sing a CR-39 solid track detector the Bragg peak location for 239Pu α-particles (5.15MeV) passing through an air gap of 3 or 4cm and a collimater of φ1mm aperture is determined according to the distribution rule of radiation damage density along charged particle tracks. For a-particles of about 1.2MeV
the Bragg peaks in CR-39 are located at about 7 μm
and the calculated value in this case is 6.14 μm. The experimental result is in good agreement with the theoretical value.