137Cs contained in books printed during the 1960s in Japan

Radioactivity values of 137Cs in printed pages and covers of hardbound books issued during the 1960s in Japan were measured by γ-ray spectrometry. The result showed that the main source of 137Cs present in the books was rice straw used to make the backing board of covers. The 1965 peak of 137Cs content of the book was explained by the variation of 137Cs content of rice straw with the harvest year and a change of the kind of board.