Statistical analyses were performed for 50 sets of equal interval data of natural terrestrial gamma-ray dose rates observed for various distances. The multiple regression analysis shows that the variance of a set of data can be expressed as a function of the length and the mean value of the data with relatively high correlation coefficient. One-dimensional spectral analyses for the 50 sets of data suggest that the structures of fluctuation are similar to one another for various distances of observation starting from 0.1 km to about 7 000 km. Each power spectral density can be approximated in the form of P (k) =0.780×10-3 m2.20 k-1.18 where k (cycle/km) and m (nGy/h) are the wave number and the mean, respectively.
Isotope125I in animal experiments is used for several purposes. One major problem with using125I is to handle it extremely carefully. The careful handling is required when using125I in animal experiments because of its higher evaporation and difficulty for sealing. When conducting animal experiments while using125I, we have encountered several serious problems but have devised new techniques and methods for a long time. In this paper, we will describe the safety handling for requirements based on our experiments. The newly devised safety handling procedures are the following : (1) a device for protecting isotope contamination during the preparation of the injectable solution, (2) collection method of airborne radioactivity from the animals that were injected, (3) enhancing the method for autoradiography of the whole body, (4) finding of elusion of125I from the tissues during fixative process, (5) estimation of the exposed time for light microscopic autoradiography.