The dosimetry characteristics of a polyvinylalcohol based radiochromic dye film containing the ditetrazolium salt nitro blue tetrazolium chloride were studied with respect to the potential use of the films for routine dosimetry in radiation processing. The useful dose range for the dosimeter film for gamma and electron irradiation is 5–50kGy depending on the concentration of the dye. The effects of irradiation temperature and humidity, as well as the stability of the response of the film before and after irradiation, were investigated and determined. Formulations for preparation of the films with different concentrations of the dye and with different pH were tested. The films were also tested in industrial gamma irradiation facilities for process control purposes by comparing their performance with transfer standard dosimeters.

Tetrazolium salts as heterocyclic organic compounds are known to form highly coloured, water insoluble formazans by reduction, which can be utilized in radiation processing dosimetry. Radiochromic films containing nitro blue tetrazolium dissolved in a polymer matrix were found suitable for dose determination in a wide dose range both by absorbance and reflectance measurements. The concept of measuring reflected light from dose labels has been discussed earlier and emerged recently due to the requirement of introducing semiquantitative label dose indicators for quarantine control. The usefulness of the method was studied using the newly developed radiochromic dye films as well as already existing ones.

The radiolytic reactions of the ditetrazolium salt nitro blue tetrazolium chloride (NBTCl2) were studied by pulse radiolysis technique in aqueous solution under reducing and oxidising conditions with the aim of potential dosimetry application. Under reducing conditions the fast formation of the tetrazolinyl radical is observed that is followed by the appearance of monoformazan (MF+), i.e. one of the tetrazolium rings is reduced to formazan. The formation of the water-insoluble diformazan, i.e. the result of the second reduction step was not observed in pulse radiolysis. Formazan formation was not found under oxidative conditions.

The ions of nitro blue tetrazolium (NBT2+) in aqueous ethanol solution are readily reduced radiolytically first to monoformazan (MF+) and then to diformazan (DF) having high linear molar extinction coefficients at the absorption maxima of similar to 522 and similar to 570-610 nm. Spectrophotometric analysis then provides potential use in high-dose dosimetry over the dose ranges of 0.1-1 and 1-30 kGy. The solution is stable for the first 24 h after the irradiation. (C) 1999 Elsevier Science Ltd. All rights reserved.

A product-overlap type gamma irradiation facility with wet storage was put into operation recently in Damascus, Syria and its technical specifications were controlled by dosimetry commissioning experiments and compared to the data specified by the supplier. In the course of this procedure detailed dose mapping using different density products was carried out, and thus the minimum and maximum dose locations within the product boxes were determined. Using these data the plant efficiency and the dose uniformity ratio have been calculated. The dose distribution was also determined vertically along the product carrier. The results were then analyzed with respect to the construction of the facility.

Two industrial scale, “ROBO” type 60Co gamma irradiation facilities have recently been put into operation in Syria and Peru, and the dosimetry commissioning of both plants have been carried out to determine dose distribution within products and to calculate plant parameters such as efficiency, dose uniformity ratio and throughput. There are some design modifications between the two plants in connection with the location of the carriers with respect to the source plaque and also to each other. The effect of these construction modifications on the plant parameters is discussed in the analysis of the dose distribution data measured in the carriers with depth and height among the four irradiation rows on both sides of the source plaque. The plant parameters were also calculated for different product densities using the technical data of the facilities, and the calculated and measured results were compared to each other.