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Flux Estimates and Detection Prospects for Lunar Geoneutrinos

Hang Hu, Yaping Cheng, Wan-Lei Guo

Abstract

The distribution of heat-producing elements (U, Th, K) within the Moon is critical for understanding its thermal evolution and formation history. Based on a refined lunar interior model, we calculate the geoneutrino fluxes at two representative detector locations that bracket the expected signal intensity. The maximum flux is found to be slightly lower than the corresponding predicted fluxes for the KamLAND site on Earth, while the minimum flux is approximately a factor of 8.63 lower than this maximum value. The angular distributions of geoneutrinos arriving at the two locations were further computed. Finally, we evaluate the detection prospects for lunar geoneutrinos using three reaction channels: inverse beta decay reaction, elastic scattering on electrons, and a novel radiochemical approach based on $\barν_e + ^3$He $\to e^+ + ^3$H. For each reaction, we calculate the expected event rates and briefly discuss the potential for measuring the total geoneutrino flux, as well as the relative contributions from U, Th, and K.

Flux Estimates and Detection Prospects for Lunar Geoneutrinos

Abstract

The distribution of heat-producing elements (U, Th, K) within the Moon is critical for understanding its thermal evolution and formation history. Based on a refined lunar interior model, we calculate the geoneutrino fluxes at two representative detector locations that bracket the expected signal intensity. The maximum flux is found to be slightly lower than the corresponding predicted fluxes for the KamLAND site on Earth, while the minimum flux is approximately a factor of 8.63 lower than this maximum value. The angular distributions of geoneutrinos arriving at the two locations were further computed. Finally, we evaluate the detection prospects for lunar geoneutrinos using three reaction channels: inverse beta decay reaction, elastic scattering on electrons, and a novel radiochemical approach based on He H. For each reaction, we calculate the expected event rates and briefly discuss the potential for measuring the total geoneutrino flux, as well as the relative contributions from U, Th, and K.
Paper Structure (8 sections, 3 equations, 9 figures, 1 table)

This paper contains 8 sections, 3 equations, 9 figures, 1 table.

Table of Contents

  1. Introduction
  2. Distributions of Th, U and K
  3. Lunar geoneutrino fluxes
  4. Detection prospects for lunar geoneutrinos
  5. IBD reaction on free protons
  6. IBD reaction on $^3$He
  7. Elastic scattering on electrons
  8. Summary

Figures (9)

  • Figure 1: Schematic cross-section of the lunar interior illustrating the Th distribution in Model 5. The PKT crust is divided into an inner region (8.2 ppm Th, angular extent 28.86$^\circ$ from the axis) and outer region (4.2 ppm Th, extending to 48.03$^\circ$), with the underlying PKT mantle slightly enriched (0.055 ppm Th) compared to the highland mantle (0.0366 ppm Th). The FHT crust has 0.235 ppm Th. A small core (380 km radius) is shown, and hypothetical geoneutrino detectors are placed in the PKT and FHT regions. This axisymmetric geometry captures the hemispheric asymmetry while simplifying the irregular PKT shape for calculations.
  • Figure 2: Lunar density versus radius.
  • Figure 3: Geoneutrino energy spectra for the PKT detector (top) and FHT detector (bottom), showing contributions from $^{232}$Th, $^{238}$U, and $^{40}$K.
  • Figure 4: Cumulative geoneutrino fluxes as functions of the distance from the PKT (top) and FHT (bottom) detectors, showing contributions from five distinct reservoirs.
  • Figure 5: Angular distributions of geoneutrinos at the PKT (top) and FHT (bottom) detectors from five reservoirs.
  • ...and 4 more figures