RESUMO
We tested an approach to estimate daily canopy net photosynthesis, A, based on estimates of transpiration, E, using measurements of sap flow and water-use efficiency, ω, by measuring δ13C in CO2 respired from shoots in the canopies of two conifers (Podocarpaceae) native to New Zealand. The trees were planted in adjacent 20-year-old stands with the same soil and environmental conditions. Leaf area index was lower for Dacrycarpus dacrydioides D.Don in Lamb (1.34 m2 m-2) than for Podocarpus totara G.Benn. ex D.Don var. totara (2.01 m2 m-2), but mean (± standard error) stem diameters were the same at 152 ± 21 mm for D. dacrydioides and 154 ± 25 mm for P. totara. Over a 28-day period, daily A (per unit ground area) ranged almost five-fold but there were no significant differences between species (mean 2.73 ± 1.02 gC m-2 day-1). This was attributable to higher daily values of E (2.63 ± 0.83 mm day-1) and lower ω (1.35 ± 0.53 gC kg H2O-1) for D. dacrydioides compared with lower E (1.82 ± 0.72 mm day-1) and higher ω (1.90 ± 0.77 gC kg H2O-1) for P. totara. We attributed this to higher nitrogen availability and nitrogen concentration per unit foliage area, Na, and greater exposure to irradiance in the D. dacrydioides canopy compared with P. totara. Our findings support earlier observations that D. dacrydioides is more adapted to sites with poor drainage. In contrast, the high retention of leaf area and maintaining low rates of transpiration by P. totara, resulting in higher water-use efficiency, is an adaptive response to survival in dry conditions. Our findings show that physiological adjustments for two species adapted to different environments led to similar canopy photosynthesis rates when the trees were grown in the same conditions. We demonstrated consistency between whole-tree and more intensive shoot-scale measurements, confirming that integrated approaches are appropriate for comparative estimates of carbon uptake in stands with different species.
Assuntos
Fotossíntese , Estômatos de Plantas , Água , Fotossíntese/fisiologia , Água/metabolismo , Água/fisiologia , Estômatos de Plantas/fisiologia , Brotos de Planta/fisiologia , Traqueófitas/fisiologia , Traqueófitas/metabolismo , Transpiração Vegetal/fisiologia , Adaptação Fisiológica , Árvores/fisiologia , Folhas de Planta/fisiologia , Folhas de Planta/metabolismo , Nova ZelândiaRESUMO
Radiological accidents occur mainly in the practices recognized as high risk and which are classified by the International Atomic Energy Agency (IAEA) as Categories 1 and 2: radiotherapy, industrial irradiators and industrial radiography. In Brazil, five important cases in industrial gamma radiography occurred from 1985 to 2018, involving seven radiation workers and 19 members of the public. The accidents caused localized radiation lesions on the hands and fingers. One of these accidents is the focus of this paper. In this accident, a 3.28 TBq192Ir radioactive source was left unshielded for 9 h in a non-destructive testing (NDT) company parking lot, and many radiation workers, employees and public, including teachers of a primary school were exposed. The radioactive source was also directly handled by a security worker for about 1.5 min causing severe radiation injuries in the hand and fingers. This paper presents radiation dose estimates for all accidentally exposed individuals. Four scenarios were considered, and three internationally recognised and updated reconstructive dosimetry techniques were used, named, Brazilian visual Monte Carlo Dose Calculation (VMC), virtual environment for radiological and nuclear accidents simulation (AVSAR) and RADPRO Calculator®. The main radiation doses estimated by VMC were the absorbed dose of 34 Gy for the security worker's finger and his effective dose of 91 mSv; effective doses from 43 to 160 mSv for radiation workers and NDT employees; and effective doses of 9 mSv for teachers in the schoolyard.
Assuntos
Exposição Ocupacional , Liberação Nociva de Radioativos , Brasil , Humanos , Exposição Ocupacional/análise , Doses de Radiação , Radiografia , RadiometriaRESUMO
The ICRP Statement on Tissue Reactions (2011), based on epidemiological evidence, recommended a reduction for the eye lens equivalent dose limit from 150 to 20 mSv per year. This paper presents mainly the dose estimations received by industrial gamma radiography workers, during planned or accidental exposure to the eye lens, Hp(10) and effective dose. A Brazilian Visual Monte Carlo Dose Calculation program was used and two relevant scenarios were considered. For the planned exposure situation, twelve radiographic exposures per day for 250 days per year, which leads to a direct exposure of 10 h per year, were considered. The simulation was carried out using a 192Ir source with 1.0 TBq of activity; a source/operator distance between 5 and 10 m and placed at heights of 0.02 m, 1 m and 2 m, and an exposure time of 12 s. Using a standard height of 1 m, the eye lens doses were estimated as being between 16.3 and 60.3 mGy per year. For the accidental exposure situation, the same radionuclide and activity were used, but in this case the doses were calculated with and without a collimator. The heights above ground considered were 1.0 m, 1.5 m and 2.0 m; the source/operator distance was 40 cm, and the exposure time 74 s. The eye lens doses at 1.5 m were 12.3 and 0.28 mGy without and with a collimator, respectively. The conclusions were that: (1) the estimated doses show that the 20 mSv annual limit for eye lens equivalent dose can directly impact industrial gamma radiography activities, mainly in industries with high number of radiographic exposures per year; (2) the risk of lens opacity has a low probability for a single accident, but depending on the number of accidental exposures and the dose levels found in planned exposures, the threshold dose can easily be exceeded during the professional career of an industrial radiography operator, and; (3) in a first approximation, Hp(10) can be used to estimate the equivalent dose to the eye lens.
Assuntos
Raios gama , Cristalino/efeitos da radiação , Exposição Ocupacional/análise , Doses de Radiação , Radiometria/métodos , Simulação por Computador , Humanos , Masculino , Modelos Anatômicos , Método de Monte Carlo , Liberação Nociva de Radioativos , SoftwareRESUMO
Aircraft crew members are occupationally exposed to considerable levels of cosmic radiation at flight altitudes. Since aircrew (pilots and passengers) are in the sitting posture for most of the time during flight, and up to now there has been no data on the effective dose rate calculated for aircrew dosimetry in flight altitude using a sitting phantom, we therefore calculated the effective dose rate using a phantom in the sitting and standing postures in order to compare the influence of the posture on the radiation protection of aircrew members. We found that although the better description of the posture in which the aircrews are exposed, the results of the effective dose rate calculated with the phantom in the sitting posture were very similar to the results of the phantom in the standing posture. In fact we observed only a 1% difference. These findings indicate the adequacy of the use of dose conversion coefficients for the phantom in the standing posture in aircrew dosimetry. We also validated our results comparing the effective dose rate obtained using the standing phantom with values reported in the literature. It was observed that the results presented in this study are in good agreement with other authors (the differences are below 30%) who have measured and calculated effective dose rates using different phantoms.
Assuntos
Aeronaves , Radiação Cósmica , Exposição Ocupacional/análise , Postura , Doses de Radiação , Radiometria/métodos , Feminino , Humanos , Masculino , Neoplasias Induzidas por Radiação/prevenção & controle , Doenças Profissionais/prevenção & controle , Imagens de Fantasmas , Lesões por Radiação/prevenção & controleRESUMO
The conversion coefficients (CCs) relate protection quantities, mean absorbed dose (DT) and effective dose (E), with physical radiation field quantities, such as fluence (Φ). The calculation of CCs through Monte Carlo simulations is useful for estimating the dose in individuals exposed to radiation. The aim of this work was the calculation of conversion coefficients for absorbed and effective doses per fluence (DT/ Φ and E/Φ) using a sitting and standing female hybrid phantom (UFH/NCI) exposure to monoenergetic protons with energy ranging from 2 MeV to 10 GeV. The radiation transport code MCNPX was used to develop exposure scenarios implementing the female UFH/NCI phantom in sitting and standing postures. Whole-body irradiations were performed using the recommended irradiation geometries by ICRP publication 116 (AP, PA, RLAT, LLAT, ROT and ISO). In most organs, the conversion coefficients DT/Φ were similar for both postures. However, relative differences were significant for organs located in the abdominal region, such as ovaries, uterus and urinary bladder, especially in the AP, RLAT and LLAT geometries. Anatomical differences caused by changing the posture of the female UFH/NCI phantom led an attenuation of incident protons with energies below 150 MeV by the thigh of the phantom in the sitting posture, for the front-to-back irradiation, and by the arms and hands of the phantom in the standing posture, for the lateral irradiation.
Assuntos
Simulação por Computador , Imagens de Fantasmas , Postura , Prótons , Radiometria/instrumentação , Irradiação Corporal Total/métodos , Adulto , Biomimética , Carga Corporal (Radioterapia) , Feminino , Humanos , Método de Monte Carlo , Especificidade de Órgãos , Doses de Radiação , Radiometria/normasRESUMO
BACKGROUND: The relevance of allergic sensitization, as judged by titers of serum IgE antibodies, to the risk of an asthma exacerbation caused by rhinovirus is unclear. OBJECTIVE: We sought to examine the prevalence of rhinovirus infections in relation to the atopic status of children treated for wheezing in Costa Rica, a country with an increased asthma burden. METHODS: The children enrolled (n= 287) were 7 through 12 years old. They included 96 with acute wheezing, 65 with stable asthma, and 126 nonasthmatic control subjects. PCR methods, including gene sequencing to identify rhinovirus strains, were used to identify viral pathogens in nasal washes. Results were examined in relation to wheezing, IgE, allergen-specific IgE antibody, and fraction of exhaled nitric oxide levels. RESULTS: Sixty-four percent of wheezing children compared with 13% of children with stable asthma and 13% of nonasthmatic control subjects had positive test results for rhinovirus (P< .001 for both comparisons). Among wheezing subjects, 75% of the rhinoviruses detected were group C strains. High titers of IgE antibodies to dust mite allergen (especially Dermatophagoides species) were common and correlated significantly with total IgE and fraction of exhaled nitric oxide levels. The greatest risk for wheezing was observed among children with titers of IgE antibodies to dust mite of 17.5 IU/mL or greater who tested positive for rhinovirus (odds ratio for wheezing, 31.5; 95% CI, 8.3-108; P< .001). CONCLUSIONS: High titers of IgE antibody to dust mite allergen were common and significantly increased the risk for acute wheezing provoked by rhinovirus among asthmatic children.
Assuntos
Alérgenos/imunologia , Asma/complicações , Asma/imunologia , Imunoglobulina E/sangue , Infecções por Picornaviridae/imunologia , Pyroglyphidae/imunologia , Rhinovirus , Animais , Estudos de Casos e Controles , Criança , Epitopos/imunologia , Expiração , Feminino , Humanos , Masculino , Óxido Nítrico/análise , Infecções por Picornaviridae/complicações , Infecções por Picornaviridae/diagnóstico , Sons Respiratórios/etiologia , Rhinovirus/genética , Rhinovirus/imunologia , RiscoRESUMO
This work compared the predicted dose to an individual due to exposure from a radioactive patient using three models (point, line, and volume), for three therapeutic regimens (hyperthyroidism, thyroid cancer, and non-Hodgkin's lymphoma). For the volume source calculations, Monte Carlo simulations employing the Visual Monte Carlo (VMC) code and the voxel phantom FAX were used. For hyperthyroid patients, the point, line, and volume source models predicted doses to exposed individuals of 54, 24, and 14 mSv, respectively, at a distance of 0.3 m, and 4.8, 4.0 and 3.3 mSv at a distance of 1 m. For thyroid cancer patients, the dose values were 85, 38, and 18 mSv at 0.3 m, and 7.6, 6.4, and 4.4 mSv at 1 m, respectively. For non-Hodgkin's lymphoma (NHL) subjects, the doses were 230, 103, and 36 mSv at 0.3 m, and 21, 17, and 10 mSv at 1 m. These results show that patient release based on point source calculations involves unnecessary conservatism.
Assuntos
Exposição Ambiental/análise , Modelos Biológicos , Medicina Nuclear , Doses de Radiação , Adulto , Feminino , Humanos , Hipertireoidismo/radioterapia , Dosagem Radioterapêutica , Neoplasias da Glândula Tireoide/radioterapiaRESUMO
UNLABELLED: In this study, the Visual Monte Carlo radiation transport code and the female voxel phantom FAX were used to calculate organ and effective doses delivered by target-source irradiation geometries associated with radioiodine therapy treatments. METHODS: Specific situations were considered: when a patient was accompanied during hospitalization, when a patient was accompanied on return to his or her residence, and when a patient received daily care at home. RESULTS: This simulation study showed that, in the 3 situations considered, the total effective dose to an individual in normal contact with the patient was less than 0.85 mSv for up to 11.1 GBq (300 mCi) of administered activity. CONCLUSION: The results of this study suggest that for these patients receiving radioiodine therapy, radiation protection procedures after hospital discharge are unnecessary.
Assuntos
Cuidadores , Simulação por Computador , Radioisótopos do Iodo/uso terapêutico , Imagens de Fantasmas , Doses de Radiação , Feminino , Humanos , Método de Monte Carlo , Neoplasias da Glândula Tireoide/radioterapia , Tomografia Computadorizada por Raios XRESUMO
Foi desenvolvido um programa de Monte Carlo que utiliza uma representação matemática do corpo humano para permitir o cálculo de fatores de calibração de sistemas de medidas in vivo. O método de calibração utiliza um simulador matemático, construído na forma de elementos de volume (voxels), obtidos pela produção de imagens do corpo humano através de ressonância magnética. O programa utiliza a técnica de Monte Carlo para simular a contaminação dos tecidos, o transporte dos fótons através dos tecidos e a detecção da radiação. Este programa simula o transporte e detecção de fótons na faixa de energia de 0,035 a 2 MeV e representa o corpo num formato de 871 fatias, de 277x148 elementos de área (pixels) cada. O programa de Monte Carlo foi utilizado para calibrar sistemas de medidas in vivo e estimar a diferença entre distribuições homogêneas e não homogêneas de radionuclídeos no pulmão. Os resultados mostram que o fator de calibração obtido 241Am na parte anterior dos pulmões difere 20 vezes do obtido para a parte posterior. O programa foi também utilizado para estimar a atividade de 137Cs em um indivíduo contaminado internamente utilizando o detector de Nal (TI) de 8"x4", e a atividade de 241Am em um segundo indivíduo contaminado internamente utilizando um detector planar de germânio