The Solenoid Spectrometer for Nuclear Astrophysics and Decays: a New Tool for the Indirect Measurement of Astrophysical Capture Reactions

The most common explosive astrophysical event is the type-1 X-Ray Burst (XRB), in which H/He-rich fuel from a binary companion star incites periodic thermonuclear runaway on the surface of a neutron star. XRBs are a location of heavy element synthesis through the rp-process, and their light curves provide macroscopic information about the system’s neutron star.

Light curve properties are sensitively dependent on the rates of radiative nuclear capture reactions on unstable neutron-deficient nuclei, such as ¹⁵O(α,γ)¹⁹Ne, which are often challenging to study directly. Indirect methods measuring particle decay branching ratios of excited states in the associated compound nucleus can provide rigorous experimental constraints to capture reaction rates in the absence of direct measurements. The Solenoid Spectrometer for Nuclear Astrophysics and Decays (SSNAPD) will be a new charged-particle detector array that utilizes segmented silicon strip detectors placed in the magnetic field of a large-bore solenoid to perform near background free measurements of such particle-decay branching ratios at the University of Notre Dame. Optimized for the detection of low-energy particles, SSNAPD is ideally suited for branching measurements of the near-threshold states that dominate capture rates relevant to explosive nucleosynthesis. This talk reports on the status of SSNAPD’s development, with a focus on experiments characterizing the silicon detector array’s capabilities in the lowest limit of relevant experimental energies.