A positronium "atom" is a system that consists of a positron and an electron that orbit each other. Campare the wavelengths of the spectral lines of positronium with those of ordinary hydrogen.

Explanation

Here, the two particales have the same mass `m` , so the reducted mass is `mu = (mm)/(m + m) = (m^(2))/(2 m) = (m)/(2)`
where `m` is the electron mass
We know that `E_(n) prop m implies (E'_(n))/(E_(n)) = (mu)/(m) = (1)/(2)`
Hence, energy levels of positronium atom are half of correspinding energy level in a hydrogen atom .
As a ruselt , the wevelength in the positronium atom spectral lines are all twice those of the corresponding lines in the hydrogen spectrum.