Nuclear mean-field shells and spin–orbit splitting
In a spherical nuclear mean field, single-nucleon states fill separately for protons and neutrons with 2j+1 states in each j level.
Key knowledge
In a spherical nuclear mean field, single-nucleon states fill separately for protons and neutrons with 2j+1 states in each j level. A harmonic central approximation gives E_N=ħω(N+3/2)−V₀, N=2n_r+l, and spin-included shell capacity (N+1)(N+2). A negative spin–orbit coefficient multiplying L·S/ħ² lowers j=l+½ relative to j=l−½ and changes shell grouping, accounting for familiar closures at 2,8,20,28,50,82,126 in this model.
Values and equations
E_N=ħω(N+3/2)−V₀; N=2n_r+l; D_N=(N+1)(N+2); H_so=g(r)L·S/ħ²; D_j=2j+1
- E_N,V₀,g,H_so
- Single-particle energy, well offset, spin–orbit coefficient and operator J
- ħ
- Reduced Planck constant J s
- ω
- Oscillator angular frequency rad s⁻¹
- r
- Radius m
- L,S
- Orbital and spin angular-momentum operators J s
- N,n_r,l,j,D_N,D_j
- Shell/radial/angular labels and state capacities
Conditions and scope
- Spin-½ nucleons, spherical independent-particle mean field, n_r=0,1,… and l≥0; j=l−½ exists only for l≥1. The eigenvalue of L·S/ħ² is l/2 for j=l+½ and −(l+1)/2 for j=l−½.
- Residual correlations, pairing, deformation and isotope-dependent shell evolution require additional models. A magic count is not a universal assertion that every nucleus at that count is stable; the source's predicted unobserved 184 closure is not declared established.
Sources · 1
References
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Evidence and review
Introduction to Applied Nuclear Physics: chapter 5 (2012): Sections 5.3.2–5.3.3, printed pages 77–79: oscillator capacities, spin–orbit dot product, split j capacities and shell regrouping. The erroneous oscillator l<n statement and missing dimensionful splitting coefficient are not copied; n_r is defined from zero and actual spin–orbit energy depends on the radial coefficient.
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