The use of positron annihilation Doppler broadening spectroscopy in the characterization of radiochromic dosimetry films

• The structural changes of two types of γ-irradiated radiochromic films were investigated using the PADB spectroscopy.
• Correlation between DB S-parameter and OD of films was observed.
• Dependence of DB parameters on the polymerization degree of films' active layer was discussed.
• The capability of PADB technique to detect the structure transition of films' active layer was demonstrated.

The positron annihilation Doppler broadening (PADB) spectroscopy has been employed to probe the defects and structural changes of various types of materials. In this work, an investigation was carried out for the first time to use PADB spectroscopy in probing the γ irradiated radiochromic films. The GafChromic MD–55 and HD–V2 radiochromic films irradiated with absorbed doses ranges of 0–80 and 0–2000 Gy, respectively, were subjected to Doppler broadening measurements employing a HPGe γ–ray spectrometer. The Doppler broadening line–shape parameters (S and W) of 511 keV annihilation radiations were discussed in terms of the polymerization degree of the active components of these dosimetry films. The S- and W-parameters were found to be dependent on the active component structures of both films. A reasonable correlation was also found between the values of the S–parameter and the optical density of these radiochromic films. In addition, the Doppler broadening line–shape parameters were successfully used to provide explanation of the observed nonlinearity of these films at the end of their dynamic dose ranges. The results demonstrate the applicability of the PADB technique to probe the physical and chemical changes occurred in the active layer of the studied radiochromic films during the solid–state polymerization reaction caused by γ irradiation of different absorbed doses.