Exclusive breakup of ${}^7\mathrm{Li}$ incident on a proton target at $5.44A$ MeV

An exclusive measurement of the breakup of ${}^7\mathrm{Li}$ incident on a proton target was performed at 38.1 MeV (5.44 MeV/nucleon), probing the direct part of the excitation to the continuum. The two cluster constituents of ${}^7\mathrm{Li}$, ${}^4\mathrm{He}$, and ${}^3\mathrm{H}$, were recorded in coincidence in the MAGNEX spectrometer and a silicon detector respectively. Both detection systems were set at forward angles and the measurement of both kinematical solutions allowed the determination of a breakup angular distribution over a wide angular range in the center-of-mass frame. Comprehensive simulations provided the detection efficiency of the system and via the appropriate kinematics the transformation of the cross sections from the laboratory to the center-of-mass reference frame. The experimental results are analyzed and discussed together with previous elastic scattering data using the Continuum Discretized Coupled Channels (CDCC) framework and are found to be in satisfactory agreement. It was found that while the breakup cross section was dominated by the nonresonant component, the most important influence on the elastic scattering was due to coupling to the $7/2^{-}$ resonance of ${}^7\mathrm{Li}$.

Figure 1

Elastic scattering of ${}^7\mathrm{Li}+p$ at 38.1 MeV. Details of the data collection and reduction are given in Ref. [6]. The solid black curve (labeled “CDCC”) denotes the full calculation, including couplings to the $\alpha +t$ continuum. The dotted red curve (labeled “1 - channel”) denotes the result of a calculation including ground state reorientation of ${}^7\mathrm{Li}$ only. The dot-dashed blue curve (labeled “2 - channel”) denotes the result of a calculation including ground state reorientation and excitation of the 0.478 MeV $1/2^{-}$ bound first excited state of ${}^7\mathrm{Li}$.

Figure 2

Two dimensional energy spectrum determined at 38.1 MeV (5.44 MeV/nucleon) representing coincidence events of the two ${}^7\mathrm{Li}$ breakup fragments: $\alpha$ energy versus triton or proton energy. The $\alpha$'s were recorded in the MAGNEX spectrometer over an angular range of ${\theta }_{\mathrm{lab}}=0^{\circ }$ to ${10}^{\circ }$, while the tritons and recoiling protons were registered in a silicon detector set at ${\theta }_{\mathrm{lab}}=5^{\circ }$. Superimposed on the experimental spectrum, denoted in black, are simulations of the first and second kinematical solutions, denoted as red and green dots respectively. The simulation represents in an excellent way the data in the left- and right-hand loci originating from $\alpha$'s in coincidence with tritons. The locus in the middle of the experimental (black) spectrum comes from coincidences of $\alpha$'s with the recoiling protons.

Figure 3

Exclusive breakup spectrum acquired in the $5^{\circ }$ silicon detector with the ${\mathrm{CH}}_2$ target ($\alpha +t$ or $p$ coincidences). Simulations for the first and second solution for $\alpha +t$ coincidences are denoted by the dot-dashed red and green lines respectively. The middle peak corresponds to $\alpha +p$ coincidences. The spectrum in blue represents an exclusive spectrum acquired with the carbon target, appropriately normalized.

Figure 4

As in Fig. 2 but for $\alpha +t$ coincidences from ${}^7\mathrm{Li}$ + ${}^{12}\mathrm{C}$ breakup.

Figure 5

Experimental and theoretical angular distributions, in the center-of-mass frame, for the ${}^7\mathrm{Li}\to \alpha +t$ breakup for ${}^7\mathrm{Li}$ incident on protons at 38.1 MeV. The experimental data, corresponding to the first kinematical solution, are denoted by filled red circles while the data corresponding to the second kinematical solution are denoted by green stars. The solid black line represents the result of the full CDCC calculation. The dot-dashed blue curve denotes the contribution of breakup via the 4.63 MeV $7/2^{-}$ resonance, multiplied by a factor of 20 in order to make it visible.