Reinhard Kirchner

Proton-proton correlations observed in two-proton radioactivity of 94Ag.

The stability and spontaneous decay of naturally occurring atomic nuclei have been much studied ever since Becquerel discovered natural radioactivity in 1896. In 1960, proton-rich nuclei with an odd or an even atomic number Z were predicted to decay through one- and two-proton radioactivity, respectively. The experimental observation of one-proton radioactivity was first reported in 1982, and two-proton radioactivity has now also been detected by experimentally studying the decay properties of 45Fe (refs 3, 4) and 54Zn (ref. 5). Here we report proton–proton correlations observed during the radioactive decay of a spinning long-lived state of the lightest known isotope of silver, 94Ag, which is known to undergo one-proton decay. We infer from these correlations that the long-lived state must also decay through simultaneous two-proton emission, making 94Ag the first nucleus to exhibit one- as well as two-proton radioactivity. We attribute the two-proton emission behaviour and the unexpectedly large probability for this decay mechanism to a very large deformation of the parent nucleus into a prolate (cigar-like) shape, which facilitates emission of protons either from the same or from opposite ends of the ‘cigar’.

Oxide fiber targets at ISOLDE

Abstract Many elements are rapidly released from oxide matrices. Some oxide powder targets show a fast sintering, thus losing their favorable release characteristics. Loosely packed oxide fiber targets are less critical since they may maintain their open structure even when starting to fuse together at some contact points. The experience with various oxide fiber targets (titania, zirconia, ceria and thoria) used in the last years at ISOLDE is reviewed. For short-lived isotopes of Cu, Ga and Xe the zirconia and ceria targets respectively provided significantly higher yields than any other target (metal foils, oxide powders, etc.) tested before. Titania fibers, which were not commercially available, were produced in a relic process by impregnation of a rayon felt in a titanium chloride solution and subsequent calcination by heating the dried felt in air. Thoria fibers were obtained either by the same process or by burning commercial gas lantern mantle cloth. In the future a beryllia fiber target could be used to produce very intense 6He beams (order of 1013 ions per second) via the 9Be(n,α) reaction using spallation neutrons.

Decay properties of very neutron-deficient isotopes of silver and cadmium

Abstract The β-decay properties of the lightest known silver and cadmium isotopes are investigated. Data for β-delayed γ-ray emission of 95–97Ag and for β-delayed proton emission of 96Ag and 97Cd are presented. The experimental findings are compared with predictions of shell-model calculations in which a variety of model spaces and effective interactions are considered.

Beta-decay of 56Cu

Abstract By measuring positrons and β -delayed γ -rays emitted from mass-separated sources, the decay of 56 Cu (4 + , T z =−1, T =1) to states in the doubly-magic nucleus 56 Ni was studied for the first time. The half-life of 56 Cu was measured to be 78(15) ms, and four β -delayed γ -rays were assigned to its decay. The resulting experimental data on Fermi and Gamow–Teller strength are compared with shell-model predictions.

Systematic study of EC decays in the 146Gd region relevant for a monoenergetic neutrino beam facility

The availability of a monochromatic neutrino source with adjustable energy could be an invaluable tool for the study of neutrino oscillations and related phenomena. We have studied the beta decay of 152Yb, 150Er and 156Yb, which could be possible candidate nuclei for the construction of such facility, using the Total Absorption Gamma Spectroscopy (TAGS) technique. The results from these measurements are compared with High Resolution (HR) data available from databases. The importance of the use of the TAGS technique is discussed.