A Novel "In-Cathode" Activation Technique for ⁴¹Ca Production Cross Section Measurements Using Accelerator Mass Spectrometry

Studies and subsequent analysis of meteoritic material has provided evidence of the presence of several short-lived radionuclides (SLRs) at the formation of the Solar System. These SLRs, named for their half-lives being less than 100 Myr and therefore "short" in terms of the age of the Solar System, are key to the understanding of the types of processes that created the Solar System. Production models rely on theoretical nuclear models, but theoretical reaction cross sections can be imprecise, making experimental measurements crucial to relieving some uncertainties on theoretical models. In particular, ⁴¹Ca is important as its half-life (t_1/2= 9.94 x 10⁴ yrs) is much shorter than other SLRs, thereby offering stricter constraints on the various irradiation scenarios from early stellar processes. Irradiation of Ca can be tricky as it is tough to make as a foil for activations and chemical treatment can add even more uncertainty. This prompted a campaign to develop a novel reaction technique that was tested at the Nuclear Science Laboratory at the University of Notre Dame. This technique utilizes an “in-cathode” reaction method, which means that natural CaF₂ material is packed into an ion source sample holder (cathode) before being irradiated and then subsequently measured without the need for any chemical processing after the activation. The setup for the irradiation was performed using a ³He beam to measure the reaction ^natCa(³He,x)⁴¹Ca. The activated sample was placed in a gamma counting station to measure any decay products and then placed directly into the ion source to be sputtered where its isotopic ratio of ⁴¹Ca/^natCa was measured using Accelerator Mass Spectrometry (AMS). Gamma spectroscopy revealed around 2-3% of the ³He beam missing the Ca material and hitting the Cu cathode. AMS results suggest the need to measure the isotopic ratio of a sample until all the activated material has been exhausted while also accounting for geometrical effects from the sputtering of material in the ion source.