Radiochemical determination of technetium-99 in environmental water samples

Abstract

This note describes a radiochemical procedure for the determination of technetium-99, a pure beta emitter (0.29 MeV maximum energy) with a half-life of 2.12 X 105 years, at levels as low as 0.5 dpm per liter of water. Most separation procedures in the literature are designed to separate much larger quantities of technetium, usually from fission products. Typical of these are the procedures collected by Anders (1). Where macroquantities are available, as in the determination of technetium for the measurement of nuclear fuel burnup (2, 2), chemical-instrumental methods are employed. These methods cannot be used at the low technetium concentrations found in the environment. Separation procedures that are designed for low concentrations are those for urine (4) and rain ( 5), but the former method does not provide adequate separation from some interfering activities and does not have adequate sensitivity, while in the latter method the technetium recovery is low and uncertain. Parallel studies that might be modified for analytical work are the search for long-lived technetium in minerals ( 6), the determination of technetium from the spontaneous fission of uranium-238 in pitchblende ores (7, 8), and the search for technetium produced in molybdenum ores by cosmic-ray neutrons (9).There is no published procedure for the determination of technetium-99 that is applicable to the analysis of large numbers of environmental water samples. With the increasing availability and use of gram to kilogram quantities of this fission product, such a procedure is needed. The present work provides a method for the determination of small amounts of technetium-99 in aqueous solutions, especially in naturallyoccurring water. EXPERIMENTALReagents. Tri-isooctylamine (TIOA), Bram Metallurgical Chemical Co., Philadelphia, Pa., reagent grade CP, was used without further purification to form 5% (V/V) solutions with xylene. The ruthenium carrier was prepared by dissolving 10 grams of C. P. ruthenium trichloride, A. D. MacKay, Inc., New York, N.Y., in 6TV HC1 and diluting to 500 ml with 6TV HC1. The ruthenium concentration was about 10 mg/ml.Tracers. Technetium-99 was obtained from Oak Ridge National Laboratory as an aqueous solution of ammonium pertechnetate. The concentration was determined by four-pi (1) E.

Determination of technetium-99 in environmental samples: A review

“…So far, a large number of analytical methods have been developed and applied for determination of 99 Tc in various environmental samples, such as soil, sediment, seaweed, seawater, groundwater, surface water and nuclear waste [4][5][6][7][8][9][14][15][16][18][19][20][21]. Table 4 15 summarizes the reported methods for 99 Tc determination along with typical recoveries and detection limits.…”

“…Because of the volatile property of Tc, it has been suggested that evaporation of water should be carried out in basic medium [4]. Some experiments [76] have shown no loss of 99 Tc during evaporation of water at 70-80 0 C, and the adjustment of water to basic medium is not necessary when the temperature is kept under 90 0 C [51].…”

“…The colloid formed in the water might coat the surface of the exchange resin, resulting in a low chemical yield of 99 Pre-concentration by co-precipitation is based on insolubility of low oxidation states of Tc, such as TcO 2 , and their strong sorption to particles or precipitate formed in the solution. In this method, reductants such as FeSO 4 or sulphite, and carrier such as FeCl 3 .6H 2 O, are firstly added to the water, and then NH 3 .H 2 O or NaOH is added to adjust pH to 9 to form Fe(OH) 2 precipitation, which carries the formed TcO 2 and separates it from the water matrices. This method has been successfully applied to pre-concentrate 99 Tc from 1-100 L seawater and rain water samples, and chemical yield of 50-80 % depending on the volume of the sample has been reported [5].…”

“…TiOA is the most common extractant applied for the separation of 99 Tc [4,8,9,74,99]. This is based on the formation of a neutral complex of TcO 4 -with TiOA in low concentration of acid.…”

“…99 Tc is a pure β -emitter with the maximum decay energy of 0.294 MeV. It can therefore be measured by radiation counting [4][5][6][7][8][9]. The β counting using gas flow Geiger-Müller (GM) counter and liquid scintillation counter (LSC) are the main techniques for 99 Tc measurement.…”