Studying the Nuclear Isomers of Thallium at the ISOLDE Decay Station

At ISOLDE, proton beams from the Proton Synchrotron Booster are used to

induce fission in an Uranium target. These fission fragments are then extracted,

mass separated and sent to the ISOLDE Decay Station to study their decay. One

such decay is that of nuclear isomers, excited states with a relatively long life-

time. All odd neutron-deficient thallium isotopes are known to have such states

that de-excite by internal decay. These high-spin isomers decay to the ground

state via an intermediate state that is populated by a high-multipole gamma

transition. These gammas could also go undetected if they are absorbed by an

electron in the inner atom in a process called electron conversion. The nuclear

isomer of Thallium has a different shape than the ground state, a fascinating

phenomenon only known to the atomic nucleus called shape coexistence. This

project intends to measure the lifetime of the non-isomeric intermediate state of

Thallium, the electron conversion coefficient, and the mixing ratio of the mul-

tipole gamma transitions to extract transition strength. These measurements will

allow us to make inferences about the shape of Thallium in the ground state

and the isomeric state.