Shell evolution approaching the N= 20 island of inversion: Structure of 26Na

G L Wilson ,G Hackman,S Triambak,D Smalley,R Kanungo,C Sumithrarachchi,N Galinski,H Al Falou,R Wadsworth,C Unsworth,A Matta,M Djongolov,U Hager,T.E Drake,F Sarazin,Drew Jamieson ,C Aa Diget ,C J Pearson ,R A E Austin ,S P Fox ,N L Achouri ,W N Catford ,D S Cross ,J N Orce ,J C Blackmon ,Sky Sjue ,A J Boston ,Robert Ashley ,K G Leach ,H C Boston ,E C Simpson ,G C Ball ,M Porter‐Peden ,N A Orr ,A B Garnsworthy ,B R Fulton ,Susannah Brown ,Spencer J Williams ,I C Celik

doi:10.1016/j.physletb.2016.05.093

Abstract

The levels in 26Na with single particle character have been observed for the first time using the d(25Na,p gamma) reaction at 5 MeV/nucleon. The measured excitation energies and the deduced spectroscopic factors are in good overall agreement with (0+1) hbar-omega shell model calculations performed in a complete spsdfp basis and incorporating a reduction in the N=20 gap. Notably, the 1p3/2 neutron configuration was found to play an enhanced role in the structure of the low-lying negative parity states in 26Na, compared to the isotone 28Al. Thus, the lowering of the 1p3/2 orbital relative to the 0f7/2 occurring in the neighbouring Z=10 and 12 nuclei -- 25,27Ne and 27,29Mg -- is seen also to occur at Z=11 and further strengthens the constraints on the modelling of the transition into the island of inversion.

Highlights

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The levels in 26 Na with single particle character have been observed for the first time using the d(25 Na, pγ ) reaction at 5 MeV/nucleon
The measured excitation energies and the deduced spectroscopic factors are in good overall agreement with (0 + 1)hω shell model calculations performed in a complete spsdf p basis and incorporating a reduction in the N = 20 gap