Investigation of $^{11}$B and $^{40}$Ca levels at 8-9 MeV by Nuclear Resonance Fluorescence

TL;DR

This study measures specific nuclear energy levels of $^{11}$B and $^{40}$Ca using nuclear resonance fluorescence with polarized gamma-ray beams, providing improved data crucial for calibration and astrophysical models.

Contribution

The paper presents new measurements of excitation energies, multipolarity mixing ratios, and branching ratios for $^{11}$B and $^{40}$Ca levels between 8 and 9 MeV, with improved accuracy and unambiguous level assignments.

Findings

Improved excitation energies for $^{40}$Ca levels.

Unambiguous $2^-$ assignment at 8425 keV in $^{40}$Ca.

Enhanced multipolarity and branching ratio data for $^{11}$B.

Abstract

We report on the measurement of $^{11}$B and $^{40}$Ca levels between excitation energies of 8 and 9 MeV using nuclear resonance fluorescence (NRF). The experiment was carried out with nearly-monoenergetic and linearly polarized photon beams provided by the High-Intensity $\gamma$-ray Source (HI$\gamma$S) facility at the Triangle Universities Nuclear Laboratory (TUNL). States in $^{11}$B are important for calibrations of NRF measurements, while the properties of $^{40}$Ca levels impact potassium nucleosynthesis in globular clusters. For $^{40}$Ca, we report on improved excitation energies and an unambiguous $2^-$ assignment for the state at 8425 keV. For $^{11}$B, we obtained improved values for $\gamma$-ray multipolarity mixing ratios and branching ratios of the 8920 keV level.