The angular momentum of a primary excited compound nucleus produced in multinucleon transfer reaction is an important quantity to evaluate cross sections to synthesize neutron-rich heavy-element nuclei as well as for surrogate reaction studies. The mechanism is, however, not enough understood due to the lack of detailed experimental data. In the present study, we determined the angular momentum of primary excited nuclei, ${}^{237,238,239}\mathrm{Np}, {}^{238,239,240}\mathrm{Pu}$, and ${}^{239,240,241}\mathrm{Am}$, produced in the multinucleon transfer channels of the ${}^{18}\mathrm{O}+{}^{237}\mathrm{Np}$ reaction. With this aim, angular distributions of fission fragments with respect to the axis perpendicular to the reaction plane were measured for each compound nucleus. The distributions show an anisotropy exhibiting an enhanced yield on the reaction plane. They are well reproduced by a saddle-point model, from which the average angular momentum is derived in the model framework. The angular momentum increases with the compound-nucleus mass, thus the number of nucleons exchanged, but shows a saturating trend toward heavier compound nuclei. These results are the first ones to point to the dependence of the angular momentum on the transfer channels.

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• Fission
• Low & intermediate energy heavy-ion reactions
• Nuclear reactions
• Transfer reactions
• A ≥ 220