A nuclidic mass formula composed of a gross term, an even-odd term and a shell term is presented as a revised version of the mass formula constructed by the present authors and published in 2000. The gross term has almost the same functional form as in the previous formula, but the parameter values in it are somewhat different. The even-odd term is treated more carefully, and a considerable improvement is realized. The shell term is exactly the same as the previous one; it was obtained using spherical single-particle potentials and by treating the deformed nucleus as a superposition of spherical nuclei. The new mass formula is applicable to nuclei with Z ≥ 2 and N ≥ 2. The root-mean-square deviation from experimental masses is 666.7 keV, which is less than that of the previous mass formula, 689.8 keV. §1. IntroductionNuclear masses are important quantities to determine the ground state properties and reactions. Since the formulation of the Weizsäcker-Bethe nuclear mass formula, 1), 2) many mass predictions have been made. At the present time, the main purpose of the study of mass formulas is to predict reliable masses of unknown nuclides, especially neutron-rich nuclides and the superheavy nuclides. Some recent mass formulas have been applied to calculations of fission barriers and r-process nucleosyntheses.One way to reproduce the known nuclear mass values is to use mass systematics. For example, the mass formulas presented by Comay et al. and Jänecke et al. 3) are based on Garvey-Kelson-like systematics, 4) which take into consideration particle-hole configurations and yield accurate predictions of known experimental masses, though it is rather difficult to apply these formulas to unknown nuclei far from known ones. In the last decade, some mass predictions designed for wide nuclidic regions have been presented. Among these, we specifically mention two sophisticated mass formulas that give not only nuclear masses but also nuclear shapes

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The production and decay of 277 112 have been investigated using a gas-filled recoil ion separator in irradiations of 208 Pb targets with a 70 Zn beam at 349.5 MeV. We have observed two -decay chains that can be assigned to subsequent decays from 277 112 produced in the 208 Pb( 70 Zn,n) reaction. After emitting four consecutive -particles, both the chains terminate by spontaneous fission decays of 261 Rf, and the decay energies and decay times of both the chains obtained in the present work agree well with those reported by a group at Gesellschaft für Schwerionenforschung (GSI), Germany. The present result gives the first clear confirmation of the discovery of 277 112 and its -decay product 273 Ds reported previously.

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An isotope of the 113th element, i.e., 278 113, was produced in a nuclear reaction with a 70 Zn beam on a 209 Bi target. We observed six consecutive decays following the implantation of a heavy particle in nearly the same position in the semiconductor detector under an extremely low background condition. The fifth and sixth decays are fully consistent with the sequential decays of 262 Db and 258 Lr in both decay energies and decay times. This indicates that the present decay chain consisted of 278 113, 274 Rg (Z 111), 270 Mt (Z 109), 266 Bh (Z 107), 262 Db (Z 105), and 258 Lr (Z 103) with firm connections. This result, together with previously reported results from 2004 and 2007, conclusively leads to the unambiguous production and identification of the isotope 278 113 of the 113th element.