Abstract

Radon makes up approximately half of the total dose of radiation were receive naturally. The majority of it comes from the inhalation of progeny of ²²²Rn and is prominent in a closed atmosphere. The continuous measurement of the levels of ²²²Rn concentration in different geographical areas is of great importance, particularly in living places. In this study, the concentration of radium and radon in 120 samples of drinking, springs and rivers water sources of north west regions of Mashhad city have been measured. Solid state nuclear track detectors were used for measuring the concentration. The average value of radon and radium concentrations in the studied area is found to be 30.2±5.1 and 18.4±2.2 Bq m^-3, respectively. The dose rate due to radon, radium and their progenies received by the population in the studied location between 0.1-0.5 mSv year^-1. The arithmetic and geometric mean concentrations are 0.2±0.05 and 0.2 mSv year^-1, respectively. The results show no significant radiological risk for the inhabitants of the studied regions.

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INTRODUCTION

There is much concern these days on the part of the public and government organizations about natural radiation and the environment, particularly for dwellings (Folger et al., 1994). Due to relatively higher doses found as a consequence of elevated radon concentrations some countries are now passing legislation to deal with the problem.

This is true particularly in cold climate countries where the energy crisis is a serious problem and where houses were built more hermetically so as to minimize ventilation conditions. Radon contributes most to the effective dose received by a population from natural sources.

It has been estimated that radon and its progeny contribute three-quarters of the annual effective dose received by human beings from natural terrestrial sources and are responsible for about half of the dose from all sources. Radon emanates to a certain degree from all types of soil and rocks (Al-Kazwini and Hasan, 2003).

The presence of ²²²Rn in the biosphere is due to its semi-disintegration period of 3.8 days which allows it to diffuse from the earth's crust into the atmosphere (Khan, 2000). The radiological importance of radon does not depend on the concentration of radon gas itself but on its short-lived decay progenies such as polonium, bismuth and lead. During breathing, radon is exhaled but the progenies being material particles may deposit on to the lungs, tracks of breathing etc. (Kearfott, 1989). Some factors that influence the diffusion of radon from soil into the air are the existence of uranium and radium in soil and rock, emanation capacity of the ground, porosity of the soil and rock, pressure gradient between the interfaces, soil moisture and water saturation grade of the medium. Radon can enter to the body via respiring, drinking and eating.

The alpha emitted by this radon and other radiation emitted from its decay products increase the absorbed dose in respiratory and digestion systems (Kendal and Smith, 2002). Nearly 50% of annually radiation dose absorption of human is due to radon which is one of the main cancers cause at respiratory and digestion systems (Li et al., 2006). Radon in water can enter the human body in two ways.

Firstly, radon in drinking water or mineral drinks can enter the human body directly through the gastro-intestinal tract and irradiate whole body which the largest dose being received by the stomach (Kusyk and Ciesla, 2002).

Assuming an average consumption of 0.5 L of water per person per day and stomach dose per Bq of radon is 5 nGy/Bq with the consider 0.12 for stomach tissue weighting factor and 20 for quality factor of α-radiation, the annual equivalent dose per Bq of radon concentration in water is about 2.19x10^-6 μSv/(year Bq L). Secondly, radon can escape from household water and became as an indoor radon source which then enter the human respiratory tract system to deliver radiation dose.

MEASUREMENT METHODS

In this study, radon was measured in the water samples using PRASSI system (Savidou et al., 2001). A total of 120 samples including 38 samples of drinking water, 56 river water samples and 26 samples of spring waterwater were tested. Figure 1 shows the sampling sites.

Radium in the water samples were measured keeping the water samples in the bottles for 35 days to let radon reach the equilibrium with radium whereby we obtained radium concentration in the samples.

Figure 2 shows the system set up of measurement including bubbler and drier column. PRASSI pumping circuit operates with constant fallow rate at 3 L min^-1 in order to degassing the water sample properly. Its detector is a scintillation cell coated with ZnS (Ag) 1830 cm³ volume.

 

Fig. 1:	(a) Mashhad location in Iran; (b) the map of Mashhad city and • shows the sampling sites of Zoshk, Shandiz and Torghabeh

 

The sensitivity of this system in continuous mode is 4 Bq m^-3 during the integration time 1 h. Numbers shown by the device is based on Bq m^-2. Using relationship Eq. 1, radon gas density is calculated based on Bq/L.

(1)

Where:

QPRASSI	=	Recorded by the device
Vtot	=	The total volume of air connections
V	=	Volume sample and within the brackets is a correction factor in the delay measurement

Radon in water samples: The third column in Table 1, radon concentration samples that have been ordered from low to high is listed. Also, the radon gas density results are shown in histogram of Fig. 3.

As it can be shown only 81/12% of the samples the last 19 samples in Table 1 have concentrations >11 Bq L^-1, particularly the sample number 120 that related to the spring in the village of Zoshk has concentration about 30 Bq L^-1.

 

Fig. 2:	The PRASSI system set up for radon measuring in the water samples

 

 

Table 1:	Radon and radium concentration data of different water samples

 

 

Fig. 3:	The histogram of radon gas concentration in 120 water samples of Shandiz, Zoshk and Torghabeh regions

 

Radium in water samples: Figure 4 shows the histogram of radium concentration in different water samples as well as the data shown in 4th column of Table 1.

 

Fig. 4:	The histogram of radium concentration in different water samples

 

The radium concentration of samples were <1 Bq L^-1 except sample number 21, drinking water of Shandiz region is about 1.87 Bq L^-1.

CONCLUSION

Results of radon concentration in the water samples showed that only 14.67% sample concentrations were higher than the normal 11 Bq L^-1, set by United States Environmental Protection Agency (USEPA). About 148 Bq L^-1 is limit amount of action or reaction that radon should be reduced. Radium concentration of all samples except sample number 21, drinking water of Shandiz were small and <1 Bq L^-1. Therefore, radon and radium concentration in the water of the regions were not high and these were appropriate.

How to cite this article:

A. Binesh and H. Arabshahi. Radon and Radium Concentrations in 120 Samples of Drinking, Springs and Rivers Water Sources of North West Regions of Mashhad.
DOI: https://doi.org/10.36478/erj.2011.117.120
URL: https://www.makhillpublications.co/view-article/1994-5396/erj.2011.117.120