J.M. Paniagua

Influence of geology and soil particle size on the surface-area/volume activity ratio for natural radionuclides

The radioactive concentrations of226Ra,232Th,235U and40K in surface soil of the province of Cáceres (Spain) were studied as a function of the geology and grain size. The activities of the four radionuclides in granitic and metamorphic soils have normal frequency distributions, with the mean value being significantly higher for the granitic soils than for the metamorphic soils. Sedimentary soils present asymmetric distributions, and their activities lie between the previous two types. The specific activities of the four radionuclides rises as the particle radius decreases. The equationAe=(P1/R)+P2 describes the dependence of the specific activityAe on radiusR, P1 andP2 being parameters that are related to the surface area and volume activities of the grains. The isotopes226Ra,232Th and235U accumulate with greater intensity on the surface of the grains than40K. This effect is more pronounced in granitic and sedimentary soils than in metamorphic soils.

Analysis of the temporal evolution of atmospheric7Be as a vector of the behavior of other radionuclides in the atmosphere

The mean weekly levels of7Be in the atmosphere of Cáceres (Spain) was measured for three consecutive years, from 1992 to 1994. The values showed a strongly seasonal behavior, conditioned fundamentally by two effects: (1) the incorporation of7Be into the low layers of the troposphere due to the displacement of masses of air from higher layers caused by the solar irradiation, and (2) the washing of7Be out of the atmosphere by rain. From the quantification of these two effects, the residence time of7Be was determined in the atmosphere at ground level as 10.3 days, with an interval for the standard error of 9.0 and 12.1 days. Modelling the temporal evolution of this radionuclide we were able to explain 90.72% of the variance of the measured activity levels. Using the effective residence time of7Be, we were able to justify the diversity of values obtained for the deposition of137Cs in different soils of the province of Cáceres due to the fallout from atmospheric nuclear blasts.

Natural radionuclide distribution in soils of Cáceres (Spain): Dosimetry implications

Abstract Levels of exposure to natural radiation have been calculated from the concentrations of natural gamma-emitting radionuclides present in the soils of the province of Caceres (Spain). The objective was to estimate the external radiation dose received by the population as a function of the place of residence, and then to draw the corresponding natural exposure rate map for the region under study. For this purpose, 263 soil samples were collected from points uniformly distributed throughout the geography of the zone. These were analysed using gamma spectrometry. The mean specific activities of 226 Ra, 235 U, 232 Th and 40 K were 38.3, 3.06, 41.0 and 653 Bq kg −1 dry weight, respectively, and the isoactivity maps for each isotope showed that the greatest concentrations occurred in granitic zones. The average value of the outdoor absorbed dose rate in air was 56.6 nGy h −1 , corresponding to an annual effective dose equivalent of 429 μSv. The range of these values is very broad, varying from a minimum of 9 nGy h −1 to a maximum of 8320 nGy h −1 in the vicinity of a uranium mine.

Surface and depth fallout distribution of137Cs and90Sr in soils of Caceres (Spain). Dose commitments due to external irradiation

An analysis has been made of the surface distribution of137Cs and90Sr in soils of the province of Cáceres (Spain), of some 20.000 km2 area, situated on the frontier with Portugal. From the distribution of depth profiles of concentrations of these radionuclides and their fit to a negative exponential, determination was made of the mean values of the respective inventories and of the corresponding137Cs/90Sr ratio. The external dose rates from the presence of these man-made isotopes in the soil are calculated and compared with that originating from the concentrations of natural radioisotopes.

The program ESPEC for the analysis of gamma spectra of environmental samples

Abstract A set of programs coded in BASIC has been developed on a microcomputer to carry out the main tasks for the gamma spectrometric analysis of environmental samples, in particular transfer of spectra, detector efficiency calibrations, and activity calculations. It could be also easily adapted to the requirements of each laboratory.

RADIOLOGICAL IMPACT OF THE ALMARAZ NUCLEAR POWER PLANT (SPAIN) DURING 1986 TO 1989 ON THE SURROUNDING ENVIRONMENT

With the object of quantifying the radiological impact that the Almaraz Nuclear Power Station, situated beside the Tajo river in Spain, induces on its ecosystem, since 1986 we have been carrying out multiple gamma-spectrometric studies and determinations of90Sr concentrations on the receptor media: surface waters, sediments, fishes, aerosols, and soils, in the two likeliest critical transmission pathways of transmission of the radioactive contamination. The principal results are summarized in the present work, and they allow the impact to be quantified, as well as the most probable source to be assigned for each of the levels detected.

Radiocesium concentration in migratory birds wintering in Spain after the Chernobyl accident

Levels of 137Cs and 134Cs resulting from the Chernobyl nuclear accident were studied in 195 birds that winter in two regions of Spain. Only five of the 12 species examined were contaminated. The average values for 137Cs vary between 1.6 and 41 Bq kg-1 fresh. In particular, the contamination for song-thrushes (Turdus philomelos) are compared between the regions of Extremadura and Valencia, 350 km east of Extremadura at the same latitude. The results show that the contamination of birds wintering in Spain decreases from east to west. The whole-body dose commitment for humans consuming these contaminated birds was calculated. The values are well below the established ICRP guideline.

Bio-availability and transfer of natural radionuclides in a mediterranean ecosystem

Abstract We have studied the soil to plant transfer coefficients for the natural radionuclides 226 Ra, 228 Ra, and 228 Th in the species Cistus ladanifer in a Mediterranean type ecosystem. The secular equilibrium that exists between 228 Ra and 228 Th in the total fraction of the soil is broken in the available fraction and, consequently, in the different vegetation fractions considered. The bio-availability of 226 Ra is similar to that of 228 Ra. There exists, nevertheless, a positive discrimination by the plant in favour of the former. The transfer from the available fraction of the soil to the different fractions in the plant present a characteristic time-depedence for each vegetation fraction.

Radioactive concentrations of the Livingston Island soils (Antartica). Dosimetry considerations

Abstract The radioactive concentrations of natural and man-made ( 90 Sr and 137 Cs) emitters were studied in soil samples collected from an area of 2.3 km 2 around the Spanish Antarstic Base on Livingston Island in the South Shetlands. The levels of radiation detected, for natural radioisotopes, as well as consequently the measured levels of effective dose equivalent rate, are of the order of half the values commonly assigned as world averages for these magnitudes.

Radiocesium and radiostrontium levels in song-thrushes (Turdus philomelos) captured in two regions of Spain

Abstract A study was carried out, in two different regions of Spain, on the radioactive contamination of the migratory species Turdus philomelos whose breeding grounds are found in central and northern Europe. The nuclides analyzed were 134 Cs, 137 Cs and 90 Sr. The analyses were carried out on birds captured during two successive campaigns after the Chernobyl accident (1986 and 1987). In the second, a distinction was made between young and adult birds. Finally, the individual whole-body dose commitment to humans consuming these birds was estimated.