Interference of ⁹¹Y with the Rapid Determination of ⁹⁰Sr Originating from the Chernobyl Fallout Debris

Abstract

An improved method for the determination of 90 Sr and 91 Y in grass ashes and other materials was developed, based on a tributylphosphate (TBP) extraction of the radio-yttrium. The interference of 91 Y with the ^-measurement of the extracted 90 Y was studied and eliminated either by graphic subtraction of the 91 Y decay diagram from the total decay plot of the yttrium fraction or by energy discrimination of these two nuclides by Cerenkov-counting. Using the latter method, the analysis of one sample of ash takes six hours. Results of 90 Sr and 91 Y acivity concentrations in grass samples collected after the Chernobyl event and of 90 Sr in various IAEA reference materials are given.

Rapid Determination of 90Sr in Foodstuffs and Environmental Material

“…Then 10 mL of water are added to the solution and it is cooled down to 5°C. The Cerenkov radiation produced by the high energy beta emission of 90 Y is measured [3] with a Canberra Packard Tri-Carb 2250 CA liquid scintillation analyzer with a selective energy window corresponding to the 90 Y signal [4,5]. The overall efficiency for the ^Y signal measurement with this window is 21%.…”

“…From this point onward the procedure is the same as that for the HDEHP extraction method from step d). [1,4,9] 5 g of ground ash residue are digested for 2 hours with 100 mL of boiling 65% HN0 3 containing 10 mg of Y carrier and 1 mg each of various holdback carriers (Cs, Ba, La, Fe and Sr) for several hours. The mixture is cooled and filtered through filter paper by gravity to remove insoluble material, which is washed thoroughly with 65% HN0 3 .…”

Determination of Strontium-90 in Environmental Samples Containing Thorium

“…During storage in laboratory conditions secular equilibrium is attained in about three weeks and the concentration of 90 Sr can then be inferred from measurement of 90 Y. After separation the 90 Y can be measured by liquid scintillation counting [6][7][8] using added scintillant, or by measuring the Cerenkov radiation produced when water is added. 6,[8][9][10][11][12][13] Cerenkov radiation (blue light) is emitted when the velocity (v) of an electron in a transparent medium with a refractive index (m) is greater than the velocity of light in the same medium.…”

“…After separation the 90 Y can be measured by liquid scintillation counting [6][7][8] using added scintillant, or by measuring the Cerenkov radiation produced when water is added. 6,[8][9][10][11][12][13] Cerenkov radiation (blue light) is emitted when the velocity (v) of an electron in a transparent medium with a refractive index (m) is greater than the velocity of light in the same medium. This condition is met when v !…”

“…Reported radiochemical separation methods for isolating 90 Y use fuming nitric acid, [14][15][16] cation exchange, 17 solvent extraction with tributyl phosphate (TBP), 8,18 di(2-ethylhexyl)phosphoric acid (HDEHP) 13,19 or dicyclohexyl-18-crown-6, 20,21 or ion chromatography. 22…”