Characteristics of Tetrazolium Violet for Radiation Processing Dosimetry

Abstract

The dosimetry characteristics of 2, 5-dipheny-3-(1-naphthyl)-2H-tetrazolinum Chloride (TV) for radiation processing has been investigated for gamma and electron beam irradiation processing. The steady state investigations of the TV solutions were undertaken using the panoramic facilities of the Institute of Isotopes (Budapest, Hungary) and the Radiation Technology Centre of the Ghana Atomic Energy Commission in Ghana. The dynamic studies were carried out using the 4 Me V LPR - type linear Accelerator of the Institute of Isotopes (Budapest, Hungary). In all cases U-V spectrophotometers were used to establish the absorbed dose by measuring the absorbance of the film or solution with the peaks occurring in the 500-600 nm range. The investigations included the effect of solute concentration and solvents used on the performance of both the solution and films systems, the effect of pH, irradiation temperature, humidity and the stability of the dosimeter system both as solutions and is in radiochromic dye films. The observations made indicate that the TV undergoes a-two electron reduction process as in other reported cases to form the violet coloured formazan, the extent of colour change being dependent on the dose, the concentration and the pH among others. The ImM-TV solutions for instance may measure doses up to 50 kGy and a radio chromic dye ·film prepared from it may go up to 60 kGy. If N2 saturated, the solutions may be used for low dose irradiation below 1kGy and the addition of alcohol also improvise the low absorbed dose measurements. The prepared solutions and films are generally stable if stored in the dark but temperature during and after irradiation affects the readout. The temperature effect therefore requires that in all cases in-plant calibration of the system be carried out. Again, it has been established that increased relative humidity increases the absorbance of the film for the same given dose, which also requires that the films must be conditioned at all times to ensure reproducible results. Finally preliminary tests carried out both in industrial gamma- and electron beam facilities have shown promise for the routine use of this dosimeter system both as a solution and as a film.