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178 Nuclear Science and Technology | Progress Report

due to its high selenium concentration. Some 228 Ra was the main contributor to the dose
studies have shown that the daily consump- estimated annual intake of 0.27 mSv, with a
tion of one unit of Brazil nuts is sufficient to contribution of 0.24 mSv. Contribution from
restore the status of selenium in obese wom- radioactive fallout, fission product 137 Cs, was
en and the elderly. Selenium is an important negligible. Based on the data obtained, it can
part of antioxidant enzymes that act in the be said that the radioactivity present in Bra-
prevention of age-related illnesses such as zil nuts does not offer health risks for a daily
cancer and cardiovascular diseases. In addition ingestion of one unit. The concentration of
to selenium, it is known that Brazil nuts also Barium in the analyzed samples ranged from
accumulate barium and radium. Due to the 22 to 3700 μg g . As high concentrations of
-1
presence of radium in these nuts, the level Ba were found in some samples, the project is
of radioactivity is 2-4 times higher than that still in progress for determination of Selenium
of other vegetable foodstuffs, of the same re- in these same samples with the objective of
gion. This accumulation of Ba and Ra has been verifying the correlation between the concen-
explained as a possible formation of organic trations of Ba and Se present in the Brazil nuts.
complexes that increases the mobility of alka-
line earth ions, particularly for these elements, Neutron activation analysis applied to the
favoring their redistribution during fruit devel- characterization of different materials
opment. Barium is not considered essential and
can be toxic depending on its chemical form. Neutron activation analysis is the elemental
2+
The Ba ion and the soluble compounds of analysis method usually chosen for the char-
barium (notably chloride, sulfide, nitrate and acterization of different matrices because of
hydroxide) are toxic to animals and humans. some features such as: small amount of sample
Several radioactive substances are considered available, minimal sample handling and high
carcinogens (Group 1 agents), according to the sensitivity for many elements.
International Agency for Research on Cancer.
The carcinogenic activity is attributed to radi- Neutron activation analysis applied
224
ation, such as the radiation emitted by Ra or in the evaluation of bismuth iodide
228
226 Ra or Ra and their decay products. purification methodology

In this project, it was proposed to evaluate the Bismuth tri-iodide (BiI ) is an attractive materi-
3
concentrations of natural ( Ra, Ra, and K) al for using as a semiconductor. However, the
226
40
228
and artificial ( Cs) radionuclides and Bari- behavior of semiconductor devices is strongly
137
um concentration in samples of Brazil nuts influenced by the presence of impurities or
acquired at final points of sale, in various contaminants remaining due to incomplete
Brazilian regions. Gamma-ray spectrometry purification of the semiconductor material.
measurements were used to determine the Small quantities of impurities present at con-
radionuclide activity concentrations and In- centrations below 1 ppb can have a significant
strumental neutron activation analysis (INAA) effect on quality of semiconductor devices. In
was the analytical method used to determine this project, BiI crystals have been grown by
3
barium concentration. the vertical Bridgman technique using com-
mercially available powder. Efforts have been
Among the radionuclides determined in sam- concentrated on the purification of the BiI and,
3
137
ples of Brazil nuts Cs, K, Ra and Ra, the the purification efficiency was assessed by
40
228
226

Instituto de Pesquisas Energéticas e Nucleares