The results of recent photoionization experiments performed on laser cooled
cesium and rubidium atoms are critically examined. The role of processes,
as ion diffusion and recombination, determining the time evolution and the
rate of the produced atomic ions is discussed. A more precise model of the
ion evolution is presented, numerically solved and compared to the experime
ntal data. (C) 2000 Elsevier Science B.V. All rights reserved.