Interaction of $^{8}\mathrm{He}$ with $^{208}\mathrm{Pb}$ at near-barrier energies: $^{4}\mathrm{He}$ and $^{6}\mathrm{He}$ production

Interaction of ${}^{8}{He}$ with ${}^{208}{Pb}$ at near-barrier energies: ${}^{4}{He}$ and ${}^{6}{He}$ production

G. Marquínez-Durán et al.

Phys. Rev. C 98, 034615 – Published 28 September 2018

Abstract

Angular distributions for the inclusive ${}^{4}{He}$ and ${}^{6}{He}$ production cross sections in the ${}^{8}{He} + {}^{208}{Pb}$ system at incident energies of 16 and 22 MeV measured at the SPIRAL facility of the GANIL laboratory are presented. Using a combination of kinematical arguments and distorted wave Born approximation (DWBA) calculations, neutron transfer reactions were inferred to be the dominant contributors to both inclusive cross sections. Model-dependent values for the ratios of two- to one-neutron stripping, $σ_{2 n} / σ_{1 n}$ , were derived and compared with previous results for ${}^{8}{He}$ and ${}^{6}{He}$ projectiles incident on other heavy targets. Three- and four-neutron stripping were inferred to be the main processes leading to ${}^{4}{He}$ production, although the exact mechanism remains to be elucidated.

Received 7 June 2018
Revised 16 August 2018

DOI:https://doi.org/10.1103/PhysRevC.98.034615

Physics Subject Headings (PhySH)

Breakup reactions Direct reactions Low & intermediate energy heavy-ion reactions Nuclear fusion Nuclear reactions Transfer reactions Unstable nuclei induced nuclear reactions

Nuclear Physics

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Vol. 98, Iss. 3 — September 2018

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Figure 1
(a) Total energy vs scattering angle for events gated on ${}^{4}{He}$ produced in the ${}^{8}{He} + {}^{208}{Pb}$ interaction at an incident energy of 22 MeV. Regions corresponding to the different production mechanisms are labeled. (b) Number of counts vs energy for events gated on ${}^{4}{He}$ summed over pixels at a scattering angle of $θ_{lab} = 94 . 5^{\circ}$ . The numbered arrows denote the energy of ${}^{4}{He}$ ejectiles corresponding to the optimum $Q$ values of Table 2 for the following reactions: (1) ${}^{208}{Pb} ({}^{8}{He}, {}^{4}{He}) {}^{212}{Pb}$ , (2) ${}^{208}{Pb} ({}^{8}{He}, {}^{5}{He} \to {}^{4}{He} + n) {}^{211}{Pb}$ , and (3) ${}^{208}{Pb} ({}^{8}{He}, {}^{6}{He}^{*}_{1.8} \to {}^{4}{He} + 2 n) {}^{210}{Pb}$ . For reactions 2 and 3, the arrows mark the centers of the energy distributions of ${}^{4}{He}$ arising from the decay of the ${}^{5}{He} 3 / 2^{-}$ ground-state resonance and the ${}^{6}{He}$ 1.8-MeV $2^{+}$ resonance, respectively; see text for further details. The narrow peak at approximately 8.8 MeV corresponds to $α$ particles from the decay of the ground state of ${}^{212}{Po}$ produced by fusion evaporation.
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Figure 2
(a) Total energy vs scattering angle for events gated on ${}^{6}{He}$ produced in the ${}^{8}{He} + {}^{208}{Pb}$ interaction at an incident energy of 22 MeV. Regions corresponding to the different production mechanisms are labeled. (b) Number of counts vs energy for events gated on ${}^{6}{He}$ summed over pixels at a scattering angle of $θ_{lab} = 70^{\circ}$ . The numbered arrows denote the energy of ${}^{6}{He}$ ejectiles corresponding to the optimum $Q$ values of Table 2 for the following reactions: (1) ${}^{208}{Pb} ({}^{8}{He}, {}^{6}{He}) {}^{210}{Pb}$ and (2) ${}^{208}{Pb} ({}^{8}{He}, {}^{7}{He} \to {}^{6}{He} + n) {}^{209}{Pb}$ . For reaction 2, the arrow marks the center of the energy distribution of ${}^{6}{He}$ arising from the decay of the ${}^{7}{He} 3 / 2^{-}$ ground-state resonance; see text for further details.
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Figure 3
Angular distributions for the ${}^{8}{He} + {}^{208}{Pb}$ elastic scattering at 16 MeV (open circles) and 22 MeV [1] (filled circles). The solid curves denote optical model fits to the data; see text for details. The dashed curve denotes the 16-MeV elastic scattering angular distribution calculated using the same optical potential parameters as at 22 MeV.
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Figure 4
Laboratory frame angular distributions of total ${}^{6}{He}$ (filled circles) and ${}^{4}{He}$ (open circles) yields at 16 (a) and 22 MeV (b). The solid curves represent fits to the data while the dashed curves and gray shaded areas denote the results of ${}^{208}{Pb} ({}^{8}{He}, {}^{7}{He}) {}^{209}{Pb}$ single-neutron stripping DWBA calculations including the uncertainties due to the use of different distorting potentials in the exit channels (see text for details).
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Figure 5
Excitation functions of the fusion (filled circles) and neutron transfer (filled triangles) cross sections for the ${}^{8}{He} + {}^{197}{Au}$ system [4] compared with the present results for the upper limit on fusion (open circle) and combined ${}^{4}{He}$ and ${}^{6}{He}$ cross sections (open triangles) for the ${}^{8}{He} + {}^{208}{Pb}$ system.
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Physical Review C

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Interaction of ${}^{8}{He}$ with ${}^{208}{Pb}$ at near-barrier energies: ${}^{4}{He}$ and ${}^{6}{He}$ production

G. Marquínez-Durán et al.

Phys. Rev. C 98, 034615 – Published 28 September 2018

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Physical Review C

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Interaction of He8 with Pb208 at near-barrier energies: He4 and He6 production

G. Marquínez-Durán et al.

Phys. Rev. C 98, 034615 – Published 28 September 2018

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Interaction of ${}^{8}{He}$ with ${}^{208}{Pb}$ at near-barrier energies: ${}^{4}{He}$ and ${}^{6}{He}$ production