Shape of nuclei of Eu and Sm isotopes in the transition region with N = 84--92

The method of collinear laser spectroscopy of ion beams at the mass separator IRIS has been used to investigate the isotope shifts and hyperfine splitting of optical lines for the series of isotopes /sup 147,//sup //sup 149,//sup //sup 151,//sup //sup 152,//sup //sup 152//sup m//sup ,//sup //sup 153//sup --//sup 156/Eu and /sup 146,//sup //sup 151/Sm. The variations of the charge radii and the electromagnetic moments for the ground states of these nuclei are determined, and also the value of the deformation parameter is estimated for the 9-hour isomeric state of 152Eu. It is shown that nuclei of the isotopes 147/sup ,/149/sup ,/151Eu have small equilibrium deformations (δ = 0.07--0.12) which increase smoothly with the number of neutrons, and in accordance with the results of previous studies the region of large deformations begins only with the nucleus 152Eu (N = 89). It is shown that present results can be explained within the framework of the deformed-potential model without inclusion of pairing, and the reason for the suppression of pairing is discussed. Qualitatively the dynamic deformation of the Eu and Sm isotopes is determined as a function of the number of neutrons. It is shown that absence of a γ transition from the isomeric state /sup 152//sup m/Eu to the ground state is determined mainly not by a change of the shape of the nucleus but by the two-particle nature of the transition