Neutrino yield and neutron shielding calculations for a high-power target installed in an underground setting

TL;DR

The paper addresses the challenge of producing a high-intensity antineutrino source in an underground setting using 8Li decay-at-rest, driven by a 600 kW proton beam on a Be target. It employs Geant4 Monte Carlo simulations with site-specific shielding to maximize 8Li production and minimize neutron backgrounds, detailing a redesigned target/sleeve geometry and an iron plus boron-loaded concrete shielding scheme. The authors validate neutron production and shielding predictions against experimental data and inter-code benchmarks, quantify Li8 yields and antineutrino fluxes, and assess activation in rock and components as well as tritium production for the Yemilab site. The study provides a practical, transferable framework for deploying high-power targets in underground laboratories without compromising detector sensitivity or safety constraints.

Abstract

With the ever increasing beam power at particle accelerator-based facilities for nuclear and particle physics, radioactive isotope production, and nuclear engineering, targets that can withstand this power, and shielding of secondary particles are becoming increasingly important. Here we present Monte Carlo (MC) calculations using the well-established Geant4 software to optimise and predict the antineutrino yield of a $^8$Li Decay-At-Rest (DAR) source. The source relies on 600~kW of beam power from a continuous wave proton beam impinging on a beryllium target, where spallation neutrons capture on $^7$Li to produce the $^8$Li. We further present an in-depth treatment of the neutron shielding surrounding this target. We show that we can produce the high antineutrino flux needed for the discovery-level experiment IsoDAR, searching for ``sterile'' neutrinos (predicted new fundamental particles) and other beyond standard model physics, while maintaining a neutron flux in the detector that is below natural backgrounds. The methods presented in this paper are easily transferable to other high-power targets and their associated shielding.

Figures (16)

• Figure 1: The layout of the IsoDAR target and the $\nu$EYE detector at Yemilab Seo:2023xku.
• Figure 2: The target: beryllium shells and cooling heavy water.
• Figure 3: The target surrounded by the Li-Be sleeve.
• Figure 4: Validation of Geant4 predictions against the experimental neutron yield data of Tilquin et al. (2005) for thick Be targets.
• Figure 5: ${}^8{\rm Li}$ contour plots inside the target sleeve volume. The beam direction is left to right.