| To improve the understanding of the evolution of nuclear structure near the shell closures at N = 126, recoil-decay tagging, which provides a very high channel selectivity, is a very important tool. At Yale, a focal plane detection system of SASSYER, a gas-filled recoil separator at A. W. Wright Nuclear Structure Laboratory, is built to utilize the recoil-decay tagging technique. Here the commissioning of the detection system is presented. Results from a commissioning experiment are compared to literature data.;In this work, delayed spectroscopy of 257Rf and its decay products was also performed at Argonne National Laboratory. The experimental results are interpreted in the framework of the Microscopic-Macroscopic model. The isotope 257Rf was produced in the fusion-evaporation reaction 205Pb(50Ti, n)257Rf. Reaction products were separated and identified by mass. A partial decay scheme with configuration assignments is proposed based on alpha hindrance factors. The excitation energy of the 1/2+[620] configuration in 253No is proposed. The energy of this 1/2+ state in a series of N = 151 isotones increases with nuclear charge, reflecting an increase in the N = 152 gap. This gap is deduced to grow substantially from 850 to 1400 keV between Z = 94 and 102. An isomeric state in 257Rf, with a half life of 160+42-31 mus, was discovered by detecting internal conversion electrons followed by alpha decay. It is interpreted as a three-quasiparticle high-K isomer. A second group of internal conversion electrons, with a half-life of 4.1+2.4-1.3 s, followed by alpha decay, was also observed. These events might originate from the decay of excited states in 257Lr, populated by electron-capture decay of 257Rf. Spontaneous fission (SF) of 257Rf was unambiguously detected, with a branching ratio of bSFRf = 0.02 +/- 0.01. |
