Preparing an Isotopically Pure ²²⁹Th Ion Beam for Studies of ^229mTh

A methodology is described to generate an isotopically pure ²²⁹Th ion beam in the 2+ and 3+ charge states. This ion beam enables one to investigate the low-lying isomeric first excited state of ²²⁹Th at an excitation energy of about 7.8(5) eV and a radiative lifetime of up to 10⁴ seconds. The presented method allowed for a first direct identification of the decay of the thorium isomer, laying the foundations to study its decay properties as prerequisite for an optical control of this nuclear transition. High energy ²²⁹Th ions are produced in the α decay of a radioactive ²³³U source. The ions are thermalized in a buffer-gas stopping cell, extracted and subsequently an ion beam is formed. This ion beam is mass purified by a quadrupole-mass separator to generate a pure ion beam. In order to detect the isomeric decay, the ions are collected on the surface of a micro-channel plate detector, where electrons, as emitted in the internal conversion decay of the isomeric state, are observed.