A VUV detection system for the direct photonic identification of the first excited isomeric state of ${}^{229}$Th

Abstract

With an expected energy of 7.6(5) eV, ${}^{229}$Th possesses the lowest excited nuclear state in the landscape of all presently known nuclei. The energy corresponds to a wavelength of about 160 nm and would conceptually allow for an optical laser excitation of a nuclear transition. We report on a VUV optical detection system that was designed for the direct detection of the isomeric ground-state transition of ${}^{229}$Th. ${}^{229(m)}$Th ions originating from a ${}^{233}$U $\alpha$-recoil source are collected on a micro electrode that is placed in the focus of an annular parabolic mirror. The latter is used to parallelize the UV fluorescence that may emerge from the isomeric ground-state transition of ${}^{229}$Th. The parallelized light is then focused by a second annular parabolic mirror onto a CsI-coated position-sensitive MCP detector behind the mirror exit. To achieve a high signal-to-background ratio, a small spot size on the MCP detector needs to be achieved. Besides extensive ray-tracing simulations of the optical setup, we present a procedure for its alignment, as well as test measurements using a D${}_2$ lamp, where a focal-spot size of $\approx$100 $\mu$m has been achieved. Assuming a purely photonic decay, a signal-to-background ratio of $\approx$7000:1 could be achieved.

17 pages, 21 figures, 4 tables

References in corpus (6)

• Enhanced effect of temporal variation of the fine structure constant in diatomic molecules
• Proposal for a Nuclear Gamma-Ray Laser of Optical Range
• Performance of a 229 Thorium solid-state nuclear clock
• On Th229 and time-dependent fundamental constants
• Determination of the extraction efficiency for ${}^{233}$U source $\alpha$-recoil ions from the MLL buffer-gas stopping cell
• Coulomb energy contribution to the excitation energy in ${}^{229}$Th and enhanced effect of $\alpha$ variation

Cited by in corpus (4)

• Frequency ratio of the ${}^{229\mathrm{m}}$Th nuclear isomeric transition and the ${}^{87}$Sr atomic clock
• Lifetime measurement of the ${}^{229}$Th nuclear isomer
• The ${}^{229}$Th isomer: prospects for a nuclear optical clock
• Feasibility Study of Internal Conversion Electron Spectroscopy of ${}^{229m}$Th