Mass distributions of fission fragments from nuclei populated by multinucleon transfer or incomplete fusion channels in ${}^{6,7}\mathrm{Li}+{}^{238}\mathrm{U}$ reactions

The multinucleon transfer reaction or incomplete fusion reaction (ICF) is a powerful tool to study fission of exotic nuclei that cannot be formed by stable heavy-ion fusion reactions. In the present work, mass distributions of fission fragments (FFs) from fissioning nuclei ${}^{241,242,243,244}\mathrm{Pu}$ and ${}^{240,241}\mathrm{Np}$ populated in multinucleon transfer or ICF reactions on ${}^{6,7}\mathrm{Li}+{}^{238}\mathrm{U}$ systems have been studied. Among these, ${}^{244}\mathrm{Pu},{}^{243}\mathrm{Pu}$, and ${}^{241}\mathrm{Np}$ are formed by the capture of unstable nuclei ${}^6\mathrm{He},{}^5\mathrm{He}$, and $t$, respectively, by the target ${}^{238}\mathrm{U}$. Identification of fissioning nuclei and determination of excitation energies have been performed by finding the details of the outgoing projectile-like fragments detected in coincidence with both the fission fragments on an event-by-event basis. The measurements of FF mass distributions and FF folding angle distributions of different ICF channels confirm that these channels are the prime factors for the modifications in the experimental ratio of asymmetric to symmetric fission yields and the width of folding angle distributions for inclusive fission reported earlier on the same reactions. Comparison among the ratio of asymmetric to symmetric fission yields from ${}^{241,242,243,244}\mathrm{Pu}$ and ${}^{240,241}\mathrm{Np}$ nuclei formed in the present reactions, available literature data, and the theoretical calculations using gef code shows that the shell correction for symmetric fission channels plays an important role in describing the experimental mass distribution.

Figure 1

Schematic diagram of the experimental setup inside scattering chamber.

Figure 2

Typical spectra involving 40 MeV ${}^6\mathrm{Li}$ beam correspond to PID versus energy of a CsI(Tl) detector (a) without any gate and (b) with the gates (see text).

Figure 3

Typical folding angle distributions for total, $\alpha$-gated, $t$-gated, and $p$-gated fissions in ${}^7\mathrm{Li}+{}^{238}\mathrm{U}$ reactions at beam energies of 31.4 and 41.4 MeV. Peak positions for $\alpha$-, $t$- and $p$-gated fissions are shown by dotted lines. The up-arrows in the left panels indicate the positions of the folding angles expected from two-body kinematics.

Figure 4

Mass distribution obtained in ${}^6\mathrm{Li}+{}^{238}\mathrm{U}$ reactions for total, $\alpha$-gated, $d$-gated, and $p$-gated fissions, at $E_{\mathrm{beam}}$ of 30, 34, and 40 MeV.

Figure 5

Same as Fig. 4 but for ${}^7\mathrm{Li}+{}^{238}\mathrm{U}$ reactions and at $E_{\mathrm{beam}}$ 31.4 and 41.4 MeV.

Figure 6

P:V ratios for total, CF, $\alpha$-gated, $t$-gated, $d$-gated, and $p$-gated fissions in reactions involving (a) ${}^6\mathrm{Li}$ and (b) ${}^7\mathrm{Li}$ projectiles.

Figure 7

Comparison of the experimental mass distribution (red filled circles) for ${}^{240,241}\mathrm{Np}$ and ${}^{241,242,243,244}\mathrm{Pu}$ nuclei with the literature data (blue hollow circle) [8].

Figure 8

Comparison of the experimental P:V ratios of nuclei populated in present transfer reactions (circles) with literature data (squares [8], triangles [24], and stars [25, 26]) and gef calculations (solid and dotted lines).