Study of the radioactive decay properties of transfermium elements at separator VASSILISSA (FLNR JINR)

Full text: Recoil separator VASSILISSA is widely used for the synthesis and study of radioactive decay properties of heavy and superheavy nuclei. Separator have high suppression factors for beam particles and background products from nuclear reactions. Slow evaporation residues, formed in complete fusion reactions with heavy ions, after passing the separator are registered by time-of-flight detectors and are implanted into semiconductor detectors, placed at the focal plane of the separator. Concrete wall, detached detectors from the experimental hall, provides extremely low background conditions, that allow one to install at the focal plane of the separator sophisticated detector arrays, including gamma and electron detectors. FLNR JINR cyclotron U400 provides high intensity heavy ion beams, that could be used together with unique radioactive targets, allowing the synthesis of heavy (neutron rich) nuclei with formation cross sections more than 1 nbarn. In this case good statistics could be obtained in short irradiation time. At the focal plane of the VASSILISSA separator α??γ ?and ?β decays of the investigated nuclei are detected. In the years 2004 - 2006 the experiments aimed to the gamma, beta spectroscopy of the transfermium isotopes, formed at the complete fusion reactions with accelerated heavy ions were performed. Isotopes of No and Lr, synthesized at the 48Ca+207,208Pb→255,256No*, 48Ca+209Bi→257Lr*, 22Ne+238U→260No* reactions were studied. The experiments with high intensity 22Ne beam showed, that for slow evaporation residues rather high (∼ 5%) transmission efficiency could be obtained. In this case for α - γ and α - β coincidences used in the study of the isotopes of 104 and 105 elements good statistics could be obtained during one month of the experiment. In the close future it is planned to study neutron rich isotopes of the Rf and Db in the reactions 22Ne + 242Pu → 264Rf*, 22Ne + 243Am →265Db*