And of atmospheric testing of nuclear weapons by world nuclear powers, which did not stop until 1980 (China).
One of my twitter followers lives in southwestern Japan. A while ago he sent me the result of the test he had it done with the ashes from burning wood pellets in his stove this winter. The lab test, using the germanium semiconductor detector, found 223.8 Bq/kg of cesium-137.
He was upset, thinking it is from Fukushima I Nuclear Power Plant, until I pointed out to him that there was no cesium-134 found. The cesium in the ashes is most likely from the fallout from atmospheric testing, and the Chernobyl accident in 1986.
He burned 600kg of wood pellets made from cedar trees in Ehime Prefecture in Shikoku Island in southwestern Japan. According to the pellet manufacturer, the concentration factor was about 375, and radioactive cesium (Cs-137) in the pellets was estimated to be about 0.59 Bq/kg.
He said he will "entomb" the ashes with concrete and bury.
The chart plotting the historical monthly fallout in entire Shikoku (4 prefectures, as they didn't start measuring the fallout in Ehime until 1977) shows the spike from the Chernobyl accident was less than that of the atmospheric testing, and larger than that from the Fukushima accident. (The chart was created from data at Japan Chemical Analysis Center. Y-axis in log scale.)
In 2012 he tested the ashes from burning the wood pellets from a different company, and to his great dismay the test found 1,000 Bq/kg of radioactive cesium (Cs-137) in the ashes. He had already spread some of those ashes on his home garden. Those pellets, it turned out, were made from trees from Europe (Sweden, Finland, Germany, Austria) that the manufacturer had started to purchase in 1994 . That manufacturer told him that it had never ever occurred to them that the trees were contaminated from the Chernobyl accident, and there was no regulation on importing. The manufacturer told him that they chose European trees because they were cheap, and supply was steady.
April 26 marks the 27th anniversary of the Chernobyl Nuclear Plant accident.