Response Dose Research Articles

Ultraviolet–near infrared luminescence characteristics of Nd:La2Be2O5 single crystals for near-infrared emitting scintillators

The fabrication of 0.1, 0.5, 1.0, and 5.0 % Nd:La2Be2O5 single crystals was carried out by the floating zone method, and photoluminescence (PL) and scintillation properties were measured. The PL spectra showed some emission lines which was derived from the 4f-4f transitions of Nd3+ ions. The scintillation spectra showed a broad emission band originating from some lattice defect and the emission lines due to the 4f–4f transitions of Nd3+ ions. The afterglow levels of Nd:La2Be2O5 were 192.3 (0.1 % Nd), 205.9 (0.5 % Nd), 228.2 (1.0 % Nd), and 315.4 (5.0 % Nd) ppm. The 1.0 % Nd:La2Be2O5 showed the highest intensity in the dose-rate response functions among the samples, and a lower detection limit was 0.003 Gy/h.

Assessing dose rate effects in TL and OSL dosimeters: A critical look into dose rate models

This work investigates theoretically possible dose rate effects in thermoluminescence (TL) and optically stimulated luminescence (OSL) materials by solving the rate equations for the stimulated luminescence process. Starting with the solution of the One-Trap–One-Recombination-Center (OTOR) model with parameters from the literature, we first showed that this model, with the chosen parameters, does not reproduce real luminescent material properties (e.g., TL curve and dose response). We then studied the physical phenomena responsible for dose rate effects in this model, and the influence of the model parameters on the dose rate response. As a result, we found that charge accumulation in the delocalized bands over unrealistic long periods (> hundreds of seconds) is responsible for dose rate effects. Such effect is caused by the particular choice of model parameters. When model parameters based on physical considerations and experimental results are chosen, no dose rate effects are observed. This work provides a deeper understanding of the luminescence process, by identifying the mechanisms that could be responsible for dose rate effects, and a theoretical foundation to the use of luminescent detectors for ultra-high dose rate dosimetry.

Near‐infrared scintillation properties of Nd-doped BaO-Bi2O3-P2O5 glasses

We synthesized BaO-Bi2O3-P2O5 glass samples with different Nd concentrations by the melt-quenching technique. The concentrations were 1.0, 5.0, 10, 15, and 20 %. We obtained transparent and homogeneous samples for 1.0–10 % Nd concentrations. The 15 % Nd-doped sample was inhomogeneous, and the 20 % Nd-doped sample contained a crystalline phase. The photoluminescence (PL) and scintillation properties of the 1.0–10 % Nd-doped samples were investigated. The samples showed PL and scintillation peaks in the near-infrared region, which were due to 4f–4f transitions of Nd3+. We tested the X-ray dose rate response functions of the samples. The 10 % Nd-doped samples showed the most intensive response among the examined samples, and the lower detection limit of dose rate was 0.06 Gy/h with our setup.

An Overview of Appropriate Medical Practice and Preparedness in Radiation Emergency Response.

Radiation emergencies involving high doses of nuclear radiation pose significant risks from exposure to ionizing radiation in various scenarios. These situations include transportation accidents involving radioactive materials, occupational exposure, nuclear detonations, dirty bombs, and nuclear power plant accidents. In addition to the immediate risks of acute radiation syndrome (ARS) and related diseases, long-term exposure can increase the risk of other health issues such as cardiovascular disease and cancer. Vulnerable populations, including pregnant women and children, face particular concern due to potential impacts on their health and the health of unborn babies. The severity of ARS depends on several factors such as radiation dose, quality, dose rate, exposure uniformity, and individual biological responses. Bioindicators are biological responses or markers that help assess the severity and effects of radiation exposure on an individual. Bioindicators can include physical symptoms such as nausea, vomiting, and diarrhea, or laboratory tests such as changes in blood cell counts and gene expression that can help in assessing and treating exposed individuals. Additionally, early prodromal symptoms such as vomiting, diarrhea, and erythema can provide important clues for diagnosis and treatment. Developing a comprehensive plan for radiation emergencies is vital for safeguarding public health, infrastructure, and the environment. First responders play a critical role in establishing safety perimeters, triage, and coordination with various stakeholders. Education and training are essential for medical personnel and the public. This article provides general recommendations and identifies challenges to effective radiation emergency preparedness and response.

Developing and using international standards for neutron ambient dose equivalent rate meters

Measurements of neutron ambient dose equivalent rates are challenging because there are no perfect instruments that cover the entire 9 orders of magnitude neutron energy range (thermal to 20 MeV). Hence quantifying performance requirements with the international standard IEC 61005 for neutron ambient dose equivalent rate meters presents unique challenges. This paper discusses the requirements of this standard, which have been refined and improved over the last 20 years. Examples of type testing results for the constancy of ambient dose rate response, variation of the response due to neutron energy, response time, and various environmental disturbances are examined. IEC 61005 provides manufacturers with internationally acceptable requirements and provides consistent test methods for compliance with stated performance requirements.

Copper(I)‐Arsine Clusters with a Near‐Unity Phosphorescence Quantum Yield for X‐Ray Scintillation and LED Applications

AbstractRare‐earth element‐free materials that exhibit strong room temperature phosphorescence (RTP) and X‐ray scintillation properties are gaining global interest incessantly in the recent years. This work reports a series of easily synthesizable cubane Cu4I4‐triarsenic clusters [Cu4I4(R3As)3L] (L = none or nitrile), that exhibit a strong yellow‐green RTP with quantum efficiencies up to 100% and short decay times (4.4–4.9 µs). The title cluster complexes display X‐ray scintillation properties with a record ultralow detection limit (18.1 nGy s−1) and a perfectly linear dose rate response within a remarkably wide dose rate window (0–640 µGyair s−1). The cluster [Cu4I4(Ph3As)3] is highlighted as an efficient phosphor for UV‐pumped white and yellow LED devices, demonstrating an excellent white spectrum with a CIE index of (0.32,0.33) and bright yellow emission, respectively. These results may stimulate the future efforts in designing highly efficient arsenic‐based RTP materials and enriching the Cu4I4 cluster family.

Dosimetry of ultra-high dose rate electron beams using thermoluminescence and optically stimulated luminescence detectors

Objective. The aim of this work is to investigate the dose rate dependence of thermoluminescence and optically stimulated luminescence detectors (TLDs and OSLDs) in a wide uniform ultra-high dose rate electron beam and demonstrate the potential use of TLDs and OSLDs to correct the ion recombination in air-filled ionization chambers. This study avoids previously reported complications related to the field size and homogeneity. Approach. Two types of OSLDs (BeO and Al2O3:C) and three types of TLDs (LiF:Mg,Ti, LiF:Mg,Cu,P, CaF2:Tm) were irradiated simultaneously in a uniform 16 MeV electron beam generated by a clinically decommissioned C-Arm LINAC, modified to deliver doses per pulse between 8.3 × 10−4 Gy and 1.255 Gy, corresponding to instantaneous dose rates between 2 × 102Gy s−1 and 3 × 105 Gy s−1. A prototype ultra-thin parallel plate ionization chamber was employed as reference detector. Main results. Reproducible results were achieved both at conventional (standard deviation of the data <2%) and at the highest dose per pulse (standard deviation of the data <4%). No trend in the dose rate response of the TLDs and OSLDs was observed in the investigated dose per pulse range. The Al2O3:C OSLD was found to be the most precise detector, with a standard deviation of the data <2% at all investigated dose rates and dose levels. Significance. The dose rate independence of the investigated TLDs and OSLDs make them good candidates for dosimetry at ultra-high dose rates, at least up to 3 × 105 Gy s−1. A dose rate independent method to measure the dose per pulse is proposed, which can be applied to characterize ultra-high dose rate electron beams and correct for ion recombination in ionization chambers.

Development of Nd-doped CsI single crystal scintillators emitting near-infrared light

0.05, 0.1, 0.5, and 1% Nd-doped CsI single crystals were synthesized by the vertical Bridgman-Stockbarger method, and the photoluminescence and scintillation properties were evaluated. Under X-ray irradiation, two emission peaks were observed at 310 and 430 nm ascribed to on- and off-center configuration self-trapped excitons, respectively. In near-infrared regions, sharp peaks were observed at 900, 1080, and 1350 nm due to 4F3/2-4I9/2, 4F3/2-4I11/2, and 4F3/2-4I13/2 transitions of Nd3+, respectively. Dose rate response functions had good linearity in the range of 0.06–6 Gy/h in all the samples, and the 0.5% Nd-doped sample showed the highest intensity among all the samples.

Optical and radiation response properties of Nd-doped BaTi4O9 crystals emitting near-infrared photons

Nd-doped BaTi4O9 crystals were prepared by the optical floating zone crystallization technique and, their optical and radiation response properties were investigated. Under X-ray irradiation, Nd-doped crystals showed a broad emission peak around 1000 nm and several sharp emission lines in the NIR ranges were confirmed. The broad and sharp emission peaks would be due to a kind of defects and the 4f-4f transitions of Nd3+, respectively. As the X-ray exposure dose rate response, 0.5–2.0 % Nd-doped BaTi4O9 crystals indicated the dynamic range from 0.006 to 60 Gy/h, which was wider than that of Pr-doped BaTi4O9 crystals reported in our previous work.

X-ray-Induced scintillation properties of Cr-Doped Mg4Ta2O9 single crystals in Near-Infrared regions

0.1 %, 0.5 % and 1 % Cr-doped Mg4Ta2O9 single crystals were synthesized by the floating zone method and their photoluminescence (PL) and scintillation properties were assessed. Cr-doped Mg4Ta2O9 single crystals showed a broad PL band between 700 and 1100 nm in the near-infrared region, which is attributed to the 4T2–4A2 (4F) transition of Cr3+. As the scintillation properties, Cr-doped Mg4Ta2O9 single crystals show broad emission bands at 300–450 and 750–1100 nm, which were attributed to charge transfer from Ta5+ to O2– and the 4T2–4A2 (4F) transition of Cr3+, respectively. The afterglow levels of the 0.1 %, 0.5 % and 1 % Cr-doped Mg4Ta2O9 single crystals were 9.5, 33.8 and 47.0 ppm, respectively. As a characteristic of a scintillation detector, the lower detection limits were 0.001 Gy/h for the 0.1 % sample, 0.003 Gy/h for the 0.5 % sample and 0.006 Gy/h for the 1 % sample based on the dose rate response function.

Characterization of a 0.8 mm3 Medscint plastic scintillator detector system for small field dosimetry

Objective. Plastic scintillator detectors (PSDs) have demonstrated ability to meet requirements of small field dosimetry. Medscint developed a 1 mm long, 1 mm diameter cylindrical PSD with effective volume of 0.8 mm3. Clinically relevant, small field dosimetric properties of this detector, combined with a novel scintillation dosimetry system—HYPERSCINT RP-200, and HYPERDOSE analysis software were evaluated in this study. Approach. This novel scintillator-based dosimetry system was characterized with 6 MV-WFF and 10 MV-FFF x-ray beams delivered by Varian TrueBeamTM linear accelerator. The detector was characterized for leakage, short-term repeatability, dose response linearity, angular response, dose rate response, and field size dependence for radiation field sizes of 0.25 × 0.25 to 10 × 10 cm2. Measured detector specific output ratios were compared with microDiamond output factors to determine small field output correction factors, Main results. The dosimetry system showed excellent short-term repeatability with standard deviation of only 0.04 ± 0.01%. It demonstrated good dose linearity with variations less than 1.0% for 14.4 cGy and above. The dosimetry system was found to be independent of dose rate and angle of irradiation, with deviations for both below 0.5%. Leakage was found to be comparable to background readings. For 6 MV-WFF energy beams, detector specific output ratios for field sizes down to 1 × 1 cm2 agreed with output factors measured with PTW TN60019 microDiamond, thus, equates to unity for these field sizes. For 10 MV-FFF energy beams, detector specific output ratios for field sizes down to 2 × 2 cm2 agreed with PTW TN60019 microDiamond output factors, thus, equates to unity for these field sizes. for field sizes down to 0.5 × 0.5 cm2 were determined to be within 6% of unity for both 6 MV-WFF and 10 MV-FFF energy beams. Significance. The HYPERSCINT RP-200 dosimetry system coupled with a 0.8 mm3 PSD showed excellent dosimetric properties and was found to be clinically relevant for relative dosimetry down to field sizes of 0.5 × 0.5 cm2 and potentially smaller.

Proton Dosimetry Using Radiation-Induced Luminescence in Micrometer-Core Germanosilicate Optical Fibers

We investigated the radiation-induced luminescence of 62.5 μm, 10 μm and 3 μm germanosilicate single- and multi-mode telecom-grade optical fibers for use as high-resolution dosimeters at dose rates ranging between 5 Gy s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and 120 Gy s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> using proton beams of varying currents and energies. Only one of the two single-mode fibers under investigation had a detectable light yield, with a dose rate threshold around 20 Gy s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . All tested multi-mode fibers showed a detectable response over the whole accessible dose rate range. All tested multi-mode fibers displayed a linear dose rate response when the proton beam energy was fixed. However, the slope of the response curve showed a strong dependence on the proton beam energy. Geometry and material differences, as well as radiation-induced attenuation effects have been ruled out as sources for the observed proton energy dependence of the dose rate response.

Strong Magnetically-Responsive Circularly Polarized Phosphorescence and X-Ray Scintillation in Ultrarobust Mn(II)-Organic Helical Chains.

Over recent years, Mn(II)-organic materials showing circularly polarized luminescence (CPL) have attracted great interest because of their eco-friendliness, cheapness, and room temperature phosphorescence. Using the helicity design strategy, herein, chiral Mn(II)-organic helical polymers are constructed featuring long-lived circularly polarized phosphorescence with exceptionally high glum and ΦPL magnitudes of 0.021% and 89%, respectively, while remaining ultrarobust toward humidity, temperature, and X-rays. Equally important, it is disclosed for the first time that the magnetic field has a remarkably high negative effect on CPL for Mn(II) materials, suppressing the CPL signal by 4.2-times at =1.6T. Using the designed materials, UV-pumped CPL light-emitting diodes are fabricated, demonstrating enhanced optical selectivity under right- and left-handed polarization conditions. On top of all this, the reported materials display bright triboluminescence and excellent X-ray scintillation activity with a perfectly linear X-ray dose rate response up to 174µGyair s-1 . Overall, these observations significantly contribute to the CPL phenomenon for multi-spin compounds and promote the design of highly efficient and stable Mn(II)-based CPL emitters.

Real-time in vivo dose measurement using ruby-based fibre optic dosimetry during internal radiation therapy

In vivo dosimetry (IVD) in a commonly used liver cancer treatment of selective internal radiation therapy (SIRT) has been done based on the post-treatment image-based dosimetry approach. Real-time IVD is necessary to verify the dose delivery and detect errors during the treatment for better patient outcomes. This study aims to develop a fibre optic dosimeter (FOD) for in vivo real-time dose rate measurement during internal beta radiation therapy, e.g., SIRT. A ruby fibre optic probe was prepared and studied the radioluminescence (RL) characteristics, including its major challenge of stem effect arising from Cherenkov radiation and luminescence from the irradiated fibre. The stem signal was suppressed adequately using the stem removal technique of optical filtering, and only 2.3 ± 1.1% stem signal was contributed to the measured RL signal. A linear dose rate response was observed during the exposure of the ruby probe to varying dose rates using a 6 MeV electron beam and a positron-emitting radionuclide fluorine-18. The ruby exhibited a temporally non-constant RL signal, which increased the RL signal by 0.84 ± 0.29 counts/sec2 during the irradiation of the maximum dose rate used in this study of 9 Gy/min for 2 min. The ability of ruby FOD to measure the absolute dose rate with sufficient stem effect suppression and the linear RL dose rate response indicates its suitability for real-time IVD during internal beta radiation therapy. Future work will investigate the time-dependent RL characteristic of ruby and validate post-treatment image-based dosimetry using ruby-based FOD.

Er-Doped Mg4Ta2O9 Single-Crystal Scintillators Emitting Near-Infrared Photons for High-Dose Field Monitoring

Mg4Ta2O9 single crystals doped with 0.01, 0.1, and 1% Er were grown using the floating zone method, and their photoluminescence and scintillation properties were studied. X-ray diffraction analysis confirmed that all samples had a hexagonal structure of Mg4Ta2O9. The samples showed that the emission peak at 1550 nm was due to 4f−4f transitions of Er3+ ions, with quantum yields of 32.9, 46.6, and 18.0% for 0.01, 0.1, and 1% doping concentrations, respectively. All samples showed scintillation with a broad emission band at 350 nm due to charge transfer from Ta5+ to O2− ions and emission peak at 1550 nm due to 4f−4f transition of Er3+ ions. The dose rate response functions showed that the detection limit for all samples was 0.06 Gy/h for scintillation detector applications.

Saturating current characteristic of 120 μm thick ZnO film and its X-ray sensing features

We report a saturating current characteristic of a 120 μm thick ZnO film and explore its X-ray sensing features. The film was deposited using a sol-gel spin coating technique. The film has a polycrystalline nature. Measurement of current-voltage (I–V) characteristic under dark condition shows two sublinear regions from 0 to 6.0 V and 6.0–8.0 V followed by a saturation region between 8.0 and 12.0 V bias voltage. The electrical resistivity in each region is found to be ∼1.0 × 1011, 1.2 × 1011 and 1.6 × 1011 Ω cm. The I–V characteristic was further recorded under X-ray irradiation. The current under the X-ray irradiation shows a linear region from 0 to 6.0 V followed by two sublinear regions from 6.0 to 8.0 V and 8.0–12.0 V with higher magnitude than the dark current. The resistivity in each region was found to decrease by ∼101 order of magnitude under X-ray. Analysis of X-ray sensing features reveals that the signal-to-noise ratio of the device is consistent between 3.0 and 12.0 V. The rise-time and fall-time are nearly 1 s. The device shows sublinear dose rate response between 0.015 and 0.293 Gy/s with a minimum sensitivity of 28.46 μC.Gy−1.cm−3 at 0.292 Gy/s. The device is also found to be visible-blind between 375 and 750 nm. The physical mechanism responsible for sublinear and saturating current characteristics have been explained based on retrapping and recombination of conduction electrons.

A stochastic reaction–diffusion modeling investigation of FLASH ultra-high dose rate response in different tissues

Purpose: The aim of the study was to propose a theory based on topology and geometry of diffusion channels in tissue to contribute to the mechanistic understanding of normal tissue sparing at ultra-high dose rates (UHDRs) and explore an interplay between intra- and inter-track radical recombination through a reaction–diffusion mechanism.Methods: We calculate the time evolution of particle track structures using a system of coupled reaction–diffusion equations on a random network designed for molecular transport in porous and disordered media. The network is representative of the intra- and inter-cellular diffusion channels in tissues. Spatial cellular heterogeneities over the scale of track spacing are constructed by incorporating random fluctuations in the connectivity between network sites, resembling molecular mass and charge heterogeneities at the cellular level.Results: We demonstrate the occurrence of phase separation among the tracks as the complexity in intra- and inter-cellular structure increases. At the strong limit of structural disorder, tracks evolve individually like isolated islands with negligible inter-track as they propagate like localized waves in space, analogous to the Anderson localization in quantum mechanics. In contrast, at the limit of weak disorder in a homogeneous medium, such as water, the neighboring tracks melt into each other and form a percolated network of non-reactive species. Thus, the spatiotemporal correlation among chemically active domains vanishes as the inter-cellular complexity of the tissue increases from normal tissue structure to fractal-type malignancy.Conclusion: Differential FLASH normal tissue sparing may result from the interplay of the proximity of tracks over the intra- and inter-cellular landscape, a transition in the spatial distribution of chemical reactivity, and molecular crowding. In this context, insensitivities in the radiobiological responses of the tumors to FLASH-UHDR are interpreted via a lack of geometrical correlation among isolated tracks. The structural and geometrical complexities of cancerous cells prevent the clustering of tracks over a timescale, in which inter-track chemical reactivities presumably prevail in normal tissues. A series of systematic experiments on radiolysis-induced diffusivity and reactivity in actual normal and cancerous tissues must be performed to classify the tissues potentially spared by FLASH-UHDRs and verify our theory.

Visible–Near Infrared Scintillation Properties of Er-Doped Bi4Si3O12 Single Crystals

We synthesized the 0.5, 1.0, 2.0, and 3.0% Er-doped Bi4Si3O12 (BSO) single crystals and researched the photoluminescence (PL) and scintillation properties in visible–near infrared ranges. The X-ray diffraction analysis indicated that the synthesized samples had single-phase structure of BSO. In transmission spectra, all the samples had some absorption peaks owing to the 4f-4f transitions of Er3+ ions. In PL and scintillation properties, all the samples had the emission peaks due to the 6p-6s transitions of Bi3+ ions and the 4f-4f transitions of Er3+ ions. Afterglow levels at 20 ms after X-ray irradiation of the 0.5, 1.0, 2.0, and 3.0% Er-doped samples were 348.9, 587.9, 616.6, and 666.6 ppm, respectively. The light yields of the 0.5, 1.0, 2.0, and 3.0% Er-doped samples were 1600, 1200, 900, and 750 ± 10% ph/MeV, respectively. The dose rate response functions of all the samples showed the linear relationship between dose rate and scintillation intensity from 0.006 to 6 Gy h−1, and the 2.0% Er-doped sample had the highest intensity among the samples

X-ray-Induced Scintillation Properties of Nd-Doped Bi4Si3O12 Crystals in Visible and Near-Infrared Regions.

Undoped, 0.5, 1.0, and 2.0% Nd-doped Bi4Si3O12 (BSO) crystals were synthesized by the floating zone method. Regarding photoluminescence (PL) properties, all samples had emission peaks due to the 6p-6s transitions of Bi3+ ions. In addition, the Nd-doped samples had emission peaks due to the 4f-4f transitions of Nd3+ ions as well. The PL quantum yield of the 0.5, 1.0, and 2.0% Nd-doped samples in the near-infrared range were 67.9, 73.0, and 56.6%, respectively. Regarding X-ray-induced scintillation properties, all samples showed emission properties similar to PL. Afterglow levels at 20 ms after X-ray irradiation of the undoped, 0.5, 1.0, and 2.0% Nd-doped samples were 192.3, 205.9, 228.2, and 315.4 ppm, respectively. Dose rate response functions had good linearity from 0.006 to 60 Gy/h for the 1.0% Nd-doped BSO sample and from 0.03 to 60 Gy/h for the other samples.

Study on the wide range gamma dose rate response for a new type thick gas electron multiplier

Study on the wide range gamma dose rate response for a new type thick gas electron multiplier