Measurement of Mn-53 in deep-sea iron and stony spherules

Cosmic-ray-produced Mn-53 (half-life, 3.7 x 10 to the 6th yr) is measured in individual and groups of deep-sea iron and stony spherules by highly sensitive neutron activation analysis. The activities found are less than 20 dpm Mn-53/kg Fe (10 to the -5th-10 to the -6th dpm Mn-53/sample) in iron spherules, with the exception of one iron spherule, whose activity is 241 + or - 73 dpm Mn-53/kg Fe. It is believed that these low activities may indicate evaporative loss of Mn-53 caused by heating in the earth's atmosphere. On the other hand, all the stony spherules are found to contain 200-260 dpm Mn-53/kg Fe, which is similar to chondritic values. It is pointed out that these spherules may be ablation debris from large objects.