Non-destructive γ spectrum analysis of polymetallic nodules from the eastern Pacific

Non-destructive γ spectrum analyses of 20 polymetallic nodules from the eastern Pacific were carried out. Numerous nuclides, such as ²³⁸U, ²³⁰Th, ²²⁶Ra, ²¹⁰Pb, ²⁰⁸Ra, ²²⁸Th, ²³⁵U, ²²⁷Ac (or ²³¹Pa) and ⁴⁰K were detected. The count rates of the nuclides in the top or bottom side of nodules facing detector were measured and the ratio R of the count rates of nuclides in the top and the bottom sides was obtained. From counts and ratios, some useful information relating to the growth and movement of the nodules, the source of nuclide and relationship between those and environment can be gotten. A new method for clear distinction between the top and bottom sides of the nodule based on the R value of ²²⁶Ra or ²¹⁰Pb was developed. In addition, one can infer the turnover of nodules according to the R value of ²³⁰Th.