The effect of scattered radiation in 60Co beams on wall correction factors for ionization chambers

The Awall correction factors used in dosimetry protocols are obtained by Monte Carlo methods that assume 60Co beams equivalent to 1.25-MeV radiation. Real 60Co beams contain lower energy components; in addition, Awall is defined differently by different authors. In the present work, Awall as defined by Rogers, Bielajew, and Nahum (1985) has been calculated by Monte Carlo methods at several energies, for a graphite cavity chamber, using the revised stopping-power data of Seltzer and Berger (1982). It is concluded that the true value of Awall for chambers designed for use in 60Co beams will not move more than 0.1% below the value calculated for 1.25-MeV photons.