Alpha Decay Studies Of The New Neutron-deficient Nuclides ²¹⁶U And ²¹⁵U

The study on the decay properties of new isotopes located far from the beta stability line is current focus of nuclear physics. For isotopes in the region Z>82 and N<126, α-emission prevails as radioactive decay mode and α-spectroscopy is the most important tool to obtain information on the nuclear structure. In the heavy nuclei region with N=124 and 126 isotones, an intruder state(πh9/2 πf7/2)8+ based on the attractive interaction of f7/2 protons and f5/2 neutrons has been significantly observed, which increases the binding energy of this configuration with increasing proton number. To extend the systematic of Iπ=8+ isomeric state in N=124 isotones and search for the most neutron-deficient uranium isotopes, an experiment for the α decay studies of the new nuclides 216 U and 215 U was performed at the gas-filled recoil separator SHANS at HIRFL in Lanzhou.New isotopes 216 U and 215 U were synthesized in the fusion reaction 180W(40Ar, xn)220-xU(x=4,5) and studied by α-decay spectroscopy. Two α-decaying states were observed in 216 U with Eα=8.384(30) Me V, T1/2=4.72?1.57?4.72 ms for the ground state and Eα=10.582(30) Me V and 8.182(30) MeV, T1/2=1.31?0.48?1.80 ms for an isomeric state. Through the analysis of the α-decay reduced width, the isomeric state is suggested to have the configuration(πh9/2 πf7/2)8+. Based on the α-particle energies measured in this work, the excitation energy of the Iπ=8+ states in216 U and 212 Th were firstly determined to be about 2239 keV and 2445 keV, respectively. For the new isotope 215 U, two α-decay chains were observed and they were assigned to the decays from ground state to ground state transitions. Based on the two α-decay chains, the α-particle energy and half-life of 215 U were determined to be 8.428(30) MeV and 0.73?0.29?1.33 ms, respectively. In addition, two new α-decay transitions of 217 U with α-particle energy of 8.210(30) MeV and 8.098(30) MeV were also observed in this experiment, and they were assigned to the decay of 217 U populating the ground state and one low-lying excited state in 213 Th, respectively.We also introduce another experiment 40Ca+175Lu for synthesis of a new isotope 211 Pa here. In this experiment, an upper-limit cross section for 211 Pa was obtained and the previously reported 212 Pa was confirmed. In addition, in order to acquire a broad experimental knowledge of neutron-deficient heavy nuclides, the methods for the production new isotopes, separation devices, detection systems, identification methods, data processing and error analysis methods will also be discussed and summaried in this dissertation.