# An alternative approach to populate and study the $^{229}$Th nuclear clock isomer

## TL;DR

This paper proposes a novel method to observe the decay of the $^{229}$Th nuclear isomer using a $^{229}$Ac ion beam, aiming to determine its energy and lifetime for applications in nuclear clocks and fundamental physics.

## Contribution

It introduces a new production and observation approach for the $^{229}$Th isomer, offering advantages over traditional methods and including feasibility analysis and experimental investigation.

## Key findings

- Feasibility of using $^{229}$Ac ion beam demonstrated
- Advantages over $^{233}$U recoil source established
- Experimental results support potential for nuclear clock development

## Abstract

A new approach to observe the radiative decay of the $^{229}$Th nuclear isomer, and to determine its energy and radiative lifetime, is presented. Situated at a uniquely low excitation energy, this nuclear state might be a key ingredient for the development of a nuclear clock, a nuclear laser and the search for time variations of the fundamental constants. The isomer's $\gamma$ decay towards the ground state will be studied with a high-resolution VUV spectrometer after its production by the $\beta$ decay of $^{229}$Ac. The novel production method presents a number of advantages asserting its competitive nature with respect to the commonly used $^{233}$U $\alpha$-decay recoil source. In this paper, a feasibility analysis of this new concept, and an experimental investigation of its key ingredients, using a pure $^{229}$Ac ion beam produced at the ISOLDE radioactive beam facility, is reported.