High-precision Penning trap mass spectrometers have been developed at several rare-isotope facilities around the world due to the extraordinary precision and accuracy that has been demonstrated in determining a fundamental property of a nucleus, its mass. Penning trap mass spectrometers determine the mass of a charged particle via a measurement of its cyclotron frequency in a strong magnetic field. At present, Penning trap mass spectrometers for rare isotopes employ a time-of-flight ion cyclotron resonance (TOF-ICR) detection scheme which is universal but typically requires at minimum rate of rare isotope ions of at least a few ions per hour. In order to overcome this sensitivity limit the group will develop, build, and install a dedicated Single Ion Penning Trap Spectrometer (SIPT) mass spectrometer using a 6 Tesla magnetic field provided by a superconducting solenoid and employing the narrowband Fourier Transform Ion Cyclotron Resonance (FT-ICR) method. The technique will be optimized for the study of very rare isotopes provided only at very low rates, one per day or week, a rate that prohibits the use of the TOF-ICR technique. The narrowband FT-ICR method uses a tuned, superconducting circuit to amplify the signal generated by a single charged particle on the electrodes of the Penning trap as it moves around inside the trap. By performing a Fourier analysis on the amplified signal, the cyclotron frequency can be determined. As narrowband FT-ICR is not as universal as TOF-ICR, it is best used on candidates with extremely low delivery rates and of great scientific interest.
The proposed SIPT mass spectrometer will have a broad significance and importance by improving our ability to determine the mass of rare isotopes with unusual ratios of the number of neutrons and protons, much different from those found in stable isotopes, as they exist on Earth. The determination of the masses of such exotic and often very short-lived rare isotopes is of utmost importance since it provides direct information on how tightly the neutrons and protons are bound in the atomic nucleus. Masses of rare isotopes serve as input data in a variety of fields of science, such as nuclear structure, nuclear astrophysics, and fundamental interactions. For example, rare isotopes are produced in abundance in stellar environments and play a key role in the star's evolution but the production on earth in rare isotope beam facilities is very challenging, and for many important isotopes the beam rates are very low. SIPT's highly sensitive technique will be capable of making a mass measurement with only a single rare isotope ion, pushing the frontier of precision mass measurements of rare isotopes to more exotic isotopes. The development of this technology will also be of benefit for future use at the Facility for Rare Isotope Beams (FRIB). We believe that the interdisciplinary nature of the SIPT project is well suited for attracting and educating students from underrepresented groups, resulting in a stronger research program and greater cultural awareness for everyone involved.
