Here's a sign of a serious leak: when Japan's radiation reaches Massachusetts. Officials in the Bay State picked up (admittedly negligible) amounts of radioactivity in rainwater on Monday, showing just how big Japan's crisis has become. Back in Japan, plutonium was found in the soil at the troubled Fukushima plant, intensifying officials’ desperation at their inability to contain the situation. The plutonium, at least some of which came from degraded fuel in the damaged nuclear reactor, was found in five different places. The vice president of the Tokyo Electric Power Company, which owns the plant, stressed that the radioactive material was too weak to be harmful to humans, and was similar to readings in other parts of Japan from nuclear particles in the atmosphere. Meanwhile, worries about the crisis sent Japan’s stock market into a dive. TEPCO stocks fell for the fifth day in a row, and an affiliated engineering company dropped 8.8 percent.