Development of a recoil ion source providing slow Th ions including $^{229(m)}$Th in a broad charge state distribution

TL;DR

This paper reports the development of a recoil ion source that produces slow thorium ions, including the isomer $^{229m}$Th, with a broad charge state distribution, enabling high-precision quantum spectroscopy for fundamental physics research.

Contribution

It introduces a novel recoil ion source design that preserves charge states and produces slow $^{229m}$Th ions suitable for trapping and spectroscopy.

Findings

Ion-flight simulations validate the source design.

The source maintains the full charge state distribution.

It provides ions at energies suitable for Paul trap capture.

Abstract

Ions of the isomer $^{229m}$Th are a topic of high interest for the construction of a "nuclear clock" and in the field of fundamental physics for testing symmetries of nature. They can be efficiently captured in Paul traps which are ideal for performing high precision quantum logic spectroscopy. Trapping and identification of long-lived $^{232}$Th$^{+}$ ions from a laser ablation source was already demonstrated by the TACTICa collaboration on Trapping And Cooling of Thorium Ions with Calcium. The $^{229m}$Th is most easily accessible as $\alpha$-decay daughter of the decay of $^{233}$U. We report on the development of a source for slow Th ions, including $^{229(m)}$Th for the TACTICa experiment. The $^{229(m)}$Th source is currently under construction and comprises a $^{233}$U monolayer, from which $^{229(m)}$Th ions recoil. These are decelerated in an electric field. Conservation of the full initial charge state distribution of the $^{229(m)}$Th recoil ions is one of the unique features of this source. We present ion-flight simulations for our adopted layout and give a final design. This source will provide Th ions in their original charge state at energies suitable for capture in a linear Paul trap for spectroscopy investigations.