Scientists working at ISOLDE, CERN’s nuclear-physics facility, have successfully performed the first ever laser-spectroscopy measurements of radium monofluoride.
The international team conducted studies of the short-lived radioactive molecule, radium monofluoride, using laser spectroscopy which employs a laser to shine light on molecules in order to reveal their energy structure. The findings of this study, published in Nature, represent a vital step towards using these molecules for fundamental physics research and beyond.
Why study radium monofluoride
Due to radium monofluoride molecules containing radium some isotopes have nuclei shaped like a pear, with more mass at one end than the other. These pear shapes amplify processes that break fundamental symmetries of nature and could expose new physics phenomena beyond the standard model. Principal investigator, Ronald Garcia Ruiz, said: “Our measurements demonstrate that radium monofluoride molecules can be chilled down to temperatures that would allow researchers to investigate them in extraordinary detail.
“Our results pave the way to high-precision studies of short-lived radioactive molecules, which offer a new and unique laboratory for research in fundamental physics and other fields.”
This new CERN experiment furthers theoretical investigations of the energy structure of radium monofluoride. Based on these investigations, scientists predicted that the molecule is amenable to laser cooling, whereby lasers are used to cool down atoms or molecules for high-precision studies. “This laser-spectroscopy study of radium monofluoride at ISOLDE provides strong evidence that the molecules can indeed be laser cooled,” says ISOLDE spokesperson Gerda Neyens.
Conducting laser-spectroscopy measurements
After Ruiz and colleagues produced radioactive radium isotopes by firing protons from the CERN’s Proton Synchrotron Booster on a uranium carbide target, radium monoﬂuoride ions were formed by enveloping the target with carbon tetrafluoride gas. The radium monofluoride ions were then sent through ISOLDE’s Collinear Resonance Ionisation Spectroscopy (CRIS), where the ions were turned into neutral molecules and exposed to a laser beam that brought them to an excited energy state at specific laser frequencies. A subset of these high energy molecules were then ionised with a second laser beam and deﬂected onto a particle detector for analysis.
The team then analysed the spectra of ionised molecules and were able to identify the low-lying energy levels of the molecules and some of the properties that demonstrate that that the molecules can be laser cooled for future precision studies.
“Our technique allowed the study of radium monofluoride molecules that have lifetimes as short as a few days and are produced at rates lower than one million molecules per second,” says Ruiz.