Comparative analysis of gamma ray spectrometers applied to Irati Formation, Paraná basin, São Paulo State, Brazil.

This paper describes the use of gamma ray spectrometry in the study of rock samples from the Irati Formation, Paraná sedimentary basin, São Paulo State, Brazil. This technique allowed to measure the natural radiation emitted by 40K, as well the radionuclides belonging to the decay series of 238U (eU = 226Ra = 214Bi) and 232Th (eTh = 228Th = 208Tl) which occur in the analyzed samples. Four gamma ray spectrometers have been utilized for comparing the results obtained: a portable sodium iodide [NaI(Tl)] scintillation detector (Digidart), a handheld bismuth germanate oxide (BGO) detector and two bench NaI(Tl) crystals, differing in their geometry (Planar and Well types). This study involved the calibration of the spectrometers, except in the case of the BGO that is factory calibrated. Afterwards, gamma ray analysis was done for 122 rock samples colleted at Partecal Quarry located at Assistência District, Rio Claro city, which have been of interest for the oil and gas sector. For comparison purposes, the obtained datasets were subjected to different statistical tests, including the analysis of variance (ANOVA) that proved to be of great value for checking the differences of the mean concentration values of eU, eTh and K. The results pointed out several factors that affect the gamma ray analysis for the natural radioelements uranium, thorium, and potassium such as the samples size, shape and geometry, detector type, shielding and counting time. These factors are of difficult control in order to get reliable radiometric measurements by this technique.

Determination of impurities in (124)I samples by high resolution gamma spectrometry.

(124)I is a radionuclide used in the diagnosis of tumors. The National Health Agency requires identification and activity measurement of impurities. Using gamma spectrometry with an efficiency calibrated high-purity germanium detector, impurities (125)I and (126)I in an (1)(24)I production sample were identified. Activity ratios of (125)I and (126)I to (124)I were approximately 0.5% and 98%, respectively.

Naturally occurring radioactive materials (NORM) in ashes from a fuel-oil power plant in Cienfuegos, Cuba, and the associated radiation hazards.

The radioactivity of NORM was measured in ashes collected from a fuel-oil power plant in Cienfuegos, Cuba, using an HPGe gamma-ray spectrometer. The (226)Ra, (210)Pb, (40)K, (232)Th and (238)U activity concentrations reached 240, 77, 59, 70 and 15 Bq kg(-1), respectively. The potential radiological hazard of these residuals was assessed. The radium equivalent activities of the samples varied from 54 to 345 Bq kg(-1). The gamma index was calculated to be lower than that of the reference values, and the gamma absorbed dose rate was higher than the average reported for the earth's crust; however, the assessed annual effective dose was slightly lower than the annual effective dose limit for public, i.e. 1 mSv. Therefore, these bottom ashes were not dramatically enriched with radionuclides and may be used as an additive for building materials without restrictions from a radiological protection point of view.

Committed effective dose determination in southern Brazilian cereal flours.

The health impact of radionuclide ingestion from foodstuffs was evaluated by the committed effective doses determined in eight commercial samples of South-Brazilian cereal flours (soy, wheat, cornmeal, cassava, rye, oat, barley and rice flours). The radioactivity traces of (228)Th, (228)Ra, (226)Ra, (40)K, (7)Be and (137)Cs were measured by gamma-ray spectrometry employing an HPGe detector of 66 % relative efficiency. The efficiency curve has taken into account the differences in densities and chemical composition between the matrix and the certified sample. The highest concentration levels of (228)Th and (40)K were 3.5±0.4 and 1469±17 Bq kg(-1) for soy flour, respectively, within the 95 % confidence level. The lower limit of detection for (137)Cs ranged from 0.04 to 0.4 Bq kg(-1). The highest committed effective dose was 0.36 µSv.y(-1) for (228)Ra in cassava flour (adults). All committed effective doses determined at the present work were lower than the International Atomic Energy Agency dose limit of 1 mSv.y(-1), to the public exposure.

Application of the Monte Carlo code DETEFF to efficiency calibrations for in situ gamma-ray spectrometry.

We studied the applicability of the Monte Carlo code DETEFF for the efficiency calibration of detectors for in situ gamma-ray spectrometry determinations of ground deposition activity levels. For this purpose, the code DETEFF was applied to a study case, and the calculated (137)Cs activity deposition levels at four sites were compared with published values obtained both by soil sampling and by in situ measurements. The (137)Cs ground deposition levels obtained with DETEFF were found to be equivalent to the results of the study case within the uncertainties involved. The code DETEFF could thus be used for the efficiency calibration of in situ gamma-ray spectrometry for the determination of ground deposition activity using the uniform slab model. It has the advantage of requiring far less simulation time than general Monte Carlo codes adapted for efficiency computation, which is essential for in situ gamma-ray spectrometry where the measurement configuration yields low detection efficiency.

Gamma spectrometry and chemical characterization of ceramic seeds with samarium-153 and holmium-166 for brachytherapy proposal.

Ceramic seeds were synthesized by the sol-gel technique with Si:Sm:Ca and Si:Ho:Ca. One set of seeds was irradiated in the TRIGA type nuclear reactor IPR-R1 and submitted to instrumental neutron activation analysis (INAA), K(0) method, to determine mass percentage concentration of natural samarium and holmium in the seed as well as to determine all existing radionuclides and their activities. Attention was paid to discrimination of Si-31, Ca-40, Ca-45, Ca-47, Ca-49, Sm-145, Sm-155, Sm-153 and Ho-166. A second sample was submitted to atomic emission spectrometry (ICP-AES) also to determine samarium and holmium concentrations in weight. A third sample was submitted to X-ray fluorescence spectrometry to qualitatively determine chemical composition. The measured activity was due to Sm-153 and Ho-166 with a well-characterized gamma spectrum. The X-ray fluorescence spectrum demonstrated that there is no discrepancy in seed composition. The maximum ranges in the water of beta particles from Sm-153 and Ho-166 decay were evaluated, as well as the dose rate and total dose delivered within the volume delimited by the range of the beta particles. The results are relevant for investigation of the viability of producing Sm-153 and Ho-166 radioactive seeds for use in brachytherapy.

Methodological analysis of gamma tomography system for large random packed columns.

Gamma ray tomography experiments have been carried out to detect spatial patterns in the porosity in a 0.27 m diameter column packed with steel Rashig rings of different sizes: 12.6, 37.9, and 76 mm. using a first generation CT system (Chen et al., 1998). A fast Fourier transform tomographic reconstruction algorithm has been used to calculate the spatial variation over the column cross section. Cross-sectional gas porosity and solid holdup distribution were determinate. The values of cross-sectional average gas porosity were epsilon=0.849, 0.938 and 0.966 for the 12.6, 37.9, and 76 mm rings, respectively. Radial holdup variation within the packed bed has been determined. The variation of the circumferentially averaged gas holdup in the radial direction indicates that the porosity in the column wall region is a somewhat higher than that in the bulk region, due to the effect of the column wall.

Determination of 51Cr and 241Am X-ray and gamma-ray emission probabilities per decay.

In this paper results of X-ray and gamma-ray emission probabilities per decay of (51)Cr and (241)Am are presented. The measurements were carried out by means of HPGe planar and REGe spectrometers. The activity of (51)Cr and (241)Am samples was determined in a 4pibeta-gamma coincidence counting system. The HPGe spectrometers were calibrated in a well defined geometry by means of (54)Mn, (55)Fe, (57)Co, (133)Ba, (152)Eu, (166m)Ho and (241)Am sources, previously standardized in a 4pibeta-gamma coincidence system. The MCNP Monte Carlo code was used for simulation of the REGe spectrometer calibration curve, for the selected geometry, and compared with the experimental curve. The experimental results were compared with data from literature.

Characterisation of uranium(VI) sorption by two environmental fungal species using gamma spectrometry.

Uranium(VI) sorption by two highly uranium-resistant air-borne fungi in a low-pH medium was measured by means of gamma spectrometry. Growth kinetics and stoichiometry of the two fungal species were also studied. Results show acceptable growth rates in synthetic medium with glucose and ammonia as carbon and nitrogen sources, respectively. Typical oxidative metabolism of carbohydrates was found. In vivo uptake of the radionuclide was negligible, but biosorption dry biomass presented a remarkable performance. The fungal strains showed potential for use in bioremediation.

Standardization of 241Am solution.

The standardization of 241 Am solution has been undertaken using a 4pibeta-gamma coincidence system. The 4pi proportional counter used for alpha detection has a 0.1 mm thick Al window in the outside wall in order to minimize gamma-ray attenuation. The extrapolation technique was applied to determine the activity of the solution. The variation of alpha efficiency has been made using external absorbers and by the electronic discrimination. The results from the two methods were compared and are in agreement within the experimental uncertainty.

Primary standardization of 72Ga.

The activity of 72Ga sources produced by irradiation at the IEA-R1 reactor have been performed in a 4pibeta-gamma coincidence system by using the extrapolation technique. The measurements were undertaken selecting two windows in the gamma-channel, in order to check the consistency of the results. A Monte Carlo calculation was performed in order to predict the behavior of the observed activity as a function of the 4pibeta detector efficiency and the results were compared to experimental values.

In situ gamma spectroscopy measurement of 41Ar during neutron activation analysis with the SLOWPOKE II reactor in Jamaica.

In situ gamma spectroscopy was used to measure 41Ar released into the laboratory due to the activation of air in the irradiation tubes of SLOWPOKE reactor during routine neutron activation analysis. The data obtained were used to predict the 41Ar distribution in the laboratory for various operating conditions of the reactor. The dose received by the analyst from the immersion in 41Ar was calculated to be 2.36 microSv gamma(-1), which is approximately 1% of the normal background exposure.

Non-destructive porosity profile measurement of amorphous materials by gamma-ray transmission.

This work presents measurements of the total porosity of TRe soil, sandstone rocks and porous ceramic samples. For determination of the total porosity, the gamma-ray transmission method and the Archimedes method (conventional) were employed. The porosity measurement using the gamma-ray methodology has a significant advantage with respect to the conventional method due to fast and non-destructive determination, and also for supplying results with a greater spatial resolution, in relation to the heterogeneity of the porosity. The conventional methodologies provide good results only for homogeneous samples. The experimental setup for the gamma-ray transmission technique consisted of a 241Am source (5953 keV), a NaI(Tl) scintillation detector, collimators, a XYZ micrometric table and standard gamma spectrometry electronics connected to a multichannel analyzer.

The interplay between the statistical correlations of gamma-ray emission probabilities and efficiency calibration.

The procedure to determine the statistical correlations between gamma-ray intensities is described here, as well as that required to take these correlations into account. The advantages of using branching-ratios and feeding fractions instead of gamma-ray intensities in the gamma-ray standards are discussed.

Measurements of nuclear data parameters of 201Tl by gamma-ray spectrometry.

201Tl is frequently used in radiopharmaceutical applications, and therefore the gamma-ray emission probabilities and half-life have been re-determined by means of gamma-ray spectroscopy. While the activity was calibrated using the sum-peak coincidence method, the half-life was obtained by the reference source method based on simultaneous counting of a reference source and the sample. Both the measurement techniques and assignment of uncertainties are presented and discussed, and the resulting data are shown to be in good agreement with previously published studies.

Use of the reference source method to determine the half-lives of radionuclides of importance in nuclear medicine.

The reference source method associated with HPGe gamma-ray spectrometric techniques has been applied to half-life determinations of radionuclides used in nuclear medicine. Simultaneous measurements were undertaken for radiopharmaceutical nuclides such as 67Ga, 99Tcm, 123I, 131I and another radionuclide as reference. Besides optimizing the analysis time, this procedure was shown to be independent of the instrumental technique, environmental and radiochemical impurity interferences for most radionuclides. However, some restrictions were observed in samples that contained impurities with the same emission energy or an energy that was very close to the energy of the radionuclide to be measured. The measurement conditions improved the quoted accuracy of the half-life by reducing the type B component uncertainty.

Precise determination of photon emission probabilities for the main X- and gamma-rays of 226Ra in equilibrium with daughters.

Within the context of a joint project between VNIIM (D.I. Mendeleyev Institute for Metrology) and LNHB (Laboratoire National Henri Becquerel), special 226Ra sources were prepared by VNIIM in order to determine as accurately as possible the absolute photon emission probabilities for the main X- and gamma-rays following the decay of 226Ra and daughters. The main purpose of this work was to supplement a previous joint study by Laboratorio Nacional de Metrologia das Radiaçoes Ionizantes (LNMRI) and LNHB to determine their relative values. Some specific point sources were produced for alpha-spectrometry measurements that were undertaken at VNIIM and also for gamma-ray spectrometry studies at VNIIM and LNHB. The 226Ra activity for the gamma-spectrometric sources was measured relative to the alpha-spectrometric sources by comparing the counts of the main gamma-rays. The total uncertainty of the activity for these sources was 0.2% (k = 1). Using calibrated germanium detectors, several X- and gamma-ray spectra were analyzed to determine the absolute photon emission probabilities of 226Ra in radioactive equilibrium with daughters. The results are presented and compared to other published values.

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.

Self-absorption correction for gamma spectrometry of powdered milk samples using Marinelli beaker.

Self-absorption was measured for the activity calculation of the 1460.8 and 2614.47 keV lines of the 40K and the 208Tl, respectively, in powdered milk samples. Five Marinelli beakers were prepared with powdered milk in different degrees of compaction and the spectra were measured with an HPGe detector. The detection efficiency versus density was obtained and the self-absorption correction factors versus density were calculated for powdered milk. The results obtained show that this factor must be considered in the calculations of activities.

Tiroides lingual. Reporte de dos casos / Lingual thyroid. Report of two cases

La glándula tiroides cumple una importante función en el organismo debido a la participación de sus hormonal en el crecimeinto, maduración y funcionamiento normal de las células y tejidos. Durante la embriogénesis, el tubérculo tiroideo debe migrar caudalmente para permitir la fusión de las prominencias laterales de la lengua, y cuando ello no ocure, queda atrapado en la base de la lengua. Se informan dos casos de niñas de 4 y 11 años de edad quienes presentaron una masa en el tercio posterior de la lengua diagnosticada como tiroides lingual, casos que fueron confirmados mediante gamagrafía de tiroides