Advances in radiative capture studies at LUNA with a segmented BGO detector

Abstract

Studies of charged-particle reactions for low-energy nuclear astrophysics require high sensitivity, which can be achieved by means of detection setups with high efficiency and low backgrounds, to obtain precise measurements in the energy region of interest for stellar scenarios. High-efficiency total absorption spectroscopy is an established and powerful tool for studying radiative capture reactions, particularly if combined with the cosmic background reduction by several orders of magnitude obtained at the Laboratory for Underground Nuclear Astrophysics (LUNA). We present recent improvements in the detection setup with the Bismuth Germanium Oxide (BGO) detector at LUNA, aiming to reduce high-energy backgrounds and to increase the summing detection efficiency. The new design results in enhanced sensitivity of the BGO setup, as we demonstrate and discuss in the context of the first direct measurement of the 65 keV resonance (Ex = 5672 keV) of the 17O(p,gamma)18F reaction. Moreover, we show two applications of the BGO detector, which exploit its segmentation. In case of complex gamma-ray cascades, e.g. the de-excitation of Ex = 5672 keV in 18F, the BGO segmentation allows to identify and suppress the beam-induced background signals that mimic the sum peak of interest. We demonstrate another new application for such a detector in form of in-site activation measurements of a reaction with beta+ unstable product nuclei, e.g., the 14N(p,gamma)15O reaction.

A multichannel algebraic scattering approach to astrophysical reactions

“…The next focus for development is to expand MCAS to evaluate radiative capture reaction data, and make predictions down to the Gamow window for reactions of astrophysical interest. The first planned candidates for this formalism are 12 C(α, γ) 16 O, 56 Ni(p, γ) 57 Cu, 12 C(p, γ) 13 N (which was recently measured at LUNA [25] with their newly-upgraded BGO detector [26], and for which sturmians have already been found [27]) and 20 Ne(p, γ) 21 Na (currently being measured at LUNA).…”

Astrophysical S-factor and reaction rate for 15N(p,γ)16O within the modified potential cluster model*

“…Notably, the main difficulty in determining reliable reaction rates of the 12 N( ) 13 O, 13 N( ) 14 O, 14 N( ) 15 O, and 15 N( ) 16 O reactions for the CNO cycles is the uncertainty in the very low cross sections at the Gamow range. Developments within the low-energy underground accelerator facility, LUNA, in the Gran Sasso laboratory [80] and recent improvements in the detection setup [81] make taking direct measurements of nuclear reactions near the Gamow range feasible. This advantage has been demonstrated in the 14 N( ) 15 O reaction, which was successfully measured down to energies of 70 keV at LUNA [82].…”

Recent results and future perspectives with solid targets at LUNA

“…In order to control and characterize the various systematic uncertainties, two different, but complementary setups were adopted for the measurements. One setup was based on a HPGe detector in close geometry, whereas the other setup utilized a high efficiency Bismuth Germanium Oxide (BGO) scintillator detector Skowronski et al (2023b). The high energy resolution of the HPGe allowed all the many transitions of the reaction to be studied and also enabled the use of the γ-shape technique to characterize the target throughout the measurement.…”