Improved background suppression for radiative capture reactions at LUNA with HPGe and BGO detectors

Abstract

Direct measurements of small nuclear reaction cross sections require a low background in the signal region of interest to achieve the necessary sensitivity. We describe two complementary detector setups that have been used for studies of p, g ( ) reactions with solid targets at the Laboratory for Underground Nuclear Astrophysics (LUNA): a high-purity germanium detector and a bismuth germanate (BGO) detector. We present the effect of a customised lead shielding on the measured background spectra in the two detector setups at LUNA. We developed a model to describe the contributions of environmental and intrinsic backgrounds in the BGO detector measurements. Furthermore we present an upgrade of the data acquisition system for our BGO detector, which allows us to exploit the features of the segmented detector and overcome some of the limitations encountered in previous experiments. We conclude with a discussion on the improved sensitivity of the presented setups, and the benefits for ongoing and possible future measurements.

The challenging direct measurement of the 65 keV resonance strength of the 17O(p,γ)18F reaction at LUNA

“…This will allow to periodically scan the E c.m. = 143 keV resonance of the 18 O(p,γ) 19 F reaction as monitor for target degradation. Finally in order to further reduce the environmental background the whole setup is surrounded by a shielding made of borated polyethylene and lead, as neutron and gamma absorber, respectively [19].…”

“…The 17,18 O(p,γ) 18,19 F and 17,18 O(p,α) 14,15 N reaction cross sections have been measured at the Laboratory for Underground Nuclear Astrophysics (LUNA), located deep underground at Laboratori Nazionali del Gran Sasso (LNGS) where muonic background is reduced by 6 orders of magnitude with respect to the surface experiments [5]. Results obtained by the LUNA collaboration [6][7][8][9][10][11] had paramount impact on the interpretation of the oxygen isotopic ratio observed in giant stars and in stardust grains [12,13].…”

Measurement and analysis techniques for a study of 12C(p,γ) and 13C(p,γ) deep underground

“…Its close-to-4π geometry and segmentation in 6 crystals are particulary advantageous for measuring very low cross-sections. In case of the 13 C(p, γ) 14 N, the detection in coincidence of all of the energy released as γ-rays allowed to place the region of interest in an almost background-free region [20], owing to the high Q-value of the reaction (∼ 7.5 MeV). For the 12 C(p, γ) 13 N, given the smaller Q-value (∼ 1.9 MeV), different approach had to be used.…”

The Study of Key Reactions Shaping the Post-Main Sequence Evolution of Massive Stars in Underground Facilities

“…Compared to experiments on the surface, where secondary cosmic radiation on shielding materials results in diminishing returns beyond a certain thickness of shielding, much more massive shielding setups of lead and copper have been used at LUNA 400 (Caciolli et al, 2009), where for experiments with solid targets, easy access to the target had to be secured (Boeltzig et al, 2018). More sophisticated, i.e., larger and multilayered, shielding configurations are foreseen in the future as a consequence of an improved understanding of the relevant backgrounds and allowed by the more spacious target station layout at the new MV facility.…”