I understand that the energy levels in the nuclear shell model go as:

$$1S_{1/2}, 1P_{3/2}, 1P_{1/2}, 1D_{5/2}, 2S_{1/2}, 1D_{3/2}$$

But what is meant by the "sd-shell"? Is it something to do with the 2S and 1D shells overlapping? Thanks in advance.

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    $\begingroup$ Can you please provide your present education level? I'll try to answer accordingly. $\endgroup$ – Yajnya Sapkota Jun 29 at 12:11
  • $\begingroup$ I am at Masters level. ZeroTheHero's answer was enough for me to figure out what I needed but a more complete answer may prove useful for other users of the site. $\endgroup$ – Tech Jun 30 at 14:45

Please look up the angular momentum of the 3D harmonic oscillator, which often approximates the nuclear potential. The states are exactly degenerate in the h.o. approximation. The $n=2$ states have $\ell=0$ (i.e. $s$ states) and $\ell=2$ ($d$ states). See also this energy diagram for the shell model, which illustrates the near degeneracy and labelling of the states in a shell.


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