Measurement of the full excitation spectrum of the 7Li(p,{\gamma}){\alpha}{\alpha} reaction at 441 keV

TL;DR

This study measures the full excitation spectrum of the 7Li(p,γ)αα reaction at 441 keV using Silicon detectors, revealing continuum contributions and a possible broad resonance, thus testing and informing ab initio nuclear calculations.

Contribution

It introduces a novel Silicon detector method to accurately measure the full gamma spectrum, enabling detailed analysis of nuclear states and continuum effects.

Findings

Evidence for significant non-resonant continuum contributions

Tentative identification of a broad 0+ resonance at 12 MeV

Improved radiative width values from R-matrix analysis

Abstract

A current challenge for ab initio calculations is systems that contain large continuum contributions such as 8Be. We report on new measurements of radiative decay widths in this nucleus that test recent Green's function Monte Carlo calculations. Traditionally, {\gamma} ray detectors have been utilized to measure the high energy photons from the 7Li(p, {\gamma}){\alpha}{\alpha} reaction. However, due to the complicated response function of these detectors it has not yet been possible to extract the full {\gamma} ray spectrum from this reaction. Here we present an alternative measurement using large area Silicon detectors to detect the two {\alpha} particles, which provides a practically background free spectrum and retains good energy resolution. The resulting spectrum is analyzed using a many-level multi channel R-matrix parametrization. Improved values for the radiative widths are extracted from the R-matrix fit. We find evidence for significant non-resonant continuum contributions and tentative evidence for a broad 0+ resonance at 12 MeV.