The terephthalate dosimeter for γ-, X- and β-radiation: dependence on dose and dose rate

Abstract

The present work describes investigations of the chemical dosimeter system terephthalic acid (TA)⇝hydroxyterephthalic acid (HTA). After measuring long-term stabilities of different TA and HTA solutions the radiation-induced HTA yields using external (X-, γ-) and internal (β-, γ-) sources are investigated at varying dose rates. On X-irradiation 18% of decomposing TA is converted to HTA. An unknown mechanism leads to a prompt decomposition of HTA beginning after some weeks and which is augmented especially by β-irradiation. Therefore, the yield of HTA is not proportional to dose after long-term irradiation. G values for the formation of HTA in 1 10 -4 MTA solutions at higher dose rates ( 2 mGy min -1) are 0.92 for 137Cs, 0.88 for 32P and 0.80 (±0.02) for 0.115 MeV X-rays. At lower dose rates G(HTA) increases, leading to a maximum at approximately 0.02 mGy min -1 for 137Cs. On varying the TA concentration in the range 5x 10 -5 −5 x 10 -3 M, the radiation-induced HTA yield increases by 30%. Consequently, TA solutions of concentration 1 x 10 -4 M are only needed at higher doses ( 100 Gy) in order to avoid a decrease in the yield of HTA associated with a depletion in TA.