Classical tests for statistical evaporation at 680 MeVAr40+

Abstract

Measurements of the partial linear momentum transfer and production cross sections for light charged particles are reported for the reaction 680 MeV 40 Arϩ nat Ag. From examination of light charged particle invariant cross section maps and comparison of experimental angular distributions and energy spectra to a reaction kinematics simulation, an average value of 85% linear momentum transfer is deduced, with a spin range of ͑0-75͒ប. Integration over energy and angle yields single and coincident light charged particle production cross sections. ͓S0556-2813͑96͒02812-9͔PACS number͑s͒: 25.70.Gh

Time Relationships between Direct Particle Emission and Fragmentation: A Probe for Nuclear Expansion Prior to Fragment Freeze-Out

“…By contrast, if the faster moving ejectile is emitted first, then the interaction will be weaker, and the pair has a much better chance for detector acceptance at small relative angle. This feature drives the relative intensities of the spectral bumps on either side of Vd;f = 0 and thus provides a good probe of the ejectile emission order [7]. In contrast, changes in the mean time delay between particle emission result only in the depletion of a narrow region of the spectrum centered at Vd;f = 0; time delay does not change the relative spectral intensities on either side of Vd f 0 [7].…”

“…However, if the time scale and/or the initiation time for fragment emission differ from that for direct particle emission, then a crucial experimental observable could be the average ejectile emission order for these two reaction classes. In this paper we present the first experimental results sensitive to both the emission order and time delays between fragments and direct particles produced in the most violent collisions of 1360 MeV "Ar with Ag [6,7]. Fragmentation, in this reaction, cannot be accounted for by a scenario of freeze-out from an expanded and thermalized nucleus.…”

“…In addition, we present velocity difference (Vd'f) spectra between unlike ejectile pairs, H-Li and 3H-Li, for opening angle y ( 7 . The velocity difference spectra probe both the mean lifetimes and the ejectile emission order [7] as discussed below. Trajectory calculations with a detection filter from the reaction simulation code MENEKA [6] are used to interpret the data.…”

“…Lifetimes have also been determined as a function of velocity for the lower energy 2H and 3H ejectiles [17]; for H or 3H energies of -10 MeV, these r values rise to )1000 fm/c, presumably due to more extensive thermalization [1]. By contrast, however, hardly any significant change of lifetime (i.e., (120 fm/c) with velocity was found for the Li [7].…”

“…For the unlike ejectile pairs, more definitive information can be gleaned by focusing on the velocity difference spectra, in which sensitivity to emission order (as well as time interval) has been demonstrated [7]. The data points in Fig.…”