Development of an RF Fragment Separator at the NSCL

Michigan State University, East Lansing MI

Investigators

Abstract

Extremely unstable neutron deficient rare isotopes play a key role in explosive astrophysical events such as X-ray bursts and Novae. An understanding of the physics of these exotic nuclei is required to interpret in a quantitative way a range of new X-ray binary observations from space based X-ray observatories. This will pave the way to address the many open questions such as the mechanism behind burst oscillations, the origin of superbursts, and the nature of the underlying neutron star. Very neutron deficient nuclei serve also as unique probes of nuclear structure. They provide tests for the limits of nuclear existence, and they show unique decay modes such as one- and two-proton emission. In addition, neutron deficient nuclei include a special class of nuclei - isotopes with equal numbers of protons and neutrons. As protons and neutrons occupy the same shell model orbitals, many nuclear structure effects appear enhanced in such nuclei. This is particularly true for one of the most neutron deficient, classically doubly magic nuclei in nature, 100Sn. Doubly-magic nuclei, where both, protons and neutrons completely fill a nuclear shell, are of particular importance in nuclear physics and serve as benchmarks and beachheads for nuclear theories. The measurement of the decay properties of 100Sn is by many considered one of the "holy grails" of nuclear physics and would provide unique insights into the beta-decay of heavy nuclei. The National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University has worldwide unique capabilities in producing extremely neutron deficient nuclei. This includes sufficient amounts of 100Sn to measure the properties of its decays, as well as all nuclei participating in the astrophysical rapid proton capture process in X-ray bursts. However, due to the nature of the projectile fragmentation mechanism used to create these nuclei, current experimental setups do not achieve the necessary beam purity. Many of the key experiments can therefore not be performed. We will build an RF Fragment Separator experiment, which will deflect unwanted rare isotope beam contaminants with an RF field, while transmitting the desired species. This device can be combined with existing experimental setups for decay and reaction studies and will allow a large group of graduate students and scientists to take full advantage of the production capabilities for neutron deficient beams at the NSCL to address fundamental questions in nuclear physics and astrophysics.