Design and commissioning of the GSI pion beam

We describe the design of the secondary pion beam-line installed at the SIS 18Tm synchrotron at GSI, Darmstadt, and discuss the commissioning results. The experiments were performed with proton and C-12 primary beams at several energies using beryllium production targets. Pion yields in a momentum range between 0.4 and 2.8 GeV/c were identified, At the highest primary beam energies of 3.5 GeV for proton and 2.0 A GeV for carbon ions, the latter beam produces the highest low-momentum pion yield while at momenta of 1.5 GeV/c the yields are comparable and at 2.8 GeV/c the proton beam is superior. A momentum resolution of around 0.5% is achieved and the time resolution (a) ranges from 100 to 15…

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

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

The superheavy element with atomic number Z=117 was produced as an evaporation residue in the 48Ca+249Bk 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-μs and a few days. Two decay chains comprising seven α decays and a spontaneous fission each were identified and are assigned to the isotope 294117 and its decay products. A hitherto unknown α-decay branch in 270Db (Z=105) was observed, which populated the new isotope 266Lr (Z=103). The identification of the long-live…

New Short-Lived Isotope U-221 and the Mass Surface Near N=126

Two short-lived isotopes 221U and 222U were produced as evaporation residues in the fusion reaction 50Ti+176Yb at the gas-filled recoil separator TASCA. An α decay with an energy of Eα=9.31(5)  MeV and half-life T1/2=4.7(7)  μs was attributed to 222U. The new isotope 221U was identified in α-decay chains starting with Eα=9.71(5)  MeV and T1/2=0.66(14)  μs leading to known daughters. Synthesis and detection of these unstable heavy nuclei and their descendants were achieved thanks to a fast data readout system. The evolution of the N=126 shell closure and its influence on the stability of uranium isotopes are discussed within the framework of α-decay reduced width.