Symposium on International Safeguards: Linking Strategy, Implementation and People - IAEA CN-220

Improved Technique for the Determination of Uranium Minor Isotopes Concentrations in Microparticles by Using Secondary Ion Mass-Spectrometer in Multicollection Mode

22 Oct 2014, 12:00

20m

Room M1 (M Building)

oral State of the Art Environmental Sample Analysis

Speaker

Ivan Elantyev (Laboratory for Microparticle Analysis)

Description

Traditional method of the analysis implies simultaneous measuring of secondary ion currents of isotopes 234U+, 235U+, 238U+, ions with mass 236 amu (236U+ and 235UH+) and hydride ions 238UH+ by using mass-spectrometer Cameca IMS1280 in multicollection mode. Calculating of uranium isotopic composition is performed using the results of 40 successive measurements of those currents (cycles). Duration of each measurement is 8 seconds. Small amounts of uranium minor isotopes are limitation for precise determination of their concentrations. To prevent the damage of the secondary ions detector the intensity of ion current should be no more than 5×105 cps. This limitation does not allow to set higher primary ion current for the increasing of minor uranium isotopes ions emission because of the signal of ions 238U+ gets too high. New technique is developed to improve the accuracy of determination of uranium minor isotopes concentrations. Process of measurement is divided on two steps. First step is a measurement of ion currents during 20 cycles by five detectors. The second step implies the elimination of ions 238U+ hitting to the detector and 10 times increasing of primary ion current. The ratio 235U/238U is calculated from the first step results, so uncertainty of determination of this value is 1.4 times bigger than with duration of 40 cycles of the measurement. The ratios 234U/235U and 236U/235U are calculated during the second step. This technique allows to determine content of 234U and 236U with 3 and 5 times less uncertainties respectively, but with different degree of the sputtering particles. Moreover the duration of each cycle was set less (1 second) to use data more efficient. The technique accordingly with every second counting provides uncertainty of determination 236U concentration 4 times less than traditional method at the same degree of sputtering particles.