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Low-energy Cross Section Measurements of ${}^{\mathsf{12}}\mathsf{C}(\mathsf{p},γ)$ Deep Underground at LUNA

Jakub Skowronski, Axel Boeltzig

TL;DR

This study targets the low-energy cross section of $^{12}$C$(p,\gamma)^{13}$N, a reaction that governs H-burning nucleosynthesis in stars and informs solar metallicity estimates via CNO neutrinos. It combines measurements at the underground LUNA facility using two target types and two detection approaches to suppress systematics: HPGe spectroscopy of prompt $\gamma$-rays and an activation method with a large, segmented BGO detector. The experiment emphasizes meticulous target characterization, in-situ stability monitoring, and cross-checks between activation and prompt measurements, with detector efficiency calibrated through standard sources and known resonances and validated by Geant4 simulations. The authors report good agreement across targets and detectors, with a plan to publish the finalized cross-section results that will constrain stellar models and solar metallicity scenarios.

Abstract

The ${}^{\mathsf{12}}\mathsf{C}(\mathsf{p},γ)$ reaction cross section is currently under investigation in the low-background environment of the Laboratory for Underground Nuclear Astrophysics (LUNA). It is being studied using different types of solid targets, and employing two complementary detection techniques: HPGe spectroscopy and activation counting. To reduce systematic uncertainties, targets have been accurately characterized and their degradation under the intense beam of the LUNA-400 accelerator monitored. We present the experimental techniques and the corresponding analyses used to extract the reaction cross section.

Low-energy Cross Section Measurements of ${}^{\mathsf{12}}\mathsf{C}(\mathsf{p},γ)$ Deep Underground at LUNA

TL;DR

This study targets the low-energy cross section of CN, a reaction that governs H-burning nucleosynthesis in stars and informs solar metallicity estimates via CNO neutrinos. It combines measurements at the underground LUNA facility using two target types and two detection approaches to suppress systematics: HPGe spectroscopy of prompt -rays and an activation method with a large, segmented BGO detector. The experiment emphasizes meticulous target characterization, in-situ stability monitoring, and cross-checks between activation and prompt measurements, with detector efficiency calibrated through standard sources and known resonances and validated by Geant4 simulations. The authors report good agreement across targets and detectors, with a plan to publish the finalized cross-section results that will constrain stellar models and solar metallicity scenarios.

Abstract

The reaction cross section is currently under investigation in the low-background environment of the Laboratory for Underground Nuclear Astrophysics (LUNA). It is being studied using different types of solid targets, and employing two complementary detection techniques: HPGe spectroscopy and activation counting. To reduce systematic uncertainties, targets have been accurately characterized and their degradation under the intense beam of the LUNA-400 accelerator monitored. We present the experimental techniques and the corresponding analyses used to extract the reaction cross section.

Paper Structure

This paper contains 4 sections, 3 figures.

Table of Contents

  1. Introduction
  2. Current Status
  3. Experimental Setup
  4. Data Analysis

Figures (3)

  • Figure 1: State of the art for the ${}^{12}\mathrm{C}(\mathrm{p},\gamma){}^{13}\mathrm{N}$ reaction cross section. Two different energy ranges of interest are highlighted for RGB and AGB stars, respectively. Direct data available in these energy ranges comes from early measurements with significant scatter and uncertainties.
  • Figure 2: Left: BGO detector in lead shielding, partially retracted (shielding open) to access target. Right: HPGe detector, here shown retracted (fully outside of the shielding) at 55° to the target.
  • Figure 3: Examples of the spectra acquired at $E_{p} = 380$ keV. The upper panel shows the spectrum from the BGO. The lower panel shows the HPGe spectrum.