Novel technique to study nuclear isomers via atomic processes

International audienceNuclear isomers can decay through multiple processes; in many cases the dominant mechanismis internal conversion (IC). This is an excitation of an atomic-electron resulting in ionizationand the creation of atomic vacancies. These vacancies are propagated towards the outer-shellsby the emission of X-rays and Auger electrons. Auger-electron emission increases the ioniccharge of decaying ions thus affecting the charge-state distribution.We propose a novel technique to identify and study nuclear isomers by investigating thecharge-state distribution of residual ions following isomeric decays. This technique is based onthe fact that the residual charge-state distribution is sensitive to the internal conversion coefficient(number of IC events occurring), which could be used to extract useful information aboutnuclear isomers.As a proof of concept, the technique has been applied to study nuclear isomers in 144Cs. Theresidual charge-state distribution of 144Cs following isomeric decays has been measured usingthe Lohengrin fission fragment mass spectrometer at the Institut Laue-Langevin, France [1].Based on a level scheme proposed in Ref. [1], we simulated the nuclear cascade decays and thesubsequent emissions of X-rays and Auger electrons in 144Cs using an Auger cascade model[2]. The simulations started in pre-ionized ions since an equilibrium charge-state distribution(q - 20) was established after the ions passed through a nickel foil 0.3 mm away from the 235Utarget.The simulation provides very good agreement with the experimental measurement and hasenabled the extraction of a limit on the isomeric lifetime, an isomeric ratio, and deduction of theunknown level X [1] to be a state at 92.2 keV