福島第一原発事故の実態把握について、2011年3月の事故以降で確定できた90Srおよび137Cs月間降下量を誤差と併せてプロットしています。134Csは事故直後は137Csとほぼ等量降下していますから、放射性セシウム全体ではこのプロットのほぼ倍量となります。ただし、90Sr、137Csはどちらもおよそ30年の半減期で減衰しますが、134Csはおよそ2年で半減します。図示した誤差は計測の統計誤差で、1シグマです。測定誤差は本来全ての測定値につき表示すべきですが、グラフが見づらくなるため、従来はあえて表示してきませんでした。
Given the social as well as scientific concerns about local contamination caused by the Fukushima Dai-ichi Nuclear Power Plant accident, the estimate of the 137Cs deposition at the MRI, Tsukuba is plotted for a few years 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). Moreover -- since 134Cs deposited in almost comparable amount -- the total radioactive cesium soon after the accident becomes mostly double. Although 90Sr and 137Cs decay gradually with a half-life of 30 years, 134Cs decays more quickly with a half-life of about 2.0 years. 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.