  In this work, according to the generalized uncertainty principle (GUP) and
time- dependent perturbation theory, the transition rate in the present of a
minimal length based on the Kempf algebra is studied. Also, we find the
absorption cross section in the framework of GUP. The modified photoelectric
effect is investigated and we show that the differential cross section of
photoelectric effect in the frame work of GUP is related to the isotropic
minimal length scale. The upper bound on the isotropic minimal length is
estimated.
