Question

What are the evidences in favor of the Nuclear Shell Model ?

Answer 1

There are multiple experimentally determined facts that indicate the shell-like structure of the atomic nucleus. Some of them are listed below :

1) Nuclei with Z and N (or both) equal to 2, 8, 28, 20, 50, 82 and 126 are extra stable. These numbers are called the magic numbers and this stability variation is analogous to stability of 2, 8, 18, 32 etc electrons in electronic shells.

2) Nuclei with N = a magic number have smaller neutron absorption cross section as compared to their immediate neighbours indicating a more stable nucleus for those values of N.

3) The electric quadrapole moment is zero for a nucleus with N or Z equal to a magic number indicating the spherical symmetry analogous to that in closed shells of atoms.

4) Nuclear species with one neutron excess of a magic number readily emit a single neutron indicating that the extra neutron is loosely bound to the rest of the nucleus.

5) Nuclei with magic number of nucleons of a particular type have more number of stable isotopes and isotones.