Laser cooling and trapping of ^{224}Ra^{+}

Abstract

We report laser cooling and trapping of ^{224}Ra^{+} ions. This was realized via two-step photoionization loading of radium into an ion trap. A robust source for ^{224}Ra atoms, which have a 3.6-day half-life, was realized with an effusive oven containing ^{228}Th, which has a 1.9-yr half-life, which continuously generates ^{224}Ra 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 ^{224}Ra 7s^{2}^{1}S_{0}→7s7p^{1}P_{1} 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 ^{226}Ra 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.