378 



THE DEEP SEA 



^- 15 



*o 10 



^0 



30 



20- 



10- 



20 



AO 



60 



80 



: Ra 

 :Io 



100 



20 



AO 



60 



80 



100cm 



Core 87 



Fig. 4. Measurements on radioactive nuclides from Pacific clay core 87 of the 

 Swedish deep-sea expedition 1947-1948. The graph shows the activities of the 

 following nuclides plotted against depth in the core: radium (Kroll, 1955); ionium 

 (Picciotto and Poulaert, unpublished). At top is shown the thorium content of 

 selected layers in the core (Picciotto and Wilgain, 1954). 



appeared to be due to a migration of the radium rather than to an 

 irregular distribution of ionium. 



The only way to resolve the problem was to measure directly 

 the ionium as well as the radium in the same samples. In 1952, 

 under the stimulus of Pettersson, a program of radioactive 

 measurements on Pacific sediment cores brought back by the 

 Albatross expedition, with European cooperation, was started. The 

 radium was measured by Kroll at Goteborg; the uranium in 

 Vienna by Hecht and his collaborators (Hahofer and Hecht, 1954) ; 

 the ionium, thorium, and protactinium were measured, for the 



