Response of radiation monitoring labels to gamma rays and electrons

Many kinds of coated or impregnated reflecting papers change color or become colored by large radiation doses. Such papers or “labels” do not generally supply dosimetry information, but may give useful inventory information, namely a visual indication of whether or not an industrial product or location has been irradiated to high doses. Among labels available worldwide, a few are suitable for indicating absorbed dose regions of slightly less than 10⁴ Gy (< 1 Mrad), and some are intended for monitoring high dose ranges (i.e., sterilization dose levels of > 10⁴ Gy or > 1 Mrad), and in some cases even up to very high dose regions (∼10⁵ to 10⁶ Gy or ∼10 to 100 Mrad). Only one labels which is expected to be commercially available, was studied for lower dose levels, 10¹-10³ Gy (1-100 krad), namely one based on polymerization of diacetylene. Tests of stability, sensitivity of ambient light, and differences in dose rate and radiation type (gamma rays and electron beams) were made on 15 kinds of labels. The results show that, for many types of indicators, diverse effects may give misleading conclusions unless countermeasures are taken. For example, some of the most commonly used labels, which contain dyes that indicate changes of pH due to release of halogen from halogenated substrates, have limited shelf life and must be protected from extreme environmental conditions. Some also show a marked rate dependence of response. Readings of color reflection optical densities on labels or long paper strips permit somewhat more precise discrimination of dose levels, and may sometimes be useful for monitoring differences in local dose distributions or area monitoring of radiation damage probabilities around particle accelerators or large radionuclide sources.