A simple technique for measuring the electron and hole mean drift distance in chemical vapor deposition polycrystalline diamond in the as-grown and in the so-called pumped state obtained by 90Sr β-particle irradiation is presented. To this purpose, the efficiency η of a diamond-based particle detector was measured using a 5.5-MeV 241Am α-particle source. In particular, two different experimental setups were specifically designed and realized in order to perform a systematic study of the device efficiency as a function of the α-particle penetration depth, both in the positive and negative bias polarization. In the first setup, air is used as an absorbing layer in order to change the energy of the impinging α particles, while in the second one, the measurements were performed in vacuum and the incidence angle was varied in the 0°–80° range. The advantages of the latter setup are evidenced. The theoretical formula for the mean drift distances of carriers is derived using a properly modified Hecht model, and fitted to the data, allowing a separate evaluation of the charge collection distances of each carrier type (λe = μeτeE and λh = μhτhE). The obtained results unambiguously show that the pumping process is much more effective on hole conduction, λh being much greater than λe in the pumped state. © 2003 American Institute of Physics.