Determination of Radioactivity Levels of Salt Minerals on the Market Journal: Canadian Journal of Physics Manuscript ID cjp-2017-0775.r1 Manuscript Type: Article Date Submitted by the Author: 29-Nov-2017 Complete List of Authors: Yüksel, Zeynep; Ondokuz Mayıs University,Faculty of Science and Arts Tufan, Mustafa; Ondokuz Mayis Universitesi, Physics Deparment Keyword: Salt, Natural radioactivity, HpGe detector, Committed effective dose, Activity concentration Is the invited manuscript for consideration in a Special Issue? : 33rd International Physics Conference of Turkish Physical Society
Page 1 of 6 Canadian Journal of Physics Determination of Radioactivity Levels of Salt Minerals on the Market Zeynep YÜKSEL 1*, M. Çağatay TUFAN 1 Ondokuz Mayıs University, Faculty of Arts and Sciences, Physics Department, 55139 Samsun Turkey Abstract: Human beings have been continuously exposed to natural radioactive rays since its existence in the world. From the end of 19th century, besides natural sources, mankind has been exposed inevitably by artificial radioactive sources with the development of technology. Radiation has beneficial effects on human beings but also can harmful consequences if overexposed. Therefore, it is important for both public and governmental institutions to know the radioactivity levels particularly in foodstuffs for human health. There have been rumours among the public that the level of radioactivity in salt minerals exported from abroad is high. In this study, the radioactivity levels of imported and domestic salts on the market shelves have been determined by using gamma spectrometry units with HPGe detector. Keywords: Salt, Natural radioactivity, HpGe detector, Committed effective dose. * Corresponding author. Tel. +90-362-3121919, Fax: +90-362-4576081 e-mail address: zeynep.boz@omu.edu.tr 1
Page 2 of 6 I. INTRODUCTION Humans have been continuously irradiated by gamma rays from the natural radioactive substances found in the earth and cosmic rays. According to the UNSCEAR Report [1], the average annual effective dose per person from natural radiation is 2.4 msv, which varies depending on the geology and altitude where people live. Terrestrial radiation exposes our bodies by two ways: internal and external exposure. The main cause of exposure of the human body to external radiation is gamma rays originating from the naturally occurring 238 U and 232 T series and 40 K radioisotopes. Internal exposure occurs by ingesting and inhaling of these radioactive nuclides. Doses taken by inhalation are due to the presence in air of dust particles containing radionuclides especially the short-lived decay products of radon. The doses caused by the ingestion of radionuclides depend on the consumption rate of food and beverages and the concentration of radioisotopes. Consumption habits are also important for dose calculation and shows cultural difference. Salt is both an important constituent of the foodstuff all over the world and consumed very much. In this work, seven different salt samples, which commercially found on the market selves, were analyzed by using gamma spectrometry technique calculated. By obtaining naturally occurring radiation levels in the salt samples, annual effective dose by in taking salt were determined for Turkey. II. MATERIALS AND METHODS In this work, seven different salt samples from different countries, were collected from the market shelves and investigated by using gamma spectrometry technique. The salt samples were crushed into grains of about 1 mm in size, dried in a temperature controlled furnace at 110 C for 24 h. Meshed soil samples were filled into cylindrical plastic containers (55 mm height by 65 mm diameter), weighed and hermetically sealed. The samples stored 45 days before counting to allow secular equilibrium between 226 Ra and its short lived decay products. 2
Page 3 of 6 Canadian Journal of Physics Gamma spectrometric analyses of the samples were carried out by using Ortec GEM30 P4 model gamma spectrometry system. System consists of a high resolution p-type coaxial HPGe detector with its own liquid nitrogen dewar, a spectroscopy amplifier, a PC based 16 K multichannel analyzer and a ADC with Gamma Vision gamma spectroscopy software. The detector has 30% relative efficiency, an energy resolution of 1.85 at 1332.5 kev of 60Co and peak-to-compton ratio of 60:1. The detector was shielded with ORTEC HPLBS1 model shielding which consists of 9.5 mm low-carbon steel casing, 101 mm certified Doe Run lead, 0.5 mm tin sheet liner and 1.6 mm soft copper sheet liner. Energy and efficiency calibrations of the spectrometry system have been made with the 60 Co point source and IAEA reference materials RGU-1, RGTh-1 and RGK-1. For the efficiency calibration, radionuclide specific efficiency method was applied [2]. Each sample and background was measured during accumulating time 86 400 s. Activity concentration of 238 U and 232 Th were calculated from the respective decay products in equilibrium. For 238 U, gamma transition lines at 351 kev and 295 kev from 214 Pb, 1764 kev 214 Bi; for 232 Th gamma transition lines at 583 kev and 860 kev from 208 Tl, 968 kev from 228 Ac were used. The activity concentrations of 40 K were calculated from the gamma transition line at 1460 kev. After determining the activity concentrations in salt samples, the committed effective doses due to ingestion of salt samples can be calculated as [3-5] = ( ) (1) where i indicates the radionuclide in the sample, U is the annual consumption ratio of food stuff (in this work salt; kg), is the activity concentration of the nuclide i (Bq/kg) and is the effective dose per unit intake (Sv Bq -1 ) for radionuclide i. The values of g for 40 K, 238 U and 232 Th for adult members of the public are6.2 10, 4.5 10 3
Page 4 of 6 and 2.3 10 respectively [4]. Annual consumption ratio of salt is 5.5 kg for Turkey[6]. III. RESULTS AND DISCUSSIONS Activity concentrations of 238 U, 232 Th and 40 K are determined as shown in Table I. The mean activity concentrations of 238 U, 232 Th and 40 K have been found as 7.32±0.9, 2.72±0.7 and 488.53±10.6 Bq/kg, respectively. Maximum activity concentrations for 40 K, 238 U and 232 Th are 3152.30±21.61 Bq/kg for Iranian, 11.34±1.31 Bq/kg for Iranian, 5.21±0.50 Bq/kg for France, and minimum values are 24.11±2.15 Bq/kg for Pakistan, 6.87±1.31 Bq/kg for France and 2.19±0.72 Bq/kg for Pakistan, respectively. Corresponding committed effective doses due to ingestion of salt samples are given in Table II. In this work, fractional absorption of radionuclide in the salt samples was also considered; these values are 1 for 40 K, 0.02 for 238 U and 0.0005 for 232 Th. By multiplying the Eq.(1) with fractional absorption coefficient, committed effective doses are obtained by ingestion. As seen from the Table II, committed effective doses vary from 0.822±0.073 to 107.493±0.736 µsv for 40 K, from 0.034±0.0065 to 0.056±0.0064 µsv for 238 U and from 0.0022±0.0005 to 0.0033±0.0003 µsv for 232 Th. However, when the total effective dose calculated, committed effective dose of 238 U and 232 Th are summed. Because the total amount of potassium in the human body is stable for a constant body mass [7]. Table I Table II IV. CONCLUSIONS 4
Page 5 of 6 Canadian Journal of Physics As seen form Table I and II, Iranian salt sample has the maximum radioactivity level and committed effective dose for 40 K. However, 40 K is not accounted for the total committed effective dose. Then 238 U and 232 Th levels should be accounted for the estimation of total committed effective dose. Mean committed effective dose has been calculated as 0.0422±0.0051 µsv for 238 U, 0.0026±0.0005 µsv for 232 Th and 0.0388±0.0022 µsv total. In UNSCEAR 2000 [1], it is reported that effective doses from ingestion of 238 U and 232 Th are 0.25 and 0.38 µsv, respectively. In this work, obtained effective doses for salt samples are lower than that of UNSCEAR 2000 values. Especially, it should be noticed that Turkish salt samples has lower level of radioactivity concentrations but the difference between salt samples does not shows much deviation each other. REFERENCES [1] United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), United Nations, New York. (2000) [2] Stoulos S., Manolopoulou M., Papastefanou C., J. Environ. Radioact. 69, 225-240 (2003). [3] International Commission on Radiological Protection (ICRP), ICRP Pub. No.68. Pergamon Press, Oxford (1994). [4] International Commission of Radiological Protection (ICRP), ICRP Pub.No. 72. Pergamon Press, Oxford (1996). [5] Radioactivity in Food and the Environment (RIFE), RIFE-10 (2005). [6] Türk Hipertansiyon ve Böbrek Hastalıkları Derneği, Türk Toplumunda Tuz Tüketimi ve Kan Basıncı Çalışması, 2008. Data available from (2017) www.turkhipertansiyon.org/tuz_160608.php [7] S.N. A. Tahir, A.S. Alaamer, J. Radiol. Protection. 28, 233-236 (2008). 5
Page 6 of 6 TABLES Table I Activity concentrations of 40 K, 238 U and 232 Th in the salt samples. Origin of salt Activity concentrations (Bq kg -1 ) sample 40 K 238 U 232 Th Cyprus 63.46±4.11 9.00±0.91 4.23±0.96 France 38.69±4.73 6.87±1.31 5.21±0.50 Iranian 3152.30±21.61 11.34±1.31 3.90±0.41 Italy 61.09±4.92 7.31±0.96 4.08±1.00 Pakistan 24.11±2.15 *BDL 4.39±0.72 Çankırı, TR 43.27±2.85 8.51±0.78 3.50±0.82 Đzmir, TR 36.83±3.24 8.22±1.00 3.96±0.76 *Blow Detection Limit, which is 0.3883 Bq/kg Table II The committed effective doses due to ingestion of salt samples Origin of salt Committed effective dose (µsv) sample 40 K 238 U 232 Th Total Cyprus 2.164±0.140 0.044±0.0045 0.0027±0.0006 0.0472±0.0005 France 1.319±0.161 0.034±0.0065 0.0033±0.0003 0.0373±0.0034 Iranian 107.493±0.736 0.056±0.0064 0.0024±0.0002 0.0586±0.0033 Italy 2.083±0.167 0.036±0.0047 0.0025±0.0006 0.0387±0.0027 Pakistan 0.822±0.073 ------ 0.0027±0.0004 0.0027±0.0004 Çankırı, TR 1.475±0.111 0.042±0.0038 0.0022±0.0005 0.0443±0.0026 Đzmir, TR 1.255±0.112 0.041±0.0049 0.0025±0.0004 0.0431±0.0026 6