Sustained human operations on the lunar surface require robust radiation protection, as the Moon lacks both a substantial atmosphere and a global magnetosphere, leaving crews exposed to galactic cosmic rays and solar energetic particle (SEP) events. The surface radiation field is also influenced by albedo secondaries, particularly neutrons and gamma rays produced when primary particles interact with lunar regolith. These secondaries can contribute substantially to biological dose. This review synthesises lunar and orbital measurements, radiation transport modelling, and experimental beam and neutron transmission studies to evaluate lunar regolith as anin situresource utilisation shielding material for surface habitats. Across published simulations, the first few tens of grams per square centimetre of regolith often reduce dose equivalent by fragmenting high linear energy transfer ions and lowering the average quality factor. At greater thicknesses, additional shielding can yield diminishing returns as secondary neutron production increases. Hybrid shielding strategies that place a hydrogen-rich material as an interior liner generally outperform shielding strategies with only regolith. Experimental results broadly support these trends and show that benchmarked Monte Carlo configurations can reproduce measured effects. https://orcid.org/0000-0003-1770-0495 Notes Article metrics 616 Total downloads 0 Video abstract views Share this article Article information Dates Received 4 February 2026 Revised 27 May 2026 Accepted 15 June 2026 Published 2 July 2026 Buy this article in print Journal RSS Sign up for new issue notifications 0952-4746/46/3/031001 Abstract Sustained human operations on the lunar surface require robust radiation protection, as the Moon lacks both a substantial atmosphere and a global magnetosphere, leaving crews exposed to galactic cosmic rays and solar energetic particle (SEP) events. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. 1. Introduction Sustained human operations on the Moon are now a near term objective of NASA’s Artemis campaign, which targets a long term presence on the lunar surface [ 1 ]. Radiation protection is an important factor for this objective because the lunar surface lacks both a substantial atmosphere and a global magnetosphere, so incident galactic cosmic rays (GCRs) and solar energetic particles (SPEs) are very weakly moderated. The Lunar Prospector carried a neutron spectrometer composed of two He proportional counters, one bare and one covered with cadmium, along with a boron-loaded plastic scintillator [ 5 ]. This configuration allows the neutron spectrum to be separated into thermal, epithermal, and fast neutron bands, enabling global maps of neutron flux and its relationship to regolith composition and hydrogen content [ 6 ]. Figure 1 shows the differential energy spectrum of fast neutrons leaking from the lunar surface from Download figure: Standard image High-resolution image Earlier measurements also include the Apollo 17 Lunar Neutron Probe Experiment (LNPE), which measured neutron density from 20 to 400 g cm using the B(n, ) Li reaction [ 9 ]. LNPE is especially valuable for this work because it is a surface experiment, and many transport studies have benchmarked their lunar neutron depth profiles against its data, as discussed in section 1.1 . Additional orbital datasets are also useful for benchmarking, even when they do not measure dose directly. The design implication is that crater siting can provide meaningful GCR reduction through sky occlusion, but it can also shift the field toward a larger neutron contribution that still needs to be managed. Dobynde and Guo (2024) developed mission guidance using their REDMoon model across the last two solar cycles (2000–2022), evaluating surface and subsurface bases with different regolith and aluminium shielding assumptions [ 147 ]. They report that background GCR exposure on the lunar surface is about 66% of interplanetary space. They also report that exposure can slightly increase just beneath the surface before decreasing to a negligible level by about 3 m depth. The key siting takeaway is that shallow burial is not automatically protective in their model, and that meters of regolith is where there is strong suppression of the radiation flux. Naito et al (2020) used PHITS to estimate effective dose equivalent at the lunar surface and in subsurface natural shielding geometries associated with holes and lava tubes [ 148 ]. They report that the effective dose equivalent due to GCR at the lunar surface reaches 1.14 mSv d , and that a single SEP event case reaches 2190 mSv/event. For shielding by terrain, they report that GCR exposure at the bottom of a 43 m deep vertical hole is below 0.08 mSv d . Inside a horizontal lava tube, the GCR exposure is less than 0.003 mSv d . The design implication is that large natural cavities provide an orders of magnitude reduction relative to surface habitats, and can convert radiation protection from a regolith layering and construction problem into a siting and access problem. The moderate reduction in dose reported for craters, holes, and lava tubes show the strong potential of using natural terrain for shielding. The common thread across all three is that partial sky occlusion gives moderate reductions, while subsurface geometries are where large reductions can appear. We now have measurements that can ground transport assumptions, including Chang’E-4 LND dose on the surface, particle albedo data from Lunar Prospector, and neutron counts per energy channel from instruments on the LRO [ 2 , 7 , 10 ]. A stronger standard for future work is to require that Monte Carlo configurations reproduce these surface benchmarks within uncertainty before using them to claim performance for habitats, and to report enough setup detail that others can reproduce the benchmark.