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

Cosmic-ray-produced ⁵³Mn ( t _1/2 = 3.7 × 10 ⁶years ) was measured in individual and groups of deep-sea iron and stony spherules by highly sensitive neutron activation analysis. The activities found were less than 20 dpm ⁵³Mn/kg Fe (10 ^-5-10 ^-6 dpm ⁵³Mn/sample) in iron spherules except one iron spherule whose activity was 241 ± 73 dpm ⁵³Mn/kg Fe. These low activities may indicate evaporative loss of ⁵³Mn due to heating in the earth's atmosphere. On the other hand, all stony spherules contained 200-260 dpm ⁵³Mn/kg Fe which is similar to chondritic values. These spherules may be ablation debris from large objects.