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

A methodology is described to generate an isotopically pure 229 Th ion beam in the 2+ and 3+ charge states. This ion beam enables one to investigate the low-lying isomeric first excited state of 229 Th at an excitation energy of about 7.8(5) eV and a radiative lifetime of up to 10 4 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 229 Th ions are produced in the α decay of a radioactive 233 U 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.