Global fallout of curium

Abstract

THE search for ^242mAm (t_1/2=152 yr) in environmental samples has involved detection of its daughter ²⁴²Cm (t_1/2=163 d) (refs 1–3). These samples were contaminated by transuranium nuclides either from a nuclear fuel reprocessing plant or from a thermonuclear test fallout. A logical consequence was then to analyse global fallout-contaminated samples for ²⁴²Cm and ²⁴⁴Cm to establish the present distribution and global contamination of our environment by these transuranium elements. We have chosen the lichen Cladonia alpestris, which is an excellent bioindicator for atmospheric fallout and we present the results here. The samples have been stored in the laboratory for 5–16 yr. Thus, ^242mAm and ²⁴²Cm were in sequelar radioactive equilibrium. The ²⁴²Cm present in the aged samples therefore represents the ^242mAm present in the fallout. The results indicate a ^242mAm/^239+240Pu activity ratio of about 0.003% in global fallout.