 Radioactive isotopes of the element xenon are produced by the atom splitting that takes place in nuclear explosions and readily seeps out even from underground tests.The advance warning of the test sent to the Chinese government reportedly said that the planned test yield was to be equivalent to approximately four kilotons in strength, but most outside estimates, based largely on seismic readings, put the yield at much less.At a meeting with President Vladimir Putin, Russian Defense Minister Sergei Ivanov stated that "the power of the tests carried out was 5 to 15 kilotons", though this early estimate is much higher than any other international estimate.