Effects Of Ionizing Radiation Research Articles

Phase composition of polycrystalline HfNx (0.45 ≤ x ≤ 1.60) and effects of low-energy ion irradiation on microstructure, texture, and physical properties

We have investigated the phase composition of HfNx as a function of x and the effects of low-energy ion irradiation on the microstructure and physical properties of polycrystalline layers grown on SiO2 at 350 °C by ultrahigh vacuum reactive dc magnetron sputtering of Hf in mixed N2/Ar discharges. X-ray diffraction and Rutherford backscattering spectrometry results show that the phases obtained in polycrystalline HfNx layers with increasing x are hcp-structure α-Hf:N (x ≲ 0.6); multiphase mixtures consisting of α-Hf, NaCl-structure δ-HfN, rhombohedral ɛ-Hf3N2, and/or ζ-Hf4N3 (0.6 ≲ x ≲ 0.9); δ-HfN single phase (0.9 ≲ x ≲ 1.3); and mixtures of δ-HfN and higher nitrides (x ≳ 1.3). HfNx layers with 0.9 ≲ x ≲ 1.2 grown under mild ion irradiation (incident ion energy Ei ≃ 7 eV and ion-to-Hf flux ratios Ji/JHf = 1−3) are underdense with mixed orientation, low in-plane stress, and rough surface morphology due to limited adatom mobilities resulting in kinetic roughening and atomic shadowing during film growth. However, the use of intense ion irradiation (Ei = 25 eV and Ji/JHf = 4−20) results in HfNx layers, which are fully dense with strongly 111-oriented texture, compressive in-plane stress, and smooth surfaces due to ion irradiation enhanced adatom surface mobilities. In addition, the latter films have lower resistivity and higher hardness. For stoichiometric δ-HfN layers, ρ decreases from 69.7 to 35.2 μΩ cm and H increases from 22.1 to 27.4 GPa, with increasing ion-irradiation intensity. However, for HfNx layers with 1.2 ≲ x ≲ 1.6, the correspondingly higher steady state atomic N surface coverages during deposition alter growth kinetics in favor of 001 texture with a fully dense structure and compressive in-plane stress.

Research on heavy ion irradiation effects on SOI SRAM

SRAM based on SOI devices has been widely used in aerospace storage devices due to its good electrical characteristics and radiation resistance. However, with the development of semiconductor technology, the feature size of devices continues to shrink, and the irradiation effects of high-energy ions have become increasingly serious. Single event effect has become the biggest threat to the failure of the spacecraft. A mixed-simulation method was used to research the heavy ion irradiation effects on SOI SRAM. SRAM consists of two coupled inverters. Firstly, the voltage changes of the inverter and SRAM output nodes under heavy ion irradiation were compared and analyzed, then the influence of the device itself and heavy ion parameters on the single particle flipping effect of the SRAM is investigated, and finally the necessary conditions for the flipping of the stored information in the SRAM are discussed and derived. The results show that heavy ion incidence does not permanently change the final state of the inverter; devices in the off state in the SRAM will undergo information flipping only when they are irradiated by heavy ions, and the threshold voltage of the N-type MOSFET is lower than that of the P-type MOSFET; an increase in the penetration depth will accelerate the flipping speed of the SRAM, but when the LET is high, the influence of the penetration depth on the flipping speed decreases; the change of the stored information in the SRAM is the result of the combined effect of pulse width and pulse height.

Ionizing Radiation Sensing with Functionalized and Copper-Coated SWCNT/PMMA Thin Film Nanocomposites.

This paper studies the ionizing radiation effects on functionalized single-walled carbon nanotube (SWCNT)/poly(methyl methacrylate) (PMMA) thin-film nanocomposites [SWNT/PMMA]. The functionalized thin-film devices are made of ferrocene-doped SWCNTs, SWCNTs functionalized with carboxylic acid (COOH), and SWCNTs coated/ modified with copper. The nanocomposite was synthesized by the solution blending method and the resulting nanocomposite was spin-cast on interdigitated electrodes (IDEs). A 160 kV X-ray source was used to irradiate the thin film and changes in the electrical resistance of the nanocomposites due to X-rays were measured using a semiconductor device analyzer. Carboxylic acid functionalized and copper-coated SWCNT/PMMA nanocomposite showed a reduced response to X-rays compared to unfunctionalized SWCNT/PMMA nanocomposite. Ferrocene-doped SWCNT showed a higher sensitivity to X-rays at lower dose rates. This is in contrast to a previous study that showed that similar nanocomposites using functionalized multi-walled CNTs (MWCNTs) had demonstrated an improved response to X-rays ionizing radiation compared to unfunctionalized MWCNTs for all dose rates. Electrical measurements were also performed using the Arduino Nano microcontroller. The result showed that a relatively economical, lightweight-designed prototype radiation sensor based on SWCNT/PMMA thin-film devices could be produced by interfacing the devices with a modest microcontroller. This work also shows that by encapsulating the SWCNT/PMMA thin-film device in a plastic container, the effect of ambient humidity can be reduced and the device can still be used to detect X-ray radiation. This study further shows that the sensitivity of SWCNT to X-rays was dependent on both the functionalization of the SWCNT and the dose rate.

Surface morphology and topography evolution of soda-lime silica glass after 1.0 MeV Si ion bombardment

Surface pattern formation on soda-lime silica glass by 1 MeV Si ion irradiation impinging at an angle of 70° with respect to the surface normal has been studied. Modification of surfaces were analyzed for total ion fluences applied between up to ions/cm2. The surface morphology and topography were studied by scanning electron microscopy (SEM), and atomic force microscopy (AFM). These surface techniques enabled the determination of roughness, characteristic wavelengths, and correlation lengths. In addition, electron dispersive spectroscopy (EDS) scans were applied on the surface topography to study the variation of the Si content on the obtained surface patterns. From the measurement of these variables, linear and non-linear regimes were established. At linear regime, the surface morphology develops from an initial flat surface giving rise to ripples for fluences up to ions/cm2. As the ion bombardment continues surface evolve into wrinkles finalizing at cellular-like structures, growing under an anomalous scaling process. The EDS scans indicate the presence of shadowing effects. The morphological changes observed can be explained in terms of a combination of thermal mass diffusion and geometrical factors during ion irradiation, including shadowing and subsequent (secondary) surface erosion effects adapted to few MeV energies.

Composite effect of helium ion irradiation and transient thermal shock on recrystallized pure W and W-Y2O3 alloys

Tungsten (W) is the material of choice for the thermal nuclear fusion reactors of the future. In this research, pure W (PW) and W-Y2O3 alloys made by the SWIP (Southwestern Institute of Physics) wet chemical process are chosen. Simulation of long-term extreme operating conditions of fusion reactor materials by annealing and recrystallization of forged tungsten materials. The thermal shock resistance of recrystallized PW and W-Y2O3 alloys to radiation by helium (He) ions at a flux of 1.4 × 1022 ions/(m2s) was investigated. The surface microscopic pictures of recrystallized W and W-Y2O3 alloys were analyzed using scanning electron microscopy (SEM) and a laser surface profiler under the conditions of helium ion irradiation and electron beam transient thermal shock. After helium ion irradiation, the surface of PW and W-Y2O3 alloys exhibits a fuzzy structure. Under the same 0.33 GW/m2 thermal shock condition, the average width of the main cracks of PW and W-Y2O3 alloys significantly increases after helium ion irradiation, indicating that helium ion irradiation can reduce the thermal shock resistance of the surface of recrystallized W materials.

Effects of irradiation on superconducting properties of small-grained MgB2 thin films

We investigate the effect of ion irradiation on MgB2 thin films with small grains of approximately 122 nm and 140 nm. The flux pinning by grain boundaries is insignificant in the pristine MgB2 films due to good inter-grain connectivity, but is significantly improved after 120-keV Mn–ion irradiation. The scaling behavior of the flux pinning force density for the ion-irradiated MgB2 thin films with nanoscale grains demonstrates the predominance of pinning by grain boundaries, in contrast to the single-crystalline MgB2 films where normal point pinning was dominant after low-energy ion irradiation. These results suggest that irradiation-induced defects can accumulate near the grain boundaries in metallic MgB2 superconductors.

The Effect of Fast Kr Ion Irradiation on the Optical Absorption, Luminescence, and Raman Spectra of BaFBr Crystals

In this work, using photoluminescence (PL), optical absorption (OA), Raman spectroscopy (RS), and atomic force microscopy (AFM), the radiation damage of BaFBr crystals irradiated with 147 MeV 84Kr ions to fluences (1010–1014) cm2 was investigated. The manifestations of the oxygen impurity contained in the studied crystals on the effects associated with ion irradiation are also considered. In unirradiated crystals, the PL spectra exhibited bands related to the oxygen impurity. Moreover, it was found that quenching and a shift of the PL maximum occur, which is due to the fact that, with increasing dose, aggregation of defects occurs. Electronic and hole aggregate color centers appear mainly in the bromide sublattice. A detailed study of the Raman spectra and comparison with the corresponding data for KBr single crystals made it possible to reveal the corresponding manifestations of the Raman modes of complex Br3−-type hole centers.

The effect of ionizing radiation on robotic trajectory movement and electronic components

Robotics applications are greatly needed in hazardous locations, e.g., fusion and fission reactors, where robots must perform delicate and complex tasks under ionizing radiation conditions. The drawback is that some robotic parts, such as active electronics, are susceptible to radiation. It can lead to unexpected failures and early termination of the robotic operation. This paper analyses the ionizing radiation effect from 0.09 to 1.5 Gy/s in robotic components (microcontrollers, servo motors and temperature sensors). The first experiment compares the performance of various microcontroller types and their actuators and sensors, where different mitigation strategies are applied, such as using Radiation-Hardened (Rad-Hard) microcontrollers or shielding. The second and third experiments analyze the performance of a 3-Degrees of Freedom (DoF) robotic arm, evaluating its componentsʼ responses and trajectory. This study enhances our understanding and expands our knowledge regarding radiationʼs impact on robotic arms and components, which is useful for defining the best strategies for extending the robotsʼ operational lifespan, especially when performing maintenance or inspection tasks in radiation environments.

Synthesis, Biological Activity, and the Effect of Ionization Radiation on the Spectral, XRD, and TGA Analysis of Cu(I), Cu(II), Zn(II), and Cd(II) Complexes

New complexes of molecular formulae of [Cu(H2L1)I] (B1), [Cu(H2L)2(ClO4)2](B2), [Zn (H2L)2(H2O)]SO4(B3) and [Cd(H2L)Cl]Cl(B4) of ligand N-phenyl-2-(p-tolylglycyl)hydrazine -1-carbothioamide (B) have been prepared and characterized by 1H-NMR, Mass spectra, FT-IR, elemental analyses, molar conductance, UV–visible spectra, magnetic susceptibility measurements, thermogravimetric analysis (TGA/DTG) and X-ray powder diffraction before and after irradiation. Elemental analyses indicate that the metal complexes have 1:1 (metal/ ligand) (B1 and B4) or 1:2 stoichiometry for complexes (B2 and B3). The results confirmed that gamma ray enhanced the stability of irradiated compounds as compared to non-irradiated compounds. XRD patterns proved that increasing the crystallinity of the samples and the particles is in nanosize range before and after gamma irradiation. These studies revealed that Cu(II) and Zn(II) complexes adopted octahedral geometry, and Cu(I) and Cd(II) complexes were found to be tetrahedral. The theoretical conformational structure analyses were performed using density functional theory for ligand and complexes at B3LYP functional with 6–31G basis set for ligand and LANL2DZ basis set for complexes. The ligand (B, A) and complexes (B1–B4) and (A1–A4) before and after irradiated have been tested for their inhibitory effect on the growth of bacteria against gram-positive (Streptococcus pyogenes) and gram-negative (Escherichia coli). Molecular docking investigation proved that the Zn(II) complex had interesting interactions with active site amino acids of topoisomerase II DNA gyrase enzymes (code: 2XCT).

Ionizing Radiation Effects on Hole Collection Backside-Illuminated p-Type Deep-Trench-Pinned Photo-MOS Pixels Under Image Acquisition

Dark current degradation, origins, and annealing behavior after x-ray irradiation are studied in a P-type, hole collecting, backside-illuminated image sensor currently being developed at STMicroelectronics and based on deep-trenched photo-MOS pixels. Different biasing conditions during irradiation, i.e. grounded or biased and sequenced, are compared. The dark current increase with total ionizing dose (TID) and the dark current annealing behavior seem to be driven by the backside interface between the P-epitaxy of the pixels and the ONO stack. Despite still being under development, this pixel architecture already exhibits both very good electro-optical performance and a better radiation hardness than pinned photodiode-based CMOS Image sensors that benefit from the same advanced CIS processing technologies. At high total dose range, the photogate challenges custom Radiation-Hardened-by-Design photodiodes by exhibiting a comparable radiation tolerance while bringing new features such as high-resolution or Correlated Double Sampling.

Swift heavy ion irradiation effect on structural, morphological and mechanical properties of Zr70Ni30 metallic glass

Metallic glass films are considered for coating applications in the nuclear field owing to their advantageous performances. However, the response to irradiation remains to be more thoroughly characterized. Zr70Ni30 metallic glass films were irradiated by 0.71MeV/u129Xe23+ ions in the fluence range from 5 × 1012 to 8 × 1013 ions cm−2. The structural, morphological, and mechanical properties were determined using grazing incidence X-ray diffraction (GI-XRD), atomic force microscopy (AFM), and nanoindentation for the as-deposited and irradiated samples. The Xe ion induced surface smoothening, thereby increasing the corrosion resistance. One-dimensional power spectral density of the AFM data of irradiated film demonstrated that the irradiation-induced evolution of the surface morphology could be attributed to a transition between viscous flow and the evaporation-condensation mechanism. The amorphous structure was unaffected after irradiation up to a fluence of 8 × 1013 ions cm−2. Nanoindentation revealed first a softening as the fluence increases up to 4 × 1013 ions cm−2, reflecting the creation of free volume defects. Then the hardness and Young’s modulus slightly increase when reaching 8 × 1013 ions cm−2. Moreover, at a critical dose of 0.008 dpa, the hardness is found to increase. Moreover, the calculation of the inelastic thermal spike model reveals the formation of the track with a radius of 7 nm.

Surface modifications of TiO2 nanostructured materials induced by 120 MeV Ag ions

The effect of swift heavy ion irradiation on structural, optical, and microstructural properties of TiO2 has been studied. Pellets prepared from TiO2 nanoparticles have been irradiated by 120 MeV Ag ions at different fluences ranging from 5 × 1011 to 1 × 1013 ions cm−2. X‐ray diffraction (XRD), Raman, UV–visible, and photoluminescence (PL) studies indicated anatase phase both in as‐prepared and irradiated pellets. XRD study revealed the crystallite size of the particles as ~16 nm, which is close to the upper limit of the particle size where anatase phase is most stable. Our study thus established the importance of the initial microstructure on the irradiation response of the nanoparticles. Though irradiation did not affect the crystal structure and the polycrystalline nature of the anatase TiO2, it suppressed the crystalline volume fraction. Poisson fitting of the suppression of XRD peak area with irradiation fluence revealed radius of the track of each 120 MeV Ag ion in TiO2 nanoparticles as ~2.1 nm. Irradiation, in addition to creating disorder, darkened the surface of the pellets because of the creation of oxygen vacancies in the TiO6 octahedra. Reorganization of these defects led to suppression of the band gap of TiO2 nanoparticles from 3.19 eV of the pristine sample to 3 eV for samples irradiated beyond a critical fluences 3 × 1012 ions cm−2. The size of the nanoparticles and their agglomeration remained unaffected by irradiation as indicated by field emission scanning electron micrographs.

Investigation of Radiation Effects in the Uranyl Mineral Metaschoepite.

The effects of water vapor and He ion irradiation on the alteration of particles of the uranyl hydroxide phase metaschoepite, [(UO2)8O2(OH)12](H2O)10, are determined. Raman spectra collected immediately postirradiation revealed the presence of a uranyl oxide phase structurally similar to γ-UO3 or U2O7. Short-term storage postirradiation at elevated relative humidity accelerated formation of the uranyl peroxide phase studtite, [(UO2)(O2)(H2O)2](H2O)2. Experiments examining the degradation of metaschoepite and the hydration of UO3 enabled spectral assignments and identification of reaction pathways. The results provide insights into thermal and radiolytic degradation products in both irradiated uranyl hydroxide phases and uranyl peroxide phases, which follow similar degradation pathways.

Effects of He ion irradiation on the structural stability and deformation behavior in Zr63.5Cu23Al9Fe4.5 and Fe80B13Si7 metallic glasses

The effects of He2+ irradiation on the structural stability and deformation behavior in Zr63.5Cu23Al9Fe4.5 and Fe80B13Si7 metallic glasses (MGs) were investigated by TEM and nano-indenter. He bubbles in Fe80B13Si7 MG distributed more narrowly along the depth direction, packed more densely and exhibited larger size. At 4 × 1017/cm2 dose, Fe3B nanocrystals generated in Fe80B13Si7 MG caused by enhanced atomic diffusion due to increased excess free volume and larger compressive stress on atoms of bubbles gaps, while Zr63.5Cu23Al9Fe4.5 MG could maintain the amorphous structure. According to serrated flow phenomenon and bubbles distribution, the underlying mechanism of the transformation in deformation behavior of MGs with increasing He dose was analyzed as follows: localized inhomogeneous deformation in as-cast MGs, homogeneous deformation in the rejuvenated stage, localized inhomogeneous deformation in the stage where small bubbles act as weak pinning, homogeneous deformation in the stage where large bubbles act as strong pinning, localized fracture in the stage where bubbles collapse.

Postsynaptic density radiation signature following space irradiation.

Introduction: The response of the brain to space radiation is an important concern for astronauts during space missions. Therefore, we assessed the response of the brain to 28Si ion irradiation (600MeV/n), a heavy ion present in the space environment, on cognitive performance and whether the response is associated with altered DNA methylation in the hippocampus, a brain area important for cognitive performance. Methods: We determined the effects of 28Si ion irradiation on object recognition, 6-month-old mice irradiated with 28Si ions (600MeV/n, 0.3, 0.6, and 0.9Gy) and cognitively tested two weeks later. In addition, we determined if those effects were associated with alterations in hippocampal networks and/or hippocampal DNA methylation. Results: At 0.3Gy, but not at 0.6Gy or 0.9Gy, 28Si ion irradiation impaired cognition that correlated with altered gene expression and 5hmC profiles that mapped to specific gene ontology pathways. Comparing hippocampal DNA hydroxymethylation following proton, 56Fe ion, and 28Si ion irradiation revealed a general space radiation synaptic signature with 45 genes that are associated with profound phenotypes. The most significant categories were glutamatergic synapse and postsynaptic density. Discussion: The brain's response to space irradiation involves novel excitatory synapse and postsynaptic remodeling.

Effect of helium ion irradiation on pure W, W-5Ta and W-5Re: a micro-tensile and nanoindentation investigation of mechanical properties

Effect of helium ion irradiation on pure W, W-5Ta and W-5Re: a micro-tensile and nanoindentation investigation of mechanical properties

Delayed plasticity during spherical nanoindentation of an iron-chromium-aluminum alloy: Effect of ferric ion irradiation

Spherical nanoindentation of an iron-chromium-aluminum alloy was conducted to study the effect of ferric-ion (Fe3+) irradiation on the time-dependent plasticity behavior in the surface layers of this alloy. It was observed that the initiation of plasticity by the appearance of displacement burst or “pop-in” event occurred after a period of waiting time in the apparent elastic regime and that Fe3+ irradiation at 360 °C and up to ∼0.5 displacements per atom could make it happen under the lower applied loads but with a reduced magnitude. Through the experimental data, an activation volume and activation energy were extracted for the delayed plasticity. The results show that Fe3+-irradiation significantly reduced its activation volume from ∼3.05b3 to ∼1.75b3 (where b = Burgers vector), but slightly increased its activation energy from ∼0.65 to ∼0.71 eV. On the other hand, high-resolution scanning transmission electron microscopy observations reveal that the irradiation at the elevated temperature created interstitial atom pair onto the (100) habit plane that can serve as the nucleation site of a 〈100〉 dislocation loop while eliminating the pre-existing dislocations. Consequently, it is indicated that heterogeneous nucleation of the dislocation loop was predominant in the delayed plasticity initiation of this alloy and that the nucleation of the interstitial-type dislocation loop was involved due to Fe3+-irradiation.

Improving the crystallinity and texture of oblique-angle-deposited AlN thin films using reactive synchronized HiPIMS

Many technologies, such as surface-acoustic-wave (SAW) resonators, sensors, and piezoelectric MEMS require highly-oriented and textured functional thin films. The best results are typically achieved for on-axis sputter geometries, but in some scenarios, this is not feasible, such as during co-deposition from multiple magnetrons or when coating substrates with high aspect ratios. Ionized physical vapor deposition (PVD) techniques such as HiPIMS can be used to accelerate the film-forming species onto the growing film using substrate-bias potentials, thus increasing adatom mobility and film texture. However, gas-ion incorporation can limit the feasibility of such synthesis approaches for defect-sensitive functional thin films. This work reports on the oblique-angle deposition of highly textured, c-axis oriented AlN (0002) films using reactive metal-ion synchronized HiPIMS. AlN thin films deposited using direct current magnetron sputtering (DCMS) and HiPIMS are discussed for comparison and the effect of ion irradiation through substrate biasing is investigated. We find that combining HiPIMS with a moderate substrate bias of only −30 V improves the crystalline quality and texture of the films significantly, while the process-gas incorporation and point defects formation can be further reduced by synchronizing the negative substrate bias potential to the Al-rich fraction of each HiPIMS pulse. In addition to a pronounced out-of-plane texture, the films show uniform polarization of the grains making this synthesis route suitable for piezoelectric applications. While the compressive stress in the films is still comparatively high, the results already demonstrate, that metal-ion synchronized HiPIMS can yield promising results for the synthesis of functional thin films under oblique-angle deposition conditions - even with low substrate-bias potentials.

Immobilization and He+ irradiation effects of Gd2Zr2O7-based ceramic waste form for radioactive waste disposal

The Gd2Zr2O7(GZO)-based ceramic waste form exhibits promising potential for radioactive waste immobilization. However, the isomorphic immobilization capacity and irradiation effects of GZO-based ceramic waste forms with varying waste loads remain inadequately understood. This study employed a facile combustion method to synthesize ceramic powders and utilized conventional sintering with a relatively short dwelling time to fabricate GZO-based ceramic waste forms. We investigated the isomorphic immobilization behavior and He ion irradiation effects of the synthesized waste forms. The outcomes demonstrate that GZO effectively immobilizes simulated waste composed of 11 types of oxides, achieving a waste load as high as 50 wt% with a single pyrochlore phase and homogeneous element distribution. Under He+ irradiation, aggravated structural degradations, including exacerbated lattice swelling, increased amorphization degree, and premature He bubble chain/microcrack formation, were observed in GZO-based waste forms with an increasing waste load.

Heavy Ion Radiation Directly Induced the Shift of Oral Microbiota and Increased the Cariogenicity of Streptococcus mutans.

Radiation caries is one of the most common complications of head and neck radiotherapy. A shift in the oral microbiota is the main factor of radiation caries. A new form of biosafe radiation, heavy ion radiation, is increasingly being applied in clinical treatment due to its superior depth-dose distribution and biological effects. However, how heavy ion radiation directly impacts the oral microbiota and the progress of radiation caries are unknown. Here, unstimulated saliva samples from both healthy and caries volunteers and caries-related bacteria were directly exposed to therapeutic doses of heavy ion radiation to determine the effects of radiation on oral microbiota composition and bacterial cariogenicity. Heavy ion radiation significantly decreased the richness and diversity of oral microbiota from both healthy and caries volunteers, and a higher percentage of Streptococcus was detected in radiation groups. In addition, heavy ion radiation significantly enhanced the cariogenicity of saliva-derived biofilms, including the ratios of the genus Streptococcus and biofilm formation. In the Streptococcus mutans-Streptococcus sanguinis dual-species biofilms, heavy ion radiation increased the ratio of S. mutans. Next, S. mutans was directly exposed to heavy ions, and the radiation significantly upregulated the gtfC and gtfD cariogenic virulence genes to enhance the biofilm formation and exopolysaccharides synthesis of S. mutans. Our study demonstrated, for the first time, that direct exposure to heavy ion radiation can disrupt the oral microbial diversity and balance of dual-species biofilms by increasing the virulence of S. mutans, increasing its cariogenicity, indicating a potential correlation between heavy ions and radiation caries. IMPORTANCE The oral microbiome is crucial to understanding the pathogenesis of radiation caries. Although heavy ion radiation has been used to treat head and neck cancers in some proton therapy centers, its correlation with dental caries, especially its direct effects on the oral microbiome and cariogenic pathogens, has not been reported previously. Here, we showed that the heavy ion radiation directly shifted the oral microbiota from a balanced state to a caries-associated state by increasing the cariogenic virulence of S. mutans. Our study highlighted the direct effect of heavy ion radiation on oral microbiota and the cariogenicity of oral microbes for the first time.