Speaker
Description
A quantitative description of the interplay between the $p$-, $s$- and $d$-shell configurations in $^{12}$Be still alludes us despite numerous attempts via direct and indirect reactions. To resolve this situation we would like to explore the possibility of a study of the $^{11}$Be($d$,$p$)$^{12}$Be reaction at a beam energy of around 10 MeV/u, using the ISS to achieve the necessary 100-keV FWHM resolution.
The available data on 12Be are ambiguous and limited [1,2]. It has been difficult to probe via transfer reactions at ideal energies, around 10 MeV/u. Measurements of the ($d$,$p$) reaction have been made before at low (5 MeV/u) [3] and high (27 MeV/u) [4] incident beam energies, both yielding new insights. However, each measurement had limiting factors which hampered the interpretation of the data. The low-energy measurement was done at large center-of-mass angles, over a narrow range, and the Q-value resolution was >100 keV resulting in an ambiguous interpretation of the excited 0+ state. Similarly, the high-energy measurements suffered from low resolution. The low-lying states are expected to be either two 1$s_{1/2}$0$d_{5/2}$ neutrons coupled to a $^{10}$Be ground state, 0$p_{1/2}$-shell configurations, or a mixture of these. Clearly, the ($d$,$p$) reaction is the ideal probe, if a suitable beam energy and spectrometer are available. As such, we would like to propose a measurement of the $^{11}$Be($d$,$p$) reaction at ISOLDE with the new ISOLDE Solenoidal Spectrometer to help resolve the long-standing uncertainties in the low-lying structure of $^{12}$Be and to better determine the $s_{1/2}$ and $d_{5/2}$ single-particle energies, which are of interest in the exploration of weak binding effects in light neutron-rich nuclei.
Such a measurement has been considered at Argonne using an in-flight produced beam, but the emittance prohibits a high-resolution measurement and furthermore a $^{11}$Be beam will not be available for several years at suitable intensities at FRIB. ISOLDE and ISS represent the ideal combination for this measurement and an opportunity to clarify our understanding of this fascinating nucleus, $^{12}$Be, removing many of the existing ambiguities. The measurement will complement a new background free measurement of the $^{10}$Be($t$,$p$)$^{12}$Be reaction at ReA using SOLARIS.
[1] H. T. Fortune, Phys. Rev. C 99, 064314 (2019)
[2] H. T. Fortune, Phys. Rev. C 99, 064314 (2019)
[3] R. Kanungo et al., Phys. Lett. B 682, 391 (2010)
[4] J. Chen et al., Phys. Lett. B 781, 412 (2018)
[5] J. Chen et al., Phys. Rev. C 98, 014616 (2018)
[6] C. R. Hoffman et al., Phys. Rev. C 89, 061305(R) (2014)
