Measurement of the Kr XVIII 3d $^2D_{5/2}$ lifetime at low energy in a unitary Penning trap

TL;DR

This study measures the radiative lifetime of a metastable state in highly ionized krypton using a novel Penning trap technique, achieving high precision and confirming theoretical predictions.

Contribution

It introduces a new method to measure metastable state lifetimes in multiply ionized atoms at low energy without active cooling.

Findings

Measured lifetime of 24.48 ms with high precision

Trap energy spread narrower than ion source by a factor of 100

Experimental results agree with theoretical predictions at 1% level

Abstract

A different technique is used to study the radiative decay of a metastable state in multiply ionized atoms. With use of a unitary Penning trap to selectively capture Kr$^{17+}$ ions from an ion source at NIST, the decay of the 3d $^2D_{5/2}$ metastable state is measured in isolation at low energy, without any active cooling. The highly ionized atoms are trapped in the fine structure of the electronic ground configuration with an energy spread of 4(1) eV, which is narrower than within the ion source by a factor of about 100. By observing the visible 637 nm photon emission of the forbidden transition from the 3d $^2D_{5/2}$ level to the ground state, we measured its radiative lifetime to be $\tau=$ 24.48 ms +/- 0.28(stat.) ms +/- 0.14(syst.) ms. Remarkably, various theoretical predictions for this relativistic Rydberg atom are in agreement with our measurement at the 1% level.