Light-charged-particle emission in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">Ar</mml:mi></mml:mrow><mml:mprescripts/><mml:mrow/><mml:mrow><mml:mn>40</mml:mn></mml:mrow><mml:mrow/><mml:mrow/></mml:mmultiscripts></mml:mrow></mml:math>-induced reactions: A probe of the very early evolution of the collisions

Charged-particle emission was studied for the reactions 222, 274, and 340 MeV $^{40}\mathrm{Ar}$+$^{116}\mathrm{Sn}$, $^{154}\mathrm{Sm}$, $^{164}\mathrm{Dy}$, and $^{197}\mathrm{Au}$. Energy and angular distributions were measured for H and He and angular distributions for Li, Be, B, C, N, and O, fissionlike fragments and evaporation residues. For H and He the data are consistent with a lowtemperature evaporative component and a high-temperature forward peaked component. For Li through O the forward-peaked emission was studied for 340 MeV $^{40}\mathrm{Ar}$ only. The evaporation residue cross sections decrease strongly with increasing $Z$ reflecting the increasing fissionability. However, the cross sections for $^{1}\mathrm{H}$ and $^{4}\mathrm{He}$ in coincidence with fission are essentially constant with $Z$. Coincidence measurements, energy spectra, and $^{4}\mathrm{He}$/$^{1}\mathrm{H}$ ratios indicate that most H/He evaporation precedes fission. This implies that the energy thermalization is very rapid indeed and that the light particle spectra can probe the very early history of the composite systems.NUCLEAR REACTIONS $^{116}\mathrm{Sn}$, $^{154}\mathrm{Sm}$, $^{164}\mathrm{Dy}$, $^{197}\mathrm{Au}$ ($^{40}\mathrm{Ar}$; H/He, fission and evaporation residues), $E=222$, 274, and 340 MeV, measured energy and angular distributions in singles mode. For $E=340$ MeV, coincidence measurements between H/He and one fission-like fragment, and angular distributions for Li, Be, B, C, N, and O in the singles mode.

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