【摘 要】
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Phosphogypsum is classified as NORM and one of the main environmental concerns of its use is the radon exhalation from this material.Phosphogypsum is a by-product from wet-acid process of phosphoric a
【机 构】
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Instituto de Pesquisas Energéticas e Nucleares Av. Prof . Lineu Prestes,2242 - Cidade Universitària,
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Phosphogypsum is classified as NORM and one of the main environmental concerns of its use is the radon exhalation from this material.Phosphogypsum is a by-product from wet-acid process of phosphoric acid production.The radioactivity present in the phosphogypsum,among other impurities,prevents its reuse for a variety of purposes.The Brazilian phosphate industry is responsible for a production of 5.5 million t/year of phosphogypsum.Several studies were undertaken in Brazil concerning the radiological impact of using the phosphogypsum as building material.As a complementary study,this paper aims to determine the activity concentration of natural radionuclides,radium equivalent concentration,external and internal hazard index and the radon exhalation rate from bricks and plates made of phosphogypsum from three industries: Ultrafertil,Fosfertil and Bunge.Samples of phosphogypsum bricks and plates were analyzed by gamma spectrometry for their radionuclide content; each sample was analyzed in triplicate.The radium equivalent activities,external and internal hazard index and radon exhalation rate were determined using theoretical models.The concentration in phosphogypsum bricks samples varied from 16 t0 392 Bq kg-1 for 226Ra; from 26 t0 253 Bq kg-1 for 232Th; from 26 t0 852 Bq kg-1 for 2IOPb and < 22 Bq kg-1 for 40K; and the concentration in phosphogypsum plates samples varied from 29 t0 388 Bq kg-1 for 226Ra; from 37 t0 273 Bq kg-1 for 232Th; from 32 t0 426 Bq kg-1 for 2IOPb and < 22 Bq kg-1 for 40K.The results of 222Rn exhalation rates from phosphogypsum plates using UNSCEAR model varied from 0.16 t0 4.3 Bq m-2 h-1,and from phosphogypsum bricks varied from 0.4 t0 5.7 Bq m-2 h-1.The results of radium equivalent,external and internal hazard index showed that plates and bricks from Ultrafertil and Fosfertil present values above the recommended limit; and those from Bunge presented values below the recommended limit.Rn exalation rates for phosphogypsum plates and bricks from all origins are the same order of magnitude of common building materials,such as sand and concrete.
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