An octupole deformation in 20Ne

A quadrupole (Y2)-plus-octupole (Y3)-deformed-shell model is applied to the first K sup(π)=0+- bands of 20Ne which is situated at the ''critical'' region in structure change between the shell-like and cluster-like ''phases''. By the use of the Volkov force as the effective interaction, the variation is performed of the total energies with the Y3-deformed wave functions. A static Y3-deformed field is realized in the physical states with definite parities. The energy spectra, the electromagnetic transition probabilities and the charge form factors in the bands are well reproduced as a whole. In the K sup(π)=0- band the Y3 deformation is large and stable; the Y3 degree of freedom is indispensable to reproducing the gap energy between the two band heads. The present model gives good agreement with the observed 0+→1- charge form factor and predicts a remarkably enhanced 3-→0+ E3 transition; the Y3 polarization growing to some extent in the 0+ state plays an important role. (auth.)