Nancy K. Umisedo

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.

Radioactivity teaching: Environmental consequences of the radiological accident in Goiânia (Brazil)

Ionizing radiation and its effects on human beings, radiation protection, and radiological accident prevention are topics usually not included in the physics courses at the Brazilian universities. As a consequence, high school teachers are not able to enlighten their students when radiological or nuclear accidents occur. This paper presents a teaching program on ionizing radiation physics, to be applied to undergraduate physics students and to physics high school teachers. It is based on the environmental consequences of the 1987 radiological accident in Goiânia. This program was applied to two undergraduate physics students, in 1999, at the Universidade Federal Fluminense, Brazil. Results of the gamma ray spectrometry measurements of samples collected in Goiânia by the students are presented.

Natural Radioactivity in Bananas

The content of 40K natural radionuclide in bananas (Musa sapientum) from the Vale do Ribeira region, Sao Paulo, Brazil, has been measured. We have collected several samples of bananas prata and nanica, its peels, leaves, and also different soils where the banana tree was planted, such as soil with a standard amount of fertilizer, the fertilizer itself and also soil without fertilizer for comparison. We have used the gamma‐ray spectroscopy technique with a NaI(T1) crystal inside a 12 cm thick lead shield to detect the gamma‐radiation. The results indicate that only part of the available potassium is absorbed by the plant, which is mainly concentrated in the banana peel.

OSL and TL techniques combined in a beryllium oxide detector to evaluate simultaneously accumulated and single doses.

Optically stimulated luminescence (OSL) and thermoluminescence (TL) are similar techniques widely used in radiation dosimetry. The main difference between these techniques is the stimulus to induce luminescence emission: TL technique uses thermal stimulation, whereas OSL uses optical stimulation. One of the main intrinsic characteristics of the OSL technique is the possibility of reading several times the dosimetric materials with a negligible loss of signal. In the case of BeO, recent studies have shown that TL stimulation up to 250°C does not affect its OSL signal. Taking the advantages of dosimetric characteristics of BeO combined with both techniques, in this study, we demonstrated the possibility of measuring accumulated and single doses in the same BeO-based detector in order to use it to improve individual monitoring of radiation workers exposed to X-ray or gamma-ray fields. Single doses were measured using TL technique by heating the detector up to 250°C, whereas accumulated doses were estimated using OSL technique in the same detector in a relatively short time of optical stimulation. The detectors were exposed to two energies: 28keV X-rays and 1.25MeV Co-60 gamma rays. The doses estimated by OSL and TL of BeO (Thermalox 995) were compared with those obtained with LiF (TLD-100) and recorded with a calibrated ionization chamber. The results indicate that combined OSL and TL signals of BeO detectors can provide additional information of accumulated dose, with additional exploration of the advantages of both techniques, such as speed in readouts with OSL, and double-check the doses using TL and OSL intensities from BeO.

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.

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.

Ionizing Radiation Dose Due to the Use of Agricultural Fertilizers

The transference of radionuclides from the fertilizers to/and from soils to the foodstuffs can represent an increment in the internal dose when the vegetables are consumed by the human beings. This work evaluates the contribution of fertilizers to the increase of radiation level in the environment and of dose to the people. Samples of fertilizers, soils and vegetables produced in farms located in the neighbourhood of Sao Paulo city in the State of Sao Paulo, Brazil were analysed through gamma spectroscopy. The values of specific activity of 40K, 238U and 232Th show that there is no significant transference of natural radionuclides from fertilizers to the final product of the food chain. The annual committed effective dose due to the ingestion of 40K contained in the group of consumed vegetables analysed in this work resulted in the very low value of 0.882 μSv.

Assessment of Low Doses During Diagnostic Procedures Using BeO Detectors and OSL Technique

Advances in imaging techniques with the use of radiation increased the quality and power of medical diagnostic. At the same time, concerns about the doses to patients arose in the radiation protection community. According to UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation), the second main contribution to the population annual dose is from exposure in medical procedures. Although the doses are relatively low in diagnostic, the number of exams for the same patient is growing, bringing especial attention to doses to children or to radiosensitive regions in the body. International organizations recommend the establishment of reference levels in diagnostic procedures and the tracking of the patient exposures. Considering this, we studied the use of optically stimulated luminescence (OSL) and thermoluminescent (TL) techniques together for assessment of skin doses in simulated (pediatric phantom) and real patients during diagnostic procedures. BeO and LiF detectors were used in mammography and radiographic procedures, and in CT examinations. The results of TL and OSL were compared to each other and to international reference levels, when it was possible. Both detectors were able to evaluate doses in the range of 15 µGy to 100 mGy. BeO detectors presented compatible results with LiF detectors for doses in the range of few mGy and low uncertainties in the range of µGy, for both, adults and pediatric patients. We can conclude that the advantages of OSL technique combined to intrinsic characteristics of BeO (tissue equivalence and flat energy response for photons up to 100 keV) can be explored for assessment of patient doses in diagnostic procedures.

Characterization of OSL dosimeters for use in dose assessment in Computed Tomography procedures

This study describes the characterization of an Al2O3:C OSLD (Landauers Luxel™ tape) for dose evaluation in Computed Tomography. The irradiations were conducted using both a constant potential X-ray equipment and a 64-slice clinical CT scanner, and the readouts were performed using a Risø TL/OSL reader. The following aspects were studied: batch homogeneity, energy response, linearity of dose response, reproducibility, reusability, and effect of uncertainties with the normalization of OSL signals per their response to beta radiation. A group of 330 dosimeters from the 452 irradiated with the same dose presented OSL signals within the interval of 4.7% from the average. The dosimeters presented energy-dependent response in good agreement with results found in the literature. The air kerma response of the OSL signal showed a linear trend for both the constant potential X-ray device and the clinical CT scanner, with differences in their slopes of approximately 10%. Reproducibility, reusability, and effect of beta normalization were analyzed by separating 72 dosimeters in 3 groups. The results obtained in this study together with those of previous works indicate that this type of dosimeter is adequate for dose evaluation in CT clinical applications.

OSL dosimetric properties and efficiency of Brazilian natural calcium fluoride pellets

Calcium fluoride (CaF2), in both natural and synthetic forms, has been exhaustively studied and explored as thermoluminescent (TL) detector. However its sensitivity to ambient light points to the applicability of CaF2 as OSL (Optically Stimulated Luminescence) detector, increasing the research about its luminescent properties. Although some properties to employ CaF2 detectors with OSL technique have been already demonstrated, there is a lack of some essential information as the OSL response to different types and energy of ionizing radiation. In order to extend the use of Brazilian natural CaF2 with OSL technique, we evaluated the efficiency and dosimetric properties of cold pressed CaF2:NaCl pellets. The CaF2 detectors presented good reproducibility and negligible fading of the signal over one month after irradiation. The dose response using OSL, TL and residual TL showed linear behavior for different radiation beams (protons, photons and alpha and beta particles), being equivalent to the results obtained with BeO and MTS (LiF) detectors through OSL and TL technique respectively. Moreover, differences were observed in OSL efficiency according the beam type and energy; CaF2 detectors presented a higher OSL and TL sensitivities to protons, photons and beta particles than to alpha particles. The energy response to photons obtained using OSL and residual TL intensities present an over response at lower photon energy similar to TL energy response. In addition, differences in the OSL curve shapes were observed according to radiation type and energy, pointing to the possibility of applying this material in mixed radiation fields and to estimate average LET (Linear Energy Transfer).