  The information about sizes and nuclear density distributions in unstable
(radioactive) nuclei is usually extracted from the data on interaction of
radioactive nuclear beams with a nuclear target. We show that in the case of
nucleus-nucleus collisions the values of the parameters depend rather strongly
on the considered theoretical approach and on the assumption about the
parametrization of the nuclear density distribution. The obtained values of
root-mean-square radii (R_{rms}) for stable nuclei with atomic weights A =
12-40 vary by approximately 0.1 fm when calculated in the optical
approximation, in the rigid target approximation, and using the exact
expression of Glauber Theory. We present several examples of R_{rms} radii
calculations using these three theoretical approaches and compare these results
with the data obtained from electron-nucleus scattering.
