Interplay of initial deformation and Coulomb proximity on nuclear decay

Alpha particles emitted from an excited projectilelike fragment $\left({\mathrm{PLF}}^{*}\right)$ formed in a peripheral collision of two intermediate-energy heavy ions exhibit a strong preference for emission towards the targetlike fragment. The interplay of the initial deformation of the ${\mathrm{PLF}}^{*}$ caused by the reaction, Coulomb proximity, and the rotation of the ${\mathrm{PLF}}^{*}$ results in the observed anisotropic angular distribution. Changes in the shape of the angular distribution with excitation energy are interpreted as being the result of forming more elongated initial geometries in the more peripheral collisions.

Figure 1

Invariant cross-section map (linear scale) of $\alpha$ particles in the ${\mathrm{PLF}}^{*}$ frame for the reaction ${}^{114}\mathrm{C}\mathrm{d}+{}^{92}\mathrm{M}\mathrm{o}$ at $E∕A=50\mathrm{MeV}$. The dotted line depicts the energy cut described in the text. The dashed line indicates the minimum angle $\left({\theta }_{lab}⩾7°\right)$ for detection of $\alpha$ particles.

Figure 2

Comparison of the angular distribution of $\alpha$ particles from the reaction ${}^{114}\mathrm{C}\mathrm{d}+{}^{92}\mathrm{M}\mathrm{o}$ at $E∕A=50\mathrm{MeV}$ with $E_{\alpha }⩽25\mathrm{MeV}$ in the ${\mathrm{PLF}}^{*}$ frame with results of the Langevin model.

Figure 3

One-dimensional potential energy diagram of $\alpha$-particle emission from the ${\mathrm{PLF}}^{*}$ indicating the influence of the ${\mathrm{TLF}}^{*}$ proximity.

Figure 4

Yield ratio for backward to forward emission as a function of the initial ${\mathrm{TLF}}^{*}{\mathrm{-PLF}}^{*}$ distance. Calculations for different initial configurations and friction are shown.