Photon Dose Rate Research Articles

Development of an online neutron beam monitoring system for accelerator-based boron neutron capture therapy in a hospital.

Boron neutron capture therapy (BNCT) is a next-generation radiotherapy, utilizing both an external neutron beam and a -containing pharmaceutical. A compact accelerator for a high intensity neutron source was installed to conduct BNCT in a hospital. The dose administered to a patient was evaluated by measuring the proton beamcurrent. Neutron intensity should be monitored in real-time by measuring the neutrons emitted from the target during BNCT irradiation. This is crucial due to potential neutron target degradation. Online neutron beam monitoring systems are required for reliable measurements of the administered neutron dose. An online neutron beam monitoring system was developed to monitor neutron intensity irradiating on the patient at the National Cancer Center Hospital (NCCH). The neutron detector comprised a back-illuminated thin Si diode of 40- thickness and an ultrathin natural LiF neutron converter of 0.05- thickness. The neutron detector was installed on the neutron target unit, regardless of whether a patient was present, without any additional modifications to the setup. The response functions for high photon dose rates of upto 100 Gy/h were measured. The pulse heights were measured using the neutron beam monitor during BNCT neutron irradiation. Neutron temporal response measured using the online beam monitor was acquired and compared with the proton beam current and the measurements at a patient position. From this measurement at the patient position, the neutron fluence rate irradiating on a patient wasobtained. The neutron events were separated from the photon events. The neutron counting rates increased rapidly with the starting of proton beam irradiation and dropped to zero upon its termination. During intermittent drops and recoveries in the proton beam, the neutron beam monitor for counting rates responded quickly, synchronizing with the beam current. A scatter plot of the neutron counting rate and proton beam current indicated a good linear correlation. A direct relationship between the online neutron beam monitor's neutron counting rates and those of the patient neutron detector showed a good correlation coefficient of 0.84. A ratio of the both neutron counting rates showed a standard deviation of 6%. The correlation coefficient and standard deviation were improved to 0.94 and 1.5%, by re-binning the neutron temporal response with longer acquisition period than 1 s. Using the online neutron beam monitor, the neutron fluence rate was obtained from the direct relationship within 1.5%. Therefore, real-time monitoring of neutron intensity was achieved within the acceptable level as per the International Commission on Radiation Units and Measurementsreport. The online neutron beam monitoring system was developed to monitor the BNCT neutron beam intensity at NCCH. The temporal response of the neutron beam monitor was synchronized with the neutron counting rate at the patient position. Using the online neutron beam monitor, the neutron fluence rate irradiating on the patient can be monitored from the direct relationship. Fluctuation of the neutron beam intensity through BNCT irradiation and the degradation of the lithium target through the lifespan of the neutron target could be monitored using the neutron beammonitor.

Impact of environmental conditions on organic matter in astrophysical ice analogues

ABSTRACT The existence of organic matter presenting a high molecular diversity in extraterrestrial environments is well documented. To understand the origin of this organic diversity, laboratory experiments were developed and showed that irradiation and thermal alteration of simple molecules such as methanol, water, and ammonia in conditions mimicking astrophysical ice environments. Ices containing water, methanol, and ammonia (H2O: MeOH: NH3) photolyzed and monitored by infrared spectroscopy, while the organic matter formed at room temperature was analyzed in situ with infrared spectroscopy and ex situ with high-resolution mass spectrometry. Those ices irradiated at 77 K and 10−8 mbar shows a significant organic molecular diversity: residual organic compounds contain up to 78 C, 188 H, 123 N, and 37 O. Most of them contains all four CHNO atoms (76–86 per cent), followed by CHO (11–17 per cent), and CHN compounds (5–6 per cent). CHNO and CHO compounds are more aliphatic (34–53 per cent), while CHN compounds are mostly condensed aromatics (83–90 per cent). In this work, our objective is to investigate impacts of environment on this organic molecular diversity by focusing on three parameters: photon dose, pressure, and heating rate during the warming process. Analyses of the residue formed showed that the heating rate and pressure weakly alter the abundance of the final organic material, while the irradiation rate reduced its abundance at high photon doses by a factor of 8. These results give insights on the impact of icy environment conditions in the evolution of astrophysical organic matter.

A calibration method for a wireless real-time CMOS pixel medical dosimeter

This study introduces and validates a novel calibration function for wireless wearable dosimeters, crucial for real-time dosimetry in interventional radiology. Focusing on enhancing accuracy and safety, it compares data from threshold-based wireless dosimeters with a full-data-read detector. The research involves a central detector and four lateral wireless dosimeters, each equipped with an identically-typed CMOS Image Sensor (CIS), subjected to various photon dose rates and doses from a certified beam. Two key calibration functions were developed: one that correlates the pixel count over a threshold with the dose rate, and the other that links the cumulative pixel value above the threshold to the total absorbed dose. These functions are essential in converting raw CIS data into precise dosimetric information.The study findings reveal that the single-pixel sensitivity of wireless prototypes is approximately 8.5 ± 0.8 ADC/nGy. Following the application of calibration functions, the responses of these prototypes align consistently with the TLD dosimeter measurements. In particular, for three of the prototypes, this calibration ensures that the measurement uncertainty remains within 6% for the dose rate and within 8% for the dose.This research confirms the effectiveness and feasibility of pixel-based wireless dosimeters in interventional radiology, highlighting the importance of integrating offline data processing for enhanced measurement precision.

Investigation of the beam quality and dose rate dependence of PAKAG polymer gel dosimeter in optical readout technique

This study aims to evaluate the optical response dependence of the PAKAG polymer gel dosimeter on photon energy and dose rate. The produced gel dosimeters were irradiated using a Varian CL 21EX medical linear accelerator with delivered doses of 0, 2, 4, 6, 8, and 10 Gy. To examine the response dependence on the delivered dose rate, dose rates of 50, 100, 200, and 350 cGy min−1 were investigated. Additionally, two incident beam qualities of 6 and 18 MV were examined to study the response dependence on the incident beam energy. The irradiated polymer gel dosimeters were readout using a UV–vis spectrophotometer in the 300 to 800 nm scan range. The results reveal that a wide variation in dose rate (50–350 cGy.min−1) influences the absorbance-dose response and the sensitivity of PAKAG gel. However, smaller variations did not show a significant effect on the response. Furthermore, the response changed insignificantly with beam quality for investigated energies. It was concluded that the optical reading response of the PAKAG polymer gel dosimeter is satisfactorily independent of external parameters, including dose rate and incident beam quality.

Behavior of silver tellurite glasses against gamma rays, neutrons, and ions using theoretical and the PHITS Monte Carlo method

Present work analyze the ionizing radiations attenuation behaviour, photon trajectories and dose rate reduction properties of silver tellurite glasses to investigate their potential application in radiation shielding. The shielding capability of five glass systems with different elemental compositions have been calculated with the help of theoretical software: Phy-X/PSD and NIST XCOM. For the photon energy range of 1.00 keV to 100.00 GeV, various shielding parameters are calculated, including attenuation coefficients (MAC, LAC), mean free path, half value layer, tenth value layer, effective atomic number, effective electron density, energy build up factors, energy absorption buildup factors, and fast neutron removal cross section. While the energy stopping potentials, projected range of ions (H+, He+, and C+) has been presented with the help of SRIM software. Additionally photon trajectories and dose rate attenuating behavior of 105 photons generated from 137Cs and 60Co sources with activity 200.00 GBq has been studied with the help of particle and heavy ion transport (PHITS) code. It is observed that at both low and high energy levels, the glass composition, labelled S4, (70TeO2-25Ag2O-2Nb2O5-2BaO-1PbO), exhibits comparable attenuation coefficients to previously recommended glass samples for radiation shielding applications. In addition to S4, nine different types of glass samples and polymers with comparable densities to our glass sample, along with water, were included for comparison. The findings indicate that among all the samples tested, S4 demonstrates the highest and comparable radiation-protective performance, positioning it favourably for such applications.

Effect of fibers and boron carbide on the radiation shielding properties of limestone and magnetite aggregate concrete

Research on new composite materials in the field of radiation shielding materials requires adequate means and meticulousness in their manufacture and characterization. In this study, concretes that use elements that theoretically improve their shielding properties are developed, such as fibers and boron-rich additions. Both magnetite and limestone concrete have been manufactured, incorporating steel fibers to improve the linear attenuation coefficient and polyvinyl alcohol to increase neutron scattering cross section. The incorporation of boron carbide is intended to increase the neutron absorption cross section. 5 mixes have been manufactured that have been tested with several gamma radiation sources (570–1280 keV) and with an Am–Be neutron source (111 GBq). The experimental results have been used to validate simulations carried out with MAVRIC® and have led to the modelling of a simplified spent nuclear fuel cask. Boron carbide produces a decrease of more than 50% on the neutron dose rate in contact with the cask. Incorporating PVA fibers supposes gain in neutron attenuation capacity of up to 13%, while fibers have a negligible effect on the photon dose rate.

Dosimetric parameters calculation for 18 MV photon beam in flattening filter (FF) and flattening filter free (FFF) linear accelerators with and without magnetic deflector and lead filter

Dosimetric characteristics of the flattening filter (FF) and flattening filter free (FFF) modes of 18 MV therapeutic photon beam were investigated with and without the magnetic deflector (MD) and lead filter. MCNP version 6.1.0 Monte Carlo (MC) code was used to simulate the 18 MV photon beam of 2100 C/D-Varian linear accelerator (LINAC) for the FF and FFF modes. The MD (uniform magnetic flux density of 1 Tesla) and lead filter (thickness of 1 mm) were modeled to remove contaminant electrons. The dosimetric parameters for different scenarios of LINAC’s head were calculated. Removing the flattening filter in the FFF mode increased the dose rate, electron contamination, skin dose, out-of-field dose, and un-flatness compared to the FF mode. While the lead filter decreased the contaminant electrons significantly, using the MD removed all secondary electrons from the beam line. The surface dose was decreased by 8.3% and 11.2% for the magnetic deflector (MD) and lead filter in the FF mode, respectively. The surface dose was decreased by 16.8% and 20.3% for the MD and lead filter scenarios in the FFF mode, respectively. The MD and lead filter decreased surface penumbra by 15.5% and 11.5% compared to the FFF mode. Removing the flattening filter from the LINAC’s head improves most of the dosimetric characteristics of the 18MV therapeutic beam. The use of a lead filter and magnetic deflector preserves the skin-sparing property of megavoltage beams that deteriorate in FFF mode. However, using a magnetic deflector does not reduce photon fluence and dose rate.

Peripheral blood lymphocytes differ in DNA damage response after exposure to X-rays with different physical properties

Introduction: In radiology, low X-ray energies (<140 keV) are used to obtain an optimal image while in radiotherapy, higher X-ray energies (MeV) are used to eradicate tumor tissue. In radiation research, both these X-ray energies being used to extrapolate in vitro research to clinical practice. However, the energy deposition of X-rays depends on their energy spectrum, which might lead to changes in biological response. Therefore, this study compared the DNA damage response (DDR) in peripheral blood lymphocytes (PBLs) exposed to X-rays with varying beam quality, mean photon energy (MPE) and dose rate. Methods: The DDR was evaluated in peripheral blood lymphocytes (PBLs) by the ɣ-H2AX foci assay, the cytokinesis-block micronucleus assay and an SYTOX-based cell death assay, combined with specific cell death inhibitors. Cell cultures were irradiated with a 220 kV X-ray research cabinet (SARRP, X-Strahl) or a 6 MV X-ray linear accelerator (Elekta Synergy). Three main physical parameters were investigated: beam quality (V), MPE (eV) and dose rate (Gy/min). Additional copper (Cu) filtration caused variation in the MPE (78 keV, 94 keV, 118 keV) at SARRP; dose rates were varied by adjusting tube current for 220 kV X-rays (0.33–3 Gy/min) or water-phantom depth in the 6 MV set-up (3–6 Gy/min). Results: The induction of chromosomal damage and initial (30 min) DNA double-stranded breaks (DSBs) were significantly higher for 220 kV X-rays compared to 6 MV X-rays, while cell death induction was similar. Specific cell death inhibitors for apoptosis, necroptosis and ferroptosis were not capable of blocking cell death after irradiation using low or high-energy X-rays. Additional Cu filtration increased the MPE, which significantly decreased the amount of chromosomal damage and DSBs. Within the tested ranges no specific effects of dose rate variation were observed. Conclusion: The DDR in PBLs is influenced by the beam quality and MPE. This study reinforces the need for consideration and inclusion of all physical parameters in radiation-related studies.

Response investigation of a new polymer gel dosimeter based on ammonium salt through MRI technique

Increasing the use of polymer gel dosimetry (PGD) in radiotherapy requires reducing its toxicity. The toxicity of the PGD components causes risks for the users as well as the environment. The aim of this study is to produce a new PGD called PAGBIT (Polymer, Amps ammonium salt, Gelatin, BIs, Thpc) based on the nontoxic monomer of 2-acrylamido-2-methylpropanesulfonic acid ammonium salt. Furthermore, this monomer is ecofriendly. The PAGBIT PGD was prepared in the laboratory in ambient conditions. PGDs were irradiated using a clinical accelerator with a dose range of 0–10 Gy. The incident photon energy and dose rate were 6-MV and 300 cGy/min, respectively. The irradiated PGDs were imaged using a 1.5T MRI scanner 9 times in a time range of 12–720 h post-irradiation. The maximum obtained sensitivity was 0.115 ± 0.005 Gy−1s−1 at 36 h post-irradiation time. The average sensitivity change as a function of post-irradiation time was 0.0017 Gy−1s−1h−1. However, the average sensitivity change as a function of scanning temperature was 0.0006 Gy−1s−1°C−1. Results showed that the differences of effective atomic number and electron density between PAGBIT and soft tissue were 2.3% and 0.3%, respectively. It was concluded that the PAGBIT is a low toxic, water equivalent PGD with noticeable temporal and temperature stabilities.

Dosimetric properties of PASSAG polymer gel dosimeter in electron beam radiotherapy using magnetic resonance imaging.

Several physical factors such as photon beam energy, electron beam energy, and dose rate may affect the dosimetric properties of polymer gel dosimeters. The photon beam energy and dose rate dependence of PASSAG gel dosimeter were previously evaluated. This study aims to assess the dosimetric properties of the optimized PASSAG gel samples in various electron beam energies. The optimized PASSAG gel samples are first fabricated and irradiated to various electron energies (5, 7, 10 and 12 MeV). Then, the response (R2) and sensitivity of gel samples are analyzed by magnetic resonance imaging technique at a dose range of 0 to 10 Gy, scanning room temperature range of 15 to 22 °C, and post-irradiation time range of 1 to 30 days. The R2-dose response and sensitivity of gel samples do not change under the evaluated electron beam energies (the differences are less than 5%). Furthermore, a dose resolution range of 11 to 38 cGy is obtained for the gel samples irradiated to different electron beam energies. Moreover, the findings show that the R2-dose response and sensitivity dependence of gel samples on electron beam energy varies over different scanning room temperatures and post-irradiation times. The dosimetric assessment of the optimized PASSAG gel samples provides the promising data for this dosimeter during electron beam radiotherapy.

Photon dose rate distribution inside and outside a brachytherapy room.

In a brachytherapy room irradiated with an Iridium-192 (192Ir) source, the spatial distributions of photon dose rates were measured and calculated for the dose distribution both inside and outside the room. The spatial distributions were measured using a thermoluminescent dosimeter (LiF-100) on the surfaces of the concrete walls and barriers of the irradiation room. The calculations were performed using the particle and heavy ion transport code system (PHITS) by considering the detailed model of the brachytherapy room and the radiation source used in the measurements. The measured and calculated doses exhibited a similar distribution pattern within and outside the brachytherapy room. To reduce the edge effect at the entrance door, the addition of a 3-mm thick lead layer on the surface of the concrete wall on the left doorstop is recommended. For the 60Co source, with the existing walls and lead door thickness, the dose at the control console and in front of the entrance maze increased by a factor of approximately 60.

FLASH Radiotherapy for the Treatment of Symptomatic Bone Metastases (FAST-01): Protocol for the First Prospective Feasibility Study.

In preclinical studies, FLASH therapy, in which radiation delivered at ultrahigh dose rates of ≥40 Gy per second, has been shown to cause less injury to normal tissues than radiotherapy delivered at conventional dose rates. This paper describes the protocol for the first-in-human clinical investigation of proton FLASH therapy. FAST-01 is a prospective, single-center trial designed to assess the workflow feasibility, toxicity, and efficacy of FLASH therapy for the treatment of painful bone metastases in the extremities. Following informed consent, 10 subjects aged ≥18 years with up to 3 painful bone metastases in the extremities (excluding the feet, hands, and wrists) will be enrolled. A treatment field selected from a predefined library of plans with fixed field sizes (from 7.5 cm × 7.5 cm up to 7.5 cm × 20 cm) will be used for treatment. Subjects will receive 8 Gy of radiation in a single fraction-a well-established palliative regimen evaluated in prior investigations using conventional dose rate photon radiotherapy. A FLASH-enabled Varian ProBeam proton therapy unit will be used to deliver treatment to the target volume at a dose rate of ≥40 Gy per second, using the plateau (transmission) portion of the proton beam. After treatment, subjects will be assessed for pain response as well as any adverse effects of FLASH radiation. The primary end points include assessing the workflow feasibility and toxicity of FLASH treatment. The secondary end point is pain response at the treated site(s), as measured by patient-reported pain scores, the use of pain medication, and any flare in bone pain after treatment. The results will be compared to those reported historically for conventional dose rate photon radiotherapy, using the same radiation dose and fractionation. FAST-01 opened to enrollment on November 3, 2020. Initial results are expected to be published in 2022. The results of this investigation will contribute to further developing and optimizing the FLASH-enabled ProBeam proton therapy system workflow. The pain response and toxicity data acquired in our study will provide a greater understanding of FLASH treatment effects on tumor responses and normal tissue toxicities, and they will inform future FLASH trial designs. : ClinicalTrials.gov NCT04592887; http://clinicaltrials.gov/ct2/show/NCT04592887. DERR1-10.2196/41812.

An investigation into the dose rate and photon energy dependence of the GENA gel dosimeter in the MeV range

PurposeIn the current study, the energy and dose rate dependence of a new genipin-based gel dosimeter, named GENA gel dosimeter, were investigated. MethodsPrepared gel dosimeters exposed using a Varian clinical linac. Beam qualities of 6 and 18 MV were applied to investigate the GENA gel dosimeter’s energy dependence. Furthermore, the gel dosimeters were exposed to 50, 100, 200, and 350 cGy/min dose rates, ranging from 0 to 8 Gy. The irradiated gel dosimeters were read out using a double beam UV–Visible spectrophotometer. The absorbance peak (AP) and area under spectrum (AUS) were evaluated. ResultsAbsorbance-dose sensitivities of (8.0 ± 0.18) × 10–3 cm–1Gy−1 and (7.8 ± 0.15) × 10–3 cm−1Gy−1 were obtained for GENA gel dosimeter for 6 and 18 MV beam qualities, respectively. Results specified no significant difference (p > 0.05) between the GENA gel dosimeter’s sensitivities irradiated using the two energies mentioned above. For the mentioned dose rates, AP-dose sensitivities of (8.2 ± 0.22) × 10−3, (8.1 ± 0.21) × 10−3, (8.1 ± 0.2) × 10−3 and (8.0 ± 0.18) × 10−3 cm−1Gy−1 were obtained, respectively. Results showed no significant difference (p > 0.05) between the GENA gel dosimeter’s sensitivities for the investigated dose rates and energies. In addition, results revealed that when the incident photon energy and dose rate changed, there were no significant differences (p > 0.05) between the GENA gel dosimeter’s dose resolution values. ConclusionsIt is concluded that the response of the GENA gel dosimeter is not dependent on the energy and dose rate (p > 0.05) within the studied energy and dose rate ranges.

Exploring the Physical and Biological Aspects of BNCT with a Carboranylmethylbenzo[b]acridone Compound in U87 Glioblastoma Cells.

Boron neutron capture therapy (BNCT) is a re-emerging technique for selectively killing tumor cells. Briefly, the mechanism can be described as follows: after the uptake of boron into cells, the thermal neutrons trigger the fission of the boron atoms, releasing the α-particles and recoiling lithium particles and high-energy photons that damage the cells. We performed a detailed study of the reactor dosimetry, cellular dose assessment, and radiobiological effects induced by BNCT in glioblastoma (GBM) cells. At maximum reactor power, neutron fluence rates were ϕ0 = 6.6 × 107 cm−2 s−1 (thermal) and θ = 2.4 × 104 cm−2 s−1 with a photon dose rate of 150 mGy·h−1. These values agreed with simulations to within 85% (thermal neutrons), 78% (epithermal neutrons), and 95% (photons), thereby validating the MCNPX model. The GEANT4 simulations, based on a realistic cell model and measured boron concentrations, showed that >95% of the dose in cells was due to the BNC reaction. Carboranylmethylbenzo[b]acridone (CMBA) is among the different proposed boron delivery agents that has shown promising properties due to its lower toxicity and important cellular uptake in U87 glioblastoma cells. In particular, the results obtained for CBMA reinforce radiobiological effects demonstrating that damage is mostly induced by the incorporated boron with negligible contribution from the culture medium and adjacent cells, evidencing extranuclear cell radiosensitivity.

FAST-01: Results of the First-in-Human Study of Proton FLASH Radiotherapy

<h3>Purpose/Objective(s)</h3> FLASH radiotherapy (RT) is delivered at ultra-high dose rates (>40 Gy/s), with preclinical animal data suggesting less toxicity to normal tissues. FAST-01 was a prospective, first-in-human study that evaluated the feasibility of a clinical workflow for proton FLASH RT in the treatment of painful extremity bone metastases. The treatment workflow was hypothesized to be feasible. In addition, this study intended to generate preliminary results regarding the safety and efficacy of this FLASH treatment. <h3>Materials/Methods</h3> FAST-01 was a single institution study under an FDA investigational device exemption (IDE) approved for 10 patients with >2 month life expectancy and 1-3 painful bone metastases in the extremities. Exclusion criteria included patients with fractures or prior RT in the treatment site(s), or lesions of the feet, hands, or wrists. Treatment was 8 Gy (RBE = 1.0) in a single fraction delivered at ≥40 Gy/s via a FLASH-enabled proton therapy system employing a single transmission proton beam. Primary study endpoints were workflow feasibility (time on the treatment table and FLASH-related treatment delays) and toxicity, and secondary endpoint was efficacy (validated pain questionnaires). Pain flare questionnaires were completed for 10 consecutive days post-RT. Pain response at each treatment site was evaluated at 3 months post-RT using the methodology of RTOG 9714. Pain, pain medication use, and adverse events (AEs) were evaluated on the day of treatment and at 15 days, 1, 2, and 3 months post-RT, and every 2 months thereafter. AEs were graded using CTCAE v5. Safety analysis included all events that were physician-attributed to be at least "possibly related" to FLASH. Photos of skin in the treatment site areas supported AE evaluations. <h3>Results</h3> Ten subjects aged 27-81 years received FLASH RT to 12 metastatic sites. No FLASH-related technical issues or delays occurred. Average time on the treatment table was 15.8 min per treated site (range 11-33 min). Follow-up ranged from 2.3-13 months (median 4.8 months). Transient pain flares occurred in 4 of 12 treated sites. Complete or partial pain relief following FLASH radiotherapy was seen in 8 of 12 sites (7 of the 10 subjects) for an overall response rate of 66.7%. Complete pain responses were 50% (6/12 sites), and partial responses were 17% (2/12 sites). AEs were mild: skin hyperpigmentation (G1, n=4), skin discoloration (G1, n=1), limb edema (G1, n=2), pruritis (G1, n=2), fatigue (G1, n=1), erythema (G1, n=1), and extremity pain (G2, n=1). <h3>Conclusion</h3> This first-in-human trial establishes the feasibility of FLASH proton radiotherapy. The treatment efficacy and the profile of AEs were favorable and were comparable to the published literature for conventional dose rate photon RT. AE and pain data collection continues for the evaluation of long-term results. These findings support the further exploration of FLASH radiation treatments for other clinical indications.

Monte Carlo optimization of a GRID collimator for preclinical megavoltage ultra-high dose rate spatially-fractionated radiation therapy

Objective. A 2-dimensional pre-clinical SFRT (GRID) collimator was designed for use on the ultra-high dose rate (UHDR) 10 MV ARIEL beamline at TRIUMF. TOPAS Monte Carlo simulations were used to determine optimal collimator geometry with respect to various dosimetric quantities. Approach. The GRID-averaged peak-to-valley dose ratio (PVDR) and mean dose rate of the peaks were investigated with the intent of maximizing both values in a given design. The effects of collimator thickness, focus position, septal width, and hole width on these metrics were found by testing a range of values for each parameter on a cylindrical GRID collimator. For each tested collimator geometry, photon beams with energies of 10, 5, and 1 MV were transported through the collimator and dose rates were calculated at various depths in a water phantom located 1.0 cm from the collimator exit. Main results. In our optimization, hole width proved to be the only collimator parameter which increased both PVDR and peak dose rates. From the optimization results, it was determined that our optimized design would be one which achieves the maximum dose rate for a PVDR at 10 MV. Ultimately, this was achieved using a collimator with a thickness of 75 mm, 0.8 mm septal and hole widths, and a focus position matched to the beam divergence. This optimized collimator maintained the PVDR of 5 in the phantom between water depths of 0–10 cm at 10 MV and had a mean peak dose rate of at 0–1 cm depth. Significance. We have investigated the impact of various GRID-collimator design parameters on the dose rate and spatial fractionation of 10, 5, and 1 MV photon beams. The optimized collimator design for the 10 MV ultra-high dose rate photon beam could become a useful tool for radiobiology studies synergizing the effects of ultra-high dose rate (FLASH) delivery and spatial fractionation.

A Discussion on Associating THz Safety with 5G Safety

A project on the development of midinfrared free‐electron laser and terahertz (THz) radiation produced by a home‐constructed electron accelerator has recently been launched in the laboratory. A study of THz technology and its applications for biology is one of the emphases and thus THz safety is in focus. This is not only due to the THz radiation itself, but also its association with 5G safety, which has recently become a topic of public concern worldwide. If THz radiation is demonstrated safe, 5G, with the same power, should be safe due to its lower photon energy. The safety issues of both radiations are discussed with different opinions. Herein, safety from physics is discussed and it is pointed out that radiation safety not only depends on photon energy but also radiation power, or the photon dose rate. Through quantitative discussion of the currently used 5G transmission station power, this study confirms that 5G is safe, while THz safety is not yet certain. Therefore, measurement of THz power, a test of THz radiation effect on DNA change, an investigation of the DNA vibration using the THz time‐domain spectroscopy, and molecular dynamics simulation of THz radiation of DNA are suggested.

The design and optimization of a radiation shield for the Tehran Research Reactor's neutron diffraction facility

In this paper, a novel optimal radiation shield for the Tehran research reactor's neutron powder diffraction facility was designed to reduce undesirable neutron and gamma dose rates. A layer-by-layer methodology was considered based on the design approach to achieve a dose rate of less than 30 μSv/hr. MCNPX was used for this purpose as a Monte Carlo radiation transport code. A combination of neutron and gamma absorbers and moderators was employed to create this shield. The results indicated that the shield's six distinct layers met the design objective, totaling 65 cm in thickness. This newly designed shield comprises 15 cm paraffin, 15 cm Portland iron concrete, another 15 cm paraffin, 5 cm solid boric acid, another 10 cm Portland iron concrete, and 10 cm lead. The neutron and photon dose rates are 9.35 and 12.81 μSv/hr, respectively, which is one-sixteenth and one-third of the current facility shield. Validation of the simulation was accomplished by comparing the results for the current shield to experimental data.

Nuclear shielding characteristics of Sm3+ doped borosilicate glasses containing Na2O, PbO and ZnO

The aim of this paper is to investigate the photon, charged particles, fast and thermal neutrons absorption characteristics and dose rates of Sm3+ doped borosilicate glasses containing Na2O–PbO–ZnO via theoretical method and simulation code. The linear attenuation coefficients of SBNPZS4 glasses are the highest whereas the mass attenuation coefficients of SBNPZS1 glasses are the highest in the present SBNPZS glasses. The SBNPZS4 has the lowest half value layer and mean free path values among the SBNPZS glasses and compared standard shielding materials therefore SBNPZS4 has the better photon absorption characteristics. The effective atomic number, effective electron density, mass energy-absorption coefficient, specific gamma ray constant, and gamma dose rate values change as SBNPZS4<SBNPZS3<SBNPZS2<SBNPZS1. The ranges of SBNPZS glasses for charged particles modify as SBNPZS4<SBNPZS3<SBNPZS2<SBNPZS1. Both fast neutron removal cross section and total cross section for thermal neutron vary in order of SBNPZS1<SBNPZS2<SBNPZS3<SBNPZS4 hence SBNPZS4 owns the highest fast and thermal neutron absorption characteristics. Consequently, SBNPZS glasses can be suggested and developed as photons, neutrons and charged particles shielding materials.

Investigation of CLYC-6 for thermal neutron detection and CLYC-7 for fast neutron spectrometry

Highly enriched 6Li and 7Li Cs2LiYCl 6 (CLYC) scintillators were investigated in view of their application as thermal neutron counter (CLYC-6) and as fast neutron spectrometer (CLYC-7) in the recently developed B-RAD radiation survey metre, an instrument designed to work in regions of high magnetic fields, currently equipped with a probe for photon dose rate measurements and γ-spectrometry. Both crystals were irradiated with a 2.5 MeV mono-energetic neutron beam from a Deuterium–Deuterium (D–D) generator and characterised in terms of neutron/γ-ray (n/γ) discrimination capability by the Pulse Shape Discrimination (PSD) method, energy resolution and quenching factor. Both crystals exhibit an excellent n/γ discrimination, quantified by a Figure of Merit higher than 2. The measured thermal energy resolution of CLYC-6 is 6%. The quenching factor for the 6Li(n,t)α thermal neutron reaction is 0.65 and for the 35Cl(n,p)35S reaction is 0.91. The measured neutron detection efficiency per unit volume of CLYC-6 is 60% higher than that of a 3He proportional counter. CLYC-7 was tested as a fast neutron spectrometer below 10 MeV, when irradiated with continuum neutron spectra from Am–Be and 252Cf sources. A proton/α-particle (p/α) discrimination was performed exploiting the PSD technique, without any unfolding procedure. The resulting spectra match the corresponding ISO spectra better than the spectra without the p/α discrimination, especially in the range 3 MeV to 5 MeV. A more sensitive PSD algorithm might help to improve particle discrimination at lower energies, while different reaction channels arise at higher energies preventing a spectrometry analysis.