Radiochemical study of sub-barrier fusion hindrance in the 19F+209Bi reaction

Production cross sections of fission product 99Mo produced in the reaction of 19F + 209Bi have been measured at the incident energies 135–83 MeV near and below the fusion barrier by radiochemical methods. The excitation function for the fusion-fission cross sections in this reaction were deduced down to 80 μb from the measured production cross sections. A systematic analysis of the fusion-fission excitation function shows that sub-barrier fusion hindrance in the heavy mass system 19F + 209Bi is different from that in the medium-heavy mass systems but similar to that in the medium-light mass system and in the heavy mass system. This work is the first radiochemical study of sub-barrier fusion hindrance in heavy mass systems.

230Th/U chronology of ore formation within the semyenov hydrothermal district (13°31′ N) at the Mid-Atlantic ridge

A radiochemical study was carried out on massive sulfides from Semyenov hydrothermal district at the Mid-Atlantic Ridge. New and published results provide evidence that 230Th/U ages obtained for massive sulfides are reliable. The sulfide deposits from the West, North-West, North-East, and East hydrothermal sites at the Semyenov hydrothermal district were formed between ∼124 ka and ∼37 ka ago. The hydrothermal activity might have started in the eastern part of the district and moved to the west by episodic ore formation.