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  • 1
    ISSN: 1434-601X
    Keywords: 25.70.Gh ; 25.70.Jj ; 25.70.Lm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract For the violent collisions of 27 MeV/nucleon40Ar with Ag, coincidence measurements have been made between heavy residues and intermediate mass fragments (3≦Z≦14) or light charged particles. From the analysis of the correlation between heavy residues (mass and velocity) and intermediate mass fragments, the main characteristics of the dominant mechanisms, fusion and partially damped collisions preceded or accompanied by a preequilibrium emission, are presented. Balances concerning mean values of parallel linear momentum, mass and atomic number, are established and confirm that a complete description of violent collisions was obtained. Then thermalization is discussed, first in terms of excitation energies derived from kinematics between heavy residues and intermediate mass fragments, and secondly in terms of initial temperature estimates derived from light charged particle spectra. Very hot nuclei (T⋍5.7–6.6 MeV) are produced over a large impact parameter range from very central collisions to medium peripheral ones. Various experimental results are compared to predictions obtained with semi-classical calculations (Landau-Vlasov equation). From their good agreement one may conclude that, depending on the impact parameter, thermal equilibrium is achieved within 4–10×10−22 s.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-601X
    Keywords: 25.70.Lm ; 25.70.Np
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Correlations between emission angles and energies of coincidentα-particle projectile-fragment pairs have been measured for the20Ne+197Au system at 390 MeV beam energy. Theα-particles observed close to the direction of the projectile-like fragment were found to result essentially from sequential projectile decay. Starting from the close-geometry data, the contribution of sequentially emittedα-particles was calculated by Monte Carlo simulations for the entire angular range. For deep inelastic events, the measured angular correlations exhibit a spectacular excess over the calculated correlation. This excess is centred close to the beam direction but on the opposite side of it with respect to the detected projectile-like fragment. The correspondingα-particles have velocities around 85% of the projectile velocity indicating emission in an early reaction phase.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-601X
    Keywords: 25.70.Lm ; Mn
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Correlations between two intermediate-mass fragments resulting from 840 MeV32S projectiles interacting with197Au were measured. The angular correlations and absolute two-fragment cross sections agree with predictions of a semi-microscopic model for direct dynamic projectile break-up. This suggests a predominantly direct mechanism for the production of intermediate-mass fragment pairs. It is argued that the intensity of such a channel which, compared to decays yieldingα particles, is much larger than observed for the sequential decay of corresponding primary excited nuclei, supports the direct-break-up interpretation. The model mechanism yields also strongly damped projectile fragments of intermediate mass.
    Type of Medium: Electronic Resource
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