Procedures for precise measurements of 135Cs/137Cs atom ratios in environmental samples at extreme dynamic ranges and ultra-trace levels by thermal ionization mass spectrometry

Abstract

Determination of Cs/Cs atom ratios has the potential to be a powerful tool for nuclear forensics and monitoring environmental processes. We present optimized chemical separation techniques and thermal ionization mass spectrometry (TIMS) protocols to obtain precise Cs/Cs atom ratios for a range of environmental sample types. We use a combination of double AMP-PAN separation and Sr-spec resin column purification to yield excellent separation from the alkali metals (Rb separation factor > 600), which normally suppress ionization of Cs. A range of emission activators for the ionization of Cs were evaluated and glucose solution yielded the optimal combination of a stable Cs beam, minimal low-temperature polyatomic interferences and improved ionization efficiency. Mass-spectrometric determination of low abundance Cs andCs is compromised by the presence of a very large Cs beam, which may be scattered and cause significant spectral interferences. These are explored using multi-static Faraday cup - ion counter methods and a range of energy filter settings. The method is evaluated using environmental samples and standards from regions affected by fallout from Chernobyl (IAEA-330) and Fukushima nuclear disasters. Where the intensity of Cs is large relative to Cs and Cs (< 30cps), minor polyatomic interferences need to be considered. In the absence of a standard with Cs/Cs < 1 × 10, we explored the reproducibility of Cs/Cs atom ratios at these high dynamic ranges and extremely low abundance (Cs ≈ 12 fg g) for sediments from an estuarine setting in SW England, UK.

Determination of Ultratrace Level 135Cs and 135Cs/137Cs Ratio in Small Volume Seawater by Chemical Separation and Thermal Ionization Mass Spectrometry

“…The improvement of ionization efficiency of the analyte by adding activators on the filament has been widely reported. For the measurement of 135 Cs, silica gel + H 3 PO 4 , TaCl 5 + H 3 PO 4 , Ta 2 O 5 , graphite, and glucose have been applied as activators, ,, and the highest ionization efficiency of 20.9% was reported by using graphite slurry. Our result using 10 μg of glucose is more than 2 times higher than the reported value.…”

“…By combining AMP-PAN with cation exchange chromatographic separation, a decontamination factor of more than 1800 for Rb was achieved, which is more than 3 times higher than the reported values. 16,28 For TIMS measurement, the 0.5 M HNO 3 eluate was evaporated to dryness and redissolved in 10 μL of 2% HNO 3 and loaded on the Re filament after being mixed with glucose. Spectra of a mass scan (m/z of 133−138) of a real sample (IAEA-375) are presented in Figure S4.…”

“…Although the determination of 135 Cs in nuclear waste using neutron activation analysis (NAA) was reported in 1973, the determination of 135 Cs in environmental samples became possible only in recent years by mass spectrometry due to its low concentration. Sector field inductively coupled plasma-mass spectrometry (SF-ICP-MS), , electrothermal vaporization-inductively coupled plasma-mass spectrometry (ETV-ICP-MS), triple quadrupole inductively coupled plasma-mass spectrometry (ICP-QQQ-MS), ,, resonance ionization mass spectrometry (RIMS), and thermal ionization mass spectrometry (TIMS) ,− have been used for this purpose. Due to the serious isobaric interference of 135 Ba and polyatomic interference (e.g., 95 Mo 40 Ar + , 97 Mo 40 Ar + , 119 Sn 16 O + , 121 Sn 16 O + ), high decontamination factors for Ba and other interfering elements are needed prior to the spectrometric measurement.…”

Determination of Ultralow Level 135Cs and 135Cs/137Cs Ratio in Environmental Samples by Chemical Separation and Triple Quadrupole ICP-MS

“…Mass spectrometry is therefore a practical technique for 135 Cs measurement in the environmental samples. Among them, resonance ionization mass spectrometry (RIMS), thermal ionization mass spectrometry (TIMS), − sector field inductively coupled plasma-mass spectrometry (SF-ICP-MS), , electric thermal vaporization ICP-MS (ETV-ICP-MS), and triple quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS) − have been used for this purpose. ICP-MS/MS is becoming the most attractive mass spectrometric technique for the measurement of 135 Cs due to its highest popularity, high abundance sensitivity, and excellent removal of barium interference by reaction cell technique.…”

Spatial pattern of plutonium and radiocaesium contamination released during the Fukushima Daiichi nuclear power plant disaster

“…Adding 135 Cs to the suite of isotopic analyses is necessary because all three reactors were boiling-water reactors with similar fuels (Reactor Units 1 & 2 - UO 2 ; Reactor Unit 3 - UO 2 /MOX) and operating conditions 23 . Also, mass-spectrometric determination of 135 Cs/ 137 Cs can achieve greater relative precisions 20 and this signal will remain useful in environmental samples for much longer ( 134 Cs t 1/2 = 2.07 a, 135 Cs t 1/2 = 2.3 Ma, 137 Cs t 1/2 = 30.08 a).…”