  We use a new version of our numerical model for particle propagation in the
Galaxy to study radioactive secondaries. For evaluation of the production cross
sections we use the Los Alamos compilation of all available experimental cross
sections together with calculations using the improved Cascade-Exciton Model
code CEM2k. Using the radioactive secondary ratios 26Al/27Al, 36Cl/Cl, 54Mn/Mn,
we show how the improved cross-section calculations together with the new
propagation code allow us to better constrain the size of the CR halo.
