Clarifying the 𝑁,𝑍 = 14 Shells near the Drip Lines from the Spectroscopy of ²²Si and ²¹Al

Evidence for a (sub)-shell closure at 𝑍 = 14 has been observed from the spectroscopy of ²²Si and ²¹Al . Using a fast ²³Si beam on a ⁹Be target, several proton-decaying resonances have been populated in ²¹Al and ²²Si , including the first measurement of the 2$^{+}_{1}$ state in²²Si with an excitation energy of 2.352(55) MeV. Relative to the known 𝑁 = 14 subshell closure in ²²O , the ²²Si 2$^{+}_{1}$ excitation energy indicates the existence of a weakened 𝑍 = 14 subshell closure. To reproduce the new spectroscopic information and known ²²Al levels, the energy of the 1⁢𝑠_1/2 orbit must be substantially decreased, which imparts Thomas-Ehrman shifts to all excited states observed in the present Letter and explains the structure of nuclei in the 𝑠⁢𝑑 shell for this region of the proton drip line.. Authors: Phillips, J. S. [Washington University, St. Louis, MO (United States)] (ORCID:0000000155125343); Charity, R. J. [Washington University, St. Louis, MO (United States)] (ORCID:0000000330204998); Dronchi, N. [Washington University, St. Louis, MO (United States); Facility for Rare Isotope Beams, East Lansing, MI (United States)] (ORCID:0000000294290314); Webb, H. [Washington University, St. Louis, MO (United States)] (ORCID:0009000395407232); Sobotka, L. G. [Washington University, St. Louis, MO (United States)] (ORCID:0000000278837711). DOE Contract: FG02-87ER40316; NA0004150; SC0021938; SC0022299; SC0023633. Subjects: 20 ≤ A ≤ 38; Direct reactions; Energy levels; Nuclear structure & decays; Proton emission; Radioactive beams; Rare & new isotopes; Shell model