Short-life neutronodeficient isotopes of rare-earth elements

In this work the following isotopes and isomers of the rare-earth elements were identified mostly for the first time and some verified: 157Tm(Tsub(1/2) = 3.6 min), 158Yb(Tsub(1/2) = 1.1 min), 159Yb(Tsub(1/2) = 1.75 min), 160Yb(Tsub(1/2) = 4.8 min), 148sup(m)Tb(Tsub(1/2) = 2.1 min), 149sup(m)Tb(Tsub(1/2) = 4.5 min), 150sup(m)Tb(Tsub(1/2) = 6.0 min) and 152Tb(Tsub(1/2) = 4.0 min). All of them were obtained in the spallation reactions on thin tantalum targets bombarded with a 660 MeV proton beam. The terbium isomers were also obtained in the heavy-ion reactions 141Pr(12C,xn) Tb and 139La(16O,xn)Tb. A method of fast extraction of rare-earth element isobars by direct separation from the tantalum targets was developed. The tantalum targets were placed in the ion source with surface ionization of the mass-separator. Semiconductor detectors were used for X-ray and γ-ray as well as α-particle spectra measurements. On the basis of experimental results, decay schemes of investigated isotopes (except 159Yb) were prepared. Some regularities in the α-decay energies were observed for isotones with N = 84 and N = 86. Two-quasiparticle states of the multiplets [π(hsub(11/2)) v (fsub(7/2))] in odd-odd Tb isotopes and [v(hsub(9/2)) v (fsub(7/2)) in even-even Gd isotopes were observed. Existence of these states indicates that the pure collective models are not sufficient to explain properties of nuclei in the region of N = 82 and Z = 64. Conclusions are presented on the method of fast isotope separation, techniques of measurements, methods of isotope (isomer) identification and their application in work with mass-separators on high-energy proton beams. (author)