CHARACTERIZATION AND PERFORMANCE TESTS OF A NEW OSL/TL PERSONAL DOSEMETER FOR INDIVIDUAL MONITORING.

We propose a personal dosemeter based on the combination of thermoluminescence (TL) and optically stimulated luminescence (OSL) detectors employing the advantages of both techniques. The new OSL/TL dosemeter using a badge manufactured in a 3D printer was tested for assessment of photon doses in simulated and actual situations of exposure. Additionally, Brazilian national performance tests adapted to the new dosemeter were run as well as the performance tests of international standards on the passive dosimetry systems. The results showed the advantages of combined OSL and TL techniques when using the three different configurations of detector combination, Al2O3/BeO, BeO/CaSO4 and Al2O3/LiF. The dosemeter allowed corrections for radiation energy without the necessity of attenuation filters, the evaluation of single and accumulated doses and the triple check of the dose values. Further, the performance tests were consistent with national and international requirements, showing the viability of application of the new dosemeter to the assessment of equivalent doses.

Three decades of occupational individual monitoring at the University of São Paulo.

As the ionizing radiation to which workers are exposed is related to possible harmful biological effect, its dose evaluation gains relevance. Although the effects of low doses are still controversial, the radiation protection authorities assume that any dose of ionizing radiation is potentially harmful to the human health and adopt the linear non-threshold model for the dose-effect relation. The Dosimetry Laboratory of the Institute of Physics of the University of São Paulo performs the external individual monitoring of workers exposed to X- and gamma-rays since 1981, with the technique of thermoluminescence. Currently, ~500 badges are provided to the university professionals mostly working in research laboratories and hospitals. Data of individual annual dose equivalent collected from 1995 to 2015 and the performance of the monitoring service are presented in this paper.

Towards a Brazilian radon map: consortium radon Brazil.

Recently, the idea of generating radon map of Brazil has emerged. First attempts of coordinating radon surveys--carried out by different groups across the country--and initial discussions on how to proceed on a larger scale were made at the First Brazilian Radon Seminary, Natal, September 2012. Conventionally, it is believed that indoor radon is no major problem in Brazil, because the overall benign climate usually allows high ventilation rates. Nevertheless, scattered measurements have shown that moderately high indoor radon concentrations (up to a few hundred Bq m⁻³) do occur regionally. Brazilian geology is very diverse and there are regions where an elevated geogenic radon potential exists or is expected to exist. Therefore, a Brazilian Radon Survey is expected to be a challenge, although it appears an important issue, given the rising concern of the public about the quality of its environment.

Using (222)Rn as a tracer of geodynamical processes in underground environments.

Radon levels in two old mines in San Luis, Argentina, were measured and analyzed, with the aim to assess the potential use of this radioactive noble gas as a tracer of geological processes in underground environments. La Carolina gold mine and Los Cóndores tungsten mine are today used as tourism mines. CR-39 nuclear track detectors were used for this purpose. Measurements were performed during both winter and summer seasons. The findings show that in these environments, significant radon concentrations are subject to large seasonal fluctuations, due to the strong dependence on natural ventilation with the outside temperature variations. For both mines, higher concentration values of (222)Rn were observed in summer than in winter; with an extreme ratio of 2.5 times between summer and winter seasons for Los Cóndores mine. The pattern of radon transport inside La Carolina mine revealed, contrary to what was believed, that this mine behaves as a system with two entrances located at different levels. However, this feature can only be observed in the winter season, when there is a marked difference between the inside and outside temperatures of the mine. In the case of Los Cóndores mine, the radon concentration pattern distribution is principally established by air current due to chimney-effect in summer and winter seasons. In both cases, the analyses of radon pattern distribution appear as a good method to trace air currents, and then localize unknown ducts, fissures or secondary tunnels in subterranean environments.

A portable Compton spectrometer for clinical X-ray beams in the energy range 20-150 keV.

Primary beam spectra were obtained for an X-ray industrial equipment (40-150 kV), and for a clinical mammography apparatus (25-35 kV) from beams scattered at angles close to 90°, measured with a CdTe Compton spectrometer. Actual scattering angles were determined from the Compton energy shift of characteristic X-rays or spectra end-point energy. Evaluated contribution of coherent scattering amounts to more than 15% of fluence in mammographic beams. This technique can be used in clinical environments.

Occupational exposure to radon and natural gamma radiation in the La Carolina, a former gold mine in San Luis Province, Argentina.

Radon and gamma radiation level measurements were carried out inside the La Carolina mine, one of the oldest gold mining camps of southern South America, which is open for touristic visits nowadays. CR-39 track-etch detectors and thermoluminescent dosimeters of natural CaF(2) and LiF TLD-100 were exposed at 14 points along the mine tunnels in order to estimate the mean (222)Rn concentration and the ambient dose equivalent during the summer season (November 2008 to February 2009). The values for the (222)Rn concentration at each monitoring site ranged from 1.8+/-0.1 kBqm(-3) to 6.0+/-0.5 kBqm(-3), with a mean value of 4.8 kBqm(-3), indicating that these measurements exceed in about three times the upper action level recommended by ICRP for workplaces. The correlations between radon and gamma radiation levels inside the mine were also investigated. Effective doses due to (222)Rn and gamma rays inside the mine were determined, resulting in negligible values to tourists. Considering the effective dose to the mine tourist guides, values exceeding 20mSv of internal contribution to the effective doses can be reached, depending on the number of working hours inside the mine.

Influence of soil and buildings on outdoor gamma dose rates in São Paulo, Brazil.

This work analyzes the influence of the most abundant natural gamma emitters in soil (226Ra, 232Th, and 40K) on the total outdoor gamma dose rate in the city of São Paulo, Brazil. A new method is introduced to determine gamma dose rates due to soil 1 m above the ground through measurements performed deep in the soil. This allows evaluation of the soil component even in places where the measurement at 1 m height is influenced by other sources (mainly the presence of buildings). The methodology was tested in non-urbanized areas by comparing direct dose rate measurements in air with those deep in soil. In addition, high-resolution gamma ray spectrometry of soil samples collected throughout the city was used to determine the natural radionuclide concentrations, allowing the comparison with the in-situ dose rate results. Measurements deep in soil followed a log-normal distribution. The fitted geometric mean (median) and geometric standard deviation of the soil contribution to the ambient dose equivalent rate at 1 m height were, respectively, 80.9(6) and 0.642(4) nSv h(-1). Compared to previous data, these values show that buildings enhance about 35% the outdoor gamma dose rate expected only from soil. The specific activities of 226Ra, 232Th, and 40K in dry soil, given by their medians, were, respectively, 41, 75, and 176 Bq k(-1). These results reveal that the terrestrial gamma dose rates in São Paulo are higher than the world average, a fact that can be attributed to high thorium concentration. Direct measurements of dose rates were compared to the corresponding values determined from radionuclide concentrations in soil. Good agreement between methods was found.

Dose measurements in chest diagnostic X rays: adult and paediatric patients.

This survey was carried out in the state of São Paulo, Brazil. The health services located in the state perform approximately 321 radiological examinations per 1000 inhabitants. A representative sample of 200 health services was selected using sampling techniques, and a postal dosimetric kit was sent to each one who agreed to participate. The kit evaluates entrance surface dose (ESD), making use of thermoluminescence dosemeters attached to the skin of patients. The radiographic technique employed and some physical data of patients were also gathered. In this stage of the survey, only chest examinations, projections AP, PA and LAT, were evaluated. A total of 917 ESD values were measured, which correspond to 588 patients and 74 examination rooms. The ESD to patients were analysed according to weight and age. Groups of standard patients (children and adults) were selected, and reference doses were determined. Large variations of ESD were observed, indicating that much can be done in order to reduce the patient doses by changing the technical parameters. Moreover, the results of ESD in paediatric radiology point to the necessity of special attention in the practice of radiological examinations in this age group.

Calibration of LR-115 for 222Rn monitoring taking into account the plateout effect.

The dose received by people exposed to indoor radon is mainly due to radon progeny. This fact points to the establishment of techniques that access either radon and progeny together, or only radon progeny concentration. In this work a low cost and easy to use methodology is presented to determine the total indoor alpha emission concentration. It is based on passive detection using LR-115 and CR-39 detectors, taking into account the plateout effect. A calibration of LR-115 track density response was done by indoor exposure in controlled environments and dwellings, places where 222Rn and progeny concentration were measured with CR-39. The calibration factor obtained showed great dependence on the ambient condition: (0.69 +/- 0.04) cm for controlled environments and (0.43 +/- 0.03) cm for dwellings.

An overview of doses to patients and irradiation conditions of diagnostic chest x ray examinations carried out in hospitals of the City of São Paulo, Brazil.

Recently the Brazilian health organisation published information conceming the number of hospitals, details of radiological equipment and frequency of medical examinations in the country. The information concerning the city of São Paulo is compiled here, complemented by a survey of absorbed doses to patients undergoing the most frequent examination: chest radiographs (postero-anterior (PA) and lateral (LAT) projections), as well as the physical parameters employed (tube voltage, current-time product, focus-film distance, field size). To collect the data, a sample of 12 hospitals (a representative sample of the 199 located in the city) was chosen, totalling 27 X ray machines. An anthropomorphic phantom was irradiated to simulate the patient. Absorbed doses were determined with thermoluminescence dosemeters placed in the phantom, externally and internally. Mean values of entrance surface dose (ESD) for PA and LAT projections were 0.22 mGy (from 0.07 to 0.61 mGy) and 0.98 mGy (from (1.30 to 4.01 mGy), respectively. The average organ doses per complete examination (PA and LAT) were 0.15 and 0.24 mGy to thyroid and lung, respectively. The thyroid was thus in the primary beam in many cases. The large variation in the ESD and organ doses indicates that much can be done in order to reduce the patient doses by adequate changes of physical parameters, without loss of image quality.

Goiânia: 12 years after the 137Cs radiological accident.

In 1987, in the city of Goiânia, Brazil, occurred one of the worst radiological accidents ever reported. The remains of 137Cs contamination in a terrain where part of a radiotherapy unit had been manipulated in 1987 were measured in 1999-2000, and some of the results are presented here. Using the technique of gamma ray spectrometry in situ and in the laboratory, the ambient dose equivalent rate at 1 m above the ground and 137Cs concentration in soil were determined. Values higher than the ones established by the Brazilian National Nuclear Energy Commission (CNEN) as action levels in 1987, namely 0.8 microGy x h and 22.5 kBq x kg(-1), were obtained in that terrain. The 137Cs distribution profile in the soil shows high values of the specific activity in a layer located at a depth of 10-40 cm from the surface, where the soil is mixed with rubble, reaching values as high as 175 kBq x kg(-1).

Characterisation of the thermally stimulated conductivity and thermoluminescence of natural topaz.

Thermally stimulated conductivity (TSC) and thermoluminescence (TL) measurements were conducted to investigate the mechanisms of charge transfer and luminescence emission in natural samples of Brazilian topaz irradiated with beta particles from a 90Sr/90Y source or with a 1.75 MeV Van de Graaff electron beam. The luminescence and conductivity were simultaneously monitored during the heating of the samples, allowing direct comparison of the TL and TSC peaks. The results show that the three main TL peaks are accompanied by corresponding TSC peaks, usually shifted to higher temperatures. Comparison of the relative TL/TSC intensities of peaks 2 and 3 indicates that the process of thermal quenching of the luminescence is probably active, which is also supported by TL/TSC measurements at different heating rates. Results on the dose response of TL/TSC peaks also reveal an interesting feature: the TL intensity shows a monotonic increase with dose in the range of study (50 Gy-3 kGy) comprising a linear-supralinear-saturation characteristic, while the TSC peaks exhibit an increase from 50 Gy to 1 kGy, followed by a small decrease for doses greater than 1 kGy. This result is interpreted in terms of a model involving multiple traps and one recombination centre.

Measurements performed in Goiânia after a new intervention action in 2001.

Brazil's worst radiological accident took place in 1987, in the city of Goiânia. In 1999 and 2000, detailed measurements of 137Cs contamination were performed in junkyard II, one of the places involved in the accident. High values of 137Cs activity per unit mass were found in soil layers at depths between 10 and 40 cm from the surface, reaching values as high as 175 kBq x kg(-1). High values of 137Cs concentration in fruits and plants were also observed. Moreover, values of ambient dose equivalent rate at 1 m above the ground were found to be higher than the limit of 1.0 microSv x h(-1) set by the Brazilian National Nuclear Energy Commission (CNEN) in 1987. In February 2000, the CNEN was informed about the results of our measurements. As consequence, in August 2001, the CNEN performed a new intervention action in the area, covering all its extension with a concrete layer and removing some plants and trees. The new remedial action reduced the dose rate to approximately 13% of the value prior to covering the site in concrete, reaching values below the CNEN limit, as demonstrated by the measurements presented here.

Remains of 137Cs contamination in the city of Goiânia, Brazil.

The results of measurements, performed in 1999, of the remaining 137Cs contamination in some of the sites where fragments of a radioactive source of a teletherapy unit had been manipulated in 1987 are presented. This episode occurred in the city of Goiânia, during Brazil's worst radiological accident ever reported. Using the technique of gamma ray spectrometry, analyses of both surface and profile soil and vegetable samples were made. High values of 137Cs activity per unit mass were found in soil layers at depths between 10 and 40cm from the surface. Some values exceeded by up to eight times the action level of 22.5 kBq x kg(-1) proposed by the Brazilian National Nuclear Energy Commission (CNEN) during the decontamination process at the time of the accident, for the first year after the accident. Absorbed dose rates at 1 m above the ground were calculated from the data of 137Cs concentration in the soil and compared with those obtained from in situ gamma ray spectrometry and from thermoluminescence dosimetry.

Ambient dose equivalent rate in Goiânia 12 years after the 137Cs radiological accident.

This paper describes the situation of ambient dose equivalent rates in four of the main foci of 137Cs contamination in the city of Goiânia, Brazil, in 1999, 12 y after one of the worst radiological accidents in the world. During the decontamination, all the buildings of the three highly contaminated sites were demolished and the top soil removed. Afterwards, the soil of two of these lots was covered with concrete, and they remain vacant today. The soil of the third of these lots, identified here as E, previously known as junkyard II, was covered only with clean soil. Three to four years after the accident, new houses were constructed on this lot, and some very poor people live and work there collecting recyclable material. Gamma ray spectrometry, with a portable survey meter, was performed in the quoted places along with outdoor measurements in many other locations of Goiânia. The average ambient dose equivalent rate due to natural background radiation from radionuclides in the soil and cosmic radiation in non-contaminated areas of the city of Goiânia is 62 nSv h(-1). In most of the highly contaminated sites during the accident, the average ambient dose equivalent rate ranged from around 100 to 1,000 nSv h(-1). The only exception was site E, where values of ambient dose equivalent rate as high as 2.6 microSv h(-1) were found.

How safe is ERCP to the endoscopist?

BACKGROUND: Interventional techniques in endoscopy such as endoscopic retrograde cholangiopancreatography (ERCP) have greatly increased since laparoscopic cholecystectomy has become widespread; mainly these techniques deal with common bile duct stones. Fluoroscopy is usually employed, and chronic exposure to X-ray, in spite of the relative low dose, can lead to potentially unhealthy conditions such as malignancies like bone marrow and other solid cancers. A median of 18 years of life is lost per fatal cancer, including the time of latency since exposure. Nor should one forget benign condition such as cataracts that can lead to partial or complete blindness and which surely impair life's quality. METHODS: Simulated examinations were carried at the University Hospital (São Paulo, Brazil) using an anthropomorphic phantom in place of the physician. Four sets of dosimeters were placed in the forehead, neck, torso, and lower abdomen (with and without a lead apron) and standard ERCP fluoroscopic techniques were employed. RESULTS: The dose equivalents were calculated and compared to the recommended exposure doses of national and international boards of radiation protection. CONCLUSIONS: Based on the results found and compared to standards, working safely means: (1) A lead (0.5 mm thickness) apron is fundamental. Without it less than one ERCP\month should be performed. (2) With an apron, 23 examinations/month are allowed. (3) No thyroid protection grants only 19 exams/month. (4) Performing ERCP without lead glasses is hazardous to the eye, allowing only seven ERCPs monthly.