12.12.2012 Views

Subatomic Physics

Subatomic Physics

Subatomic Physics

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

544 Collective Model<br />

deformation. The entire deformed nucleus can rotate, and this type of collective excitation<br />

leads to the appearance of rotational bands. The deformed nucleus acts as<br />

a nonspherical potential for the much more rapid single-particle motion; the energy<br />

levels of a single particle in such a potential can be investigated, and the result is<br />

the Nilsson model, (7) already mentioned at the end of the previous chapter.<br />

We shall begin the discussion in the present chapter with deformations and<br />

rotational excitations because these two features are easiest to understand and give<br />

the most spectacular effects.<br />

18.1 Nuclear Deformations<br />

As early as 1935 optical spectra revealed the existence of nuclear quadrupole moments.<br />

(8) We have encountered the quadrupole moment in Section 14.5, and we<br />

have seen there that it measures the deviation of the shape of the nuclear charge<br />

distribution from a sphere. The existence of a quadrupole moment hence implies<br />

nonspherical (deformed) nuclei. For the discussion of nuclear models, the sign and<br />

magnitude of the deformation are important. As we shall see below, the quadrupole<br />

moments far away from closed shells are so large that they cannot be due to a single<br />

particle and thus cannot be explained by the naive shell model. The discrepancy<br />

is particularly clear around A ≈ 25 (Al, Mg), 150

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!