Data on atmospheric (129)I concentrations and (129)I/(137)Cs ratios for suspended air particulate matter dispersed in eastern Japan just after the 2011 nuclear accident in Fukushima, Japan

Data of the atmospheric activity concentrations (in Bq/m(3)) of (129)I dispersed into the environment as aerosol immediately after the nuclear accident at Fukushima Daiichi Nuclear Power Plant in 2011 are presented. The radioactivity of (129)I was determined in suspended particulate matter (SPM) collected on filter tapes at 41 SPM monitoring sites in Fukushima and other prefectures in eastern Japan including the metropolitan area. For quantitative determination of (129)I in SPM samples by accelerator mass spectrometry (AMS), (129)I was chemically separated. Prior to the (129)I measurement, the (137)Cs activity was determined for the same SPM sample by gamma-ray spectrometry using Ge-semiconductor detectors. Combining activity concentrations of the two nuclides, an activity ratio of (129)I/(137)Cs (in Bq/Bq) was calculated for each SPM sample. In our research project, atmospheric activity concentrations of (129)I and (137)Cs, and their activity ratios were obtained for 920 SPM samples. Scientific discussion related to those data was described in the research article entitled “Time-series variations of atmospheric (129)I concentrations and (129)I/(137)Cs ratios in eastern Japan just after the 2011 nuclear accident in Fukushima, Japan” (Ebihara et al. 2022), where 363 data sets were presented. The remaining 557 data sets are presented in this article, so this data article makes up for the original research article (Ebihara et al. 2022). Blank values were obtained for whole analytical procedure. In addition, those for reagents and filters (both bland-new and used filters) were analyzed for assessing the contribution of the (129)I activity from these samples. Those data also are presented in this article.