Development of Ultracold Francium Atomic Sources Towards the Permanent EDM Search

Francium (Fr), which is the alkali atom in the 7th period, can be obtained as ultracold atoms with laser cooling and trapping techniques, and could be employed for the experiments on searches for the permanent electric dipole moment (EDM) of an electron. In order to improve the sensitivity of the electron EDM search, development of a high-intensity source of Fr atoms is essential. We demonstrated a production of a high intensity ²¹⁰Fr ion beam with a rate of 5 × 10 ⁶ ions/s by a fusion reaction with bombardment of an accelerated ¹⁸O beam onto a fixed gold target in RIKEN. The Fr products inside the gold target were extracted from the gold surface as an ion beam focused with an electrostatic field. We also discussed the method to produce ²²¹Fr by α-decay of ²²⁵Ac. A neutron-rich ²²¹Fr isotope can be obtained as a daughter nucleus of this decay.