Elsevier

Nuclear Physics A

Volume 432, Issue 2, 14 January 1985, Pages 525-554
Nuclear Physics A

Target-fragment angular distributions for the interaction of 86 MeV/A 12C with 197Au

https://doi.org/10.1016/0375-9474(85)90258-1Get rights and content

Abstract

Target-fragment angular distributions were measured using radiochemical techniques for 69 different fragments (44 ⩽ A ⩽ 196) from the interaction of 86 MeV/A 12C with 197Au. The angular distributions in the laboratory system are forward-peaked with some distributions also showing a backward peaking. The shapes of the laboratory system distributions were compared with the predictions of the nuclear firestreak model. The measured angular distributions differed markedly from the predictions of the firestreak model in most cases. This discrepancy could be due, in part, to overestimation of the transferred longitudinal momentum by the firestreak model, the assumption of isotropic angular distributions for fission and particle emission in the moving frame and incorrect assumptions about how the lightest (A < 60) fragments are produced. No evidence was found for any significant number of target fragments moving sidewise to the beam direction in apparent contradiction to the expectation of hydrodynamical-model calculations. The laboratory-frame angular distributions were transformed into the moving frame using various assumptions about the moving frame velocity. The resulting light-fragment distributions showed an asymmetry in the moving frame indicative of their production in a fast process without the establishment of statistical equilibrium. No evidence was found for any production of the light fragments by a very asymmetric fission mechanism. The fission-fragment distributions were compared to standard formulas and an average fissioning-system angular momentum of J = 40−50h̵ was deduced. It was not possible to find a moving frame in which the heavy (A > 145) fragment distributions were symmetric about 90°.

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    This work was supported in part by the US Department of Energy under contract DE-AC03-76SF00098, and DE-AM06-76RL02227, task agreement DE-AT06-76ER70035, Mod A007, the Swedish Natural Science Research Council, the BFMT (Bonn) and the Norwegian Research Council for Science and the Humanities.

    Present address: Los Alamos National Laboratory, Los Alamos, NM 87545, USA.

    ∗∗

    Present address: NCSF, San Francisco, CA, USA.

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