An important decay channel of recently discovered metastable antiproto
nic helium atoms is the emission of an electron, i.e., the Auger trans
ition. The rate of this process for a number of states of the He-3 (p)
over bar e, He-4 (p) over bar e and He-6 (p) over bar e systems is ca
lculated and a substantial isotopic effect is found. While the reduced
mass of heavy I,articles increases slightly with increasing nucleus m
ass, the Auger transition rate decreases by about a factor of three. T
he explanation of this strong amplification is given and the role of t
his effect in experiments is discussed.