Cherenkov counting of 90Sr and 90Y in bark and leaf samples collected around Fukushima Daiichi Nuclear Power Plant

Bayesian multiple linear regression method for simultaneous determination of Cherenkov counting efficiencies of 89Sr, 90Sr and 90Y from mixed standard including 89Sr and 90Sr

In this study, Bayesian linear regression was employed to simultaneously determine Cherenkov counting efficiencies for ⁸⁹Sr, ⁹⁰Sr, and ⁹⁰Y from a mixed standard. Among the two codes utilized, PyMC3 and Stan, the latter produced more reliable posterior distributions for the three efficiencies, particularly for ⁹⁰Sr which is challenging to estimate due to its minimal activity changes. Validation showed excellent agreement between the activities determined with Stan's estimates and the certified activities, implying the applicability of the Bayesian approach.

Stabilization/Solidification of Strontium Using Magnesium Silicate Hydrate Cement

Magnesium silicate hydrate (M–S–H) cement, formed by reacting MgO, SiO2, and H2O, was used to encapsulate strontium (Sr) radionuclide. Samples were prepared using light-burned magnesium oxide and silica fume, with sodium hexametaphosphate added to the mix water as a dispersant. The performance of the materials formed was evaluated by leach testing and the microstructure of the samples was also characterized. The stabilizing/solidifying effect on Sr radionuclide in the MgO–SiO2–H2O system with low alkalinity is demonstrated in the study. The leaching rate in a standard 42-day test was 2.53 × 10−4 cm/d, and the cumulative 42-day leaching fraction was 0.06 cm. This meets the relevant national standard performance for leaching requirements. Sr2+ was effectively incorporated into the M–S–H hydration products and new phase formation resulted in low Sr leaching being observed.

Development of an interference-filter-type external-cavity diode laser for resonance ionization spectroscopy of strontium

A frequency tunable external-cavity diode laser (ECDL) using a narrow bandwidth (∼0.3 nm) interference filter has been developed for resonance ionization spectroscopy of strontium (Sr) with high isotopic selectivity. Improved wavelength and single mode stabilities of this interference-filter-type ECDL (IF-ECDL) over a commonly used (also home-made) Littrow-type ECDL were theoretically expected and experimentally confirmed by both a wavelength meter and a home-made Fabry-Perot interferometer. The measured spectral profile of the dominant isotope ⁸⁸Sr using our IF-ECDL in the 689.4 nm intercombination transition shows that the Lorentzian component (∼1.3 MHz) of the spectrum width is consistent with the obtained fringe width of the interferometer. High ⁹⁰Sr isotopic selectivity of ∼10⁴ with respect to ⁸⁸Sr is expected in this transition, which indicates that even if the manufacturing accuracy is not comparable to commercial Littrow-type ECDLs, our compact IF-ECDL having sufficient wavelength stability is a promising laser source for background-free analysis of radioactive ⁹⁰Sr in marine samples.

(90)Sr in teeth of cattle abandoned in evacuation zone: Record of pollution from the Fukushima-Daiichi Nuclear Power Plant accident

Here we determined the ⁹⁰Sr concentrations in the teeth of cattle abandoned in the evacuation area of the Fukushima-Daiichi Nuclear Power Plant (FNPP) accident. ⁹⁰Sr activity concentrations in the teeth varied from 6–831 mBq (g Ca)⁻¹ and exhibited a positive relationship with the degree of radioactive contamination that the cattle experienced. Even within an individual animal, the specific activity of ⁹⁰Sr (Bq (g Sr)⁻¹) varied depending on the development stage of the teeth during the FNPP accident: teeth that were early in development exhibited high ⁹⁰Sr specific activities, while teeth that were late in development exhibited low specific activities. These findings demonstrate that ⁹⁰Sr is incorporated into the teeth during tooth development; thus, tooth ⁹⁰Sr activity concentrations reflect environmental ⁹⁰Sr levels during tooth formation. Assessment of ⁹⁰Sr in teeth could provide useful information about internal exposure to ⁹⁰Sr radiation and allow for the measurement of time-course changes in the degree of environmental ⁹⁰Sr pollution.

Determination of low-level radiostrontium, with emphasis on in situ pre-concentration of Sr from large volume of freshwater sample using Powdex resin

An improved analytical method was developed for determining of low levels of radiostrontium in environmental freshwater samples. Emphasis was placed to the in situ pre-concentration of radiostrontium with Powdex resin in large volumes (100-300 L) of freshwater samples from many locations without using of deleterious substances such as NaOH and mineral acids. Measuring electric conductivity (EC) of water samples enabled the estimation of the amount of Powdex resin required for quantitative recovery of Sr from the large water samples in the field. The Powdex resin that adsorbed Sr was brought back to the laboratory, and Sr adsorbed in the resin was eluted by 8 M HNO3 together with Sr carrier added. Strontium was radiochemically separated by the cation exchange method for β counting after removal of most of the Ca using Ca(OH)2 precipitation. Through the procedure the Sr chemical yield was 88% on average. This analytical method was verified by analyzing 170 L of water samples with different salinity values, to which a known amount of (90)Sr was added. The detection limits of (90)Sr activities obtained using the 170 L water samples was estimated to be approximately 0.1 mBq L(-1) for a counting time of 100 min. The method was also applied to environmental samples collected from Ibaraki and Fukushima prefectures; their (90)Sr activities ranged from 0.16 to 0.93 mBq L(-)(1).