A high-dose intercomparison study involving red 4034 perspex and radiochromic dye films

The present dosimetry intercomparison exercise involved the National Bureau of Standards (NBS) Gaithersburg MD, USA; the National Physical Laboratory (NPL) Teddington, and Harwell Laboratory, UK. It was undertaken as an extension of previous intercomparison exercises and forms part of an on-going calibration and quality-assurance programme for those in-plant dosimetry systems widely used in radiation sterilisation. Two dosimetry systems, Harwell red 4034 Perspex and Far West Technology radiochromic dye film (FWT-60-00) were used. The dosimeters were irradiated with cobalt-60 gamma radiation at absorbed dose rates in the range 1-4 Gy s-1 to absorbed doses in the range 10-35 kGy. Irradiations were carried out at each of the participating laboratories, and the irradiated dosimeters were carried by hand between laboratories to eliminate any possibility of maltreatment which might occur if conventional modes of transport such as air freight were used. A minimum of four dosimeters were irradiated at each dose and the elapsed time between irradiation and spectrophotometric reading of the dosimeters varied from one to nine days. The following comparisons were made: laboratory spectrophotometric readings at the accepted measurement wavelengths (radiochromic film: 605 nanometers (nm); red 4034 Perspex: 640 nm); dosimeter thickness measurements; estimates of absorbed dose. Measurement precision was in all cases better than ± 1.5% one sigma. The agreement obtained between laboratory estimates of absorbed dose and between spectrophotometric readout was within ± 2% for both dosimetry systems. (author)