Irradiation System Research Articles

Thermal effect of a 445\xa0nm diode laser on five dental implant systems: an in vitro study

The purpose of this in vitro study was to assess the thermal effect of the 445 nm diode laser on five dental implant systems. In an ailing implant protocol, five commercial dental implant systems were subjected to 445 nm diode laser energy at different wattages [W], exposure times, and modes (continuous wave [CW] vs. pulsed and contact vs. non-contact) of laser beam delivery. Scanning electron microscopy (SEM) allowed the evaluation of irradiated implant surfaces. A total of 2880 temperature response curves were recorded. The 445 nm wavelength caused temperature increases of more than 10 °C at or above the 0.8 W power level working in CW mode for 5 s and in pulsed mode at 3 W for 20 s with 10% duty cycle. Highest rises in temperature were seen in the Straumann Pure ceramic implant, lowest in the Ankylos system. SEM analysis revealed no surface alteration in all systems in non-contact mode. The applied laser is not inherently safe for the decontamination of ailing implants. From the results of this study it was concluded that different dental implant materials and geometries show different temperature response curves when subjected to 445 nm diode laser energy. Clinicians ought to be aware of this. Therefore, manufacturers of laser devices should provide implant-specific laser parameters for the decontamination process. However, both laser irradiation systems can prevent harmful rises in temperature and surface alteration when used at moderate laser parameters.

Scalable, effective, and rapid decontamination of SARS-CoV-2 contaminated N95 respirators using germicidal ultraviolet C (UVC) irradiation device

Particulate respirators such as N95s are an essential component of personal protective equipment (PPE) for front-line workers. This study describes a rapid and effective UVC irradiation system that would facilitate the safe re-use of N95 respirators and provides supporting information for deploying UVC for decontamination of SARS-CoV-2 during the COVID-19 pandemic. To assess the inactivation potential of the proposed UVC germicidal device as a function of time by using 3 M 8211-N95 particulate respirators inoculated with SARS-CoV-2. A germicidal UVC device to deliver tailored UVC dose was developed and test coupons (2.5 cm2) of the 3 M-N95 respirator were inoculated with 106 plaque-forming units (PFU) of SARS-CoV-2 and were UV irradiated. Different exposure times were tested (0–164 s) by fixing the distance between the lamp and the test coupon to 15.2 cm while providing an exposure of at least 5.43 mWcm−2. Primary measure of outcome was titration of infectious virus recovered from virus-inoculated respirator test coupons after UVC exposure. Other measures included the method validation of the irradiation protocol, using lentiviruses (biosafety level-2 agent) and establishment of the germicidal UVC exposure protocol. An average of 4.38 × 103 PFU ml−1 (SD 772.68) was recovered from untreated test coupons while 4.44 × 102 PFU ml−1 (SD 203.67), 4.00 × 102 PFU ml−1 (SD 115.47), 1.56 × 102 PFU ml−1 (SD 76.98) and 4.44 × 101 PFU ml−1 (SD 76.98) was recovered in exposures 2, 6, 18 and 54 s per side respectively. The germicidal device output and positioning was monitored and a minimum output of 5.43 mW cm−2 was maintained. Infectious SARS-CoV-2 was not detected by plaque assays (minimal level of detection is 67 PFU ml−1) on N95 respirator test coupons when irradiated for 120 s per side or longer suggesting 3.5 log reduction in 240 s of irradiation, 1.3 J cm−2. A scalable germicidal UVC device to deliver tailored UVC dose for rapid decontamination of SARS-CoV-2 was developed. UVC germicidal irradiation of N95 test coupons inoculated with SARS-CoV-2 for 120 s per side resulted in 3.5 log reduction of virus. These data support the reuse of N95 particle-filtrate apparatus upon irradiation with UVC and supports use of UVC-based decontamination of SARS-CoV-2 during the COVID-19 pandemic.

Biofluid Metabolomics of Mice Exposed to External Low-Dose Rate Radiation in a Novel Irradiation System, the Variable Dose-Rate External 137Cs Irradiator

An important component of ionizing radiation (IR) exposure after a radiological incident may include low-dose rate (LDR) exposures either externally or internally, such as from 137Cs deposition. In this study, a novel irradiation system, VAriable Dose-rate External 137Cs irradiatoR (VADER), was used to expose male and female mice to a variable LDR irradiation over a 30 d time span to simulate fall-out-type exposures in addition to biofluid collection from a reference dose rate (0.8 Gy/min). Radiation markers were identified by untargeted metabolomics and random forests. Mice exposed to LDR exposures were successfully identified from control groups based on their urine and serum metabolite profiles. In addition to metabolites commonly perturbed after IR exposure, we identified and validated a novel metabolite (hexosamine-valine-isoleucine-OH) that increased up to 150-fold after LDR and 80-fold after conventional exposures in urine. A multiplex panel consisting of hexosamine-valine-isoleucine-OH with other urinary metabolites (N6,N6,N6-trimethyllysine, carnitine, 1-methylnicotinamide, and α-ketoglutaric acid) achieved robust classification performance using receiver operating characteristic curve analysis, irrespective of the dose rate or sex. These results show that in terms of biodosimetry, dysregulated energy metabolism is associated with IR exposure for both LDR and conventional IR exposures. These mass spectrometry data have been deposited to the NIH data repository via Metabolomics Workbench with study IDs ST001790, ST001791, ST001792, ST001793, and ST001806.

Utilizing the Faxitron MultiRad 225 X-ray irradiation system for the construction of mouse chronic whole brain radiation model.

Radiation-induced brain injury (RBI) is a common complication of radiotherapy for head and neck tumors while its mechanism is not fully understood. Animal whole-brain radiation (WBR) models are of key importance in experimental radiation research, and an appropriate radiation source is essential. Previous animal WBR models were administered by clinical linear accelerator to induce the pathophysiological changes of RBI. In the current study, we adopted Faxitron MultiRad 225 X-ray irradiation system to construct a mouse WBR model with a single dose of 30 Gy. In the acute phase of this mouse WBR model, brain edema and blood-brain barrier (BBB) damage were found mild. However, two months later, the results of immunofluorescence showed that astrocytes and microglia were activated continuously, and the number of immature neurons in dentate gyrus (DG) area of hippocampus was significantly reduced, in accordance with the features of chronic pathophysiological changes. Besides, data of MRI scans and behavior tests illustrated the structural changes of brain tissue and cognitive impairment in the chronic phase. To sum up, this mouse WBR model using the Faxitron MultiRad 225 irradiation system with a single dose of 30 Gy is feasible to simulate the RBI-related chronic pathophysiological changes.

Commissioning of the Radiation Monitor Calibration Laboratory (LabCal) of IDQBRN for cesium-137 irradiation system

The provision for the Brazilian Army of equipment that provides reliable and safe measurements, enabling decision-making based on radioprotection parameters, leads to the need to investigate the metrology of the calibration system used in the Radiation Monitor Calibration Laboratory (LabCal) of the Institute of Chemical, Biological, Radiological and Nuclear Defense (IDQBRN). To this end, the commissioning in cesium-137 is of primary importance in this process. In order to check the conformity of the radiator system, in this work, the ambient dose equivalent rate, , was obtained experimentally for several configurations to compare them with the appropriate theoretical concepts. For this, the distance between the source of Cesium-137 (36.9 GBq in 01/22/2015) and the ionization chamber was varied from 500 to 3000 mm at 250mm intervals. To obtain lower ambient dose equivalent rates, 15 and 32 mm thick lead attenuators were used. The mathematical model that best fit the experimental values was analyzed. In all cases, the potential function offers better fit, since the coefficients of determination obtained are approximately equal to 1, obeying the Law of the Inverse Square of the Distance, according to theoretical foundation. Moreover, it was evaluated that the relative deviations are below the limits established by the relevant standard.

Method development and mechanistic study on direct pulsed laser irradiation process for highly effective dechlorination of persistent organic pollutants

Chlorine-based compounds are typical persistent organic pollutants (POPs) that are widely generated in industrial production. This paper reports an effective and rapid pulsed laser irradiation technique for the dechlorination of hexachlorobenzene (HCB), a model pollutant, without additional catalysts or supports. The effects of the laser parameters, including the laser wavelength and power, on the dechlorination efficiency, were also investigated. The optimized results showed that a lower laser wavelength of 266 nm with 10 mJ/pulse power exhibited the highest dechlorination efficiency with 95% within 15 min. In addition, the laser beam effect was examined by designing the direct-pulsed laser single and multipath irradiation system. The results showed that improving the laser beam profile resulted in more than 95% dechlorination efficiency within 5 min. Thus, the dechlorination reaction proceeded much faster as the surface area that the laser beam came in contact with increased due to the multipath system than the single pathway. Gas chromatography identified benzene as the final product of HCB with pentachlorobenzene (PCB), tetrachlorobenzene (TeCB), trichlorobenzene (TCB), dichlorobenzene (DCB), and chlorobenzene (CB) as intermediate products. The mechanism of HCB dechlorination was explained by a comparison of theoretical calculations with the experimental results. The present study reports an advanced technique for the complete dechlorination of chlorobenzenes, which holds great application potential in environmental remediation.

Degradation of hexavalent chromium and methyl orange by the synergistic system of graphitic carbon nitride and electron beam irradiation

Hexavalent chromium (Cr(VI)) and methyl orange (MO) are highly toxic and difficult to treat. Electron beam irradiation (EB) can produce ·OH, H·, ·O2−, hydrated electron (eaq−) and other active substances, which have strong redox ability to pollutants. However, the penetration capacity of EB is limited (the penetration depth of water is 10 cm). Therefore, the photocatalytic method of graphitic carbon nitride (CN) was used as the synergistic method of EB in this project to degrade Cr(VI) and MO. The results showed that the maximum treatment efficiency of 100 mg L−1 Cr(VI) and 50 mg L−1 MO with liquid surface height of 5 cm was 95.0% and 99.1%, respectively, which was much higher than that of single photocatalytic method (39.5%, 23.4%) and EB (79.6%, 92.1%), and the efficiency of synergistic treatment was higher under acidic condition. When the liquid depth increased to 30 cm, the efficiency of synergistic system decreased by 14.7% and 15.2% for the degradation of Cr(VI) and MO, respectively, less than the single EB treatment (47.2%, 45.7%). Additionally, the performance of the morphology, the light absorption performance, and the separation of photogenerated electron-hole pairs of the CN were evaluated before and after the synergistic system. Lastly, the mechanism illustrates that the electron and thermal effects of EB, eaq−, photogenerated electrons played key roles for the Cr(VI) reduction, and the electron and thermal effects of EB, ·O2−, photogenerated holes played key roles for the MO degradation. This study provides a new opportunity for the synergistic system of photocatalyst and EB in the treatment of pollutants.

Synergistic effect of photobiomodulation and phthalocyanine photosensitizer on fibroblast signaling responses in an in vitro three-dimensional microenvironment.

Photobiomodulation (PBM) is a promising medical treatment modality in the area of photodynamic therapy (PDT). In this study, we investigated the effect of combined therapy in a 3D microenvironment using aluminum chloride phthalocyanines (AlClPc) as the photosensitizing agent. Normal human fibroblast-containing collagen biomatrix was prepared and treated with an oil-in-water (o/a) AlClPc-loaded nanoemulsion (from 0.5 to 3.0μM) and irradiated at a range of fluences (from 0.1 to 3.0J/cm2) using a continuous-wave light-emitting diode (LED) irradiation system (660nm). PBM at 1.2J/cm2 and AlClPc/NE at 0.5μM modified the fibroblast signaling response under 3D conditions, promoting collagen synthesis, ROS production, MMP-9 secretion, proliferation of the actin network, and facile myofibroblastic differentiation. PBM alone (at 1.2J/cm2 and 0.3J/cm2) had no significant effect on any of these parameters. The combined therapy affected myofibroblastic differentiation, inflammatory response, and extracellular matrix pliability, and should thus be examined further in subsequent studies considering that no side effects of PBM have been reported. Even though significant progress has been made in the field of phototherapy in recent years, it is necessary to further elucidate the detailed mechanisms underlying its effects already shown in 2D conditions to increase the acceptance of this beneficial and non-invasive therapeutic approach.

Photoinduced spin-Hall resonance in a k3 -Rashba spin-orbit coupled two-dimensional hole system

We study the band structure modulation and spin-Hall effect of an irradiated two-dimensional heavy-hole system with ${k}^{3}$-Rashba spin-orbit coupling. We find that the band structure becomes anisotropic under the illumination by the light. Most remarkably, in the presence of linearly polarized light a pair of additional spin-degeneracy points, apart from the $\mathrm{\ensuremath{\Gamma}}$ point, emerge in the energy dispersion. The locations of these points are solely determined by the amplitude of the incident light. If this degeneracy occurs around the Fermi level, the spin-Hall conductivity exhibits a resonance. Away from the degeneracy points, the light rotates the average spin polarization. The possible effects of ${k}^{3}$-Dresselhaus spin-orbit coupling are also discussed.

A customizable aluminum compensator system for total body irradiation.

PurposeTo develop a simplified aluminum compensator system for total body irradiation (TBI) that is easy to assemble and modify in a short period of time for customized patient treatments.MethodsThe compensator is composed of a combination of 0.3 cm thick aluminum bars, two aluminum T‐tracks, spacers, and metal bolts. The system is mounted onto a plexiglass block tray. The design consists of 11 fixed sectors spanning from the patient's head to feet. The outermost sectors utilize 7.6 cm wide aluminum bars, while the remaining sectors use 2.5 cm wide aluminum bars. There is a magnification factor of 5 from the compensator to the patient treatment plane. Each bar of aluminum is interconnected at each adjacent sector with a tongue and groove arrangement and fastened to the T‐track using a metal washer, bolt, and nut. Inter‐bar leakage of the compensator was tested using a water tank and diode. End‐to‐end measurements were performed with an ion chamber in a solid water phantom and also with a RANDO phantom using internal and external optically stimulated luminescent detectors (OSLDs). In‐vivo patient measurements from the first 20 patients treated with this aluminum compensator were compared to those from 20 patients treated with our previously used lead compensator system.ResultsThe compensator assembly time was reduced to 20–30 min compared to the 2–4 h it would take with the previous lead design. All end‐to‐end measurements were within 10% of that expected. The median absolute in‐vivo error for the aluminum compensator was 3.7%, with 93.8% of measurements being within 10% of that expected. The median error for the lead compensator system was 5.3%, with 85.1% being within 10% of that expected.ConclusionThis design has become the standard compensator at our clinic. It allows for quick assembly and customization along with meeting the Task Group 29 recommendations for dose uniformity.

Local Preirradiation of Infarcted Cardiac Tissue Substantially Enhances Cell Engraftment.

The success of cell therapy for the treatment of myocardial infarction depends on finding novel approaches that can substantially implement the engraftment of the transplanted cells. In order to enhance cell engraftment, most studies have focused on the pretreatment of transplantable cells. Here we have considered an alternative approach that involves the preconditioning of infarcted heart tissue to reduce endogenous cell activity and thus provide an advantage to our exogenous cells. This treatment is routinely used in other tissues such as bone marrow and skeletal muscle to improve cell engraftment, but it has never been taken in cardiac tissue. To avoid long-term cardiotoxicity induced by full heart irradiation we developed a rat model of a catheter-based heart irradiation system to locally impact a delimited region of the infarcted cardiac tissue. As proof of concept, we transferred ZsGreen+ iPSCs in the infarcted heart, due to their ease of use and detection. We found a very significant increase in cell engraftment in preirradiated rats. In this study, we demonstrate for the first time that preconditioning the infarcted cardiac tissue with local irradiation can substantially enhance cell engraftment.

A performance analysis of a new secondary standard dosimetry laboratory irradiation system

This study reviews the performance analysis of a commercial 137Cs irradiation system that has recently been installed in the Secondary Standard Dosimetry Laboratory (SSDL) at the Soreq Nuclear Research Center (SNRC).The SSDL is responsible for calibrating calibration facilities and for calibrating most protection level radiation monitoring instruments used in medical, nuclear, industrial and academic settings in Israel. Until recently, these monitoring instruments have been calibrated by a 40-year-old irradiation system.At the end of 2018, a new Hopewell Designs Inc. ® irradiation system was installed at our SSDL. This system employs the most advanced radiation safety standards, along with 21st century source automation methods. In this work, we review the system’s performance. Our analysis shows excellent results in terms of repeatability, robustness, linearity, and beam uniformity. Additionally, the system accuracy was tested by participating in an international IAEA postal audit, and here too, excellent results were obtained.

Selective hydrogenation of cinnamaldehyde to cinnamyl alcohol over palladium/zirconia in microwave protocol

Hydrogenation of aldehydes (RHO) is one of the frequently used reactions in organic synthesis and pharmaceuticals industries. In this contribution, we have synthesized control shaped and nano-sized tetragonal zirconia (t-ZrO2), palladium supported on zirconia (Pd/t-ZrO2) and nickel promoted palladium supported on zirconia (Ni-Pd/t-ZrO2) though modified microwave irradiation method. All the prepared samples were characterized by Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), X-ray Diffractometry (XRD), Thermal Gravimetric Analysis (TGA), Brunauer-Emmett-Teller (BET) surface area and pore size analysis, and Fourier Transform Infrared Spectroscopy (FT-IR). Theoretical calculation (DFT) revealed high interaction of Pd with t-ZrO2(101) surface. Furthermore, adsorption energy, support relaxation and charge transfer studies confirmed the stability of Pd on t-ZrO2(101) surface. The catalytic activity of catalysts was tested for cinnamaldehyde (CAL) hydrogenation in a modified microwave reactor. The comparative study of microwave irradiated (MW) and conventional heating (C-Heating) systems show supremacy of MW over C-Heating by a factor of 46% under optimal reaction parameters for Pd/t-ZrO2 catalyst. The stability, life span, conversion and selectivity of Pd/t-ZrO2 under MW system suggest the applicability of the catalysts for a variety of organic hydrogenation reactions.

OC-0305 Acceptance procedure of a novel Flash irradiation system with standard dosimetric tools

OC-0305 Acceptance procedure of a novel Flash irradiation system with standard dosimetric tools

Construction and validation of an ultraviolet germicidal irradiation system using locally available components.

Coronavirus disease (COVID-19), the disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, is responsible for a global pandemic characterized by high transmissibility and morbidity. Healthcare workers (HCWs) are at risk of contracting COVID-19, but this risk has been mitigated through the use of personal protective equipment such as N95 Filtering Facepiece Respirators (FFRs). At times the high demand for FFRs has exceeded supply, placing HCWs at increased exposure risk. Effective FFR decontamination of many FFR models using ultraviolet-C germicidal irradiation (UVGI) has been well-described, and could maintain respiratory protection for HCWs in the face of supply line shortages. Here, we detail the construction of an ultraviolet-C germicidal irradiation (UVGI) device using previously existing components available at our institution. We provide data on UV-C dosage delivered with our version of this device, provide information on how users can validate the UV-C dose delivered in similarly constructed systems, and describe a simple, novel methodology to test its germicidal effectiveness using in-house reagents and equipment. As similar components are readily available in many hospitals and industrial facilities, we provide recommendations on the local construction of these systems, as well as guidance and strategies towards successful institutional implementation of FFR decontamination.

Skin tolerant inactivation of multiresistant pathogens using far-UVC LEDs

Multiresistant pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) cause serious postoperative infections. A skin tolerant far-UVC (< 240 nm) irradiation system for their inactivation is presented here. It uses UVC LEDs in combination with a spectral filter and provides a peak wavelength of 233 nm, with a full width at half maximum of 12 nm, and an irradiance of 44 µW/cm2. MRSA bacteria in different concentrations on blood agar plates were inactivated with irradiation doses in the range of 15–40 mJ/cm2. Porcine skin irradiated with a dose of 40 mJ/cm2 at 233 nm showed only 3.7% CPD and 2.3% 6-4PP DNA damage. Corresponding irradiation at 254 nm caused 11–14 times higher damage. Thus, the skin damage caused by the disinfectant doses is so small that it can be expected to be compensated by the skin's natural repair mechanisms. LED-based far-UVC lamps could therefore soon be used in everyday clinical practice to eradicate multiresistant pathogens directly on humans.

Binary central stars of planetary nebulae identified with Kepler/K2

ABSTRACT We present the identification of 34 likely binary central stars (CSs) of planetary nebulae (PNe) from Kepler/K2 data, seven of which show eclipses. Of these, 29 are new discoveries. Two additional CSs with more complicated variability are also presented. We examined the light curves of all ‘possible’, ‘likely’, and ‘true’ PNe in every Kepler/K2 campaign (0 through 19) to identify CS variability that may indicate a binary CS. For Campaigns 0, 2, 7, 15, and 16, we find 6 likely or confirmed variables among 21 PNe. Our primary effort, though, was focused on Campaign 11 which targeted a Galactic bulge field containing approximately 183 PNe, in which we identified 30 candidate variable CSs. The periods of these variables range from 2.3 h to 30 d, and based on our analysis, most are likely to be close binary star systems. We present periods and preliminary classifications (eclipsing, double degenerate, or irradiated systems) for the likely binaries based on light-curve shape. From our total sample of 204 target PNe, with a correction for incompleteness due to magnitude limits, we calculate a binary fraction of PN central stars to be 20.7 per cent for all the observed PNe, or 23.5 per cent if we limit our sample only to ‘true’ PNe. However, these fractions are almost certainly lower limits due to the large angular size of the Kepler pixels, which leads to reduced sensitivity in detecting variability, primarily as a result of dilution and noise from the nebula and neighbouring stars. We discuss the binary population of CSs based on these results as part of the total known sample of close binary CSs.

Simulation of the multi-purpose gamma irradiator dose distribution based on the GEANT4 and GPU system

Gamma irradiation systems are used extensively in the industry in order to sterilize medical devices, disinfect hygienic products and increase the shelf life of agricultural products. The method of gamma irradiation is superior to the older methods of heat or chemical treatment because it is by far a simpler operation. In this method, only one parameter, the exposure time is controlled, whereas in the other mentioned methods five or six different parameters need to be controlled. The design of irradiation systems generally includes the size and the location of products, and the arrangement of source rack pencils. In order to optimize the design of the gamma irradiation systems, it is needed to study the product’s dose distribution in a wide range of densities. The Monte Carlo algorithm is an effective way for simulating the irradiation systems which is being used by a variety of codes. Since this method requires a high computation time, it is necessary to speed up the simulation and design the systems by various methods such as using graphics processing units which having a highly parallel design makes them more suitable for algorithms that process a large number of data than central processing units. In this work, a GEANT4-based computational code is developed to adapt on the GPU using the CUDA programming. Since the developed GEANT4-based code utilizes a graphical processor of NVIDIA (in particular a series GTX660 Ti NVIDIA’s GPU), it leads to speed up the process of simulation. Using this computational technique, a IR-136 gamma irradiator is simulated and the results of the simulation are benchmarked against previously published work. In the present work, a new setup of the industrial irradiator system is considered. The results of the simulations using CPU and GPU are compared with the available experimental dosimetry data. The dose calculation in the new setup is significantly faster using GPU in comparison to the GEANT4 code performed by CPU. The system specification used in both the routine GEANT4 code performed by CPU and the GEANT4-based algorithm performed by GPU are the same. The results show that computational speed when using GEANT4-based code with GPU is superior to using GEANT4 code with CPU, and the deviation between the two sets of data is less than 3%. The speed-up factor is averagely about 3300.

Investigation of scattered dose in a mouse phantom model for pre-clinical dosimetry studies

Tissue-equivalent phantoms are suitable tools for radiation dosimetry investigations. The goal of this study was to determine the scattered dose in a simple phantom model of a mouse with a xenographic tumour using experimental dose measurements and Monte-Carlo calculations. We manufactured a cubic polymethyl methacrylate (PMMA) phantom with an extrusion on its side to model both normal tissue and xenograft tumour of a tumour-bearing mouse. The phantom was positioned in a novel add-on collimator, designed by our research group, to enable targeted irradiation of the xenograft tumour with a dose of 20 Gy using a137Cs gamma irradiator. EBT3 GAFchromic film was utilized to measure the dose distribution within the phantom. EGSnrc MC code was used to simulate the irradiation system and to calculate the dose distribution in the phantom for comparison with the film dose measurements. Good agreement was observed between film dose measurements and simulation results based on gamma index analysis. The results demonstrate that the out of field dose (dose to the normal tissue) is of the order 8–9% of the prescribed dose when irradiating the xenographic tumour of the phantom. Our physical phantom is a useful tool to assess the out of field dose when irradiating xenographic tumours.

Shielding of viruses such as SARS-Cov-2 from ultraviolet radiation in particles generated by sneezing or coughing: Numerical simulations of survival fractions

SARS-CoV-2 and other microbes within aerosol particles can be partially shielded from UV radiation. The particles refract and absorb light, and thereby reduce the UV intensity at various locations within the particle. Previously, we demonstrated shielding in calculations of UV intensities within spherical approximations of SARS-CoV-2 virions within spherical particles approximating dried-to-equilibrium respiratory fluids. The purpose of this paper is to extend that work to survival fractions of virions (i.e., fractions of virions that can infect cells) within spherical particles approximating dried respiratory fluids, and to investigate the implications of these calculations for using UV light for disinfection. The particles may be on a surface or in air. Here, the survival fraction (S) of a set of individual virions illuminated with a UV fluence (F, in J/m2) is assumed described by S(kF) = exp(-kF), where k is the UV inactivation rate constant (m2/J). The average survival fraction (S p) of the simulated virions in a group of particles is calculated using the energy absorbed by each virion in the particles. The results show that virions within particles of dried respiratory fluids can have larger S p than do individual virions. For individual virions, and virions within 1-, 5-, and 9-µm particles illuminated (normal incidence) on a surface with 260-nm UV light, the S p = 0.00005, 0.0155, 0.22, and 0.28, respectively, when kF = 10. The S p decrease to <10−7, <10−7, 0.077, and 0.15, respectively, for kF = 100. Results also show that illuminating particles with UV beams from widely separated directions can strongly reduce the S p. These results suggest that the size distributions and optical properties of the dried particles of virion-containing respiratory fluids are likely important to effectively designing and using UV germicidal irradiation systems for microbes in particles. The results suggest the use of reflective surfaces to increase the angles of illumination and decrease the S p. The results suggest the need for measurements of the S p of SARS-CoV-2 in particles having compositions and sizes relevant to the modes of disease transmission.