Preparation of radioactive arsenic pulpdevitalizing agent

An arsenic pulp-devitalizing agent, As2O3, was labelled with 76As and 74As and its radiochemical and chemical impurities were investigated. 76As and 74As were produced by nuclear reactions, (n, γ) and (γ, n), respectively. As for 76As, the reagent was sealed in a polyethylene capsule and irradiated for two hours with thermal neutrons. The total neutron flux was 5.1 x 1011 n/cm2/sec. 74As was prepared by irradiating the target, the reagent sealed in a glass tube, for two hours with 18 MeV γ-rays produced by a linear accelerator. The intensity of the γ-rays was about 106 γ/min. The target was cooled with dry ice and ethanol throughout the period of irradiation. Decay curves for both nuclides were obtained by means of β-ray measurement using a GM-counter. The half-life was 26.5 hours for 76As and 18 days for 74As, which were well accorded with the reported values. γ-ray measurement by means of an NaI (Tl) counter also certified the radiochemical purity of the samples. As for 76As, the maximum range (1,400 mg Al/cm2) and the maximum energy (2.7 MeV) of β-rays were verified by the absorption curve. A sublimation test showed no chemical impurities. The various states of valence of arsenic were detected by means of paper chromatography developed with 20% acetic acid (saturated)-butanol system and determined by measuring the radioactivity of each fraction. The ratios of As(III) were 96 - 98% and 55 - 58% for the 76As and 74As samples, respectively. However, all of the valence of arsenic was converted to As(III) by annealing the target at 1600C in an air bath. The specific radioactivity of 76As and 74As was 6 - 7 mCi/g and 0.3 mCi/g of As2O3, respectively. These amounts were sufficient for the tracer of pulp-devitalizing agent. (Nakanishi, T.)