Generation of Si2+ ions and precise irradiation of chosen areas on six siliceous rocksAmorphization of a material exposed to radiation can result from ionization and collision cascades of atoms. Their relative influence on the extent of damage is usually determined by the mass and energy of the incident radiation source, as well as the type of target material36. Neutron radiation, in particular interacts with atoms in the target material to produce energetic ions with a continuum of energies ranging from a few tens of electron volts (eV) to upwards of 100,000 eV37. A fast neutron traversing a solid will occasionally impart sufficient energy to a target nucleus to dislodge the target atom from its stationary lattice site. This newly moving target atom is then responsible for subsequent displacement damage in the solid (damage is only indirectly due to the neutron). The displaced atom is known as a Primary Knock-on Atom (PKA). The PKA will depart its lattice site with kinetic energy ranging from 101 to 105 eV (the maximum PKA energy for light target atoms can be even higher). The ensemble of possible knock-on energies, convoluted with the probabilities of specific energy transfers (from neutron to stationary lattice atom) is known as the PKA spectrum38. In mineral phases present in granite, the PKA spectrum is much more complicated than in a monoatomic metal, because the PKA species can be either a light anion such as oxygen or a much heavier cation such as calcium. These PKA species variations themselves lead to different characteristics in the PKA spectrum associated with each species.Light ions such as oxygen predominantly induces changes in a material through the loss of electronic energy (via ionization), whereas when exposed to heavy ion radiation39, the change is triggered predominantly by the loss of nuclear energy (due to collisional damage). Hence, the PKA spectrum created by neutrons impinging on granitic silicates creates a broad range of electronic to nuclear stopping ratios. Therefore, utilizing medium-weight ions such as Silicon is a strategic choice, as it emulates the broak range of the PKA spectrum generated by neutrons impinging on granitic silicates, as Si2+ ions introduces competing effects of atomic displacement due to nuclear energy loss and localized non-equilibrium disorder and excitation arising from electronic energy loss40. Hence, Si2+ ions were chosen for irradiating the minerals, utilizing two unique energies: 2 MeV and 10 MeV. The ion ranges, as determined by SRIM-200841, are listed in Supplementary Table 1. Specifically, for 2 MeV Si2+ ions, the range is in the order of 1600–1730 nm, while for 10 MeV Si2+ ions, it extends to about 4060–4340 nm. The selection of these energies aims to investigate the impact of varied ion penetration depths, including both shallow and deep ranges, on the swelling behavior and the overall loss in nanoindentation modulus.The irradiations were conducted employing a Source of Negative Ions by Cesium Sputtering (SNICS) ion source and a tandem accelerator as shown in Fig. 1, with specific radiation conditions detailed in Table 1. The peak displacement per atom (DPA—a measure of cumulative damage in irradiated materials due to atomic displacements arising from nuclear and electronic collisions) resulting from ion radiation and the corresponding ion penetration depths are illustrated in Supplementary Fig. 2, which includes data from the current study and previous studies22,25,26,27,28,29,33,42,43,44,45,46 that utilized ion radiation on silicate minerals.Fig. 1: Generalized schematic of the accelerator, end chambers, and copper masks.a The Source of Negative Ions by Cesium Sputtering (SNICS) source generates Si ions, which are accelerated to either 2 or 10 MeV and then directed by the magnet into the dedicated end station for irradiation studies. b Illustration of sample masking on siliceous rocks prior to exposure to Si2+ ion radiation: The minerals exhibit expansion within the two exposed windows of the sample surface subjected to radiation.Table 1 Experimental parametersCoarse-grained igneous rocks typically used as aggregates in concrete were examined. The minerals of specific interest were quartz and feldspars (albite, anorthite, and microcline) as they compose a significant fraction of granitic rocks. The entire range of samples, comprising 6 samples and 12 windows, is illustrated in Fig. 1c. A copper mask was used to shield and protect the region outside the windows during the irradiation process, delineating the contrast between the irradiated and pristine regions, as depicted in Fig. 1b. The Raman images showing the mineral distribution within the different windows are displayed in Fig. 2. The corresponding mineral compositions quantified using a Raman imaging quantification protocol adopted by Polavaram and Garg47 are listed in Supplementary Table 2. The samples, comprising multiple minerals, were classified into granite and diorite rock types using the chart shown in Supplementary Fig. 3 and the known mineral composition of the rocks (listed in Supplementary Table 2). The presence of coarse crystals on the order of 1 mm indicated that the samples were granites and diorites, as rhyolites and andesites have a very fine-grained texture with crystals that are not visible to the naked eye.Fig. 2: Composite Raman images of the sample set used in this study.In the Raman images of samples 1 and 2, quartz is the only phase detected. Similarly, the Raman images of samples 3 and 4 reveal the presence of anorthite (CaAl2Si2O8), augite ((Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6), and minor amounts of hornblende ((Ca,Na)2(Mg,Fe,Al)5(Al, Si)8O22 (OH)2) and quartz (SiO2). Samples 5 and 6 display the presence of albite (NaAlSi3O8), microcline (KAlSi3O8), biotite (K(Mg,Fe)3AlSi3O10(F,OH)2), and quartz (SiO2). Unmapped phases are indicated by black color.Relating local phase chemistry with volumetric expansions using multi-modal imagingMultimodal imaging, integrating information from diverse imaging techniques, enables the investigation of structural, chemical, and mechanical changes induced by dynamic phenomena48,49, facilitating the analysis of common effects resulting from irradiation50,51,52,53. This allows for a thorough examination of manifestations arising from irradiation, contributing to a deeper understanding of its underlying mechanisms, and has broader applications in assessing degradation in various systems exposed to different conditions54,55,56. In this study, Fig. 3 displays the images obtained through various imaging techniques, including optical, laser profilometry, Raman, and SEM-EDS imaging, for one of the sample windows (sample 6, window 2 irradiated with 10 MeV, 1016 ions/cm2 Si2+ radiation). For the sake of brevity, all correlative images for the other samples and their corresponding windows are reported in Supplementary Figs. 5–15.Fig. 3: Multi-modal imaging of sample 6, window 2 irradiated with 10 MeV, 1016 ions/cm2 Si2+ radiation.A Microscopy and profilometry – Optical images of pristine and irradiated surfaces revealing structural features, SEM back-scattered images revealing compositional contrast, laser profilometry images showing surface height and difference profiles, B SEM-EDS images illustrating the distribution of constituent elements in the different phases, with increasing gray values indicating higher concentration of the element, and C Raman imaging displaying distinct phases including albite, biotite, microcline, and quartz. The optical, surface height, and the height difference images possess a lateral resolution of 1.37 μm/pixel (20 nm vertical resolution). The Raman images have a resolution of 20 μm/pixel, while the SEM-EDS images have a resolution of 5 μm/ pixel.The mineral distribution within the area depicted in Fig. 3 was identified through Raman imaging, with corresponding Raman images presented in Fig. 3C. The analysis revealed the presence of two distinct types of albite (NaAlSi3O8) and biotite (K(Mg,Fe)3AlSi3O10(F,OH)2), exhibiting different Raman spectra despite sharing the same chemical composition (as determined from the SEM-EDS images shown in Fig. 3B). The back-scattered image in Fig. 3A clearly illustrates the contrast between the biotite and albite-quartz regions, with the latter consisting of lower atomic weight elements as compared to biotite which contains iron. When considering the albite in both the windows of samples 5 and 6, the elemental ratio by weight was determined from SEM-EDS images as follows: 0.93 ± 0.06 for Na/Al, 0.13 ± 0.08 for Ca/Al, and 0.03 ± 0.03 for K/Al. These ratios are consistent with the composition of the albite region in the feldspar ternary diagram57. Moreover, the SEM-EDS images in Fig. 3B reveal that the regions in the SEM-EDS images corresponding to the two biotite minerals revealed by Raman imaging exhibit identical elemental distributions, indicating that they could be either polymorphs or grains with different crystalline orientations49. Therefore, any potential variations in the irradiation behavior of these phases can be attributed to differences in crystalline structure or orientation, despite having identical elemental composition.The height images presented in Fig. 3A represent the height profiles of the same surface, measured before (height-pre) and after (height-post) irradiation. These images provide a direct visual comparison of the surface topography before and after irradiation These images were normalized using the same reference plane as the height-pre image, allowing for direct comparison and measurement of the expansions and contractions resulting from irradiation. The height difference image in Fig. 3A is obtained by directly subtracting the height-pre image from the height-post image, where darker shades of blue indicate more expansion. The small red areas in the center of the image are not indicative of mineral contraction, but rather the result of surface chip-off that occurred during irradiation. Moreover, a distinct contrast can be observed among the areas corresponding to albite, quartz, and biotite minerals in Fig. 3A, arising from their unique response to radiation exposure. For instance, the intensity of the blue shade is higher for quartz compared to albite, indicating a higher RIVE for quartz.The irradiation response of silicate minerals such as those present in granites depends on various properties including the ionicity and proportion of Si-O bonds, the dimensionality of silicate polymerization (DOSP), atomic packing efficiency, composition, and physical properties (density, melting point, elastic moduli)25. Specifically, the nature of chemical bonding plays a crucial role in the crystalline-amorphous transition, with highly covalent bonds being susceptible to irradiation damage58,59,60. The Si-O bond, being the most covalent in silicates, acts as a potential ‘weak link’ in terms of irradiation damage accumulation. This bond is less likely to recombine into the crystalline state, favoring the assumption of a regular local coordination geometry, making it a weak bond during amorphization. Consequently, the proportion of these ‘weak links’ or Si-O bonds relative to the total number of bonds in a mineral influences its irradiation behavior. Additionally, using weight % of SiO2 as a criterion for amorphization offers another measure of the covalent bond proportion in the structure. Furthermore, the degree of structural connectivity, quantified by DOSP, is crucial for deducing amorphization behavior25. In minerals like quartz (SiO2), the Radiation-Induced Volumetric Expansion (RIVE) tends to be highest due to the substantial proportion of Si-O bonds.Atomic density, as measured by packing density, directly influences particle trajectories resulting from ion bombardment. Alternatively, atomic packing may be more closely related to the probability of in-cascade recombination of defects during irradiation58. Packing efficiency measures the proportion of atomic-scale space-filling relative to the unit cell volume but does not represent structural topology, as does DOSP. The melting point is also crucial, characterizing the breakdown of a mineral structure under highly energetic conditions and is related to bonding and composition. The shear modulus correlates with the critical amorphization dose as it relates to the material’s ability to attenuate energy elastically within collision cascades25.The total RIVE of granite, or any composite rock for that matter, is typically higher than the sum of the individual RIVE values of its constituent minerals16,61,62. This phenomenon arises due to various factors, such as the overall structural and compositional characteristics of the rock, the presence of interfaces and grain boundaries, stress transfer mechanisms between different minerals, and the collective response of the microstructure of the rock to irradiation. As a result, the non-uniform RIVE of minerals within the rock leads to the formation of voids and cracks. These cracks are influenced by the heterogeneous distribution of phases present in the rock, exacerbating the variations in expansion and contraction behavior across different mineral constituents. Subsequently, these cracks propagate and contribute to additional expansion within the grains and crystals, amplifying the overall volumetric changes resulting from their internal damage16. Together, these effects are accounted in the reported overall expansions measured using laser profilometry in this study.When ions bombard the surface of a rock, they induce expansion within a superficial layer of rock. This expansion is constrained by the underlying substrate. In contrast, when exposed to neutron radiation, the bulk of the rock experiences unconstrained expansion. However, this expansion is regulated by the heterogeneously expanding rock-forming minerals. Hence, the ion RIVE observed at the surface of a rock differs from neutron RIVE occurring across the entire bulk of a rock due to variations in physical constraints and the depth of irradiation damage. Despite these disparities, one of the primary goals of this study is to evaluate if ion radiation can be utilized effectively to mimic neutron radiation damage.To ensure reliable comparisons across multiple radiation conditions, we found it was meaningful to focus on step-height measurements directly obtained from laser profilometry. Step height, quantified using a method described in Supplementary Note 1, is a difference in roughness between the irradiated and pristine surfaces and provides a consistent and reliable metric for quantifying and comparing the extent of damage. From Supplementary Fig. 18a, it is evident that, overall, the step height of each mineral increases as the fluence increases, for each energy of the Si2+ ions. Similarly, when the energy is increased while maintaining a constant fluence in Supplementary Fig. 18b, the step-height increases for each mineral, suggesting that RIVE is indeed occurring under the chosen ion radiation conditions. Additionally, we determined the apparent deformations (calculated as the ratio of experimental step-height to ion range derived from SRIM-200841) for each mineral. For instance, quartz exhibits a variation of 4.2% – 14.8% across diverse radiation conditions. Similarly, albite exhibits a range of 3.3% – 6.8%, anorthite 3.1% – 8%, and microcline 5.1% – 6%. In general, higher Si2+ ion fluence or energy results in more pronounced mineral damage, leading to volumetric expansion and density reduction. Overall, these values are in the ranges comparable to their RIVE values upon neutron radiation16,17.Microscale mineral-specific mapping of modulus variation on damaged surfacesThe overall elastic modulus of a polycrystalline rock upon irradiation is predominantly governed by the change in elastic modulus of individual crystals and the combined characteristics of grain boundaries within the rock63,64. The presence of grain boundaries in minerals can significantly influence their overall behavior and may lead to alterations in the irradiated modulus compared to that of pure, single-phase minerals65. Additionally, grain boundaries can introduce structural discontinuities, such as lattice defects and mismatched interfaces, which can affect the mechanical response and elastic properties of the material. Moreover, there can be significant differences in the measured modulus between the grain center and the grain boundaries at higher radiation fluences, attributed to defect annihilation processes66. It is practical to assume that the Poisson’s ratio of minerals, such as quartz and feldspars, remains consistent upon radiation at both the grain centers and boundaries. Moreover, it is shown later that the change in Poisson’s ratio upon irradiation is relatively insensitive to the determination of irradiated modulus.Supplementary Fig. 19 depicts a fused Raman and optical image of sample 4, window 2, where distinct ROIs labeled 1–20 are identified on both the pristine and irradiated locations of augite and anorthite. Corresponding nanoindentation modulus maps are also presented. Supplementary Fig. 20 shows a plot illustrating the reduced modulus derived from different peak loads applied to the ROIs outlined in Supplementary Fig. 19. This plot provides strong evidence of consistency in the reduced modulus across diverse peak loads (coefficient of variation <0.03). Moreover, the standard errors for reduced modulus of augite and anorthite are below 0.77 GPa and 0.66 GPa, respectively. These values also serve as evidence for the consistency in the reduced modulus of a mineral within a specific window.Previous work by Oliver and Pharr67 has established the existence of a well-defined representative depth of indentation associated with a specific peak load when using a Berkovich tip. The stress zone beneath the surface probed by the nanoindenter tip represents a statistically significant fraction of the material at maximum load, suggesting that it characterizes the volume representative of the material68. To ensure accurate results, a peak load of 10 mN was selected for modulus mapping, which corresponded to the highest capacity of the instrument. It is essential to note that the maximum depth of penetration, specifically 910 nm for irradiated anorthite (494 nm for quartz, 1330 nm for albite, and 1436 nm for microcline), with a peak load of 10 mN, remains confined within the irradiated layer. Importantly, the depth of the irradiated layer determined from SRIM-200841 exceeds 1600 nm for all minerals considered. As a result, the mechanical properties determined by the indenter likely represent the characteristics of the irradiated layer. Moreover, these properties account for the collective behavior of all phases present throughout the entire depth, extending to the end of the representative depth. Additionally, the analysis of Raman images reveals that in locations where the specific mineral phase images do not overlap, the observed mineral is consistently present from the surface down to a depth of 1450 nm, which is within the axial resolution limit of the Raman microscope. Moreover, using EDS images to ensure the presence of a single mineral along the indentation depth would result in inaccuracies, as it cannot differentiate polymorphs and mineral grains with different crystalline orientations. Therefore, we can make a reasonable assumption that the indents were made at locations where only a single phase was present throughout the indentation depth.Based on the above considerations, we conducted nanoindentation, specifically at the center of the grains. Considering that a peak load of 10 mN results in both elastic and plastic deformations, we adopted the relationship between the reduced modulus measured from nanoindentation (\({E}_{R}\)) and the elastic modulus of the film (\({E}_{F}\)), as reported by Pharr et al.69. We further established a direct dependence of the relative elastic modulus on the relative reduced modulus, in the context of this study, as outlined in Supplementary Note 3.In the previously mentioned window depicted in Fig. 3, we present nanoindentation mapping in Fig. 4 illustrating variations among different minerals and individual grains. To ensure accurate analysis, we integrated the optical image (shown in Fig. 4a) of sample 6-window 2 with the corresponding Raman image. From this integrated image, we carefully selected multiple regions (54 × 54 μm, 3 μm spacing, as indicated in Fig. 4a) that are located within a grain in the phase map of a specific mineral. Subsequently, nanoindentation modulus maps were collected for these selected areas. The pristine data was collected from areas on the same grain that extended beyond the irradiated window, while the irradiated data was collected from areas within the irradiated region on the same grain, to make a reliable comparison. The corresponding fused images for the other windows can be found in Supplementary Figs. 21–32. These images specifically highlight the nanoindentation areas where modulus maps were collected. The reduced moduli of these minerals measured before and after irradiation are provided in Supplementary Table 4. In Fig. 4b, we present the individual nanoindentation modulus maps obtained from both the pristine and irradiated regions of the indicated minerals (Supplementary Figs. 21–32 shows the corresponding maps for the other windows). Specifically, for the two types of albites (Al-1 and Al-2), the probability density distribution of the reduced modulus reveals a noticeable leftward shift, indicating a reduction in modulus upon irradiation. The mean modulus decreased from 75 GPa to 70 GPa for albite-1 and from 92 GPa to 59 GPa for albite-2, as depicted in Fig. 5c, d. Remarkably, the spread of the curves remain consistent, indicated by low relative changes in standard deviation of 9.6% and 3.7% for albite-1 and albite-2, respectively. This consistent spread suggests a uniform reduction in modulus across the entire surface of the minerals.Fig. 4: Nanoindentation modulus mapping on pristine and irradiated locations.a Fused Raman and optical image of sample 6, window 2 irradiated with 10 MeV, 1016 ions/cm2 Si2+ radiation. b Nanoindentation modulus maps obtained from multiple locations (1–4), marked within white squares in part (a) on pristine and irradiated areas of albite (Resolution: 3 μm/pixel). The shift in the peak of the probability density distribution of reduced modulus upon irradiation is illustrated for albite-1 and albite-2 in (c).Fig. 5: Comparison of relative modulus and integrated DPA.Results from this study, data from Luu et al.9, and Krishnan fitting15 are shown in (a) for quartz, albite, anorthite, and microcline. The comparison of ion-irradiated relative modulus from this study with that from Luu et al. 16 is shown in (b).To quantify the extent of irradiation damage incurred, we analyze the mechanical properties by examining the drop in elastic modulus, which allows us to understand the stiffness and integrity of different minerals upon radiation exposure. The nanoindentation modulus of a specific mineral can exhibit variations from grain to grain, even within the same window. In the case of pristine quartz, we observed a 10.8% coefficient of variation in modulus between different windows, while for pristine anorthite, we observed a 7.9% coefficient of variation within the same window among different grains. To account for these variations and ensure meaningful comparisons, we chose to compare the modulus of a specific grain before and after radiation exposure. As described earlier, nanoindentation modulus maps were collected on both the pristine and irradiated locations of the same grains. By calculating the ratio of the irradiated modulus to the pristine modulus, we obtained the relative modulus, which allowed for comparisons across multiple radiation conditions. Notably, the relative modulus exhibited a low coefficient of variation for a particular mineral grain within a specific window (2.8% for anorthite). This approach helped mitigate the influence of variations in modulus observed between different grains and windows, enabling a more meaningful and consistent analysis of the relative changes in modulus due to radiation exposure. From Supplementary Fig. 33a, it can be observed that the relative modulus decreases as the fluence increases under constant energy conditions. Likewise, when the energy is increased while maintaining a constant fluence (Supplementary Fig. 33b), the relative modulus also decreases for each mineral. In general, as the fluence or energy of the Si2+ ions increases, the extent of damage incurred by the minerals becomes more pronounced, leading to a loss of structural integrity of the sample and, ultimately, resulting in increased levels of amorphization.Figure 5a shows the comparison of the relative modulus with integrated DPA (listed in Supplementary Table 1) for quartz, albite, anorthite, and microcline. The integrated DPA is represented by the area under the Displacement Per Atom (DPA) versus the depth profile (shown in Supplementary Fig. 4) obtained from SRIM-200841. It provides a measure of the cumulative displacement experienced by atoms within a material, reflecting the total atomic-scale rearrangements occurring within a specific volume of the mineral. By considering factors such as fluence, target mineral, ion species, and ion energy, the integrated DPA serves as a comprehensive parameter for comparing the extent of damage across different minerals and irradiation conditions. It combines these diverse parameters into a single metric, enabling meaningful comparisons and facilitating the integration of findings from various studies. By comparing the relative modulus with integrated DPA, both from this study and data from Luu et al.26 (Fig. 5a), the mean relative errors are observed to be 8.9% for quartz, 5.8% for albite, and 2.3% for microcline. Notably, although Luu et al.26 utilized 3 MeV Si2+ ions, the relative modulus exhibits good agreement for microcline while showing some disagreement for the 10 MeV cases of quartz and albite. The overall trend aligns with the observed decrease in relative modulus with an increase in integrated DPA. Figure 5b presents a comparison between the relative modulus obtained in this study through ion radiation with that obtained from Luu et al. (R2 = 0.53). The curves for this study show that irrespective of the energy of the ions (2 and 10 MeV), the drop in relative modulus is directly linked to the total atomic-scale displacements quantified using integrated DPA. Hence, although 10 MeV Si2+ ions produce the highest concentration of DPA at higher depths of ~ 4060-4340 nm (compared to ~ 1600-1730 nm for 2 MeV Si2+ ions), the relative modulus could still be comparable if the integrated DPA values are similar.Zhang et al.70 and Krishnan et al.21 conducted Molecular Dynamics (MD) simulations and reported the relative modulus at maximum volume change upon irradiation (at saturation of defects or full amorphization) as shown in Supplementary Table 5. The corresponding deviations from the experimental relative modulus quantified in this study are also reported. In 2019, Krishnan et al.71 found a power law scaling relationship between the relative modulus and the cube of relative density of siliceous minerals during disordering. Leveraging this relationship, we calculated the relative modulus from the relative density (shown in Supplementary Note 4) and plotted it in Fig. 5a for comparison. By comparing the fitted relative modulus with experimental relative modulus obtained from nanoindentation, the mean relative errors are observed to be 8.3% for quartz, 5.0% for albite, 10.3% for anorthite, and 3.4% for microcline.It should be noted that discrepancies may arise due to variations in mineral purity between previous studies and our research. For instance, the albite mineral in samples 5 and 6 could have been classified as oligoclase or anorthoclase if it had a slightly different Ca/Al or K/Al ratio, respectively. Moreover, studies using simulations to determine damage parameters often assume pure samples in their model. Such variations in mineral composition would result in distinct irradiation behaviors, leading to potential differences in the observed effects.Comparing extent of irradiation damage: minerals in pure form vs inclusions in composite rocksWhile irradiation damage in pure minerals has been extensively studied using neutron16, ion25, and electron72 radiation, investigations on multi-phase rocks have been relatively scarce in the past. In the previous sections, we emphasized the significance of analyzing the irradiation behavior of minerals within composite environments. Therefore, it is crucial to compare the behavior of pure, single-phase minerals with their behavior as inclusions in a composite environment when exposed to identical radiation conditions. In this study, we investigated the behavior of quartz in different settings: as a pure phase in samples 1 and 2, and as an inclusion in samples 5 and 6 within the composite rocks (Fig. 6a). To evaluate the irradiation-induced changes, we compared the relative modulus with fluence for pure quartz and quartz as an inclusion in Fig. 6a (corresponding Raman images are shown in Fig. 6a). Additionally, we compared the apparent deformation (calculated as the ratio of experimental step-height to ion range obtained from SRIM-200841) with integrated displacement per atom (DPA) for both scenarios in Fig. 6c. Notably, a rapid increase in apparent deformation is observed at lower integrated DPA values, suggesting an initial phase where the silicate microstructure accommodates expansive processes more readily. Subsequently, a more gradual increase occurs at higher DPA values, indicating a diminishing capacity for further expansion, possibly reaching the limit of maximum volume change or full amorphization. Our findings also indicate a high level of agreement, with a mean deviation (δ) of 0.6% for the relative modulus and 2.8% for apparent deformation between the two cases. To provide a direct visual comparison, Fig. 7d, e illustrate the relative modulus and apparent deformation, respectively, for both pure and inclusion quartz.Fig. 6: Comparing irradiation behavior of quartz-inclusion and quartz-pure.a Raman images of quartz in different windows of samples 5 and 6 (having quartz as an inclusion), and samples 1 and 2. The relative modulus is compared with fluence in (b) and the apparent deformation is compared with integrated DPA in (c) for pure quartz and quartz as an inclusion. The relative modulus and apparent deformation of quartz as an inclusion are compared with that of pure quartz in (d, e), respectively where the dashed line indicates the line of equality. The error bars represent the standard error.Fig. 7: Comparison of ion RIVE and neutron radiation equivalent expansions.a Comparison of apparent deformation and fluence in quartz, albite, anorthite, and microcline showing results from this study, neutron radiation equivalent expansions at 25 °C, and data from Luu et al.26 (3 MeV Si2+ ions). Comparison of apparent deformations from neutron radiation equivalent expansions (calculated from Eq. (3)) and experimental ion radiation expansions for quartz, albite, anorthite, and microcline irradiated with (b) 2 MeV and (c) 10 MeV Si2+ ions.These findings indicate a reasonable consistency between the irradiation response of pure quartz and that of quartz present as inclusion within a composite environment, such as granite. The similarity in irradiation behavior suggests that the results obtained here on various minerals are widely applicable and inherent to each mineral, giving a high degree of confidence to mineral-specific irradiation responses documented here.Comparisons with prior literature and calculated neutron radiation equivalent expansionsUsing ion radiation as a surrogate to mimic neutron radiation damage is receiving growing attention despite being challenged by factors such as differences in the primary knock-on atom spectrum, accelerated damage rates, the effect of the injected interstitial, and the shallow penetration depth giving rise to surface effects and a limited analysis volume73. Despite these challenges, ion radiation offers several advantages for emulating reactor conditions, including the ability to induce high damage rates in a short time frame, minimal activation, availability of ion beam laboratories with suitable accelerators, and precise control over experimental parameters such as temperature, damage rate, and damage level74. However, in order to successfully replicate reactor conditions, it is crucial to accurately capture the complete extent of the irradiated microstructure formed in the reactor73. In this study, we have successfully characterized the physical (expansions) and mechanical (modulus) properties of ion-irradiated surfaces with nano- and micron-scale resolution, respectively. The subsequent step involves establishing the comparability of the resulting damage levels with those induced by neutron radiation. This validation is pivotal in confirming the viability of ion radiation as a reliable method for emulating the neutron radiation damage and ensuring the fidelity of our experimental approach.To obtain a comparison between ion and neutron radiation, the fundamental hypothesis is that displacements per atom is an effective measure of irradiation-induced damage independently of the particle used for the experiment. Additionally, assuming that aggregates can be reasonably described as randomly oriented polycrystalline assemblages, the effective irradiation behavior such as dimensional change and change of elastic properties of neutron-irradiated aggregates is considered isotropic75. Ion radiation-induced DPA profiles along the implanted depth are determined using SRIM-200841 assuming Kinchin and Pease (K-P) models76 and are provided as displaced atoms per volume per ion fluence, as$${{dpa}}_{i}=\frac{{Mda}\left(z\right)}{\rho v{\rm{{\rm N}}}}\times \phi$$
(1)
where \(M\) denotes the molar weight of the pristine mineral, \({da}\) signifies the number of displaced atoms calculated from SRIM, \(\rho\) denotes the density of the pristine mineral, \({v}\) is the volume, \(\phi\) is the ion fluence, and \({\rm{{\rm N}}}\) represents Avogadro’s constant. Abundant findings from a comprehensive study by Bykov et al.77 on neutron-irradiated rock-forming minerals in test reactors has led to the formulation of empirical models correlating the RIVE of minerals with factors like fast-neutron fluence and irradiation temperature. Monte Carlo N-particles (MCNP) simulations show that neutrons with energies higher than 10 keV produce nearly 100% of the cumulative DPA in minerals. Using MCNP on common rock-forming minerals to model irradiation in Russian reactors AM, BR-5 (OK-50), BR-5 (M-1), BR-10 (OK-70), and BOR-60 VEK16, it becomes feasible to find the correspondence between cumulative DPA and neutron fluence, expressed as$${{dpa}}_{n}=\kappa \times \Phi$$
(2)
where \(\kappa\) is a constant for a specific mineral and a specific reactor (ranges between 1.4 × 10–22 and 5.8 × 10–22 dpa/n.cm–2), relating neutron irradiation-induced DPA and integrated neutron fluence, and \(\Phi\) is the neutron fluence.Consequently, the empirical RIVE models can be reformulated to express them as functions of the DPA and irradiation temperature. The ion RIVE estimates are derived from the following expression, hypothesizing that Eqs. (1), (2) can be related (\({{dpa}}_{i}\) ~ \({{dpa}}_{n})\):$${\widetilde{\varepsilon }}^{* }(z)=f\left(\frac{1}{\kappa }\frac{{Mda}(z)}{\rho {\rm{{\rm N}}}}\times \xi \phi ,{T}_{{irr}}\right)$$
(3)
Where \({\widetilde{\varepsilon }}^{* }\) corresponds to the unconstrained volumetric expansion, \(\xi\) is the ratio of fluence at energy E > 10 keV against the integrated fluence, and \({T}_{{irr}}\) denotes the irradiation temperature (25–40 °C). It is assumed here that the ion irradiation-induced heating is dissipated by convection.Ion-irradiation produces non-uniform DPA profiles, and the implanted film is structurally constrained by the pristine substrate. Hence, the development of high lateral stresses (in the order of 0.5–1 GPa) is inevitable. While the existence of mechanisms including irradiation-induced assisted viscous or plastic flow can be hypothesized, it has been observed in several studies28,78,79 that the post-ion irradiation step height approaches the total expected change of volume multiplied by the implanted depth at full amorphization. The apparent deformation in the direction opposite to the beamline is obtained by the integration of \({\widetilde{\varepsilon }}^{* }\) over the implanted depth (illustrated as blue solid lines in Fig. 7a). Additionally, when the implanted depth is fully amorphized, it is observed that the apparent deformation along the direction of the ion beam, is comparable to the neutron irradiation-induced volumetric expansion, or the cumulative contribution of the dimensional change in all directions14,26,28. Finally, it is assumed that expansions in this study are fully redistributed in the vertical direction opposite to the beamline given the constraint posed by the thick unirradiated volume of substrate and masked material around the exposed windows.Figure 7a presents the apparent deformations of quartz, albite, anorthite, and microcline resulting from Si2+ ion radiations at fluences of 1015 and 1016 ions/cm2. It also includes the apparent deformation profiles calculated using the neutron radiation equivalent expansions from Eq. (3), encompassing a fluence range of 1014–1017 ions/cm2 Si2+ radiation. Each plot presents two solid blue lines enclosing an envelope region shown in light blue as the RIVE estimates obtained from Eq. (3) depends on \(\kappa\) and \({T}_{{irr}}\) which have a range of values (\(\kappa\) ranges between 1.4 × 10-22 and 5.8 × 10–22 dpa/n.cm-2 and the irradiation temperature ranges between 25 and 40 °C). At full amorphization for quartz, the calculated neutron radiation equivalent expansions correspond to an apparent deformation of 17.2% when irradiated with 10 MeV Si2+ ions. Similarly, albite, anorthite, and microcline have expansions of 6.9% and 6.8%, and 7.4%, respectively, under the same radiation conditions. Comparing these neutron radiation equivalent results with experimental ion radiation expansions in Fig. 6b, c reveals a high level of agreement, with overall mean deviations (δ) of 2.6% for quartz, 0.8% for albite, 1.0% for anorthite, and 1.5% for microcline. Interestingly, the case of 10 MeV Si2+ ions (Fig. 7c) demonstrates a lower RMSE of 1.29% volumetric expansion (with a mean relative error of 19.3% and a higher coefficient of determination of 0.86) compared to the 2 MeV case (Fig. 7b, RMSE of 1.82% volumetric expansion, mean relative error of 26.3%, and coefficient of determination of 0.76).Observing the apparent deformations (reported in Supplementary Table 3), it is evident that the values could be higher for 2 MeV cases compared to 10 MeV cases (for e.g., anorthite expands 8.0% with 2 MeV and 7.2% with 10 MeV Si2+ ions). However, 10 MeV Si2+ ions produce higher step-heights compared to 2 MeV Si2+ ions (29.4 nm v/s 129.7 nm) as the expansion is directly linked to the total atomic-scale displacements quantified using integrated DPA. On the other hand, apparent deformations consider the penetration depth of ions, normalize the damage, and the obtained ratio may not follow the same trend as the expansion. For a given energy level, it increases with increasing fluence and also provides a consistent metric to make a comparison with other ion radiation conditions.Figure 7a also includes a comparison of the apparent deformation with the findings from Luu et al.26, demonstrating mean relative errors of 34.0% for quartz, 29.7% for albite, and 11.4% for microcline. Although Luu et al. used 3 MeV Si2+ ions, the apparent deformations can be compared, as it normalizes the expansion values with respect to the penetration depth of the ions, which increases with increasing energy of the ions. The maximum experimental expansions for various minerals quantified in this study are also consistent with the expansion ranges resulting from neutron radiation: quartz ~ 18%, feldspars ~8% (δ < 3.2%)16,17. These findings validate the effectiveness of ion radiation as a reliable method for emulating neutron radiation in siliceous aggregates in concrete, confirming the comparability of resulting damage levels and validating the fidelity of our experimental approach.Limitations and opportunitiesIon radiation presents a set of limitations and opportunities in the context of studying irradiation damage. We note three major limitations as follows. First, ion radiations involve interstitial ion depositions and can introduce altered swelling behavior at the stopping depth of incident particles80. Second, exposure of a material to ion radiation turns its surface into a point defect sink. This results in enhanced damage, enabling inhomogeneous swelling and a distinct microstructural evolution in the vicinity of the surface. Third, the controlled penetration depth of ions restricts the extent of potential damage to shallow depths81. However, despite these limitations, ion radiation offers immense potential for understanding and emulating neutron radiation damage in siliceous minerals. For e.g., the ability to inflict targeted damage at specific depths in a material result in the creation of thin, damaged layers on the surface which can be easily analyzed from an analytical instrumentation point of view. Specifically, in this study, we were able to quantitatively record mineral-specific step-height changes due to the formation of such thin layers. These step-height changes were then transformed to apparent deformation values which were found to be in strong agreement with RIVE values expected for these minerals upon neutron radiation. Thus, these ion radiation results open promising pathways for replicating neutron radiation damage in siliceous minerals.In summary, ion radiation is emerging as a powerful surrogate for neutron radiation, offering advantages in replicating reactor conditions with high damage rates, minimal activation, and precise experimental control. In this study, we were able to precisely evaluate irradiation damage induced by ion radiation by seamlessly integrating diverse yet complementary imaging techniques. Specifically, our findings facilitate the determination of mineral-specific apparent deformations and relative elastic modulus values in siliceous minerals commonly found in the aggregates of the concrete component of the nuclear power plants. By investigating such key siliceous minerals prone to irradiation damage, we report apparent deformations of 14.8% for quartz, followed by albite at 6.8%, anorthite at 7.2%, and microcline at 6% under 10 MeV, 1016 ion/cm2 Si2+ radiation. Concurrently, the relative modulus experiences distinct reductions: quartz descends to 80.3%, albite to 79%, anorthite to 81.2%, and microcline to 83.9%. To add to the validity of these mineral-specific measurements, we report strong similarity between damage manifestations (apparent deformation and relative modulus) in quartz irrespective of its presence as inclusion in granite or existence in a pure, monolithic form (mean deviation<2.9%) underscoring the broad applicability and intrinsic nature of mineral-specific irradiation responses, resulting in high confidence in our reported results. Finally and most importantly, the remarkable agreement (R2 = 0.86, RMSE = 1.29% for 10 MeV Si2+) between ion radiation-based deformations and neutron radiation equivalent expansions proves that ion radiation can be a dependable surrogate for simulating neutron radiation damage in silicates. Collectively, this study firmly establishes the validity of ion radiation as an effective and reliable surrogate for neutron radiation damage in silicate minerals, opening up pathways toward rapid assessment of aging concrete in nuclear power plants.
Silicon ion radiation as a viable surrogate for emulating neutron radiation damage in silicates
