# High-Resolution Laser Spectroscopy of Long-Lived Plutonium Isotopes

## TL;DR

This study used advanced laser spectroscopy techniques to measure isotope shifts, hyperfine structures, and charge radii of long-lived plutonium isotopes, achieving unprecedented precision and marking the heaviest element analyzed with collinear laser spectroscopy.

## Contribution

It is the first application of collinear laser spectroscopy to the heaviest element, plutonium, providing highly precise measurements of isotope shifts and nuclear properties.

## Key findings

- Measured isotope shifts for specific plutonium transitions.
- Extracted hyperfine factors for $^{239,241}$Pu.
- Achieved an order of magnitude improvement in charge radius uncertainties.

## Abstract

Long-lived isotopes of plutonium were studied using two complementary techniques, high-resolution resonance ionisation spectroscopy (HR-RIS) and collinear laser spectroscopy (CLS). Isotope shifts have been measured on the $5f^67s^2\ ^7F_0 \rightarrow 5f^56d^27s\ (J=1)$ and $5f^67s^2\ ^7F_1 \rightarrow 5f^67s7p\ (J=2)$ atomic transitions using the HR-RIS method and the hyperfine factors have been extracted for the odd mass nuclei $^{239,241}$Pu. Collinear laser spectroscopy was performed on the $5f^67s\ ^8F_{1/2} \rightarrow J=1/2\; (27523.61\text{cm}^{-1})$ ionic transition with the hyperfine $A$ factors measured for $^{239}$Pu. Changes in mean-squared charge radii have been extracted and show a good agreement with previous non-optical methods, with an uncertainty improvement by approximately one order of magnitude. Plutonium represents the heaviest element studied to date using collinear laser spectroscopy.