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The Lunar Lander Neutron and Dosimetry (LND) Experiment aboard theChang$'$E-4 Lander on the lunar-far side measures energetic charged and neutralparticles and monitors the corresponding radiation levels. During solar quiettimes, galactic cosmic rays (GCRs) are the dominating component of chargedparticles on the lunar surface. Moreover, the interaction of GCRs with thelunar regolith also results in upward directed albedo protons which aremeasured by the LND. In this work, we used calibrated LND data to study the GCRprimary and albedo protons. We calculate the averaged GCR proton spectrum inthe range of 9 368 MeV and the averaged albedo proton flux between 64.7 and76.7 MeV from June 2019 (the 7th lunar day after Chang$'$E-4$'$s landing) toJuly 2020 (the 20th lunar day). We compare the primary proton measurements ofLND with the Electron Proton Helium INstrument (EPHIN) on SOHO. The comparisonshows a reasonable agreement of the GCR proton spectra among differentinstruments and illustrates the capability of LND. Likewise, the albedo protonmeasurements of LND are also comparable with measurements by the Cosmic RayTelescope for the Effects of Radiation (CRaTER) during solar minimum. Ourmeasurements confirm predictions from the Radiation Environment and Dose at theMoon (REDMoon) model. Finally, we provide the ratio of albedo protons toprimary protons for measurements in the energy range of 64.7-76.7 MeV whichconfirms simulations over a broader energy range.

Primary and albedo protons detected by the Lunar Lander Neutron and Dosimetry (LND) experiment on the lunar farside