Page 51 - PR 2014 2016 07 Nuclear Science and Technology

Nuclear Science and Technology | Progress Report 193

lower concentration of radionuclides analyzed acterized for this purpose using a technique
when compared with plants grown by the called double exposure and sensitivity intrinsic
producer, as these were grown in pots with factor. The characterized plastic was efficient
organic substrate and addition of fertilizer, for the application and the calibration fac-
whose analysis showed low concentrations tor corresponded to 1.60 ± 0.10 tracks • cm •
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of radionuclides studied. Based on data from (kBq • m • day) in relation to the CR39 factor,
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national literature who studied the Brazilian equivalent to 2.8 ± 0.2 tracks • cm • (kBq • m •
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fertilizer, it can be concluded, to the plants from day) . The detector showed a higher efficiency
the producer, the fertilizer has a great influence at a higher dose. The activities determined by
in the concentration of radionuclides studied. passive detection varied from 100 ± 10 Bq • m
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up to (2,4 ± 0,3)·103 Bq • m , highlighting the
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Assessment of natural radioactivity in commercial biggest exhalation rates for granite Iberê Mom-
marble and granite of Espírito Santo State basa. Considering the marbles, activity values
varied from 80 ± 10 Bq • m up to 200 ± 25 Bq •
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Concentrations of natural radionuclides Ra, m highlighting only the Cintilante and Branco
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226
40
232 Th and K in granite and marble samples Extra with higher values. The values obtained
were determined, considering the main ex- for surface exhalation rate were approximate-
traction mining of Espírito Santo state, south- ly equal, except for granites Iberê Mombasa
eastern Brazil. For all studied sites, three and Iberê Prado with values above 1 Bq • m
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samples were sealed in 100 mL high density • h . The measures by gamma spectrometry
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polyethylene bottles. Each sample rested for showed that the 226 Ra concentrations varied
4 weeks to reach the secular equilibrium of from 1.9 ± 0.2 Bq•kg up to 483 ± 55 Bq•kg ,
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238 U and Th series before measured by high with the highest value for granite Iberê Mom-
232
resolution gamma spectrometry, and the ac- basa. The 232 Th concentrations ranged from
quired spectra were analyzed with the soft- 3.2 ± 0.4 Bq·kg1 to 224 ± 6 Bq•kg , whose larg-
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ware WinnerGamma. The self-absorption cor- est value was observed for the gray granite
rection was considered for all samples, using Corumbá. The K concentrations ranged from
40
an expression and method specially developed 8.8 ± 1.8 Bq•kg up to 1642 ± 67 Bq•kg , with
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for this purpose. The concentration of 226 Ra the largest value observed for granite Iberê
was determined by the weighted arithmetic Vitara. The radio equivalent value showed
mean of 214 Pb and 214 Bi concentrations, the that most samples can be defined as category
concentration of Th by the weighted arith- I, below 370 Bq•kg , except for the granites
232
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228
metic mean of Ac, Pb and Bi concentra- Cinza Corumbá, Iberê Crema Bordeaux and
212
212
40
tions, and the concentration of K by its single Iberê Mombasa that can be classified as class
1460 keV transition. The radium equivalent II (up to 740 Bq•kg ). The evaluated granites
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and gamma index were calculated from the show internal and external exposure rates
activity concentrations of Ra, Th, and 40K. below 1.0 mSv • y except the granites Cinza
226
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232
The emanated radon was measured using an Corumbá, Iberê Crema Bordeaux and Iberê
exhalation chamber and the passive detector Mombasa that exceed the value range of 1.0
technique, with a solid state nuclear tracks to 3.2 mSv • y for this index. For the annual
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detectors (SSNTD) being exposed in NRPB/SSIH exposure dose, only the granites Gray Corum-
dosimeters. During exposure, a commercial bá, Iberê Crema Bordeaux and Iberê Mombasa
detector CR39 ® and a national plastic called exceeded 1.5 mSv • y . For the alpha exposure
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Durolon ® were used. The last one was char- index only the Iberê Crema Bordeaux and Iberê