Grant: Subatomic Physics Envelope - Research Tools and Instruments

The charge radius of a nucleus is among its most fundamental properties. Studies of nuclear charge radii are essential to understanding the internal structure of nuclei, to interpreting atomic and nuclear precision tests of the standard model of particle physics, and to explaining the abundance of elements in the universe. Present techniques to measure absolute charge radii are not applicable to elements that have no stable or extremely long-lived isotope. With the exception of uranium and thorium, we currently have no experimental data beyond the element bismuth. We are proposing a new method that allows us to measure the absolute charge radius by observing its subtle effect on the wavelength of atomic transitions in sodium-like highly charged ions and comparing to first-principles calculations. Unlike in neutral, heavy atoms, these computations can be carried out with the required precision. TITAN-EBIT is an electron-beam ion trap online at the radioactive beam facility ISAC at TRIUMF, Canada's National Accelerator Laboratory, which accepts heavy, radioactive isotopes, for example francium and radium, and charge-breeds them into sodium-like ions. In the EBIT, electron-ion collisions will leave the ions in excited states, and the subsequent spontaneous decay towards the electronic ground state can be observed with a spectrometer. The lowest energy de-excitation, 3p1/2 -> 3s1/2, which is most sensitive to nuclear size effects, is located in the extreme ultraviolet region, with wavelengths about one hundred times shorter than visible light. Precision spectroscopy in this wavelength domain is challenging, as the spectrometer has to be operated under ultra-high vacuum (UHV) conditions. This application requests funds to purchase a state-of-the-art UHV spectrometer that can be interfaced to the TITAN-EBIT. With this setup, our Canadian-US-French collaboration will aim to provide the first experimentally determined absolute nuclear charge radii for unstable elements in the trans-lead region.