Gamma and Beta Decay Spectroscopy of 190W, 205Au and 203Au.

Three exotic, neutron-rich nuclides with isomeric states have been analysed and the results discussed in this thesis: 190W, 205Au and 203Au. The nuclides were produced using rela-tivistic projectile fragmentation of a 1 GeV per nucleon 208Pb beam on a thick (2.5 g/cm2) Be target. Fragments were separated and identified in-flight using the GSI Fragment Separator before implantation in a stopper. The RISING gamma spectrometer was used to observe the decay of isomeric states. 190W is a deformed nuclide displaying behaviour consistent with K-isomerism. Gamma transitions observed in a previous experiment indicated decay from a 10- isomer via a rotational band to the ground state, although one of the transitions within this band is absent in the present analysis. Gamma coincidence and time-difference measurements have been made, resulting in a modified decay scheme. Reduced hindrance factors, potential energy surface and blocked BCS calculations have also been used to enable possible values of spin-parity for the isomer to be assigned. In contrast, 205Au and 203Au are on, or close to, the N=126 closed shell and their isomeric states are due to spin isomerism. Both nuclides were produced in the first "active stopper" experiment at GSI, allowing the detection of both internal conversion electrons and beta-delayed gamma rays. An isomer whose decay has high multipolarity (M4) was detected in 205Au, and some evidence found that the isomeric state decays in two ways: by gamma decay to the ground state and by beta-decay to excited states in 205Hg. The absence of such an isomer in 203Au is discussed in the light of shell model calculations