  The abundance anomalies in chemically peculiar B-F stars are usually
explained by diffusion of chemical elements in the stable atmospheres of these
stars. But it is well known that Cp stars with similar temperatures and
gravities show very different chemical compositions. We show that the abundance
patterns of several stars can be influenced by accretion and (or) nuclear
reactions in stellar atmospheres. We report the result of determination of
abundances of elements in the atmosphere of hot Am star: Sirius A and show that
Sirius A was contaminated by s-process enriched matter from Sirius B (now a
white dwarf). The second case is Przybylski's star. The abundance pattern of
this star is the second most studied one after the Sun with the abundances
determined for about 60 chemical elements. Spectral lines of radioactive
elements with short decay times were found in the spectrum of this star. We
report the results of investigation on the stratification of chemical elements
in the atmosphere of Przybylski's star and the new identification of lines
corresponding to short lived actinides in its spectrum. Possible explanations
of the abundances pattern of Przybylski's star (as well as HR465 and HD965) can
be the natural radioactive decay of thorium, and uranium, the explosion of a
companion as a Supernova or nucleosynthesis events at stellar surface.
