In the present investigation, analysis of radon concentration in 20 water and soil samples collected from different locations of Bikaner and Jhunjhunu districts of Rajasthan, India has been carried out by using RAD7 an electronic Radon detector. The measured radon concentration in water samples lies in the range from 0.50 to 22 Bq l⁻¹ with the mean value of 4.42 Bq l⁻¹, which lies within the safe limit from 4 to 40 Bq l⁻¹ recommended by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, 2008). The total annual effective dose estimated due to radon concentration in water ranges from 1.37 to 60.06 μSV y⁻¹ with the mean value of 12.08 μSV y⁻¹, which is lower than the safe limit 0.1 mSv y⁻¹ as set by World Health Organization (WHO, 2004) and European Council (EU, 1998). Radon measurement in soil samples varies from 941 to 10,050 Bq m⁻³ with the mean value of 4561 Bq m⁻³, which lies within the range reported by other investigators. It was observed that the soil and water of Bikaner and Jhunjhunu districts are suitable for drinking and construction purpose without posing any health hazard.

The soil and water have different radon concentrations due to which its exposure to inhabitants varies substantially from place to place ( UNSCEAR, 1988 ). Two of the ²²²Rn descendent, ²¹⁴Po and ²¹⁸Po, are α emitters, and they contribute over 90% to the total radiation dose received due to radon exposure ( Gruber, Maringer, & Landstetter, 2009 ).

The health hazard associated with radon arises from the inhalation and ingestion of short lived decay products of radon. When the radon gas is inhaled in to the lungs, most of it is pumped out and does not build up in the respiratory system. However small fraction of the radon that reaches the interior region of the lungs can damage the DNA in sensitive lung tissue and cause cancer. Moreover radon decay products that are suspended in air are inhaled during breathing in our respiratory system. Due to the short half life period of radon decay products, they decay almost completely in the lungs. During these decays alpha particle is emitted which can transfer large amount of energy to vulnerable cells in lungs, thereby leading to many health hazards.

Soil and water supply are the two major source of radon entering into home. Among which soil is the main source of health problems caused due to radon gas. The health hazards from radon in drinking water causes lung cancer, from inhaling radon discharged from water used in the homes, and stomach cancer, from ingesting radon in drinking water ( USEPA, 1991 ).

In our recent work, the activity concentration of natural radionuclides found in the soil samples of Jodhpur and Nagaur districts of Rajasthan was higher than the permissible limit ( Rani, Mittal, Mehra, & Ramola, 2015 ). Geographically Jhunjhunu and Bikaner are adjoining districts to the reported areas. Radon originates from the decay of natural uranium and is a progeny of radium that is present in soil and water. The radon concentration in soil and ground water is proportional to radium concentration at a particular place. Hence the measurement of radon concentration in water and soil of Jhunjhunu and Bikaner districts of Rajasthan assumes significance.

Such a study will be helpful in determination whether the soil and water of these districts can be used for construction and drinking purpose without posing any health hazard to the inhabitants. However literature survey shows that no attempt has been made towards the measurement of radon concentration in water and soil in Jhunjhunu and Bikaner districts of Rajasthan. In the present study the radon concentration in water and soil from Jhunjhunu and Bikaner districts of Rajasthan, India has been investigated systematically.

Rajasthan is located in North West of India. It lies between 23°30′ and 30°11′ north latitude and 69°29′ and 78°17′ east longitude. Fig. 1 shows the geographic location of Rajasthan in India, as well as the location of the sampling sites.

The map showing the sample locations in Northern Rajasthan.

Bikaner district is located in the North Western part of Rajasthan. It is bounded between 27°11′ and 29°03′ North latitude and 71°54′ and 74°12′ East longitude. In North it is bounded by Sriganganagar and Hanumangarh districts, in East by Chum, in South by Jodhpur and Nagaur districts and West partly by Jaisalmer districts and partly by Pakistan. Like Nagaur district it is also a part of Thar Desert. The soil of Bikaner district is predominantly light texture, weak structure and well drained. The minerals commonly found in this district are lignite, gypsum, clay and limestone.

Jhunjhunu district is situated in Northern part of Rajasthan. It lies between 27°38′ and 28°31′ North latitude and 75°02′ and 76°06′ longitude. It is bounded by Churu and Sikar districts of Rajasthan in North-West, South-West and South-East and Hisar and Mahendragarh districts of Haryana in North-East. The South and North-East part of Jhunjhunu district is covered by Alwar group of rocks. Aravali hills are also present in some areas of this district. Mainly Desertic and sand dunes soils are found in this district. Out of three copper producing belts in India, the Khetri copper belt is located in this district. The minerals commonly found in this district are copper, iron, cobalt, limestone, granite and marble.

The 0.7 L RAD7's internal sample cell hemisphere is coated inside with an electrical conductor. At the center of hemisphere a solid state, ion-implanted, planner, silicon alpha detector (semiconductor) is placed which converts α radiation directly to an electrical signal. The inside of a conductor is charged relative to the detector to a high potential of 2000–2500 V using a power circuit, thereby creating an electric field throughout the volume of cell which propels positively charge particle onto the detector. For determination of radon concentration RAD7 uses only the polonium-218 and for thoron uses only polonium-216 signal.

In order to analyze the radon concentration, the stainless steel probe (Durridge Co., USA) with holes near the tip was inserted in the soil at a specific depth of 100 cm. Fig. 2 shows the schematic diagram of soil gas monitoring using RAD7 detector. The probe was then connected to RAD7 detector through desiccant tube containing CaSO₄ and inert filters having pore size 1 μm for sucking the soil gas from the underground soil. The depth of the sampling point is determined by the length of the probe inserted into the ground, taking into the consideration the location of the sampling points on the probe shaft. In order to prevent the mixing of soil gas with fresh air the hole was properly sealed around the probe. The soil gas is sucked through the tube pipe into the measuring instrument for 5 min pumping phase and counts for four 5 min cycles for getting the accurate results. During the soil gas measurement at each site sniff protocol and grab mode were used.