V. Gómez Escobar

AN ENVIRONMENTAL NOISE STUDY IN THE CITY OF CACERES, SPAIN

Abstract An urban noise survey was conducted in the city of Caceres (Extremadura, Spain). In order to select the different points where measurements were to be taken, the streets were classified according to their use in communicating the different zones of the city. The four categories considered were all through roads (service roads were excluded): arterial roads outside the central zone, arterial roads in the central zone, other two-way roads connecting different zones, other one-way roads. The first two categories were found to be statistically indistinguishable, and together with the third had the highest noise levels—median Leq above 70 dB(A). The one-way roads were some 5 dB(A) quieter. Thus the sound levels in Caceres, a small city, are quite high, with 90% of our measurements surpassing an Leq of 65 dB(A) during working hours. Finally, relationships were established between the equivalent level, traffic flux, and the main noise level percentiles, with results in good agreement with those of other authors. We can also conclude that city noise can be usefully studied by classifying the streets according to their use.

Radioactivity in bottled mineral waters.

Consumption of bottled mineral water is a growing practice and is sometimes a necessity rather than a choice. In this work, a study of the radioactive content of a wide selection of commercial bottled mineral waters for human intake was carried out. The origins of the analyzed waters were very different, coming from various locations in France, Portugal and Spain. Their total alpha and beta activity concentrations were determined and also gamma spectrometry was used to detect some radionuclides. In some cases, the waters presented high values of the total alpha and beta activity concentrations surpassing the reference levels established by the CSN, the Spanish. Regulatory Organization. In these cases, a determination of uranium and 226Ra was also performed by using low-level liquid scintillation counting. The results revealed a strong correlation between radioactive content and dry residue, and lead one to conclude that high radioactive content is mainly related to the mineralization in waters of underground origin.

DETERMINATION OF 222RN AND 226RA IN AQUEOUS SAMPLES USING A LOW-LEVEL LIQUID SCINTILLATION COUNTER

Abstract A method for measuring 222 Rn and 226 Ra in aqueous samples has been studied. The technique uses low-level liquid scintillation counting from vials containing an insoluble high efficiency mineral oil scintillation cocktail. A Wallac 1220 TM Quantulus LS counter was used for all the experiments. The optimum pulse-shape discrimination value was evaluated by using the minimum detectable activity criterion for each condition of measurement. Experiments on the optimum volume and sample-cocktail ratio, the influence of shaking, type of vial and diffusion of radon from vials were carried out. The study was applied to the determination of very low levels of 222 Rn and 226 Ra from aqueous environmental samples. The results reached using this method were very satisfactory and even better than from other more laborious procedures.

Radiological characterization of a uranium mine with no mining activity

We report a radiological study of a uranium mine located in Extremadura, in the south-west of Spain, in which mining work had ceased. One interest in the work is that the results can be used as a reference for the future evaluation of the effects produced by the restoration program. The radiological parameters selected to estimate the impact of the inactive mine were: 222Rn in air and water, 222Rn exhalation, effective 226Ra in soils and sediments, and natural uranium and 226Ra in water. Chemical analyses of water samples and measurements of meteorological variables were also made. Average values of these radiological parameters are presented. We characterize the zone radiologically and estimate the influence of the mine on the basis of some of these parameters, while others are used to reflect the status of the installation, information which could be very useful in the near future when restoration is complete.

Extractive procedure for uranium determination in water samples by liquid scintillation counting.

An extractive procedure for uranium determination using liquid scintillation counting with the URAEX cocktail is described. Interference from radon and a strong influence of nitrate ion were detected in this procedure. Interference from radium, thorium and polonium emissions were very low when optimal operating conditions were reached. Quenching effects were considered and the minimum detectable activity was evaluated for different sample volumes. Isotopic analysis of samples can be performed using the proposed method. Comparisons with the results obtained with the general procedure used in alpha spectrometry with passivated implanted planar silicon detectors showed good agreement. The proposed procedure is thus suitable for uranium determination in water samples and can be considered as an alternative to the laborious conventional chemical preparations needed for alpha spectrometry methods using semiconductor detectors.

Sequential method for the determination of uranium, thorium and 226Ra by liquid scintillation alpha spectrometry.

A new procedure for the determination of uranium, thorium and 226Ra from the same aliquot of an aqueous sample using extractant scintillators and liquid scintillation alpha spectrometry is proposed. The procedure is designed such that the same aqueous phase can be used in all the stages, with slight modifications. The procedure is thus very simple, requiring little manipulation of the sample. Testing of the procedure was performed obtaining satisfactory results and high reproducibility.

Procedures for the determination of 222Rn exhalation and effective 226Ra activity in soil samples.

Two methods for measuring 222Rn exhalation and effective 226Ra in soil samples were studied. In the first determination, the method employed was based on the adsorption of radon onto activated charcoal and subsequent measurement of the activity of its daughters with an HPGe (high-purity germanium) detector. In the second, vials containing an aqueous suspension of the sample, mixed with an insoluble high efficiency mineral oil scintillation cocktail, were measured using a low-level liquid scintillation counter. Studies of optimum sampling time, efficiency in both procedures, variation of 226Ra efficiency with quenching, as well as the effect of sample amount and granulometry upon the quenching parameter, were carried out. The two methods were applied to the determination of 222Rn exhalation and effective 226Ra in environmental samples.

Gamma and alpha spectrometry for natural radioactive nuclides in the spa waters of Extremadura (Spain)

Abstract Gamma and alpha spectrometry of waters from several spas of Extremadura (Spain) were performed in order to determine their radioactivity. For the gamma spectrometry, the sample was measured directly using an HpGe detector with a Marinelli beaker. The nuclide 222Rn was determined by measuring the emissions from its daughters 214Pb and 214Bi and assuming transient equilibrium. Each sample was measured for several days in order to check that 214Pb and 214Bi decay with the half-life of 222Rn. Concentrations of 222Rn ranged from 3.5 to 234 Bq/l. Alpha spectrometry of uranium, thorium and 226Ra was performed by chemical separation of these elements from the samples and then using PIPS detectors for the measurement of the sources. Uranium concentrations were in general below 1 μg/l (with one exception), thorium specific activities were of the order of 10−5 Bq/l, and 226Ra activity ranged from 4.5 to 71 mBq/l. These results allow some conclusions to be established about the environmental behaviour of these radionuclides.

Gross alpha- and beta-activities in rainwater and airborne particulate samples. Influence of rainfall and radon

Abstract Measurements of α and β radioactivity were made each month during the years 1993 and 1994 for rainwater samples, and each week for airborne particulate samples collected using air filters at a clear site. The relationship between the measured activities of rainwater and the amount of rainfall was studied. An experimental study of the 220 Rn and 222 Rn decay products was made for the air-filtered samples and led to the conclusion that a waiting period of 5 days is necessary between the sampling time and the time of the activity measurement.

Study of the peak shape in alpha spectra measured by liquid scintillation

Liquid-scintillation counting allows the measurement of alpha and beta activities jointly or only of the alpha-emitting nuclides in a sample. Although the resolution of the alpha spectra is poorer than that attained with semiconductor detectors, it is still an attractive alternative. We describe here attempts to fit a peak shape to experimental liquid-scintillation alpha spectra and discuss the parameters affecting this shape, such as the PSA (pulse-shape analyser) level, vial type, shaking the sample, etc. Spectral analysis has been applied for complex alpha spectra.