High-precision mass measurement of 24Si and the development of a CID gas cell (CIDGC)

Nuclear masses have been studied for over a century, with critical data providing important constraints in nuclear physics studies. Penning trap mass spectrometry (PTMS) is one of the most precise methods for measuring the masses of exotic nuclei at rare isotope facilities. PTMS is performed at Michigan State University's National Superconducting Cyclotron Laboratory (NSCL) at the Low Energy Beam and Ion Trap (LEBIT) facility, where both stable and rare isotope masses have been measured to high precision. The aim of this work was to measure the mass of 24Si and investigate the impact of this mass on the competition between the rapid proton capture and αp capture at the 22Mg waiting point.These two nucleosynthetic processes take place on the surface of neutron stars in a binary system with a low mass population II star when a critical point is reached during accretion of H/He-rich material from the companion star. An explosion will occur triggering a thermonuclear runaway where the two processes are initiated, accompanied with a Type-I X-ray burst. The X-ray burst is the only observable, so nuclear physics data is needed to constrain observational data such as reaction rates for these nucleosynthetic processes. Variations within the uncertainty of the 23Al(p, γ) 24Si reaction rate lead to significant shifts in simulated X-ray light curves, where the ground state mass of 24Si is currently the dominant source of the reaction rate uncertainty (19 keV). The Penning trap measurement performed at LEBIT improved the mass uncertainty of 24Si by a factor of 5 more precise than previous results. The atomic mass excess of 24Si, 10 753.8(37) keV, substantially reduces the uncertainty of the 23Al(p, γ) 24Si reaction rate, which constrains the onset temperature of the (α, p) process at the 22Mg waiting-point to a precision of 9%.A key process needed to perform this measurement is stopping the beam in a gas stopper before extracting and injecting into a Penning trap to perform the measurement. An issue with stopped beam experiments is rare isotopes are often extracted as a molecule as well as the presence of contaminant molecules. The development of a gas catcher that would be used to perform collision-induced dissociation (CID) was pursued and investigated with a prototype CID gas catcher (CIDGC). The entrance membrane for the CIDGC is a 20 nm Si3N4 membrane with the gas catcher filled with ultra-pure He at 2.5 mbar. Dissociated ions are extracted using an ion surfing technique facilitated by a circular RF carpet. The extracted ions are sent downstream using an RFQ ion guide and injected into a residual gas analyzer for analysis. The early results with online beam show that ions are successfully transported through the CIGDC, but no sign of ions delivered from the beam stopping facility were yet observed.