| dc.description.abstract |
Natural radioactivity is present in the earth's crust from the beginning of life on earth. There are
three categories of radioactive elements such as primordial (which existed even before the
creation of the earth), cosmogenic (due to the interaction of cosmic rays), and manmade (due to
human actions). Primordial radionuclides are residues from the Big Bang, from ancient
supernova explosions, etc which occurred before the formation of the solar system. Radioactivity
present in the soil, rocks, and water was due to primordial radionuclides like uranium, thorium,
potassium, etcand is called natural radioactivity. Thus, all inhabitants on the earth are exposed
to radiations. Human beings are continuously exposed to radiations from both natural and
artificial sources. The human population receives ionizing radiation from radon, thoron, their
progeny, cosmic radiations, terrestrial radiations, consumer products, nuclear medicine, medical
X-ray, etc. Ionizing radiations are those which have sufficient energy to ionize an atom or
molecule by eliminating an electron from them. These ionizing radiations are responsible for the
stochastic and deterministic effect associated with human health. Radon, thoron, and its progeny
is the source of more than half of total ionizing radiation exposure to the general public. It is
estimated that out of 2.2 mSv of dose, which an individual receives annually from low-level
exposure, 1.27 mSv is due to radon isotopes and their short-lived progeny.
Radiological impacts of Radon on human health make this field a very interesting topic among
researchers over the world. In order to provide a realistic assessment of these radionuclides in
the environment, it is required to conduct a harmonized survey using reliable monitoring
techniques.The assessment of radiological exposure to the public via air, water, and the soil is
very important because of its associated health hazards. Thus keeping in mind the importance
of the radon study and research gap in this field, the present investigation has three main aspects
of precedence in radon studies. The first aspect is concerned with the measurement of indoor
radon, thoron, and decay products. It is very important for inhalation dosimetry and to identify
radon prone region. The second aspect is concerned with the radon measurement in groundwater
(underground and surface water sources). The third aspect is concerned with radon/thoron
measurement in soil samples and exhalation studies. This will be helpful to specify the location
of soil for selection as a raw material for construction.
Both techniques i.e, passive and active are used for the assessment of radionuclides activity. For
measurements of indoor radon and thoron concentration LR-115 type II detector based pin-holes
dosimeter and scintillation detector based Smart RnDuo were used. For measurements of indoor
radon and thoron progeny, the deposition based direct radon/thoron progeny sensors were used.
For measurement of indoor/outdoor gamma level, the Geiger-Muller tube-based Survey meter
(Polimaster PM 1405) was used. For measurement of dissolved radon concentration in water
samples the scintillation detector based Smart RnDuo with water bubbler was used. For
measurement of radon mass exhalation and thoron surface exhalation of soil samples, a
scintillation detector based Smart RnDuo with an exhalation chamber was used. For
measurements of 226Ra, 232Th, and 40K activity of soil samples the gamma-ray spectroscopy was
used.
The present work is organized into seven chapters such as Introduction, Literature review,
Methodology, and next three chapters comprise the experimental work for indoor air, water, and
soil, and conclusions & future scope. The results of present investigation compared with various
limits stated by national/international agencies and with the outcomes of other investigations. In
indoor study, seasonal investigation indicates that radionuclides are higher in winter season
compared and dwelling-wise distribution indicates it is high in modern and mud houses.
However, in particular seasons, indoor radon in some dwellings exceeds the reference level of
100 Bqm-3
but for all dwellings it was within the action level of 200 Bqm-3
given by WHO.
Thus, it is concluded that no radiological hazards are associated with the dwellings of the study
region of district Faridabad, Palwal, and Gurugram. In water study, radon level is found higher
in underground water sources like bore well, hand pump, and tap water compared to surface
water sources like pond and canal. All the outcomes of radon in the water of the present
investigation have been found exceed the maximum contamination limit of US-Environmental
Protection Agencybut all samples have been found well below the recommended safety limit of
WHO. Thus, it is concluded that the water sources of the present study region of Southern
Haryana, India are safe in a contest of radiological hazards due to radon and the public can
continue to use these water sources for drinking purposes.Results of high thoron surface
exhalation ensured the high indoor thoron concentration but thoron itself is not a serious concern
for dwellings of the study region as the quantification of dose contribution either from thoron or
its progeny alone suggests that the majority of the dose will come from thoron progeny (~98%)
with a very little contribution (~2%) from thoron gas. Also, the radioactivity of radium, thorium,
and potassium is found higher compared to the world's mean value. Radiation hazard indices
indicate that there is no radiological hazard associated with the soil of the study area. |
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