Influence of sulphuric acid contaminants on Fricke dosimetry

The sulphuric acid used for the preparation of the Fricke dosimeter solutio n may contain trace impurities that can affect the yield of ferric ions. Tw o methods, pre-irradiation or oxidation with hydrogen peroxide, have been p roposed to reduce the influence of these impurities. Fricke users sometimes omit this treatment. In the present work Fricke solutions prepared From si x different brands and qualities of sulphuric acid were compared in order t o study any influences of the acid on the ferric ion yield. It was shown th at the use of analytical grade sulphuric acid from one manufacturer resulte d in a reduction of the ferric ion yield of about 5% at an absorbed dose of similar to 20 Gy. If this solution were to be used for an absolute dose de termination together with epsilon(m)G values from the literature the absorb ed dose would be underestimated by the same amount.