The estimate of the ¹³⁷Cs deposition at the MRI, Tsukuba is presented for several months after the accident in March, 2011

Given the social as well as scientific concerns about local contamination caused by the Fukushima nuclear accident, the estimate of the ¹³⁷Cs deposition at the MRI, Tsukuba is plotted for several months after the accident in March, 2011 in the figure. The estimate was computed based on the value obtained by measuring the aliquot of the sample water (wet + dry depositions). Since cesium is distributed between the liquid and the solid phases, the accurate value is not obtained unless the concentration of the whole sample by evaporation was achieved. Probably, current values are sorts of underestimation. Moreover -- since ¹³⁴Cs deposited in almost comparable amount -- the total radioactive cesium becomes mostly double. An error depicted is a statistical one for the activity measurement (1σ). Although the error should have been displayed essentially, since it is hard to see a graph with many errors, the errors have not been displayed conventionally.

The whole sample measurement by evaporation concentration should be carried out in order to obtain the precise value instead of an estimate, requiring more time. Since the activity levels of the atmospheric deposition sample were extraordinarily elevated compared with those prior to the accident, the evaporation concentration process is now underway with paying attention to the contamination of the laboratory rooms and a worker's possible exposure. Kind understanding is much appreciated.

Moreover, since the activity background of laboratory and measurement room environments, and detectors, etc. were sharply increased due to the pollution by the accident, regarding the measurement of the pre-Fukushima samples, problems of the contamination must occur not only in an evaporation process but also in other analytical processes. Therefore, it is difficult to obtain precise observation data for the pre-Fukushima samples for the time being. Decontamination of working environment, change of detectors, etc. are, however, carried out gradually, thus the improvement of the working environment is pursued. The precise data are to be obtained in the near future; please give us the time needed for such procedures.