Page 54 - PR 2014 2016 07 Nuclear Science and Technology

196 Nuclear Science and Technology | Progress Report

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discharge. The activity concentrations of Ra, from 0.049 cm•y to 0.40 cm•y .
226
228 Ra and Pb in four short marine cores, col-
210
lected from the continental platform to up- Radon as an indicator of environmental
per slope of Southwest Atlantic Ocean, were contamination by hydrocarbons in free-phase
determined. Taking into account the results
obtained, sedimentation rates and the ages of Contaminated sites by NAPL (Non-Aqueous
each sediment layer were determined using Phase Liquids) may lead to safety risks to hu-
210
the geochronological dating method with Pb. man health and to ecosystems, restrictions
All sediment samples were totally acid-digest- to urban development and decrease of real
ed in microwave (Figure 31). The sequential estate value. Radon gas as an indicator for
radiochemical separation of 226 Ra, 228 Ra, 210 Pb the analysis of subsurface soil gas, once this
were performed, obtaining in the end the pre- noble gas presents good solubility in a wide
cipitation of Ba(Ra)SO and PbCrO . The gross α range of NAPL, being partially retained in the
4 4
226
measurements of Ra and gross α measure- NAPL contamination, was used. Therefore, a
ments of Ra and Pb from the precipitates decrease of the activity of radon in the con-
210
228
were carried out in a gas-flow low background taminated soil gas can be expected, due to
proportional counter. Concerning all cores an- the high capacity of partitioning of radon in
alyzed, the activities concentrations of 226 Ra NAPL, which allows that the NAPL retain part
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ranged from 14 Bq•kg to 154 Bq•kg ; the of the radon previously available in the soil
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concentrations of Ra ranged from 17 Bq•kg pores. The survey was carried out at a disused
228
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210
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to 45 Bq•kg ; and the concentrations of Pb industry, contaminated by low volatile NAPL,
ranged from 20 Bq•kg to 2073 Bq•kg . High located at southeast of São Paulo city, from
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values of 210 Pb were observed on the top of June 2014 to May 2015. Radon was evaluated
all the cores studied, mainly related to atmo- by passive detection methodology with CR39
spheric deposition. The results obtained in this solid state nuclear track detectors (SSNTD)
work were of the same order of magnitude of in ten monitoring stations installed in the
those reported in the literature available on contaminated area investigated and named
non-contaminated areas of Southeast Brazil- “A” to “J” (Figure 32). Radon concentrations
ian Coast. Sedimentation rates fall with the average for the eight monitoring stations
increase of water column depth and ranged at non-contaminated locations varied from

Figure 31. Vertical profile (cm) of natural isotopes Ra, Ra,
226
228
total and unsupported (ns) Pb concentrations (Bq•kg ) along
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210
a short marine sedimentary profile in SW Atlantic Ocean.
Ra-226 Ra-228 Pb-210 Pb-210ns
0
5
20
25
20
25
30
35
40
222
45 Figure 32. Map of isoconcentrations of Rn activity
0 250 500 750 1000 obtained with SSNTD detectors in winter.

Instituto de Pesquisas Energéticas e Nucleares