Pionium in the elementary particle decays
  Some atomic decays of elementary particles with pionium ($\pi^+\pi^-$-dimesoatom) in the final state are considered. Only for K-meson atomic decays are the corresponding branching ratios big enough to make their experimental study realistic. The $O(\alpha)$ order corrections to the lifetime of pionium are also calculated. 
Z.K. Silagadze