebra. Finally, certain Borel subalgebras of a general root-reductive Lie algebra are seen to correspond bijectively with Borel subalgebras of the commutator subalgebra, which are understood in terms of the special cases.

Damped reaction dynamics in 197Au + 208Pb collisions at 29 MeV/nucleon

Abstract Velocity and angular distributions of neutrons from the reaction 197Au + 208Pb at E A =29 MeV were measured in coincidence with charged reaction products. The neutron emission pattern is found to erolve smoothly with atomic number and energy of the coincident fragments, up to the highest degrees of energy dissipation observed. The velocity distribution of neutrons in coincidence with any type of fragment is essentially bimodal and can be understood in terms of sequential emission from fully accelerated primary projectile-like and target-like fragments. A relatively weak nonequilibrium neutron component is also observed. Neutron multiplicities and spectral slope parameters, as well as the deduced emitter velocities indicate consistently that, even for highly dissipative collisions associated with intermediate-mass fragments, the average damping of kinetic energy available in the entrance channel is incomplete.

Hot composite systems with A>200 and T>6 MeV

Neutron multiplicities have been measured in coincidence with the light charged particles evaporated in the backward direction for the reaction 84Kr+197Au at 32 MeV/u. A method id presented which makes possible an evaluation of the recoil velocity, excitation energy and temperature of hot and thermalized heavy composite systems formed for different impact parameters. Temperatures larger than 6 MeV are found for the most dissipative collisions.