α decay of 97249Bk and levels in 95245Am

α decay of 249Bk has been investigated by measuring its α and γ-ray spectra, both in singles and in coincidence modes. The α spectrum of a freshly purified 249Bk sample was measured with a high-resolution, double-focusing magnetic spectrometer. γ singles, γ-γ coincidence, and γ-α coincidence spectra were also recorded. The absolute intensity of the 327.45-keV γ ray has been determined to be (1.44±0.08)×10-5% per 249Bk decay. Assignments of previously known single-particle states were confirmed. A new rotational band was identified in the α singles spectrum and Am K x rays have been observed in its decay. This single-particle state, with an energy of 154 keV, has been assigned to the 3/2-[521] Nilsson state. This is the lowest excitation energy for this orbital in any Am nucleus. More precise energies and intensities of the 249Bk α groups and γ-ray transitions are provided

To wet or not to wet: that is the question

Wetting transitions have been predicted and observed to occur for various combinations of fluids and surfaces. This paper describes the origin of such transitions, for liquid films on solid surfaces, in terms of the gas-surface interaction potentials V(r), which depend on the specific adsorption system. The transitions of light inert gases and H2 molecules on alkali metal surfaces have been explored extensively and are relatively well understood in terms of the least attractive adsorption interactions in nature. Much less thoroughly investigated are wetting transitions of Hg, water, heavy inert gases and other molecular films. The basic idea is that nonwetting occurs, for energetic reasons, if the adsorption potential's well-depth D is smaller than, or comparable to, the well-depth of the adsorbate-adsorbate mutual interaction. At the wetting temperature, Tw, the transition to wetting occurs, for entropic reasons, when the liquid's surface tension is sufficiently small that the free energy cost in forming a thick film is sufficiently compensated by the fluid- surface interaction energy. Guidelines useful for exploring wetting transitions of other systems are analyzed, in terms of generic criteria involving the "simple model", which yields results in terms of gas-surface interaction parameters and thermodynamic properties of the bulk adsorbate.Comment: Article accepted for publication in J. Low Temp. Phy

Ca-48+Bk-249 Fusion Reaction Leading to Element Z=117: Long-Lived alpha-Decaying (270)Db and Discovery of Lr-266

[Introduction] The superheavy element with atomic number Z ¼ 117 was produced as an evaporation residue in the 48 Ca þ 249 Bk fusion reaction at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. The radioactive decay of evaporation residues and their α -decay products was studied using a detection setup that allowed measuring decays of single atomic nuclei with half-lives between sub- μ s and a few days. Two decay chains comprising seven α decays and a spontaneous fission each were identified and are assigned to the isotope 294 117 and its decay products. A hitherto unknown α -decay branch in 270 Db ( Z ¼ 105 ) was observed, which populated the new isotope 266 Lr ( Z ¼ 103 ). The identification of the long-lived ( T 1 = 2 ¼ 1 . 0 þ 1 . 9 − 0 . 4 h) α -emitter 270 Db marks an important step towards the observation of even more long-lived nuclei of superheavy elements located on an “ island of stability. ”peerReviewe