2013 Volume 12 Issue 2 Pages 122-132
We discuss the half-life of radioactive substances in the environment, define the residence half-life, and derive the calculation method. The residence half-life is an index to represent migrations of radioactive compounds. It becomes positive or negative for the evaluation periods. To examine the index, we calculate the residence half-lives of Fukushima and Tokyo prefectures by using published ambient dose rates. Through the calculations, low and high frequency phenomena hidden in the change of ambient dose rate are separated by Fourier transformation and the inverse one. From the low-frequency component, we calculated plural residence half-lives for a continuous period, i.e., residence half-life function. The function shows that radioactive substances migrated, as the flow of air increases together with the advent of spring.
