[en] We have measured two-fragment reduced-velocity correlation functions of the intermediate mass fragments (IMF: 3 ≤ Z ≤ 7) produced in multifragment final states for the Kr + Nb system (E/A = 35, 45, 55, 65, and 75 MeV). From the measured correlation functions we extract mean IMF emission lifetimes (τ) which are observed to decrease from τ ∼ 400 fm/c at E/A = 35 MeV to τ ∼ 125 fm/c at E/A = 55 MeV. For beam energies in excess of E/A 55 MeV, no further decrease in τ is observed, indicating a possible saturation of the mean emission lifetime for IMF produced in multifragment exit channels

[en] The authors have measured two-fragment reduced-velocity correlation functions of the intermediate mass fragments (IMF: 3 ≤ Z ≤ 7) produced in multifragment final states for the Kr + Nb system (E/A = 35, 45, 55, 65 and 75 MeV). From the measured correlation functions they extract mean IMF emission lifetimes (τ) which are observed to decrease from (τ) ∼ 400 fm/c at E/A = 35 MeV to τ ∼ 125 fm/c at E/a = 55 MeV. For beam energies in excess of E/A = 55 MeV, no further decrease in τ is observed, indicating a possible saturation of the mean emission lifetime for IMF produced in multifragment exit channels

[en] Multifragment azimuthal correlation functions have been measured as a function of beam energy and impact parameter for the Ar+Sc system (E/A = 35 to 115 MeV). The observed azimuthal correlation functions - which do not require corrections of dispersion of the reaction plane - exhibit strong asymmetries which are dependent on impact parameter and beam energy. New results for high-order correlations will be presented

[en] The strength of the final-state interactions between emitted particles depends on the spectrum of time delays between their emissions. Measured correlation functions reflect these interactions, and therefore time-scale information can be obtained by comparisons to associated reaction simulation calculations. We illustrate the sensitivity of the method to the emitter lifetime as well as the attention to several of the details needed for its effective use. Application to one set of data is shown

[en] In heavy-ion induced nuclear reactions one can produce transient systems with excitation energies up to 5 MeV per nucleon and spins up to ≅100 ℎ. The equilibrium statistical model can predict the mean lifetime for particle emission from moderately hot nuclei provided they are completely thermalized. However, as the excitation energy is increased, one expects to reach a situation of incomplete equilibration and hence a breakdown of the simplest equilibrium model. Determinations of the lifetime for (or intervals between) particle or fragment emissions can be useful both for testing the equilibrium model at low temperatures as well as for characterizing pre-equilibrium emission from partially thermalized nuclei. The net effect is best demonstrated by means of a correlation function, which can be interpreted by comparison to a reaction simulation. By such comparisons one can characterize the mean time intervals between emissions. The simulation programs MENEKA and COULGAN have been written for this purpose; they are Monte Carlo programs based on the following elements: a) Particles are emitted from the surface of an excited nucleus with a distribution of orbital angular momenta. b) Emission energies of the particles are chosen to reproduce experimental measurements or theoretical calculations. c) The distribution of time delays between particle emissions is given by exponential decay laws. d) A three-body trajectory is followed for the two particles and for the recoil nucleus. e) An event is accepted as a valid coincidence if the particle pair satisfies experimental requirements of detector thresholds and geometry. Particle trajectories are calculated numerically using time steps that are controlled by the requirement for energy conservation. An ancillary program SHOWTRAJ can be used to display and study trajectories event by event. (orig.)

[en] Nuclear reactions often proceed via fusion of projectile and target into a thermalized compound nucleus. For hot compound nuclei of temperature ≅1-5 MeV one expects that a chain of particles (neutrons, protons, alphas ...) will be evaporated with a variety of time intervals of ≅10^-22-10^-20 s. The determination of these emission times is a major challenge for nuclear physicists. Such time intervals are too short to measure directly, but they do lead to final-state interactions between charged-particle pairs due to their mutual Coulomb repulsions. Therefore, one expects correlations between the charged-particle paris that depend on their velocities and separation distances at birth, i.e. the flight distance of the first particle before birth of the second. The KALLIOPI program is a reaction simulation designed to predict the particle-particle correlations as a function of predicted or assumed values of the mean emission times. By comparison of the simulated results to experimental data one can test the basic predictions of decay rates for particle ejection from a hot nuclear emitter. (orig.)

[en] We use trajectory calculations to analyze small-angle particle-particle correlations for three typical situations: ⁴⁰Ar+¹⁹⁷Au (E/A=60 MeV)→²H-²H pairs and ¹H-¹H pairs, ²⁰Ne+⁵⁹Cu (E/A=30 MeV)→n-n pairs. For the ²H-²H pairs our analysis of the gentle featureless anticorrelations suggests that the major driving force is Coulomb repulsion after a range of average time delays from ∼5x10^-21 s for the ²H pairs of lower energy to ∼10^-22 s for the ²H pairs of higher energy. Simulations are used to illustrate the separate dominance of source size and lifetime in the space-time extent of the emitter. For lifetimes ≤10^-22 s the emitter size dominates; for longer lifetimes the time delays become predominant. The peaks at ∼20 MeV/c in the correlation functions for ¹H-¹H pairs can be accounted for by diproton ejection which decays into protons with a Q value of ∼0.35 MeV and a decay width of ∼1 MeV (or a meanlife of 6x10^-22 s). The positive correlations between neutron pairs can be accounted for by dineutron ejection which decays into neutrons with a near zero Q value and a decay width of ∼0.25 MeV (or a meanlife of ∼2x10^-21 s). If these diproton and dineutron clusters do indeed have a metastable existence, then one should reexamine the notion that their associated small-angle correlations reflect the space-time extent of the emission source

[en] Complete two-fragment velocity systematics have been measured over the entire range of fragmentation products for the system ⁵⁶Fe +¹⁹⁷Au at 50 and 100 MeV per nucleon. Fragment emission lifetimes are estimated from the reduced velocity (V_rel/ √Z₁+Z₂ ) correlation functions by a direct comparison with results from a classical three-body trajectory calculation. Furthermore, we examine the validity of the reduced velocity, V_red, as a scaling parameter for constructing mixed-fragment (Z₁≠Z₂) correlation functions over the full measured range (5≤Z_i,j≤53) of fragment pairs excluding fission

[en] Complete two-fragment velocity systematics have been measured over the full range of fragmentation products for the system ⁵⁶Fe+¹⁹⁷Au at 50 and 100 MeV/A. Fragment emission lifetimes can be estimated using intensity interferometry by comparing mixed-fragment (Z₁≠Z₂) reduced velocity (V_rel/√(Z₁ + Z₂)) correlation functions with results from a classical three-body trajectory calculation in which the Coulomb influence and recoil effects of the emitting source are explicitly included. We have chosen to use the trajectory code MENEKA for this comparison. (author)

[en] Intermediate mass fragments have been studied from the reaction ⁸⁶Kr+⁶³Cu for ⁸⁶Kr beam energies of 486, 550, 640, and 730 MeV. Average center-of-mass (c.m.) energies are nearly constant with the c.m. angle and vary little with incident energy. Furthermore, the angular distributions are well approximated by 1/sinθ_c.m.. From this and other evidence we conclude that equilibration has occurred prior to fissionlike asymmetric binary breakup of the composite nucleus in the predominant mechanism for IMF production