Subatomic Physics

8.8. References 235
Isospin doublets occur in mirror
nuclides for which Z =
(A ± 1)/2. An example is
shown in Fig. 8.6. The ground
state and the first five ex-
cited states have isospin 1
2 .
Equation (8.36) predicts an
energy shift of 1.3 MeV, which
is in reasonable agreement
with the observed shift of 0.86
MeV.
An example of an isospin
triplet is shown in Fig. 8.5.
The ground states of 14 Cand
14 O form an I = 1 triplet
with the first excited state
of 14 N. All three states
have spin 0 and positive parity.
The energies agree reasonably
well with the prediction
of Eq. (8.36). Quartets
and quintets have also been
found, (14) and the existence of
isospin multiplets in isobars is
well established.
8.8 References
Figure 8.6: Level structure in the two isobars 7 Li and
7 Be. These two nuclides contain the same number of nucleons;
apart from electromagnetic effect, their level schemes
should be identical. J x denotes spin and parity of a level,
I its isospin. Parity will be discussed in Chapter 9. [For
reference see F. Ajzenberg-Selove, Nucl. Phys. A490, 1
(1988).]
General references to invariance properties are given in Section 7.6. In addition to
these, the following books and articles are recommended.
Rotations in ordinary space and the ensuing quantum mechanics of angular
momentum are important in all parts of subatomic physics. We have only scratched
the surface. For further details, the texts by Messiah and Merzbacher are useful.
The subject is treated in more detail in D.M. Brink and G.R. Satchler, Angular
Momentum, Oxford University Press, London, 1968.
The early ideas concerning isospin are lucidly described in E. Feenberg and E.
P. Wigner, Rep. Prog. Phys. 8, 274 (1941), and in W. E. Burcham, Prog. Nucl.
Phys. 4, 171 (1955). A later review is D. Robson, Annu. Rev. Nucl. Sci. 16,
119 (1966). The book Isospin in Nuclear Physics (D. H. Wilkinson, ed.), North-
Holland, Amsterdam, 1969, provides a review of the entire field. Even though many
14 J. Cerny, Annu. Rev. Nucl. Sci. 18, 27 (1968); W. Benenson and E. Kashy, Rev. Mod. Phys,
51, 527 (1979); F. Ajzenberg-Selove, Nucl. Phys. A449, 1 (1986).