Measurement of high dose rates by photon activation of indium foils

Photon activation of indium foils is proposed as a dosimetry technique for high dose rate measurements in a Co-60 irradiation facility. The irradiated indium nuclei may be raised to its metastable isomers of In-113m and In-11 5m. The isomer In-115m, with appreciable induced radioactivity, was selecte d for dose-rate measurements. Based on the photon flux distribution and the derived dose rates, which were simulated by the MCNP code, the dependence of dose rate measurement sensitivity of indium. foils with respect to photo n energy at various irradiation distances is described. For practical uses, the radioactivity of In-115m was linearly related to the dose rate respons e at the specified irradiation positions. By comparing with a calibrated do simetry system, the measurement deviation of the indium dosimeter, over dos e rates ranging from 10 to 10(4)Gy/h, was evaluated and exhibited an uncert ainty of +/- 7%. Other related characteristics including measurement sensit ivity and range, linearity with respect to the variation of dose rate, and limitations of the indium dosimeter were evaluated to justify it as an alte rnative for monitoring dose rate in an irradiation field. (C) 2001 Elsevier Science Ltd. All rights reserved.