Determination of Characteristic vs Anomalous ¹³⁵Cs/¹³⁷Cs Isotopic Ratios in Radioactively Contaminated Environmental Samples

Abstract

A contamination with the ubiquitous radioactive fission product 137Cs cannot be assigned per se to its source. We used environmental samples with varying contamination levels from various parts of the world to establish their characteristic 135Cs/137Cs isotope ratios and thereby allow their distinction. The samples included biological materials from Chernobyl and Fukushima, historic ashed human lung tissue from the 1960s from Austria, and trinitite from the Trinity Test Site, USA. After chemical separation and gas reaction shifts inside a triple quadrupole ICP mass spectrometer, characteristic 135Cs/137Cs isotope signatures (all as per March 11, 2011) were obtained for Fukushima- (∼0.35) and Chernobyl-derived (∼0.50) contaminations, in agreement with the literature for these contamination sources. Both signatures clearly distinguish from the characteristic high ratio (1.9 ± 0.2) for nuclear-weapon-produced radiocesium found in human lung tissue. Trinitite samples exhibited an unexpected, anomalous pattern by displaying a low (<0.4) and nonuniform 135Cs/137Cs ratio. This exemplifies a 137Cs-rich fractionation of the plume in a nuclear explosion, where 137Cs is a predominant species in the fireball. The onset of 135Cs was delayed because of the longer half-life of its parent nuclide 135Xe, causing a spatial separation of gaseous 135Xe from condensed 137Cs, which is the reason for the atypical 135Cs/137Cs fractionation in the fallout at the test site.

Innovative ICP-MS/MS Method To Determine the 135Cs/137Cs Ratio in Low Activity Environmental Samples

“…Two 137 Cs certified reference materials (CRM) from the International Atomic Energy Agency (IAEA) were analyzed. Both CRMs, IAEA-330 and IAEA-375, were selected as they are often used in the literature to validate 135 Cs/ 137 Cs analytical protocols. ,,− ,,, They correspond to spinach and soil samples collected in Ukraine and Russia in 1990, respectively, and show a 135 Cs/ 137 Cs ratio characteristic of the Chernobyl fallout. The compatibility of the measured and published 135 Cs/ 137 Cs ratios was monitored by calculating the E n score ( E n ), given by eq . E normaln 0.25em score = false| IR measured − IR published false| U IR measured 2 + U IR published 2 0.25em Where IR measured and IR published correspond to 135 Cs/ 137 Cs isotopic ratios measured with our method and those published in the literature, and U IR corresponds to their uncertainty at k = 2.…”

“…The higher these parameters are the more the production of 136 Xe from 135 Xe is favored, inducing the depletion of 135 Cs and, consequently, the decrease of the 135 Cs/ 137 Cs ratio. Low 135 Cs/ 137 Cs atomic ratios of 0.52 ± 0.02 and 0.35 ± 0.02 (decay-corrected to March 11th, 2011) have been reported for Chernobyl and Fukushima fallout, respectively. ,,− Conversely, for short neutron exposure times, such as those that occurred during the atmospheric testing of nuclear weapons, the characteristic 135 Cs/ 137 Cs ratio is much higher (2.62 ± 0.48, decay-corrected to March 11th, 2011). ,,,, The 135 Cs/ 137 Cs ratio is therefore a particularly powerful indicator of the 137 Cs source, and it can provide a long-lived fingerprint of nuclear releases. This high potential is nevertheless limited by the fact that its measurement in environmental samples is associated with several analytical challenges. ,,, …”

“…A specific radiochemical procedure is therefore needed to isolate the radiocesium from the sample matrix and to purify it from all other elements generating mass interferences. Usually, Cs is separated from the matrix using highly selective molecules such as ammonium molybdophosphate (AMP) and then interferents by combining the properties of anion and cation exchange resins. ,,, In addition, due to the low radiocesium concentration in the environmental samples (i.e. collected outside of exclusion zones and former nuclear testing areas), large quantities of samples must be processed to detect 135 Cs. , …”

Developing Accelerator Mass Spectrometry Capabilities for Anthropogenic Radionuclide Analysis to Extend the Set of Oceanographic Tracers

“…Cs extraction and purification is based on the procedure described in Zok et al (2021). A Cs extraction with Ammonium phosphomolybdate hydrate (AMP, Alfa Aesar) is followed by an anion exchange column [Dowex 1-X8 (100-200 mesh), Alfa Aesar] and a cation exchange column [AG 50W-X8 (100-200 mesh), Bio-Rad Laboratories, Inc.].…”

Identification, isolation, and characterization of a novel type of Fukushima-derived microparticle

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the two radiocesium isotopes 134 Cs (T 1/2 = 2.01 y) and especially 137 Cs (T 1/2 = 30.08 y) are relevant for long-term radioprotection considerations. Quite recently, long-lived 135 Cs (T 1/2 = 2.3•10 6 y) has attracted interest for environmental sciences, as it allows for the identification of a source via its distinct 135 Cs/ 137 Cs ratio [2][3][4][5]. Unfortunately, analysis of this ratio by desktop mass spectrometry requires relatively high activities/amounts of both radionuclides and is challenging for ultratrace levels.

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