(Table 1, pages 779) Alpha track determination of growth rates of manganese nodules, Pacific Ocean

Analyses of the total alpha radioactivity distribution in 31 North Pacific manganese nodules yield an average growth rate of 6.8 ( 2) mm /m.y. Samples from a single box core show almost identical total activity vs. depth profiles, regardless of nodule size or shape. A characteristic feature of many nodules examined is an apparent change (steepening) in slope of the alpha activity profile between depths of 0.5-1.5 mm. This feature may reflect a fundamental feature of nodule growth, possibly mobility of 230Th or its daughters in a regular way, interrupted growth, or nodule turnover. Near-surface decreases in total alpha activity probably result from 226Ra loss.

对北太平洋31个锰结核（manganese nodules）中的总α放射性（alpha radioactivity）分布进行分析后，得到其平均生长速率为6.8(2) 毫米/百万年（mm/m.y.）。单一箱式岩心（box core）采集的样本，其总放射性活度随深度的剖面分布几乎完全一致，不受锰结核尺寸或形态的影响。本次检测的多数锰结核呈现出一项典型特征：在0.5~1.5毫米的深度区间内，α活性剖面（alpha activity profile）的斜率出现明显变化（趋于陡峭）。该特征或可反映锰结核生长的本质特性，其成因可能包括230钍（230Th）及其衰变子体的规律性迁移、生长过程中断，或是锰结核发生翻转。近表层区域的总α放射性活度降低，大概率源于镭-226（226Ra）的流失。