Conservators at the National Library of Australia have turned to beta-radiography (a form of x-ray photography) as a method of establishing ownership of library acquisitions. The library has adopted beta-radiography as an alternative to rubber stamping or embossing books and other library material for ownership purposes: in the method being adopted, ¹⁴C is used to produce the x-ray photographs of sample pages of the material, showing the structure of the paper and the individual peculiarities of the pages: no two sheets of paper would be identical and beta-radiographs record this uniqueness. By using this system, library material becomes easily identifiable without the material being marked in any way. -- AATA