$\gamma$-ray Spectroscopy using a Binned Likelihood Approach

TL;DR

This paper introduces a Bayesian likelihood method for gamma-ray spectroscopy that analyzes the entire spectrum, including complex overlaps and backgrounds, to accurately determine reaction cross sections and branching ratios.

Contribution

It presents a novel statistical approach that models the full gamma-ray spectrum for improved analysis of complex cascades and coincidence data in nuclear physics.

Findings

Enhanced accuracy in branching ratio measurements for $^{18}$O(p,$$)$^{19}$F.

Reduced uncertainties by a factor of 4 compared to literature values.

Effective analysis of complex spectra with overlapping peaks and backgrounds.

Abstract

The measurement of a reaction cross section from a pulse height spectrum is a ubiquitous problem in experimental nuclear physics. In $\gamma$-ray spectroscopy, this is accomplished frequently by measuring the intensity of full-energy primary transition peaks and correcting the intensities for experimental artifacts, such as detection efficiencies and angular correlations. Implicit in this procedure is the assumption that full-energy peaks do not overlap with any secondary peaks, escape peaks, or environmental backgrounds. However, for complex $\gamma$-ray cascades, this is often not the case. Furthermore, this technique is difficult to adapt for coincidence spectroscopy, where intensities depend not only on the detection efficiency, but also the detailed decay scheme. We present a method that incorporates the intensities of the entire spectrum (e.g., primary and secondary transition peaks, escape peaks, Compton continua, etc.) into a statistical model, where the transition intensities and branching ratios can be determined using Bayesian statistical inference. This new method provides an elegant solution to the difficulties associated with analyzing coincidence spectra. We describe it in detail and examine its efficacy in the analysis of $^{18}$O(p,$\gamma$)$^{19}$F and $^{25}$Mg(p,$\gamma$)$^{26}$Al resonance data. For the $^{18}$O(p,$\gamma$)$^{19}$F reaction, the measured branching ratios improve upon the literature values, with a factor of 4 reduction in the uncertainties.