Many-particle many-hole states near the magic number 20 have been investigated in the relativistic mean field formalism using the fixed configuration method. Neutron particle-hole states in neutron-rich nuclei with $N\sim 20$, { \em i.e.} $^{ 30,32,34}$Mg,and $^{ 28,30}$Ne are studied to find out the ground state configuration. The ground state of $^{ 32}$Ne,Mg as well as possibly $^{ 34}$Mg comes out actually as particle-hole states. Proton-neutron excitation across the shell gap at 20 in nuclei with $N=Z$, { \em i.e.} $^{ 32}$S, $^{ 36}$Ar, $^{ 40}$Ca and $^{ 44}$Ti is investigated as possible origins of superdeformed configuration. Observed superdeformed bands in $^{ 36}$Ar and $^{ 40}$Ca can be described as many-particle many-hole states.
Categories: nucl-th