Abstract
Cylindrical and spherical ion-acoustic solitons in electron-positron-ion plasma have been investigated. The reductive perturbation method has been used to derive a modified Korteweg-de-Vries (mKdV) equation. The numerical solutions of the mKdV equation are presented for both geometries. We found that the amplitude and width of ion-acoustic solitons decrease with an increase in positron concentration. It is also shown that adiabatically hot ions play a destructive role in the formation of solitons in both geometries.