Abstract
The FBX dosemeter consists of 0.20 mM of ferrous ammonium sulphate, 5.0 mM of benzoic acid and 0.20 mM of xylenol orange in 0.05 N sulphuric acid. The dye xylenol orange contains impurities of semi-xylenol orange, cresol red and iminodiacetic acid. These impurities affect both the G(Fe3+), the number of ions formed per 100 eV, value and the molar absorption coefficient of the ferric-xylenol orange complex in the FBX system. The authors report detailed investigations regarding G(Fe3+) and molar absorption coefficient values using xylenol orange obtained from different manufacturers. Values measured by other laboratories are also included. It seems that xylenol orange of improved purity is now available and even though the molar absorption coefficient of the ferric-xylenol orange complex still varies for xylenol orange obtained from different companies, the G(Fe3+) value is relatively constant. This means that it is now possible to use a standard calibration graph for the FBX dosemeter in the form of ferric ion concentration against absorbed dose.