A history of fallout study in our environment since 1957

Abstract

  Since 1957, radiochemical analyses of monthly depositions of ⁹⁰Sr and ¹³⁷Cs in radioactive fallout in Japan have been carried out by the Meteorological Research Institute (MRI). These radionuclides in the ocean have been also measured and studied. These long-lived radionuclides were released mainly by atmospheric nuclear weapons tests conducted in late 1950s and early 1960s. As a consequence monthly deposition of ⁹⁰Sr and ¹³⁷Cs in Tokyo, Japan had been increasing early 1960s and those reached to 170 Bq m^-2 month^-1 for ⁹⁰Sr and 550 Bq m^-2 month^-1 for ¹³⁷Cs in June 1963, respectively. ¹³⁷Cs activity in surface water in the western North Pacific Ocean was also high which ranged from 10 Bq m^-3 to 100 Bq m^-3 in late 1950s and early 1960s. Both monthly deposition and activity level in surface water of artificial radionuclides originated from nuclear weapon tests decreased in late 1960s because atmospheric weapons tests were prohibited. In a long record of both monthly deposition and activity level in the surface water of artificial radionuclides, we also see an increase of them due to released radionuclides from the Chernobyl accident occurred in 1986.