Activity Concentrations Of Environmental Samples Collected In Samarkand Region Of Uzbekistan

The results of the investigations of the activity concentration of natural radionuclides in certain building materials and foodstuff samples obtained from the Nurabad district of the Samarkand region of Uzbekistan are presented. The gamma radiation spectra of the samples were measured in Marinelli beaker geometry on γ- spectrometer with a Ge(Li) detector and energy resolution 6% on the 1332 keV line of 60Co. A personal computer and standard computer programs were used to accumulate and process the spectra. The characteristic density of the samples ranged from 140 to 1810 g/l. The activity concentration of 40K was observed to be comparatively higher than that of both 226Ra and 232Th in all the studied samples. The results reveal that the low activity of 137Cs in the samples is attributed due to its half-life decay period.

The American Journal of Applied Sciences (ISSN -2689-0992)

INTRODUCTION
The exposure of human beings to ionizing radiation from natural sources is a continuous and inevitable reality of life on Earth that can cause adverse biological consequences, such as DNA damage and cancer [1,2,3]. The causes of radioactivity in the atmosphere are known to be from naturally occurring radioactive materials and are classified as being of terrestrial or cosmic origin [4]. Radionuclides such as 238 U, 226 Ra, 232 Th, 228 Ra, 228 Th, and 40 K are the significant source of natural radiation exposure due to their natural occurrence in the Earth's crust or atmosphere. The average annual dose rate of radiation from naturallyoccurring radionuclides in a sample population is estimated to be 2.4 mSv.y -1 [5]. Besides, the use of radioactive isotopes for peaceful and military purposes has caused significant pollution to the environment with artificial radionuclides [6]. The study of radioactivity in the environment is useful in protecting human health and the environment from the adverse effects of ionizing radiation and is, therefore, of great importance [7]. Foodstuffs contain both natural and artificial radionuclides, which, after ingestion, can create a dose-effect [5]. An enormous contribution to dose exposure comes from the most crucial fission product, 137 Cs. The literature of the current paper includes this type of studies [8,9]. It is known that the whole life of a human being and its activity connected with living quarters. Therefore, in the construction of residential buildings, the study of the radiation characteristics of building materials is of considerable interest.
The current work presents gamma spectrometric studies of 226 Ra, 232 Th, 40 K, 137 Cs in some building materials (burnt brick, cement, sand, limestone), and daily foodstuff (sugar, tea, table salt).

MATERIALS AND METHODS
A total of four samples of building materials and three samples of three kinds (domestic sugar, table salt, and tea imported from China) were selected for the measurements of activity concentrations from the Nurabad district of Samarkand region, Uzbekistan. All measurements were carried out in the Nuclear Physics Laboratory of Samarkand State University. The investigations were performed in Marinelli beaker geometry on γ-spectrometer with a Ge(Li) detector (V=100 cm 3 ) ∆Eγ=6 keV at Eγ=1332 keV). An IBM PC performed the registration and processing of the spectrometric data for 6 hours, and the data were automatically recorded every hour in the memory of the PC. For calibration of the registration efficiency of γ-radiation for the processing of the measured spectra, we used the volumetric standard sources OMACH 232 Th, 226 Ra, 40 K and 137 Cs with a density of inert fillings ρ = 140-1810 g/l [10]. The error in the determination of the specific activity of radionuclide was δ(A)=8-16 %. When determining the specific activity of 137 Cs, the error reaches up to δ(A)=25 %.

RESULTS AND DISCUSSION
The gamma spectra of the analyzed building material samples revealed the gamma radiation line of the naturally radioactive nuclide 40 K with the intensity of 1460 keV and gamma radiation, radionuclides belonging to the natural radioactive families of 238 U, 232 Th. lime. Moreover, in general, the intensity of the background spectrum is much greater than that of the radionuclides being studied. As can be seen, the radioactivity of the studied building materials is mainly due to gamma radiation generated by the decay of natural radionuclides 40 K, 232 Th, 226 Ra, and partially 137 Cs (Fig. 1.).
The results of foodstuffs gamma-spectra reveal (Fig. 2):  In the spectrum of gamma radiation of sugar, the intensity of gamma lines identified by radionuclides is determined at the background level;  A gamma-line of natural radionuclide 40 K with an energy of 1460 keV and a weak gamma-line of uranium-series radionuclide -226 Ra (1764 keV) identified in the gammaray tea spectrum, which exceeds the intensity of those gamma-lines in the background spectrum.  In the gamma spectrum of table salt, detected lines of gamma radiation of the thorium radionuclide 208 Tl (583 keV; 2614 keV) are determined at the background level; the intensity of the gamma line 226 Ra (1764 keV) exceeds the intensity of this line in the background spectrum.
Thus, the sugar radioactivity was determined at the background level, the table salt radioactivity is due to 226 Ra, and the green tea radioactivity is primarily due to 40 K and partially 226 Ra.
The specific activity of radionuclides detected in the studied samples' spectra is determined by the intensity of the corresponding analytical lines.   Worldwide average activity levels can be accessed in UNSCEAR report [11].
As can be seen from the

Figure 2. Gamma-spectra of some foodstuff
The primary source of radioactive elements contained in soil and sand are soil-forming rocks. Soil and water (clay) are used as raw materials for the production of burnt bricks [12]. Therefore, in a burnt brick, the natural radionuclides contained in the soil are determined.
Comparing the individual data values in are used as the starting material for cement production. In lime, the smallest amount of radionuclides is determined. As indicated in [13] relatively low content of radioactive elements characterizes limestones. This is likely why the concentration of radioactive elements in lime is determined in the smallest amount in our research.
In the gamma spectra of bricks, lime, and sand, a weak gamma line of the technogenic radionuclide 137 Cs with an energy of 661 keV is identified. In contrast, in the gamma spectrum of cement, this line is not detected in the sensitivity limit of the gamma spectrometer. Sugar, by its formation, belongs to the group of carbohydrates-disaccharides and has the structure formula С12Н22О11. The most common disaccharides are sucrose (cane and beet sugar). Carbohydrates are an essential class of naturally occurring compounds that contain a carbon group. Carbohydrates include sugar, starch, cellulose, and some antibiotics. As seen from the gamma spectrum of sugar, the technology for producing sugar purifies it from various elements, including radioactive elements that determine in primary sources (beets, cane). Ordinary table salt, which is common in nature, is sodium chloride and has a NaCl-type structure. The spectrum shows one weak gamma line of the natural radionuclide 226 Ra (1764 keV), which exceeds this line's intensity in the background spectrum. Table  salt in nature exists as a saline solution or substantial deposits in the earth's crust and surface. In any case, the source of salt deposits was the water of the ancient seas. It formed a deposit of table salt and salt lakes. Some seas dried up millions of years ago, and others still exist with abundant water. Table salt is obtained mainly by mining stone or self-seeding salt extracted from salt lakes, which naturally deposits itself. Ra is associated with an impurity of other minerals. Tea is obtained from the leaves of a shrubby plant. In the course of their development, plants carry out a complex cycle of synthesis of compounds necessary for existence both on land and in the aquatic environment. At the same time, along with organic substances, all known natural radionuclides accumulate in plants. Thus, in plants can be present radionuclides that contained in the soil, in water, and air. In the gamma spectrum of the tea we studied, gamma lines of natural radionuclides 40 K and 226 Ra were detected, the intensity of which exceeds the background. In this case, no other natural radionuclides were detected in the sensitivity limit of the gamma spectrometer. In the spectra of gamma radiation of sugar, salt and tea line technogenic radionuclide 137 Cs was not detected.

CONCLUSION
In the present study, a gamma spectrometry based the Ge(Li) detector was employed for determination of the activity concentration of 226 Ra, 232 Th, 40 K, and 137 Cs in samples of some building materials and foodstuffs in Samarkand region in Nurabad, Uzbekistan. The observed activity concentrations means of radionuclides, apart from 40 K, were under the worldwide means by UNSCEAR as shown in table 1.
In summary, the results obtained can be useful in obtaining information on the degree of the radioactivity of samples used in this work for comparison to future monitoring studies.