IFMIF-DONES, short for International Fusion Materials Irradiation Facility–Demo Oriented Neutron Source, exists for one purpose: to qualify the structural and functional materials that will make a demonstration fusion reactor, or DEMO, buildable, licensable and safe. A 125-milliampere, 40-megaelectronvolt deuteron accelerator strikes a flowing liquid lithium target, and the resulting d-Li fusion reactions bathe test modules in a neutron spectrum closely resembling the one that will batter a reactor’s first wall. The test cell itself is a heavily shielded, atmosphere-isolated enclosure containing the lithium target and the High Flux Test Module, or HFTM, where thousands of miniature material specimens will be irradiated for years. Every critical design question, from displacements per atom in the steel to nuclear heating, gas production, activation and radiation dose rates in neighbouring rooms, depends on an accurate geometric model of this chamber.

The tool of choice for such analyses is the Monte Carlo method, in which codes like MCNP track millions of individual neutrons through a mathematical replica of the facility. But Monte Carlo codes do not read engineering CAD drawings directly. The team’s workflow begins with a laborious pre-processing stage: simplifying the CAD geometry, homogenizing volumes, and hunting down interferences between components using tools such as SpaceClaim. The cleaned-up ‘neutronic CAD model’ is then converted into constructive solid geometry, or CSG, the surface-based representation that Monte Carlo codes understand, using conversion programs like McCad, SuperMC or the newer GEOUNED. Crucially, the conversion must also describe the void spaces around solids, invisible in the original drawings but essential for particle transport. Every model is then stress-tested by firing particles inward from a surrounding sphere, with a strict quality gate: less than one particle lost per million, and computed volumes cross-checked against the CAD originals to flag outliers.

The first DONES test cell model, designated ‘mdl6.9’, was inherited from the earlier IFMIF/EVEDA design phase and adapted to the new baseline. The changes were substantial. DONES uses a single accelerator rather than the two originally foreseen, so one deuteron source was deactivated in the McDeLicious neutron source routine, leaving a dummy beam duct behind. The medium- and low-flux test modules of IFMIF, including the Tritium Release and Creep Fatigue Test Modules, were dropped, leaving only the HFTM, then a ‘thin’ version roughly five centimetres thick holding three rows and eight columns of specimen capsules. The quench tank, which catches the high-speed lithium jet, sat outside the test cell to suppress tritium production. Shielding consisted of magnetite heavy concrete, four metres thick on the downstream and lateral walls and 3.5 metres upstream, manually layered in the model so that different variance-reduction ‘importance’ values could be assigned to each layer to tame statistical noise.

Engineering reality soon overtook that baseline. The target assembly adopted a ‘bayonet back-plate’ design sealed with a gasket, the quench tank was moved inside the test cell to cure lithium-flow instabilities and mitigate neutron streaming, and the HFTM was redesigned with a thicker 4-by-8 capsule array to hold more samples. The result was ‘mdl8.3.0’, the first model truly oriented to DONES rather than its predecessor, with detailed target and HFTM geometry built directly from the engineering CAD data, a shielding plug blocking the second beam duct, and the lithium inlet and outlet enclosed in a shielded interface cell. A comprehensive suite of nuclear analyses on damage doses, gas production and heating followed. Later, the team restructured the model around a modular ‘skeleton’ concept, with space-holders for major components that can be swapped in and out as designs mature, dramatically reducing the modelling effort needed for each design update.

That modular version, ‘mdl9.2.1’, also embraced one of the most striking architectural changes to the facility: the inner monolithic concrete shielding was divided into eleven removable biological shielding blocks, or RBSBs, each designed with dogleg joints to frustrate neutrons seeking a straight path out. The bayonet back-plate was reverted to an integrated configuration after it became clear that no gasket material could survive the brutal irradiation at the target region. Detailed piping layouts were filled into the lower shielding plugs, and a neutron beam tube was added to guide particles from the test cell to a neighbouring room for complementary experiments. Materials were standardized too: EUROFER steel compositions aligned with DEMO neutronics activities, and reference ordinary and heavy concrete with certified production data, borrowed from ITER calculations, was adopted for the shielding.

The current baseline, ‘mdl9.2.7’, goes further still. The RBSB engineering was refined, the inner steel liner thickened for better heat removal, the upper shielding plugs modified to accommodate HFTM piping, and the test cell cover plate filled with shielding to plug streaming paths through the block gaps. Heavy concrete remains inside the RBSBs, prized for both shielding power and thermal conductivity, while the surrounding bucket structure switches to cheaper ordinary concrete. Most ambitiously, the entire test cell geometry has been integrated into the 2022 baseline model of the DONES main building, allowing analysts to assess radiation impact on the accelerator area, the access cell above the test cell and downstream experimental rooms, and even to run large-scale safety evaluations of public dose through sky-shine and direct radiation pathways.

But how much geometric detail does a Monte Carlo model actually need? The team attacked this question with a series of sensitivity studies centred on damage dose, measured in displacements per atom, the key metric for materials qualification. Because DPA varies by orders of magnitude across the HFTM, neither the average nor the peak alone is a fair comparator; the researchers therefore devised the ‘volume-DPA product’, or VDP, which weights dose by the volume experiencing it. Three model variants were compared against the full model: two retained detailed target and HFTM geometry within progressively smaller envelopes, while a third reduced everything to a crude block of lithium, a EUROFER backplate and a uniform mixture of steel, sodium and EUROFER. The two detailed variants agreed with the full model to within one percent on VDP and two percent on VDP10, but the crude block diverged badly, over-moderating the neutrons and misrepresenting the target structures.

That finding licensed a validated lightweight model for accelerated simulations and design optimization loops. It preserves the essentials, the lithium target, EUROFER backplate, HFTM body, capsules and reflectors, while homogenizing the helium cooling channels into the structural material at their exact volume fractions of 31 percent helium and 69 percent SS316LN steel. Benchmarked against the full model with the McDeLicious d-Li source and the FENDL-3.1d nuclear data library, the simplified version matched total neutron flux within two percent for the central four capsule columns, where the precious material samples actually sit. Deviations grow toward the lateral capsules, which serve mainly as reflectors, so the authors caution against using the lightweight model for dedicated analyses of the outer columns. In the opposite direction, the team also built the first HFTM model with explicit specimen-level payload geometry, the CLCv2.0 capsule loading configuration reaching an 85 percent EUROFER volume fraction, and found that flux and damage doses barely changed compared with the homogeneous mixture, a reassuring consequence of the high neutron energies and long mean free paths involved.

Finally, the researchers demonstrated a mesh-based alternative to CSG. Using a fast tetrahedral meshing workflow, exporting the CAD model to STL, meshing it with TetGen in minutes, and post-processing into Abaqus format for MCNP6, they produced an unstructured mesh HFTM of 157,000 elements and slotted it into the test cell model in place of the CSG version. The flux contours from the two approaches overlap almost perfectly, proving the method viable for rapid design iteration, though at a cost: the mesh model needed roughly 13,500 CPU-hours for a billion particle histories against 950 hours for CSG, a penalty the team attributes to one-to-one matching of mesh sets and expects to slash by merging same-material sets. Together, the model lineage, the validated simplifications and the mesh demonstration give the fusion community a traceable, quality-controlled computational backbone for DONES, one that will help decide, years before first beam, whether the materials of a fusion power plant can truly endure.

Subject of Research: Neutronics geometry model development for the IFMIF-DONES test cell

Article Title: Neutronics model developments for the IFMIF-DONES test cell

Article References: Qiu, Y., Serikov, A., Alvarez, I., Mota, F., Čufar, A., Becerril, S., & Castellanos, J. (2026). Neutronics model developments for the IFMIF-DONES test cell. Frontiers in Nuclear Engineering, 5, Article 1783403. https://doi.org/10.3389/fnuen.2026.1783403

Image Credits: AI Generated

DOI: 10.3389/fnuen.2026.1783403

Keywords: IFMIF-DONES, neutronics, Monte Carlo simulation, MCNP, fusion materials, test cell, High Flux Test Module, damage dose, CAD-to-MC conversion, unstructured mesh, radiation shielding, DEMO

The study, carried out by Fatma Akyıldız, used the EpiXS software package together with the EPICS2017 photon cross-section library, which is based on ENDF/B-VIII.0, to calculate a comprehensive set of photon interaction parameters for each compound over the energy range of 0.015 to 15 MeV. The quantities evaluated included the mass attenuation coefficient, the linear attenuation coefficient, the half-value layer, the effective atomic number, the effective electron density, the equivalent atomic number, the total kerma coefficient, and both the exposure buildup factor and the energy absorption buildup factor. All fifteen substances were treated under identical computational conditions, allowing the effects of elemental composition and density to be separated cleanly.

The fifteen compounds were deliberately chosen to span different pharmacological classes and different elemental makeups. Amphetamine and nicotine are liquids composed almost entirely of carbon, hydrogen, and nitrogen. Caffeine, meprobamate, and the barbiturates pentobarbital and phenobarbital contain substantial oxygen fractions. Diazepam and chlordiazepoxide stand apart because they include chlorine, an element with a considerably higher atomic number than any other constituent in the dataset. Densities ranged from 0.936 g cm⁻³ for amphetamine to 1.56 g cm⁻³ for heroin, and the author notes that where directly traceable experimental densities were unavailable, database-derived adopted values were used rather than new measurements.

The most striking compositional effect appears at low photon energy. At 15 keV, diazepam shows the highest mass attenuation coefficient of the entire set, 3.0084 cm² g⁻¹, followed closely by chlordiazepoxide at 2.9168 cm² g⁻¹. These values are far above those of the chlorine-free compounds because even a modest chlorine fraction, roughly 12 percent by weight in diazepam and 11.8 percent in chlordiazepoxide, strongly enhances photoelectric absorption, which scales steeply with atomic number. Among the chlorine-free substances, those with higher oxygen or nitrogen content, such as meprobamate at 1.1282 cm² g⁻¹ and caffeine at 1.0782 cm² g⁻¹, outperform the carbon-rich compounds. Phencyclidine, or PCP, gives the lowest value at 0.7875 cm² g⁻¹, with amphetamine, methadone, and nicotine close behind.

This separation collapses rapidly as photon energy rises. In the Compton-dominated region around 1.5 MeV, the mass attenuation coefficients of all fifteen compounds fall within a narrow band from 0.05391 to 0.05706 cm² g⁻¹, and at 15 MeV they span only 0.01766 to 0.01854 cm² g⁻¹. The difference between the highest and lowest values shrinks from nearly a factor of four at 15 keV to just a few percent in the megaelectronvolt range, because Compton scattering depends mainly on electron density rather than atomic number. Once the mass coefficients converge, bulk density becomes the dominant discriminator of attenuation per unit thickness. Heroin, with the highest density in the series, then delivers the highest linear attenuation coefficient and the smallest half-value layer, 24.82 cm at 15 MeV, while low-density amphetamine shows the weakest performance with a half-value layer of 41.41 cm.

The effective atomic number tells the same story in a different language. At 15 keV, diazepam and chlordiazepoxide reach values of 11.180 and 11.001 respectively, while PCP and amphetamine sit at the bottom with 4.860 and 4.989. Around 1 MeV, all curves converge to a broad minimum as Compton scattering takes over, with values ranging from about 3.117 for PCP to 4.486 for diazepam. Above the pair-production threshold of 1.022 MeV, the effective atomic numbers climb again, reaching 3.476 to 5.089 at 15 MeV, because pair production carries a stronger dependence on atomic number than Compton scattering. The effective electron density follows a related but not identical pattern, since it counts electrons per unit mass and therefore weights both elemental fractions and atomic masses.

The total kerma coefficient, which quantifies the kinetic energy transferred from photons to secondary charged particles per unit mass, behaves differently from the attenuation coefficients altogether. Rather than declining monotonically with energy, KermaTot falls from its 15 keV maximum to a minimum near 50 to 80 keV and then rises steadily toward 15 MeV, where values reach approximately 3.28 to 3.48 × 10⁻¹¹ Gy·cm² per photon. At 15 keV, diazepam and chlordiazepoxide again lead with 6.4387 × 10⁻¹² and 6.2254 × 10⁻¹² Gy·cm² per photon, while PCP records the lowest value at 1.2716 × 10⁻¹² Gy·cm² per photon. This U-shaped profile reflects the increasing energy carried away by secondary charged particles at high photon energies even as the overall interaction probability drops.

The buildup factors reveal the most dramatic behavior in the entire study. Unlike the Beer–Lambert law, which counts only uncollided primary photons, buildup factors account for scattered photons that reach a point of interest after multiple interactions within the material. Using the geometric progression fitting method with equivalent atomic numbers interpolated from reference elements, the study calculated both exposure and energy absorption buildup factors at penetration depths from 1 to 40 mean free paths. At shallow depths the differences are modest, but they explode with penetration. At 80 keV and 40 mean free paths, PCP produces an energy absorption buildup factor of 1.182 × 10⁵ and an exposure buildup factor of 2.654 × 10⁵, meaning scattered photons multiply the dose by more than five orders of magnitude. Amphetamine follows at 1.069 × 10⁵, while chlordiazepoxide and diazepam remain more than an order of magnitude lower, at 3.752 × 10³ and 3.341 × 10³ respectively.

The physical explanation lies in the competition between absorption and scattering. PCP and amphetamine, being carbon-hydrogen-nitrogen-rich with low equivalent atomic numbers, absorb few low-energy photons photoelectrically, so photons survive to scatter repeatedly and accumulate. The chlorine-containing benzodiazepines, by contrast, remove a larger fraction of photons through photoelectric absorption before they can multiply. By 15 MeV and 40 mean free paths, the buildup factors converge to narrow ranges of roughly 7.8 to 8.2 for both quantities, and the ordering even reverses slightly, with diazepam highest and PCP lowest, showing that PCP’s dominance is confined to the low and intermediate energy region where Compton multiple scattering outpaces photoelectric removal.

The author emphasizes that these compounds are not proposed as practical radiation shielding materials, and that the findings are limited to theoretical calculations for idealized, homogeneous bulk forms defined by the adopted compositions and densities. Experimental verification, along with assessment of physical, chemical, and mechanical properties, would be needed before any shielding application could be considered. Nevertheless, the dataset offers a quantitative reference for computational photon transport, dosimetric evaluations, and radiation protection analyses involving pharmaceutical and organic media, and it demonstrates that no single parameter can capture the full photon interaction response of a material. Low-energy attenuation is governed by composition, thickness-dependent attenuation by density, and buildup by the interplay of absorption and multiple scattering across both energy and depth.

Subject of Research: Photon interaction parameters and radiation shielding characteristics of psychoactive substances

Article Title: Comparative investigation of photon interaction parameters in psychoactive substances: the role of molecular composition

Article References: Comparative investigation of photon interaction parameters in psychoactive substances: the role of molecular composition. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: radiation physics, photon attenuation, psychoactive substances, mass attenuation coefficient, buildup factors, effective atomic number, EpiXS, EPICS2017, diazepam, PCP, radiation shielding, dosimetry

The material at the heart of this work is lunar regolith, the loose, fragmented layer of rock, mineral grains, and glassy particles that blankets the lunar surface to depths of several meters. Regolith is the product of billions of years of meteorite impacts that pulverized the lunar crust, and its composition varies across the Moon but generally includes silicate minerals, oxides of iron, titanium, calcium, and aluminum, and a significant fraction of agglutinates, which are irregular glassy particles welded together by micrometeorite impacts. Because this material is already sitting on the lunar surface in essentially unlimited quantities, it represents the single most obvious feedstock for any serious attempt at in-situ resource utilization, the strategy of living off the land beyond Earth.

Additive manufacturing, more commonly known as 3D printing, offers a natural fit for this challenge. Unlike conventional construction, which relies on large machinery, formwork, and a skilled workforce, additive manufacturing builds structures layer by layer from a digital design, using only the material that is actually needed. On the Moon, where every machine must be shipped from Earth and operated in a vacuum, under extreme temperature swings, and amid abrasive dust, the appeal of a compact, automated, digitally controlled fabrication system is hard to overstate. A single printer, paired with a regolith harvesting and processing system, could in principle fabricate walls, foundations, radiation shields, landing pads, and infrastructure components on demand, adapting each design to local terrain and mission requirements without waiting for resupply missions.

What distinguishes the new study is its emphasis on reconfigurability. Most visions of printed lunar habitats assume a one-way process: a structure is designed, printed, and fixed in place forever. But mission planners increasingly recognize that lunar bases, like the missions that precede them, will need to evolve. Equipment will be replaced, modules will be repurposed, and habitats will need to expand or contract as crew rotations and scientific priorities change. Building blocks that can be printed, assembled, disassembled, and reassembled into new configurations would give lunar architects a flexibility that monolithic printed structures cannot provide. Instead of demolishing a wall to build a new room, crews could simply take the wall apart and reprint or reposition its elements elsewhere.

Achieving this vision requires solving a chain of interlocking technical problems, and the researchers address them across the full workflow. The first step is feedstock preparation. Raw lunar regolith, whether actual Apollo-era samples or, more commonly in laboratory research, lunar regolith simulants that replicate the mineralogy and particle size distribution of the real material, must be sieved, sorted, and in some cases processed into a form suitable for printing. The sharp, irregular, and glassy nature of regolith particles makes them abrasive and difficult to flow uniformly, so particle engineering plays a crucial role in producing a feedstock that a printer can handle reliably.

The second step is the printing process itself, and here the study examines how regolith-based materials behave when deposited layer by layer. A central tension in lunar construction chemistry is the binder problem. On Earth, concrete gains its strength from Portland cement, whose production requires water and generates carbon dioxide through the calcination of limestone. Neither the water nor the emissions are acceptable on the Moon, where water is a precious resource and there is no atmosphere to pollute. Alternatives under investigation across the field include geopolymer chemistry, in which alkaline solutions activate the aluminosilicate minerals in regolith to form cement-like binders; sintering, in which concentrated heat from lasers, microwaves, or focused sunlight fuses regolith particles into solid masses without any binder at all; and small quantities of imported bonding agents, such as polymers, used as economically as possible.

Each route involves trade-offs that the researchers weigh in detail. Sintering produces genuinely binder-free structures, a major advantage for long-term self-sufficiency, but the vacuum environment complicates heat transfer and can trap gases released from the regolith, causing porosity and cracking. Thermal expansion mismatches between layers and the extreme thermal cycling between lunar day and night, where surface temperatures can swing by more than two hundred degrees Celsius, add further stresses. Geopolymers and chemical binders can deliver strong, dense components at lower processing temperatures, but they introduce dependence on reactants that must either be sourced locally or transported from Earth. The study’s framework for reconfigurable blocks is designed to accommodate this uncertainty: because the blocks are modular, a printing process can be refined or even replaced over time without abandoning the structures already built from earlier batches.

Mechanical performance is, of course, the bottom line for any structural material, and the reported work includes evaluation of the printed blocks under conditions relevant to lunar service. Compressive strength is the primary metric, since lunar habitats will mostly experience compressive loads from overlying regolith shielding piled on top of habitats to protect crews from galactic cosmic rays and solar particle events. Several meters of regolith cover are typically proposed for radiation protection, which means the underlying structure must bear substantial static loads in one-sixth of Earth’s gravity. The blocks must also tolerate internal pressurization, because habitats will hold breathable atmosphere at pressures that push outward on the walls, creating tensile stresses that brittle, sintered regolith handles poorly. Strategies to address this include placing habitat pressure vessels inside regolith-block shells, reinforcing blocks with fibers or mesh, and designing interlocking geometries that distribute loads across many contact surfaces rather than relying on mortar joints.

The interlocking geometry is where the reconfigurable concept becomes tangible. Rather than printing large monolithic panels, the researchers envision blocks with engineered shapes, analogous to LEGO bricks or precision masonry units, that can be stacked into curved walls, domes, and vaults and later separated without destructive force. Digital design tools allow each block’s geometry to be optimized for its position in a structure, embedding channels for cables and pipes, sockets for mounting hardware, or keying features that align with robotic grippers. This last point matters because much of the assembly on the Moon will likely be performed by robots rather than astronauts. Robotic arms placing regolith blocks in a vacuum environment avoid the hazards of EVA, and modularity suits robotic manipulation far better than amorphous printed masses, since discrete units with well-defined geometry can be grasped, positioned, and verified with existing machine-vision techniques.

Looking toward actual missions, the researchers situate their work within the broader context of NASA’s Artemis program and international plans for a sustained lunar presence, including the proposed Moon Village concept championed by the European Space Agency. The surface of the Moon is expected to host multiple cooperating installations in the coming decades, from the Gateway-linked Artemis Base Camp at the lunar south pole to landing infrastructure, power plants, telescopes, and pilot plants for extracting oxygen and metals from regolith. All of these will need construction materials, radiation shielding, thermal management, and foundations, and all of them will benefit from a standardized, printable, reconfigurable building system. The authors position their building blocks not as a finished habitat but as a scalable construction primitive, a verified unit of lunar architecture around which future designs, standards, and robotic systems can converge.

Significant engineering hurdles remain before regolith blocks are stacked on the lunar surface. Testing with genuine lunar samples is rare and limited by the tiny quantities of Apollo material available, so validation ultimately depends on simulants whose fidelity to the real thing is imperfect and whose behavior under vacuum, radiation, and thermal cycling differs in ways that are still being characterized. Printing at useful scale in vacuum, with lunar gravity and without Earthlike supply chains, has yet to be demonstrated in an operational setting, although parabolic flights and vacuum-chamber experiments continue to close the gap. The new study contributes a coherent pathway through this landscape: a demonstration that regolith can be additively manufactured into discrete, mechanically sound, reconfigurable blocks, and a design philosophy in which habitats grow and change with the missions they serve. If the approach matures as hoped, the first permanent structures on the Moon may not be transported there at all, but printed in place from the ground beneath future astronauts’ boots, one reconfigurable block at a time.

Subject of Research: Additive manufacturing of lunar regolith into reconfigurable building blocks for lunar habitation.

Article Title: Additive manufacturing of lunar regolith for reconfigurable building blocks toward lunar habitation

Article References: McCallum, C., Liang, Y., Tushar, N., Xu, B., Zhao, B., Zeng, H., & Shou, W. (2026). Additive manufacturing of lunar regolith for reconfigurable building blocks toward lunar habitation. npj Advanced Manufacturing. https://doi.org/10.1038/s44334-026-00111-x

Image Credits: AI Generated

DOI: 10.1038/s44334-026-00111-x

Keywords: lunar regolith, additive manufacturing, 3D printing, lunar habitation, in-situ resource utilization, Moon base, space construction, sintering, geopolymer binders, reconfigurable building blocks, Artemis program, radiation shielding