Monoenergetic Photons Research Articles

Nanoscale dosimetry for a radioisotope-labeled metal nanoparticle using MCNP6.2 and Geant4.

Metal nanoparticles (MNPs) labeled with radioisotopes (RIs) are utilized as radio-enhancers due to their ability to amplify the radiation dose in their immediate vicinity. A thorough understanding of nanoscale dosimetry around MNPs enables their effective application in radiotherapy. However, nanoscale dosimetry around MNPs still requires further investigation. This study aims to provide insight into the radio-enhancement effects of MNPs by elucidating nanoscale dosimetry surrounding MNPs labeled with Auger-emitting RIs. We particularly focus on distinguishing the respective dose contributions of photons and electrons emitted by Auger-emitting RIs in the context of dose enhancement. A 50nm diameter NP of silver (Ag) core and gold (Au) shell (Ag@Au NP) was assumed to emit mono-energetic electrons and photons (3, 5, 10, 20, and 30keV), or the energy spectrum corresponding to one of three Auger-emitting RIs (103Pd, 125I, and 131Cs) from the Ag core. Nanoscale radial dose distributions around a single radioactive Ag@Au NP were evaluated in spherical shells of water. Monte Carlo simulations were conducted using single-event and track structure transport methods implemented in MCNP6.2 and Geant4-DNA-Au physics, respectively. To evaluate the extent of radio-enhancement by the Ag@Au NP, two scenarios were considered: Ag@Au NPs (Au shell included) and Ag@water NPs (Au shell replaced by water). The radial doses of 10, 20, and 30keV electrons estimated by both codes were comparable. However, the radial doses of 3 and 5keV electrons by MCNP6.2 were much larger near the NP surface than those by Geant4. There was a dose enhancement of a few % to tens % by the Au shell in the region of the NP surface to 10µm, depending on the electron energy. The radial doses of photons with the Au shell were higher up to their secondary electron ranges than those without the Au shell. The maximum dose enhancement factor of photons occurred at 20keV and was 63.4 by MCNP6.2 and 50.5 by Geant4. The overall radial doses of electrons were 1-2 orders of magnitude larger than those of photons. As a result, in cases of RIs emitting both electrons and photons, the radial doses up to electron ranges were dominantly governed by electrons. The dose enhancement estimated by both codes for the RIs ranged from a few % except in the immediate vicinity of the NP surface. Given the dominant contribution of electrons to radial doses of MNP labeled with Auger-emitting RIs, physical dose enhancement expected by interactions with photons was hindered. Since there are no available RIs emitting exclusively photons, achieving enhanced physical doses within a cell through a combination of MNPs and RIs appears currently unattainable. The radial doses of photons near the NP surface exhibited considerable discrepancies between the codes, primarily attributed to low-energy electrons. The difference may arise from higher cross-sections of Au inelastic scattering in Geant4-DNA-Au compared to MCNP6.2.

Assessment of foetal dose and occupational exposure for pregnant workers in nuclear medicine using the Taiwanese pregnancy phantom.

For pregnant workers in nuclear medicine, radiation doses can pose a risk to their foetus. However, foetal radiation doses cannot be measured directly. In this study, a method of estimating foetal radiation doses was developed through simulations and measurements of phantoms of pregnant women in the three trimesters. The uterus and abdominal surface doses for monoenergetic photons (137Cs) and medical diagnostic X-rays were measured, and uterine dose conversion coefficients (UDCCs) were calculated. The accuracy of the UDCC estimates were validated for measurements from thermoluminescent dosemeter (TLD) chips and TLD badges on the abdomen or chest. The foetal effective dose could be estimated using TLD chips and TLD badges on the abdomen or chest, or through literature estimation method. The proposed method can be used to easily and accurately estimate foetal effective doses from chest-worn TLD badges, ensuring accurate estimation in the early stage of pregnancy when a worker may not yet be wearing an abdominal badge. A flowchart for applying the UDCC method to approximate a foetal dose is also provided to ensure that total doses remain below the maximum of 1mSv recommended in the International Commission on Radiological Protection 103 guidelines.

The possibility of using the DKS-AT1123 dosimeter for radiation monitoring of medical electron accelerators with the energy of more than 10 MeV

In the Russian Federation, there is a constant increase in the number of radiation medical installations with electron accelerators. Over the past 4 years, their number has increased 2.5 times. These installations contain pulsed electron accelerators that generate pulsed bremsstrahlung radiation with a maximum energy from 6 to 21 MeV. Currently, there are no devices designed for dosimetry of the pulsed photon radiation with energy of more than 10 MeV in the state register of measuring instruments of the Russian Federation. The most widely used radiation monitoring device for pulsed electron accelerators is the DKS-AT1123 X-ray and gamma radiation dosimeter designed for dosimetry of pulsed bremsstrahlung radiation with an energy of up to 10 MeV. The purpose of this work is to evaluate the possibility of using this device for dosimetry of pulsed bremsstrahlung radiation with a maximum energy of up to 20 MeV. The authors calculated the energy spectra of bremsstrahlung radiation for a point source with a maximum energy of 20 MeV behind flat concrete screens with a thickness of 1 m, 2 m and 3 m by the Monte Carlo method using the GEANT4 calculation program. The energy dependence of the registration efficiency of the DKS-AT1123 dosimeter was extrapolated to the energy range of 10–50 MeV in the kerma-approximation without taking into account the energy transfer by secondary electrons. It was assumed that it corresponds to the energy dependence of the total mass attenuation coefficient for the absorbed energy of gamma quanta in water. Using conversion coefficients for converting the fluence of monoenergetic photons into the effective dose rate at an anterior-posterior radiation incidence on the human body, real dose rates were calculated, and using the energy dependence of the dosimeter readings, the predicted results of measuring the unit dose rate with the DKS-AT1123 dosimeter behind a concrete protection with a thickness of 1, 2 and 3 m were obtained. It is shown that the maximum expected underestimation of the measurement results will not exceed 40% and practically does not depend on the thickness of the concrete shield in the thickness range from 1 to 3 m. To account for this underestimation, it is necessary to use the value of additional measurement error due to the energy dependence of the sensitivity of this device for the photon radiation energy of more than 10 MeV, equal to 70%. This makes it possible to use the measurement results obtained using this dosimeter to adequately characterize the state of radiation safety during operation of pulsed electron accelerators with a maximum energy of up to 20 MeV. It is possible to use a correction factor to the measurement results equal to 1.63 ±0.04 to compensate for this underestimation. The proposed approach can be used to create a methodology for using this dosimeter for radiation monitoring of medical electron accelerators with the energy of up to 20 MeV, if there are correction factors for radiation protection configurations and radiation energies encountered in practice.

Earth-catalyzed detection of magnetic inelastic dark matter with photons in large underground detectors

Inelastic dark matter with moderate splittings, O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O} $$\\end{document}(few to 150) keV, can upscatter to an excited state in the Earth, with the excited state subsequently decaying, leaving a distinctive monoenergetic photon signal in large underground detectors. The photon signal can exhibit sidereal-daily modulation, providing excellent separation from backgrounds. Using a detailed numerical simulation, we examine this process as a search strategy for magnetic inelastic dark matter with the dark matter mass near the weak scale, where the upscatter to the excited state and decay proceed through the same magnetic dipole transition operator. At lower inelastic splittings, the scattering is dominated by moderate mass elements in the Earth with high spin, especially 27Al, while at larger splittings, 56Fe becomes the dominant target. We show that the proposed large volume gaseous detector CYGNUS will have excellent sensitivity to this signal. Xenon detectors also provide excellent sensitivity through the inelastic nuclear recoil signal, and if a future signal is seen, we show that the synergy among both types of detection can provide strong evidence for magnetic inelastic dark matter. In the course we have calculated nuclear response functions for elements relevant for scattering in the Earth, which are publicly available on GitHub.

The Use of Variance Reduction Techniques for Photon Dose Estimation in the Design of Radiotherapy Facilities at 10 and 15 MeV via Monte Carlo Simulations

In the context of designing radiotherapy facilities, typical dose estimation methods involve analytical approaches, as outlined in International Atomic Energy Agency (IAEA) Safety Reports Series No. 47 (IAEA 47). These methods are known for their ease of use and rapid calculations, but they could lead to either overestimation or underestimation of radiation doses. Hence, the integration of Monte Carlo (MC) methods is considered valuable. In this particular study, a radiotherapy facility was modeled using MCNP version 6.2, and dose calculations were conducted using analytical techniques following both IAEA 47 guidelines and MC simulations. The study focused on monoenergetic photon cone beams with energies of 10 and 15 MeV. Notably, the beam’s orientation prevented primary radiation from reaching the dose location at the entrance of the maze, allowing only scatter radiation to contribute to the tally. Given the challenges associated with obtaining reliable and accurate results through standard MCNP calculations, the investigation focused on the use of weight windows as a variance reduction technique. The findings revealed that the IAEA method tends to provide conservative results only when the same conditions were replicated in the MC simulations. In fact, approximately 50% of the final dose estimated through MC methods accounted for factors that were not considered in the analytical calculations. The primary contributor to scattering (averaging around 30%) was identified as the floor and ceiling. This study underscores the need for caution when relying solely on the analytical approach, as it may not consistently yield conservative outcomes.

Comparative study of radiation ionizing on the MRCP-AM phantom before and after using the Bi2O3[formula omitted]AlF3[formula omitted]CaO[formula omitted]B2O3 shielding glass by PHITS Monte Carlo simulation

The estimation of radiation hazards to the human body before and after the use of shielding glass is the next level of research on its radiation shielding properties. In this work, the glass compositions of the xBi2O3−20AlF3−20CaO− (60-x)B2O3 (where 0≤x≤40 mol%) were prepared by the melt-quenching method. The adult male mesh-type reference computational phantoms (MRCP-AM) were used to represent the whole human body, including the shape, chemical composition, and densities of every organ. The absorbed dose and effective dose rate on the phantom before and after using the shielding glass (thickness 1.0 cm) were estimated by PHITS Monte Carlo simulation. The mono-energetic photon of 0.662 MeV was irradiated with an anterior-posterior (AP) direction. In addition, the physical properties and gamma-ray shielding properties of the glasses, including the density (ρ), molar volume (Vm), mass attenuation coefficient (μm), half-value layer (HVL), Zeff, and Neff, were investigated by PHITS and XCOM in an energy range of 0.015 MeV–15 MeV, as well as comparison with experimental methods at different energy (133Ba, 137Cs, and 60Co sources). The results found that the addition of the Bi2O3 content into the glass structure affects the increase of the ρ, Vm, μm, Zeff, and Neff but the decrease of the HVL. In addition, the comparative study of radiation dose on the MRCP-AM phantom before and after using the shielding glass by PHITS Monte Carlo simulation demonstrated that the 40Bi2O3 glass sample can reduce damage to the brain, liver, left lung, right lung, prostate, skin, and thyroid, which are equal to 30.34%, 28.93%, 29.33%, 29.70%, 21.15%, 25.72%, and 21.99%, respectively, when compared with no shielding materials. The effective dose rate in MRCP-AM with shielding glass revealed significantly less damage than without shielding glass.

Extrapolation of Monte Carlo–Derived Noble Gas Air-Submersion Effective Dose Rate Coefficients for Selected Occupational Settings to Other Geometries and Radionuclides

External exposures to airborne radioactivity at nuclear power sites are typically based on semi-infinite clouds with uniform concentrations and corresponding effective dose rate coefficients (EDRCs), along with the simplifying assumption that the radioactive clouds extend to infinity around the receptor of interest. The two regulatory models that are typically employed for finite-cloud adjustments to submersion doses, namely, Regulatory Guide 1.183 for hemispherical clouds and the International Commission on Radiological Protection (ICRP) document ICRP-30 for spherical clouds, were purposely oversimplified to facilitate their implementation. As a result, dose projections can be significantly underestimated under certain circumstances, particularly with radionuclides emitting low-energy photons and/or particles. In addition, these adjustments do not account for scatter radiation off surrounding walls, ceilings, and floors of typical occupational settings. In recognition of these limitations and for the mitigation thereof, Veinot et al. published an article [Rad. and Environ. Biophy., Vol. 56, p. 453 (2017)] that provided monoenergetic photon, electron, and positron EDRCs based on elaborate Monte Carlo computations for submersion in three typical occupational settings at nuclear facilities (namely, an office, a laboratory, and a warehouse). Included in the article were also EDRCs for exposure to 45 noble gases airborne within the said occupational settings. However, extrapolation of the results to other settings was limited due to geometry variations. Even so, as described in the present paper, the Veinot et al. article provided the basis for the definition of a straightforward model for extrapolation of the Monte Carlo–derived EDRCs to other occupational settings and radionuclides. The objective of the EDRC extrapolation model in this paper is to provide a simple but comprehensive approach to licensing-basis submersion dose calculations consistent with the recommendations in ICRP Publication 103. The model is reasonably accurate and applicable to submersion volumes that are smaller than an office and larger than a typical warehouse, as would be needed for control room habitability evaluations. It is emphasized that the model is only suitable for the external dose computation of airborne noble gases and particulates; dose contributions via the inhalation pathway and from direct shine from contaminated surfaces need to be evaluated separately. The EDRC extrapolation model was programmed into an Excel workbook (OccuSetEDRCs-R0.xlsx) that is available to interested parties; see Supplementary Data section for further details. The model can handle all 1252 radionuclides in ICRP-107 and submersion volumes ranging between about 40 and 4000 m3, with an upper estimated error of about 10% on average for large submersion volumes.

Research on natAg(γ,xn)103-106Ag reaction cross sections with the bremsstrahlung end-point energy of 70 and 75 MeV

The flux-weighted average cross sections of natAg(γ,xn)103-106Ag reactions were measured with the bremsstrahlung end-point energy of 70 and 75 MeV using an activation and off-line γ-ray spectrometric technique. The GEANT4 code was used for the simulation of the bremsstrahlung spectra. The cross sections of natAg(γ,xn) 103-106Ag reactions as a function of mono-energetic photons were theoretically calculated by using the TALYS-1.96 code. The data of the present work and literature at different bremsstrahlung end-point energy are found to be in agreement with the theoretical values within the uncertainty limit. It can be seen that the flux-weighted average cross sections of the natAg(γ,xn)105.106Ag reactions increase with bremsstrahlung energy up to the Giant Dipole Resonance region. Thereafter, a small decrease trend with the bremsstrahlung energy was seen due to the opening of another reaction channel.

Comparison of calibration coefficients for a vinten ionization chamber simulated using four Monte Carlo methods

The Vinten 671 ionization chamber (VIC) was modelled using Monte Carlo (MC) programs EGSnrc, Penelope, and TOPAS. Several national measurement institutes have VICs with well-characterized response relationships and have measured calibration coefficients for many radionuclides. Twelve radionuclides with various decay emissions were assessed as well as 14 monoenergetic photon sources and 10 monoenergetic electron sources. Calibration coefficients were calculated based on the energy deposited in the simulated VIC nitrogen gas volume and compared to experimental values from the literature.

Experimental and Monte Carlo study of energy response of BEO-based OSL detectors within photon energy range up to 15 MeV.

Response of personal dosemeters to high energy photon radiation is of great interest nowadays due to a spread of new radiation technologies and the expansion of occupational exposure domains. ICRU95 publication has expanded the range of relevant photon energies upwards, setting new horizons for individual monitoring. Beryllium oxide (BeO) material is increasingly popular due to its excellent optically stimulated luminescence (OSL) properties, simple readout and reasonable energy response in the low energy (below 100keV) range. The study considers energy dependence of OSL response at higher photon energies. Energy deposition of monoenergetic photons with energy up to 15MeV in the BeO chips of various thickness was modeled with Monte Carlo MCNP 6.2 code. Benchmark experiments were conducted at LINAC with high voltage of 6, 10 and 15 MV resulting in respective incident photon spectra. The findings of this study add knowledge regarding behavior of BeO personal dosemeters in the photon fields within the energy range above 3MeV.

Gamma-ray attenuation properties of polymer biomaterials: Experiment, XCOM and GAMOS results

This study aims to compute and measure the linear attenuation coefficients of two biomaterials used in the human body as synthetic materials. These are used as bone cement and have applications in contact lens production and dentistry (coded as P1) also glass ionomer cement is a frequently preferred material in restorative dentistry applications (coded as P2). In the computational part of the study, a mono-energetic photon source between 1 keV and 20 MeV was used in the simulations performed using the GAMOS 6.2 program. In the experimental part, the linear attenuation coefficients of polymer materials were measured by using different radioactive sources at 6 different certain energies ranging from 511 to 1332 keV. A gamma spectrometer consisting of a NaI (Tl) detector was used for this purpose. Using the XCOM code, the experimental and simulation results were compared to the theoretical results, and a very good agreement was found between them. The simulation results demonstrated that the Monte Carlo technique can be used as an alternative to calculating the mass attenuation coefficients at the desired gamma energy, particularly for physically difficult to produce samples.

Multiple scattering double Compton model: determination of intrinsic efficiencies by calculating electron energies

ABSTRACT For the measurement of the energy spectra generated by photons up to 320 keV (X-rays) that can be considered by the superposition of a set of monoenergetic photons, several types of detectors have been used, mainly Ge detectors. Each spectrum can be considered as the superposition of a beam of monoenergetic photons that contain a photoelectric peak, a Compton distribution, the characteristic radiation, and a multiple scattering region, which is located between the Compton edge and the photoelectric peak. In this article, a theoretical model is developed for finding the multiple scattering region. To this end, double Compton scattering is proposed, wherein the electron in motion after the first collision suffers a second Compton scattering by a photon going in the same direction. Using the theory of special relativity and the Lorentz invariants, the kinetic energy of the electron in motion is calculated. Then, with the obtained value and the new Klein–Nishina formula, the cross-section of the absorbed electrons is calculated as a function of its kinetic energy. The model fits correctly for the multiple scattering region from four sources with a conventional multichannel analyser and its associated electronics.

M-TAG: A modular teaching-aid for Geant4

Geant4 is a versatile Monte Carlo radiation transport simulation toolkit with a steep learning curve. This work introduces a user-code called M-TAG (Modular Radiation Teaching-Aid for Geant4), built on top of Geant4. M-TAG is designed to help gradually introduce the Geant4 toolkit to new users.The goal of Geant4 is to record quantities from the simulated radiation as it is transported through geometries. M-TAG simplifies the inclusion of new geometric elements and detector components in the simulation by including new classes. M-TAG also provides basic validated examples for some common detector development tasks. Geant4 intercom modules, called messenger classes, manage these classes. To validate M-TAG, simulations were performed to calculate the range of positrons in water. One hundred million decays at the center of a water-filled sphere with a radius of 1 m were allowed for fluorine-18, carbon-11, oxygen-15 and gallium-68. These results were compared to literature values. An inexperienced Geant4 user was tasked with creating a simulation model for a plastic scintillator-based detector and conducting basic tests to assess the effectiveness of M-TAG as a teaching tool. The simulation involved calculating the dose to the detector's sensitive volume using a 2x2 cm planar monoenergetic photon source spanning energies from 20 to 100 keV. One billion particles were simulated twice: once with the actual detector geometry and once with the sensitive volume replaced by water. The validity of M-TAG was also verified by computing dose ratios and comparing them with mass-attenuation ratios obtained from NIST XCOM data sets.The mean positron travel distances were within the distribution of literature values. Simulated positron energy spectra means were within 1.8% of literature means. Simulated dose ratios agreed with literature values within uncertainties.We have developed and verified a modular Geant4 teaching aid called M-TAG. It was used to introduce a new user to Geant4, who used it to perform further validation simulations.

Air kerma rate from radionuclides distributed in forest ecosystem

This study evaluates the air kerma rate in radioactively contaminated forests. The air kerma rates created by plane sources of monoenergetic photons in the energy range 0.02–3 MeV located at different depths in soil up to 50 g cm−2 and at different heights in the forest medium from 0.05 to 50 m were calculated using numeric solution of the transport (Boltzmann) equation. To simplify the practical use of the results obtained by solving the Boltzmann equation, the study additionally includes approximation formulae for calculating air kerma rate separately from contaminated soil, crowns and trunks of trees in a forest ecosystem for 20 radionuclides - fission products that significantly contribute to the external dose. Biomaterial of trunks and crowns was modeled as uniformly distributed in corresponding layers and homogeneously mixed with air. Different distributions of radionuclides in soil were considered including plane source located at different depths, exponential and uniform distribution. Based on the results, the effect of forest biomass presence as an absorbing and scattering medium on the air kerma rate at 1 m above soil was evaluated. The estimated relative difference in air kerma rate at 1 m above soil in the forest medium and in free air for monoenergetic photon sources with energies 0.1 MeV, 0.66 MeV and 3 MeV did not correlate significantly with the energy of photons. Its maximum value in forest medium with biomass density of 5 kg m−3 was 15–20% for the source at soil depth ∼0.3 g cm−2, decreasing to less than 5% when it is at soil depth greater than 7 g cm−2. An example calculation of the air kerma rate dynamics is presented for the initial period after radioactive fallout considering weathering processes (rainfall and wind action) that contribute to the transfer of activity from the canopies to the forest floor. The differences in air kerma rate values, as an integral characteristic of the gamma radiation field from a radioactive cloud in the forest and in the open area, were evaluated.

Calculation and verification of multi-MeV photon scattering coefficient

It is necessary to estimate the scattering radiation contribution accurately and quickly in the radiation shielding calculation and design, and the photon scattering coefficient is a key parameter in this process. In real engineering applications, the radiation source is typically a multi-MeV photon beam, however, it can be challenging to determine precise parameters from the available literature. In this work, we used the Geant4 Monte Carlo code to simulate the scattering coefficients of monoenergetic photons with incident energies between 0.01 and 20 MeV at all angles of reflection with different scattering materials and thickness, and built a database, the Geant4 simulated results are in good agreement with the literature data. It then presents an algebraic approach and develops a MATLAB program to calculate multi-MeV photon scattering coefficient based on monoenergetic photon scattering coefficient simply by importing the photon spectrum. The results calculated using this approach basically coincide with Geant4 simulation, and agree well with the experimental results within the error range allowed. We can more accurately estimate the scattering radiation dose at the point of interest with the aid of a theoretical formula through this approach, thus significantly improve the computational efficiency in engineering radiation shielding calculation and design.

Construction of voxel-based Portunus haanii phantom and its absorbed fractions and specific absorbed fractions calculation based on Monte Carlo simulations

ObjectiveTo build the database of the absorbed fractions (AFs) and specific absorbed fractions (SAFs), in order to accurately assess the internal radiation dose in non-human biota. MethodsA voxel-based Portunus haanii phantom was established based on the computed tomography (CT) images. A set of AFs and SAFs were calculated with Monte Carlo toolkit Geant4 for the emission of monoenergetic photons and electrons with energies ranging from 10 ​keV to 5 ​MeV. ResultsThe mass of the voxel-based Portunus haanii phantom (392.2 ​g) was in agreement with the actual mass (389.2 ​g), indicating the reliability of the phantom. The calculated AFs and SAFs, based on the voxel-based Portunus haanii phantom, provided precise and reliable data for conducting internal radiation dose calculations specifically tailored to the Chinese Red Swimming Crab (Portunus haanii). The results indicated that the self-AFs and self-SAFs were affected by both the radiation energy and the mass of the source/target organ. Moreover, the AFs and SAFs for cross irradiation, were not only dependent on the energy and the mass of the target organ, but also on the relative position of the source and target organs. ConclusionThese results serve as a valuable resource for accurately evaluating the internal radiation exposure of this species.

Reproducibility study of Monte Carlo simulations for nanoparticle dose enhancement and biological modeling of cell survival curves

Nanoparticle-derived radiosensitization has been investigated by several groups using Monte Carlo simulations and biological modeling. In this work we replicated the physical simulation and biological modeling of previously published research for 50 nm gold nanoparticles irradiated with monoenergetic photons, various 250 kVp photon spectra, and spread-out Bragg peak (SOBP) protons. Monte Carlo simulations were performed using TOPAS and used condensed history Penelope low energy physics models for macroscopic dose deposition and interaction with the nanoparticle; simulation of the microscopic dose deposition from nanoparticle secondaries was performed using Geant4-DNA track structure physics. Biological modeling of survival fractions was performed using a local effect model-type approach for MDA-MB-231 breast cancer cells. Physical simulation results agreed extraordinarily well at all distances (1 nm to 10 μm from nanoparticle) for monoenergetic photons and SOBP protons in terms of dose per interaction, dose kernel ratio (often labeled dose enhancement factor), and secondary electron spectra. For 250 kVp photons the influence of the gold K-edge was investigated and found to appreciably affect the results. Calculated survival fractions similarly agreed well within one order of magnitude at macroscopic doses (i.e. without nanoparticle contribution) from 1 Gy to 10 Gy. Several 250 kVp spectra were tested to find one yielding closest agreement with previous results. This highlights the importance of a detailed description of the low energy (< 150 keV) component of photon spectra used for in-silico, as well as in-vitro, and in-vivo studies to ensure reproducibility of the experiments by the scientific community. Both, Monte Carlo simulations of physical interactions of the nanoparticle with photons and protons, as well as the biological modelling of cell survival curves agreed extraordinarily well with previously published data. Further investigation of the stochastic nature of nanoparticle radiosenstiziation is ongoing.

Axionlike particle production at beam dump experiments with distinct nuclear excitation lines

Searches for axion-like particles (ALPs) are motivated by the strong CP problem in particle physics and by unexplained dark matter in astrophysics. In this letter, we discuss novel ALP searches using monoenergetic nuclear de-excitation photons from a beam dump, using IsoDAR as an example. We show that IsoDAR can set limits that close a gap in traditional QCD axion searches using the ALP-photon coupling, as well as provide sensitivity to large regions of new parameter space in models where ALPs couple to nucleons and electrons. We also show how isotope decay-at-rest experiments may be designed to improve potential ALP production and optimize detection sensitivity.

Skeletal dosimetry in a microCT image-based rat model for external photon irradiation

Human skeletal dosimetry has experienced great developments in radiation protection in recent years by using the heterogeneous skeletal model. While for the rats experimentally used in radiation medicine, the investigation on skeletal dosimetry were mainly based on the homogeneous skeletal model, leading to inaccurate assessments of dose to radiosensitive tissues of red bone marrow (RBM) and bone surface. The purpose of this study is to develop a rat model with heterogeneous skeletal system and to investigate the dose difference in bone tissues for external photon irradiation. The high resolution of microCT images of a rat weighing 335g were segmented into bone cortical, bone trabecular, bone marrow as well as other organs to construct the rat model. The absorbed dose to bone cortical, bone trabecular and bone marrow were calculated respectively by using Monte Carlo simulation for 22 external monoenergetic photon beams between 10keV and 10MeV under four different irradiation geometries conditions (left lateral [LL], right lateral [RL], dorsal-ventral [DV], ventral-dorsal [VD]). The calculated absorbed dose data were expressed as dose conversion coefficients and presented in this article, and the effect of irradiation conditions, photon energies and bone tissues density on the skeletal dose was discussed. The results showed that the dose conversion coefficients varying the photon energy for bone cortical, bone trabecular and bone marrow exhibit different trends and have the same sensitivity to irradiation conditions. The dose difference in bone tissues indicated that bone cortical and bone trabecular have significant attenuation effect on the energy deposition in bone marrow and bone surface for photon energies below 0.2MeV. The set of dose conversion coefficients in this work can be used to determine the absorbed dose to skeletal system for external photon irradiation and to supplement the rat skeletal dosimetry.

Intra-brain vascular models within the ICRP mesh-type adult reference phantoms for applications to internal dosimetry

Objective. Phantoms of the International Commission on Radiological Protection provide a framework for standardized dosimetry. The modeling of internal blood vessels—essential to tracking circulating blood cells exposed during external beam radiotherapy and to account for radiopharmaceutical decays while still in blood circulation—is, however, limited to the major inter-organ arteries and veins. Intra-organ blood is accounted for only through the assignment of a homogeneous mixture of parenchyma and blood [single-region (SR) organs]. Our goal was to develop explicit dual-region (DR) models of intra-organ blood vasculature of the adult male brain (AMB) and adult female brain (AFB). Approach. A total of 4000 vessels were created amongst 26 vascular trees. The AMB and AFB models were then tetrahedralized for coupling to the PHITS radiation transport code. Absorbed fractions were computed for monoenergetic alpha particles, electrons, positrons, and photons for both decay sites within the blood vessels and for tissues outside these vessels. Radionuclide S-values were computed for 22 and 10 radionuclides commonly employed in radiopharmaceutical therapy and nuclear medicine diagnostic imaging, respectively. Main results. For radionuclide decays, values of S(brain tissue ← brain blood) assessed in the traditional manner (SR) were higher than those computed using our DR models by factors of 1.92, 1.49, and 1.57 for therapeutic alpha-emitters, beta-emitters, and Auger electron-emitters, respectively in the AFB and by factors of 1.65, 1.37, and 1.42 for these same radionuclide categories in the AMB. Corresponding ratios of SR and DR values of S(brain tissue ← brain blood) were 1.34 (AFB) and 1.26 (AMB) for four SPECT radionuclides, and were 1.32 (AFB) and 1.24 (AMB) for six common PET radionuclides. Significance. The methodology employed in this study can be explored in other organs of the body for proper accounting of blood self-dose for that fraction of the radiopharmaceutical still in general circulation.