Is the Deformation ParameterβDifferent for Different Kinds of Transitions?

It is shown on the basis of isospin arguments that the deformation parameter ${\beta }_2$ for $2^{+}$ first excited states is expected to be a function of the external field producing the transition. This is contrary to the usual assumption based on the collective model that $\beta$ is an intrinsic property of the nucleus and is, therefore, the same for all kinds of transitions. Data available in the literature support the expectation.