Each nucleus has only one polar central axis with an even number of
nucleons on it in combination with one or two equatorial symmetric
coaxial ring systems.
There are TWO ring systems possible in a symmetric co-axial
combination located around the central axis: coined an INNER and an
OUTER RING
system.
Only the two highest numbered magic numbers: T=82 and T=126 seem to
be equipped with this inner ring system.
Overview of the system:
For T=8 we count the nucleons (dots) from top to bottom:
On the axis = 2 nucleons
On the single ring: 6 nucleons
For T=20, we count dots from top to bottom:
On the axis =4 nucleons
On the three (3) rings: 4,8,4 = 16 nucleons
(4+16=20)
ALTERNATIVE:
For T=20, we could even count from top to bottom:
On the axis =6 nucleons
On the three (3) rings: 4,6,4 = 14 nucleons
(6+14=20)
For T=28, we count dots from top to bottom:
On the axis =8 nucleons
On the three (3) rings: 6,8,6 = 20 nucleons
(8+20=28)
For T=50, we count dots from top to bottom:
On the axis =12 nucleons
On the five rings: 6,8,10,8,6,= 38 nucleons
(12+38=50)
For T=82, we count dots from top to bottom:
On the axis =16 nucleons
On the seven (7) OUTER rings: 6,8,10,12,10,8,6,= 60 nucleons
On the single (1) INNER ring: =6 nucleons
(16+60+6=82)
For T=126, we count dots from top to bottom:
On the axis = 20 nucleons
On the nine (9) OUTER rings: 6,8,10,12,10,8,6,= 86 nucleons
On the three (3) INNER ring: =6,8,6=20 nucleons.
(20+86+20=126).
Leo Vuyk.
Peculiar shape coexistence occurs even in the doubly magic nucleus,
why?
Probably because there two alternative geometries possible for Magic
number T=20 !!!
For T=20, we count dots from pole to pole:
On the axis =4 nucleons
On the three (3) rings: 4,8,4 = 16 nucleons
(4+16=20)
ALTERNATIVE: (SEE Ca-40 examples below)
For T=20, we could even count from pole to pole:
On the axis =6 nucleons
On the three (3) rings: 4,6,4 = 14 nucleons
(6+14=20)
Found in the literature:
“Exotic shapes in 40Ca and 36Ar studied with Antisymmetrized
Molecular Dynamics”
By: Y. Kanada-En’yo, M. Kimura∗ and H. Horiuchi∗∗(AUG 2002)
http://arxiv.org/PS_cache/nucl-th/pdf/0208/0208078v1.pdf
Owing to the experiments of gamma-ray measurements, many excited bands
in the nuclei
near 40Ca have been recently observed [1,2]. The rotational bands with
large moments of
inertia are hot subjects relating with super deformations in sd-shell
nuclei. In 40Ca, there
exist many low-lying bands, which imply the coexistence of various
shapes. It is interesting
problem why the shape coexistence occurs even in the doubly magic
nucleus. The shape
coexistence problem and the mechanism of deformations in these sd-
shell nuclei is one of
the attractive subjects.
Other literature examples :
Evidence from Nuclear Masses on Proposed Closed Shells at 20 Nucleons
Low, W.; Townes, C. H.
Physical Review, vol. 80, Issue 4, pp. 608-611 (1950)
Combining microwave measurements of sulfur and chlorine masses with
mass spectroscopic and nuclear reaction information, the effect of
nuclear shell structure on masses in the region of 20 neutrons or
protons is investigated. It is found that except for Ca40, nuclei with
20 neutrons or protons do not show any special stability.
DOI: 10.1103/PhysRev.80.608
1d32-1f72 Energy Splitting at Ca-40.
L.B. HUBBARD (Argonne & UC, Berkeley & MIT) , H.P. JOLLY
(Massachusetts U., North Dartmouth) . Feb 20, 1969. 5pp.
Published in Phys.Rev.178:1783-1788,1969.
L. B. HUBBARD*, †
Division of Biological and Medical Research, Argonne National
Laboratory, Argonne, Illinois
Physics Department and Laboratory for Nuclear Science, Massachusetts
Institute of Technology, Cambridge, Massachusetts
H. P. JOLLY‡
Physics Department, Southeastern Massachusetts Technological
Institute, North Dartmouth, Massachusetts
Received 22 August 1968
The low-lying levels of nuclei near closed shells are commonly assumed
to be of pure, single-particle model configurations. On this basis the
single-particle and single-hole energies used in shell-model
calculations are taken from the experimental energy spectra of these
nuclei. In recent years, however, both direct-reaction experiments and
theoretical calculations have shown that there is considerable
configuration mixing in the Ca40 ground-state wave function,
associated with a depression in the ground-state energy. Since the
underlying approximation is not valid, the use of experimental energy
differences as the single-particle energies in shell-model
calculations is not justified. From calculations of the effects of
mixing on the A=39 and A=41 nuclei, as well as on Ca40, it is found
that the conventional experimental splittings overestimate the
important 1d3/2-1f7/2 energy difference by at least 1 MeV. A smaller
error is contained in the "experimental" 2s1/2-1f7/2 splitting.
Similar effects occur in the oxygen region, but the overestimation in
the 1p1/2-1d5/2 splitting is much smaller, since the mixing is
considerably less.
© 1969 The American Physical Society
URL:
http://link.aps.org/doi/10.1103/PhysRev.178.1783
DOI:
10.1103/PhysRev.178.1783