Laser cooling and trapping of 224Ra+

We report laser cooling and trapping of 224Ra+ ions. This was realized via two-step photoionization loading of radium into an ion trap. A robust source for Ra224 atoms, which have a 3.6-day half-life, was realized with an effusive oven containing Th228, which has a 1.9-yr half-life, which continuously generates Ra224 via its α-decay. We characterized the efficacy of this source and found that after depleting built-up radium the thorium decay provides a continuous source of radium atoms suitable for ion trapping. The vacuum system has been sealed for more than 6 months and continues to trap ions on demand. We also report a measurement of the Ra224 7s21S0→7s7p1P1 transition frequency: 621043830±60 MHz, which is helpful for efficient photoionization. With this measurement and previous isotope shift measurements we find that the frequency of the same transition in Ra226 is 621037830±60 MHz, which disagrees with the most precise measurement, 621038489±15 MHz, which is used for the recommended value in the National Institute of Standards and Technology Atomic Spectra Database.