Study of an MeV Nuclear Resonance to Increase Sodium Detection by Ion Beam Analysis

Blood percolation into implanted glucose sensors for diabetics limits sensor lifetime to 3-7 days. Na$^+$ mobile ions from blood permanently damage Si-based devices. Ion Beam Analysis (IBA) can detect Na in sensors. However, due to the low atomic number of Na (Z=11) and low mass ratio of Na to Si, Na that has percolated into implanted sensors is difficult to detect via standard 2 MeV $^{4}$He Rutherford backscattering. Nuclear resonance can increase the Na scattering cross-section. This work characterizes a $\sim4.7$ MeV resonance, annotated $^{23}$Na($\alpha$,$\alpha$)$^{23}$Na, between $^{23}$Na atoms and $\alpha$ particles. To increase precision of measurements for resonance energy, width, and factor, ion beam energy is calibrated via 3 signals: $5.486\pm0.007$ MeV emission of $\alpha$ particles by $^{241}$Am, and two nuclear resonances, $4.265\pm0.055$ MeV $^{4}$He with $^{12}$C, and $3.038\pm0.003$ MeV $^{4}$He with $^{16}$O. The $^{23}$Na($\alpha$,$\alpha$)$^{23}$Na nuclear resonance is found to have an energy of $4.696\pm0.180$ MeV and cross-section increase of $41\pm7.0\%$. Increase of Na detection in IBA via the studied resonance is statistically significant. Future research can determine if the cross-section increase is sufficient for Na detection in glucose sensors.