Effects of entrance channels on breakup fusion induced by ${}^{19}\mathrm{F}$ projectiles

The study of breakup fusion of ${}^{19}\mathrm{F}$ with ${}^{154}\mathrm{Sm}$ target was studied through offline $\gamma$ ray spectrometry. Partial cross sections of evaporation residues produced in this reaction were measured in center-of-mass energies ranging $\approx \mathrm{3–30}$ MeV above the fusion barrier. The excitation functions of the evaporation residues populated through $xn/pxn$ channels were found to be satisfactorily reproduced by statistical model calculations, whereas for the $\alpha$ emitting channels the cross sections show an enhancement over the theoretical predictions. The critical angular momentum deduced from the measured cross sections was found to be in good agreement with statistical model calculations. The degree of fusion incompleteness in the ${}^{19}\mathrm{F}+{}^{154}\mathrm{Sm}$ reaction is estimated by comparing the fusion excitation functions with coupled channels calculations and the extracted fusion function with the universal fusion function. The large cross sections observed for incomplete fusion products support the interpretation that this suppression of fusion is caused by ${}^{19}\mathrm{F}$ breaking up into charged fragments before reaching the fusion barrier. The incomplete fusion probability was also found to increase with the reduced mass and charge of the entrance channel, indicating the influence of entrance channel mass asymmetry and Coulomb repulsion on incomplete fusion. The present analysis shows the presence of strong clustering in the ${}^{19}\mathrm{F}$ projectile as $\alpha$ and ${}^{15}\mathrm{N}$.

Figure 1

Typical $\gamma$ ray spectrum of the residues populated in the ${}^{19}\mathrm{F}+{}^{154}\mathrm{Sm}$ system at $E_{\mathrm{lab}}\approx$ 109.4 MeV, recorded for about 300 s and 20 min after the ending of irradiation of stack.

Figure 2

Measured excitation functions of evaporation residues ${}^{169–167}\mathrm{Lu}$, and ${}^{167}\mathrm{Yb}$ populated via $xn$ ($x=4,5,6$) and $pxn$ ($x=5$) emission channels in the system ${}^{19}\mathrm{F}+{}^{154}\mathrm{Sm}$ at $E_{\mathrm{lab}}\approx 78–110$ MeV. Different symbols represent the measured cross sections and dashed/dash-dotted curves represent the cross sections of pace-4 code. the data points shown in figures include the errors and uncertainties.

Figure 3

Measured excitation functions of evaporation residues ${}^{166–164}\mathrm{Tm}$ and ${}^{162,161}\mathrm{Ho}$ associated with $\alpha xn$ ($x=3,4,5$) and $2\alpha xn$ ($x=3,4$) emission channels in the system ${}^{19}\mathrm{F}+{}^{154}\mathrm{Sm}$ at $E_{\mathrm{lab}}\approx 78–110$ MeV. Different symbols represent the measured cross sections and solid curves represent the cross sections of pace-4 code. The data points shown in figures include the errors and uncertainties.

Figure 4

Critical angular momentum (${\ell }_{\mathrm{crt}}$) derived from the fusion cross sections for the ${}^{16}\mathrm{O}$ (triangle), ${}^{19}\mathrm{F}$ (square), and ${}^{20}\mathrm{Ne}$ (circle) induced reactions as a function of reduced charge of the system at $E^{*}=72$ MeV. Solid lines represents the prediction of the sum-rule model [37].

Figure 5

Measured CF cross sections (circle) along with the ccfull calculations (solid line). The dashed line shows the ccfull calculations scaled down by a factor of 0.79.

Figure 6

Measured CF function $F\left(x\right)$ for the ${}^{19}\mathrm{F}+{}^{154}\mathrm{Sm}$ system (solid circle) along with the UFF (solid line). The dashed line shows the UFF scaled down by a factor of 0.79.

Figure 7

Incomplete fusion strength function ($S_{\mathrm{ICF}}$) as a function of reduced mass ($A_{\mathrm{Red}}$) and reduced charge ($Z_{\mathrm{Red}}$) for the ${}^{16}\mathrm{O}, {}^{19}\mathrm{F}$, and ${}^{20}\mathrm{Ne}$ induced reactions.

Figure 8

Incomplete fusion strength function ($S_{\mathrm{ICF}}$) for the ${}^{16}\mathrm{O}$ (triangle), ${}^{19}\mathrm{F}$ (square), and ${}^{20}\mathrm{Ne}$ (sphere) induced reactions as a function of reduced charge ($Z_{\mathrm{Red}}$) of the system. Solid lines represent the calculations from the empirical formula [57] for the respective projectiles.