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1.
J Vis Exp ; (182)2022 Apr 13.
Artigo em Inglês | MEDLINE | ID: mdl-35499345

RESUMO

Most human body proteins' activity and functionality are related to configurational changes of entire subdomains within the protein crystal structure. The crystal structures build the basis for any calculation that describes the structure or dynamics of a protein, most of the time with strong geometrical restrictions. However, these restrictions from the crystal structure are not present in the solution. The structure of the proteins in the solution may differ from the crystal due to rearrangements of loops or subdomains on the pico to nanosecond time scale (i.e., the internal protein dynamics time regime). The present work describes how slow motions on timescales of several tens of nanoseconds can be accessed using neutron scattering. In particular, the dynamical characterization of two major human proteins, an intrinsically disordered protein that lacks a well-defined secondary structure and a classical antibody protein, is addressed by neutron spin echo spectroscopy (NSE) combined with a wide range of laboratory characterization methods. Further insights into protein domain dynamics were achieved using mathematical modeling to describe the experimental neutron data and determine the crossover between combined diffusive and internal protein motions. The extraction of the internal dynamic contribution to the intermediate scattering function obtained from NSE, including the timescale of the various movements, allows further vision into the mechanical properties of single proteins and the softness of proteins in their nearly natural environment in the crowded protein solution.


Assuntos
Proteínas Intrinsicamente Desordenadas , Nêutrons , Anticorpos , Difusão , Humanos , Análise Espectral
2.
J Chem Phys ; 156(19): 194505, 2022 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-35597655

RESUMO

We characterize a concentrated 7.3 m CaCl2 solution, combining neutron diffraction with chloride isotopic substitution (Cl-NDIS) in null water and molecular dynamics (MD) simulations. We elucidate the solution structure, thermodynamic properties, and extent of ion pairing previously suggested as concentration-dependent and often not observed at lower concentrations. Our Cl-NDIS measurements designate the solvent-shared ion pairing as dominant and the contact ion pairing (CIP) as insignificant even under conditions close to the solubility limit. The MD models parameterized against neutron diffraction with calcium isotopic substitution (Ca-NDIS) overestimate CIP despite successfully reproducing most of the Cl-NDIS signal. This drawback originates from the fact that Ca2+-Cl- interactions were primarily "hidden" in the Ca-NDIS signal due to overlapping with Ca2+-Ow and Ca2+-Hw contributions to the total scattering. Contrary, MD models with moderate CIP and possessing generally good performance at high concentrations fail to reproduce the NDIS measurements accurately. Therefore, the electronic polarization, introduced in most of the recent MD models via scaling ionic charges, resolves some but not all parameterization drawbacks. We conclude that despite improving the quality of MD models "on average," the question "which model is the best" has not been answered but replaced by the question "which model is better for a given research." An overall "good" model can still be inappropriate or, in some instances, "bad" and, unfortunately, produce erroneous results. The accurate interpretation of several NDIS datasets, complemented by MD simulations, can prevent such mistakes and help identify the strengths, weaknesses, and convenient applications for corresponding computational models.


Assuntos
Simulação de Dinâmica Molecular , Difração de Nêutrons , Íons , Difração de Nêutrons/métodos , Nêutrons , Soluções , Água/química
3.
Ying Yong Sheng Tai Xue Bao ; 33(4): 909-914, 2022 Apr.
Artigo em Chinês | MEDLINE | ID: mdl-35543041

RESUMO

Cosmic-ray neutron sensing (CRNS) method was recently used to monitor soil moisture in farmland. But its spatial representation and accuracy needs further study. A field experiment was carried out to evaluate the applicability of CRNS for monitoring soil moisture in winter wheat farmland of the North China Plain. The spatial weight of CRNS detector was simulated by the ultra rapid adaptable neutron-only simulation for environmental research (URANOS) model and the CRNS-estimated soil moisture was compared with the measured soil moisture. The results showed that the CRNS detection radius obtained by URANOS simulation was 127-139 m, and that the weight distribution showed good agreement with the theoretical value. The determination coefficient (R2) and the root-mean-square error (RMSE) between CRNS-estimated soil moisture and measured soil moisture reached 0.64 and 0.05 cm3·cm-3, respectively. The CRNS-estimated soil moisture was sensitive to the changes of overall moisture in the detection area, with seasonal variation of measurement accuracy. In conclusion, cosmic-ray neutron sensing is a continuous and reliable method for monitoring total water content in winter wheat fields.


Assuntos
Solo , Água , China , Fazendas , Nêutrons , Triticum , Água/análise
4.
Sci Rep ; 12(1): 5579, 2022 04 02.
Artigo em Inglês | MEDLINE | ID: mdl-35368025

RESUMO

Shear sonic wave velocity (Vs) has a wide variety of implications, from reservoir management and development to geomechanical and geophysical studies. In the current study, two approaches were adopted to predict shear sonic wave velocities (Vs) from several petrophysical well logs, including gamma ray (GR), density (RHOB), neutron (NPHI), and compressional sonic wave velocity (Vp). For this purpose, five intelligent models of random forest (RF), extra tree (ET), Gaussian process regression (GPR), and the integration of adaptive neuro fuzzy inference system (ANFIS) with differential evolution (DE) and imperialist competitive algorithm (ICA) optimizers were implemented. In the first approach, the target was estimated based only on Vp, and the second scenario predicted Vs from the integration of Vp, GR, RHOB, and NPHI inputs. In each scenario, 8061 data points belonging to an oilfield located in the southwest of Iran were investigated. The ET model showed a lower average absolute percent relative error (AAPRE) compared to other models for both approaches. Considering the first approach in which the Vp was the only input, the obtained AAPRE values for RF, ET, GPR, ANFIS + DE, and ANFIS + ICA models are 1.54%, 1.34%, 1.54%, 1.56%, and 1.57%, respectively. In the second scenario, the achieved AAPRE values for RF, ET, GPR, ANFIS + DE, and ANFIS + ICA models are 1.25%, 1.03%, 1.16%, 1.63%, and 1.49%, respectively. The Williams plot proved the validity of both one-input and four-inputs ET model. Regarding the ET model constructed based on only one variable,Williams plot interestingly showed that all 8061 data points are valid data. Also, the outcome of the Leverage approach for the ET model designed with four inputs highlighted that there are only 240 "out of leverage" data sets. In addition, only 169 data are suspected. Also, the sensitivity analysis results typified that the Vp has a higher effect on the target parameter (Vs) than other implemented inputs. Overall, the second scenario demonstrated more satisfactory Vs predictions due to the lower obtained errors of its developed models. Finally, the two ET models with the linear regression model, which is of high interest to the industry, were applied to diagnose candidate layers along the formation for hydraulic fracturing. While the linear regression model fails to accurately trace variations of rock properties, the intelligent models successfully detect brittle intervals consistent with field measurements.


Assuntos
Inteligência Artificial , Lógica Fuzzy , Modelos Lineares , Redes Neurais de Computação , Nêutrons
5.
Sensors (Basel) ; 22(7)2022 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-35408196

RESUMO

A CS-30 cyclotron has been in operation at King Faisal Specialist Hospital and Research Center (KFSHRC) since 1982. The CS-30 cyclotron has been used to produce medical radioisotopes for positron emission tomography (PET) and single-photon emission computed tomography (SPECT). Some of the nuclear reactions of radionuclide production are associated with the intense release of a wide range of fast neutrons. In this work, we investigated the radionuclides produced from neutron interactions with the cyclotron facility walls. Activation isotopes were determined by performing gamma ray spectrometry utilizing a high-purity germanium (HPGe) detector. The major radionuclides found were 152Eu, 154Eu, 134Cs, 65Zn and 60Co. Activation isotope accumulation had increased the dose rate inside the facility. The surface dose rates were measured at all of the surrounding walls. The maximum surface dose rate was found to be 1.2 µSv/h, which is much lower than the permissible occupational exposure of 15 µSv/h based daily 5 work hours.


Assuntos
Ciclotrons , Exposição Ocupacional , Nêutrons , Exposição Ocupacional/análise , Tomografia por Emissão de Pósitrons , Radioisótopos
6.
Radiat Environ Biophys ; 61(2): 325-334, 2022 May.
Artigo em Inglês | MEDLINE | ID: mdl-35411404

RESUMO

Atmospheric dispersion modeling was performed for a postulated design basis accident at a SLOWPOKE research reactor. The MCNP-5 computer code was used to estimate the neutron flux spectrum which was then used in the ORIGEN-S code to perform core depletion calculations and determine the radiological source term. The HotSpot health physics code was then used to model the atmospheric transport of the radioactive material released to estimate the resulting doses to the population downwind of the reactor. The highest total effective dose (TED) for a release from the reactor's exhaust stack in predominant meteorological conditions, stability class C, was 0.37 mSv, while a maximum TED of 4.29 mSv was estimated for a release at ground level. Ground deposition was estimated to be 3900 kBq/m2. It was shown that any hypothetical release of radioactive material resulting from such an accident would have no significant adverse effect on the municipal water reservoir close to the reactor.


Assuntos
Poluentes Radioativos do Ar , Monitoramento de Radiação , Liberação Nociva de Radioativos , Poluentes Radioativos do Ar/análise , Nêutrons
7.
Sci Rep ; 12(1): 5863, 2022 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-35393505

RESUMO

Neutron Capture Enhanced Particle Therapy (NCEPT) boosts the effectiveness of particle therapy by capturing thermal neutrons produced by beam-target nuclear interactions in and around the treatment site, using tumour-specific [Formula: see text]B or [Formula: see text]Gd-based neutron capture agents. Neutron captures release high-LET secondary particles together with gamma photons with energies of 478 keV or one of several energies up to 7.94 MeV, for [Formula: see text]B and [Formula: see text]Gd, respectively. A key requirement for NCEPT's translation is the development of in vivo dosimetry techniques which can measure both the direct ion dose and the dose due to neutron capture. In this work, we report signatures which can be used to discriminate between photons resulting from neutron capture and those originating from other processes. A Geant4 Monte Carlo simulation study into timing and energy thresholds for discrimination of prompt gamma photons resulting from thermal neutron capture during NCEPT was conducted. Three simulated [Formula: see text] mm[Formula: see text] cubic PMMA targets were irradiated by [Formula: see text]He or [Formula: see text]C ion beams with a spread out Bragg peak (SOBP) depth range of 60 mm; one target is homogeneous while the others include [Formula: see text] mm[Formula: see text] neutron capture inserts (NCIs) of pure [Formula: see text]B or [Formula: see text]Gd located at the distal edge of the SOBP. The arrival times of photons and neutrons entering a simulated [Formula: see text] mm[Formula: see text] ideal detector were recorded. A temporal mask of 50-60 ns was found to be optimal for maximising the discrimination of the photons resulting from the neutron capture by boron and gadolinium. A range of candidate detector and thermal neutron shielding materials were simulated, and detections meeting the proposed acceptance criteria (i.e. falling within the target energy window and arriving 60 ns post beam-off) were classified as true or false positives, depending on their origin. The ratio of true/false positives ([Formula: see text]) was calculated; for targets with [Formula: see text]B and [Formula: see text]Gd NCIs, the detector materials which resulted in the highest [Formula: see text] were cadmium-shielded CdTe and boron-shielded LSO, respectively. The optimal irradiation period for both carbon and helium ions was 1 µs for the [Formula: see text]B NCI and 1 ms for the [Formula: see text]Gd NCI.


Assuntos
Compostos de Cádmio , Pontos Quânticos , Boro , Método de Monte Carlo , Nêutrons , Telúrio
8.
Mol Pharm ; 19(4): 1135-1145, 2022 04 04.
Artigo em Inglês | MEDLINE | ID: mdl-35298163

RESUMO

Boron neutron capture therapy (BNCT) is a radiation therapy for cancer. In BNCT, the internalization of boron-10 atoms by cancer cells induces cell death through the generation of α particles and recoiling lithium-7 nuclei when irradiated with low-energy thermal neutrons. In this study, we aimed to construct exosomes [extracellular vesicles (EVs)]-based drug delivery technology in BNCT. Because of their pharmaceutical advantages, such as controlled immune responses and effective usage of cell-to-cell communication, EVs are potential next-generation drug delivery carriers. In this study, we successfully developed polyhedral borane anion-encapsulated EVs with modification of hexadeca oligoarginine, which is a cell-penetrating peptide, on the EV membrane to induce the actin-dependent endocytosis pathway, macropinocytosis, which leads to efficient cellular uptake and remarkable cancer cell-killing BNCT activity. The simple and innovative technology of the EV-based delivery system with "cassette" modification of functional peptides will be applicable not only for BNCT but also for a wide variety of therapeutic methodologies.


Assuntos
Terapia por Captura de Nêutron de Boro , Peptídeos Penetradores de Células , Vesículas Extracelulares , Compostos de Boro , Terapia por Captura de Nêutron de Boro/métodos , Nêutrons
9.
Rev Sci Instrum ; 93(2): 024703, 2022 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-35232149

RESUMO

To build a proton beam accelerator that can be applied to a boron neutron capture therapy system based on an electrostatic accelerator, a high-voltage direct-current (DC) power supply system equivalent to the generation of neutrons should be provided. The symmetrical Cockcroft-Walton voltage multiplier method is suitable for stable acceleration of the proton beam in the tandem electrostatic accelerator in this system. Before the second step-up with the Cockcroft-Walton circuit, the design of the inverter is prioritized by preponderantly considering the first voltage and resonance frequency. Moreover, the optimized stacking number is determined with consideration of the ripple voltage, voltage drop, average output voltage, and fundamental harmonics, and a design is performed to set related parameter values to be stable in the flat-top region of the voltage. A high-voltage DC power supply system of 1.2 MV/45 mA is needed for a stable terminal energy of 2.4 MeV/20 mA. Such a design can be optimized by securing reliable data using a simulation tool on the basis of theoretical calculations. This will become a formidable touchstone in manufacturing technology based on acquiring practical know-how for setting up a tandem electrostatic accelerator-based boron neutron capture therapy system in the future.


Assuntos
Terapia por Captura de Nêutron de Boro , Simulação por Computador , Fontes de Energia Elétrica , Nêutrons , Aceleradores de Partículas , Eletricidade Estática
10.
Appl Radiat Isot ; 184: 110179, 2022 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-35272229

RESUMO

Neutron area monitors do not often have a good adjustment of their dose response functions to the ICRP74 neutron fluence-to-H*(10) conversion function between 10 and 20 MeV. The objective of this work is to establish a methodology to combine the dose response functions of Berthold LB6411 and WENDI-II, adjusting this combined function to the ICRP74 conversion function: this combination shows an almost perfect adjustment between 0.5 and 20 MeV. Thus, this article presents an easy and cheap alternative to the recalibration in D-T generators.


Assuntos
Nêutrons , Radiometria , Doses de Radiação , Radiometria/métodos
11.
Appl Radiat Isot ; 184: 110117, 2022 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-35272232

RESUMO

A low cost and easily implemented target system for neutron activation was developed that takes advantage of the neutron flux produced as a by-product during the cyclotron production of medical isotopes. Samples are placed in close proximity to an 18O(p,n)18F target on a cyclotron operating between 18 and 22 MeV for irradiation. Analysis of the samples by gamma spectroscopy shows that activation is proportional to the neutron exposure, and the mass of the element present in the sample.


Assuntos
Ciclotrons , Ouro , Raios gama , Nêutrons , Prata
12.
Appl Radiat Isot ; 184: 110163, 2022 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-35303629

RESUMO

Degradation of material properties under neutron irradiation generates a requirement for studying effects on materials in a fusion environment and optimizing radiation-resistant materials for future applications. In the present work, the durability of stainless steel (SS) alloy used in ITER-like fusion devices is studied. We have predicted the amount of radionuclides produced in the material upon neutron irradiation at various locations is determined using the ACTYS, neutron activation code, for a typical one-dimensional geometry of ITER-like fusion reactor. The ACTYS code is further used to determine the gas production from 55Fe, 59Ni, and other long-lived radionuclides in the material. To further stress the importance of gas production in fusion materials, a comparative study of gas production cross-sections as given in various standard data libraries is examined using TALYS-1.8 and is presented in the paper.


Assuntos
Radioatividade , Radioisótopos , Ligas , Nêutrons , Aço Inoxidável
13.
Appl Radiat Isot ; 184: 110187, 2022 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-35339808

RESUMO

In this study, the production parameters of 199Au nanoparticles (199AuNPs) have been investigated by a two-part study. The first part is about investigating the indirect method of producing non-carrier-added (NCA) 199Au radionuclide. MCNPX-2.6, TALYS-1.9, and ALICE/ASH-0.1 codes were applied as the theoretical approach to simulate the core of Tehran research reactor (TRR) for determining the activity of 199Au, specifying the production yield of 199Au, and calculating the excitation function of P198t(n,γ)P199t→A199u reaction. As the corresponding experimental approach, two 11 mg and 15.5 mg samples of enriched 198Pt metal powder were irradiated by thermal neutrons for 21 h and 10 min. The liquid-liquid extraction (LLX) technique has been used with a different solvent for each sample. LLX using ethyl acetate and LLX using Di-(2-Ethylhexyl) phosphoric acid (HDEHP) were applied for the 15.5 mg and the 11 mg samples respectively. The chemical yield of 199Au was calculated more than %99 for the 15.5 mg sample, and more than %80 for the 11 mg sample. The second part is about synthesizing 199AuNPs in an average size of 50 nm by using Turkevich method.


Assuntos
Nanopartículas Metálicas , Platina , Ouro , Irã (Geográfico) , Nêutrons
14.
Appl Radiat Isot ; 184: 110188, 2022 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-35358808

RESUMO

Radiotherapy is one of the most common methods for treating malignant diseases, whose ultimate goal is to deliver lethal doses to tumor cells. One of the unwanted consequences of radiotherapy is secondary radiation outside the treatment field, which imposes additional doses to healthy tissues and organs, specifically neutron doses, which we aim to evaluate. Therefore, this study aims to measure the fast neutron equivalent dose and the risk of secondary cancer in the thyroid, chiasm, and lenses in the treatment of the pelvic area. In this study, CR-39 detectors were used to measure the equivalent fast neutron dose in different sections of the RANDO Phantom (thyroid, chiasm, and lenses) and were irradiated by the energy of 18 MV on Varian Clinac 2100 C-D linear accelerator. CR-39 detectors were calibrated with predetermined doses by an Am-Be neutron source. Then, after etching and reading processes, the equivalent dose of fast neutrons was determined. According to the results, the fast neutron doses in the thyroid, right and left eye lenses, and chiasm were 0.613 ± 0.024, 0.835 ± 0.040, 0.866 ± 0.016, and 0.685 ± 0.045 mSv/Gy, respectively. Moreover, the secondary cancer risks in the unshielded organs are 0.004, 0.029, 0.030, and 0.025 for the thyroid, right and left eye lenses, and chiasm, respectively. In conclusion, the contribution of neutrons to the secondary doses in the out-of-field organs is significant and should not be ignored.


Assuntos
Segunda Neoplasia Primária , Glândula Tireoide , Humanos , Nêutrons , Aceleradores de Partículas , Imagens de Fantasmas , Fótons , Radiometria/métodos , Dosagem Radioterapêutica
15.
Anal Chem ; 94(12): 5023-5028, 2022 03 29.
Artigo em Inglês | MEDLINE | ID: mdl-35298136

RESUMO

The limits of detection (LOD) and quantitation (LOQ) in the mass domain, for broadband vibrational spectroscopy with neutrons on the TOSCA spectrometer at the ISIS Pulsed Neutron and Muon Source (UK), have been studied. The well-known 3σ and 10σ approaches are used through a specifically developed analytical procedure that is based on the calculation of the integrated spectral intensities in selected energy-transfer ranges, as a function of mass of standard reference materials and calibrants, such as ZrH2, 2,5-diiodothiophene, and low-density polyethylene. The analysis shows that the blank, that is, the instrument setup without the analyte, plays a critical role in the measurement performance, especially for small specimen quantities. The results point that TOSCA enables detection of 128 µmol (LODH) and quantitation of 428 µmol (LOQH) of elemental hydrogen analytes in ZrH2. The determined values for this and other standards allow for the assessment of the calibration curve design and instrument sensitivity and define a method to be used for inelastic neutron scattering spectrometers such as TOSCA, or VESPA, the new beamline under construction at the European Spallation Source in Lund (Sweden).


Assuntos
Hidrogênio , Nêutrons , Calibragem , Limite de Detecção , Análise Espectral
16.
Bull Exp Biol Med ; 172(5): 561-565, 2022 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-35348958

RESUMO

The dynamics of proliferative activity of the L-929 cell culture of mouse fibroblast-like cells in the phase of logarithmic growth was compared with some heliogeophysical parameters (Ap and ULF indexes of geomagnetic activity, vertical component of the interplanetary magnetic field, and intensity of fluctuations of secondary cosmic radiation estimated by the neutron monitoring near the Earth's surface). Among the considered heliogeophysical parameters, only the magnitude of fluctuations of minute-to-minute changes in the neutron monitor indicator reliably and negatively correlates with the rate of cell culture reproduction. Considering that the amplitude of secondary cosmic fluctuations is about 5%, which is 0.1% of the total ray flux, and proliferative activity varies in the range of 30-50%, the probability of a direct biotrophic effect of this physical factor is extremely low. It seems likely that proliferative activity of L-929 cell culture is directly affected by another environmental factor, the marker of which is the intensity of neutron counting rate fluctuations.


Assuntos
Radiação Cósmica , Animais , Campos Magnéticos , Camundongos , Nêutrons , Atividade Solar
17.
Anal Chim Acta ; 1202: 339686, 2022 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-35341531

RESUMO

Boron is an important element in nuclear reactor technology due to its high neutron absorption cross section of 10B isotope. Isotopic composition of B (IC, 10B/11B atom ratio) determination in finished neutron absorbers is a necessity under chemical quality control (CQC). We report an innovative greener method for rapid and non-destructive approach of isotopic composition determination of B in "as received" boron based ceramic neutron absorbers including boron carbides and hexa-borides by external (in air) Particle Induced Gamma-ray Emission (PIGE) using 3.5 MeV proton beam. It involves irradiation of "as received" powder samples wrapped in a thin Mylar film and measurement of prompt gamma rays at 429, 718 and 2125 keV from 10B(p,αγ)7Be, 10B(p,p'γ)10B and 11B(p,p'γ)11B, respectively, using a HPGe detector system. The method was standardized with natural and enriched B4C powders. For validation, the results of isotopic composition obtained from "as received" samples were compared with that obtained from pellet samples using both external and vacuum chamber PIGE methods. IC values obtained for natural to 10B enriched samples (19.8-67 atom % of 10B) are very encouraging with 1-2% and 0.3-0.7% uncertainties from single and replicate sample experiments. The method is truly non-destructive as the samples can be returned back as such after the experiment as they are not radioactive. Compared to existing PIGE method for isotopic composition of B, the developed method keeps promise for wide applications as it is simple, sensitive and rapid and it does not require vacuum, pellet preparation with a binder, exact mass of the sample and beam current measurement.


Assuntos
Boro , Nêutrons , Cerâmica , Raios gama , Isótopos
18.
Health Phys ; 122(4): 480-487, 2022 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-35244615

RESUMO

ABSTRACT: A shielded neutron irradiation facility has been constructed to contain a 74 GBq plutonium-beryllium neutron source at the University of Utah. Due to lack of information and recent use, the GEANT4 Monte Carlo Toolkit was used to perform dose assessments and validation of the designed shield and beam port for storage and operational geometries where the source was to be placed. Borated polyethylene was used as the primary shielding material with a lead-lined beam port to collimate neutrons and reduce gamma rays within the active beam profile. The lead lining was found to reduce the gamma-to-neutron ratio within the profile to 0.259 ± 0.001 and maintain an average neutron flux of 4,633.7 ± 10.2 n cm-2 s-1. The measured dose rate of the source at 30 cm from its constructed storage configuration was found to be 22.3 ± 1.1 µSv h-1 and in good agreement with simulated values. This was also close to the target rate of 20 µSv h-1, the public limit for whole-body dose accumulation, imposed on the design. Measurements of the source during its retrieval and placement into the shield show good agreement with the simulated results and provide a strong validation for the future use of the source in experiments at the University of Utah.


Assuntos
Berílio , Plutônio , Raios gama , Método de Monte Carlo , Nêutrons , Plutônio/análise
19.
Technol Health Care ; 30(S1): 37-46, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-35124582

RESUMO

BACKGROUND: According to statistics of the Ministry of Health and Welfare in 2017, the second leading cause of death in Taiwan was lung cancer. OBJECTIVE: Routine treatment planning does not consider photoneutron dose equivalent (PNDE) of patient induced secondary radiation resulting from primary exposure of lung cancer. However, such treatment is potentially important for improving estimates of health risks. METHODS: This study used 10, 30, 50, 70, and 90 kg of polymethylmethacrylate (PMMA) phantoms as patient to measure PNDE varying anatomical area during lung cancer of intensity modulated radiotherapy (IMRT) treatment. Paired thermoluminescent dosimeters (TLD-600 and 700) were calibrated using university reactor neutrons. TLDs were inserted into phantom which was closely corresponded of the represented tissues or organs. RESULTS: Neutron doses (ND) of organ or tissue (N⁢DT) were determined in these phantoms using paired TLDs approach. The risks of incurring fatal secondary malignancies, maximum statistical and total errors were estimated. Evaluated PNDE ranged from 0.80 ± 0.12 to 0.56 ± 0.08 mSv/Gy for these phantoms. CONCLUSION: The estimated N⁢DT decreased with increasing distance that is from the central axis. Evaluated PNDE and N⁢D𝑠𝑘𝑖𝑛 for these phantoms were discussed. This investigation also identified secondary risks associated with PNDE relating to radiation protection.


Assuntos
Neoplasias Pulmonares , Radioterapia de Intensidade Modulada , Humanos , Neoplasias Pulmonares/radioterapia , Nêutrons , Imagens de Fantasmas , Polimetil Metacrilato , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Intensidade Modulada/efeitos adversos , Radioterapia de Intensidade Modulada/métodos
20.
Phys Med ; 95: 167-175, 2022 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-35183907

RESUMO

PURPOSE: Whole-body photoneutron (PN) energy-specific dosimetry on phantom surfaces and 360°angular fast PN distribution dosimetry on and around polyethylene (PE) phantom organs for prostate cancer in 10 cm × 10 cm and 20 cm × 20 cm field sizes of 18 MV X-rays of Varian Clinac 2100C linear accelerator. METHODS: Novel "Sohrabi neutron dosimetry methods" including "miniature passive neutron dosimeter/spectrometer" and "strip polycarbonate neutron dosimeters" were applied. Energy-specific PN dose equivalents on surface as well as 360°fast PN dose equivalent angular distributions on and around PE phantom organs; head, neck, thorax, arms, pelvis, thighs and legs were determined. RESULTS: Matrix of surface (skin) energy-specific PN dose equivalents including total thermal, total epithermal, total fast, sum total thermal + epithermal and sum total thermal + epithermal + fast, and 360°angular fast PN dose equivalent responses were determined. The results indicate that data matrix of 20 cm × 20 cm field size provides higher PN dose equivalent values than those of 10 cm × 10 cm field size for surface points even remote from the central axis and for all 360°angular fast PN dose equivalent distributions on organs studied. CONCLUSIONS: Matrix of energy-specific PN dose equivalents was obtained demonstrating that the Sohrabi neutron dosimetry methods applied are unique for energy-specific PN dose equivalent studies as well as for 360°angular PN dose equivalent distribution data for PN-SPC risk estimation. The dosimetry methods can be specifically applied to many other exotic applications in health physics, medical physics, space flight dosimetry, and nuclear science and technology.


Assuntos
Nêutrons , Radiometria , Humanos , Masculino , Aceleradores de Partículas , Imagens de Fantasmas , Radiometria/métodos , Raios X
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