Measurement of Radon Exhalation Rate, Annual Effective Dose and Radium Activity from Marine Sediments Samples Collected From Abian Beach, Aden Gulf, Yemen

The behavior of radon in marine sediments collected from Abian beach, Abian Governorate, Aden Gulf, Yemen, was studied by using Alpha Guard PQ2000 PRO radon detector. The activity concentration of radon in the sediments was found to be ranging from 64.84 to 166.93±11.85Bq.m with mean value 103.88±8.80Bq.m. The radium content in the sediments ranged from 20.01 to 56.06Bqkg with mean value 33.51Bqkg, while the area exhalation rate of Rn ranged from 6.73 to 18.49Bqmh with mean value 11.22Bqmh also the mass exhalation rate of Rn ranged from 0.151 to 0.424Bqkg h with mean value 0.253Bqkgh, respectively for the studied samples of marine sediments. The annual effective dose was found to be ranging from 1.63 to 4.21mSvy, with an average of 2.62mSvy. Average value of radon concentrations from marine sediments samples were compared with other literature values.


Introduction
Ra is a radioactive element existed in soil, rock, sand, water, animals and plants. 226 Ra has entered the human body from the soil by vegetarian food, its (like calcium) concentrated in the bones. This led to bombard the bone marrow and mutate tissue. Subsequently, 226 Ra can Cause many health hazards like anemia, sores, bone cancer and other problems. 226 Ra is the parent of 222 Rn, after decay 226 Ra, 222 Rn gas distribution in soil, rock, water and sediments [1,2]. Radon is a natural radioactive gas which has no odor, color, or taste. Therefore, it can only be detected with special equipment. Radon is one of the most radioactive and toxic gases. According to the International Commission on Radiological Protection, 40% -75% of exposure of human by natural radioactive sources comes from radon and its daughter nucleus. Radon is a known carcinogenic agent, and being viewed by the World Health Organization (WHO) as the leading reason of lung cancer after smoking [3,4]. Radon decays into its daughters giving tiny radioactive particles. When inhaled, these radioactive particles can damage the cells that line the lung. Long-term exposure to radon can lead to lung cancer; the only cancer is proven to be associated with inhaling radon. The daughters are solid particles and when they are inhaled they release radiation (alpha and beta) into the lungs, which can potentially cause cancerous cell growth (in the lungs) [5,6]. When the atmosphere contains 222 Rn gas and its decay daughters, the bronchial epithelium received the big part of ionizing radiation, in addition, the extra thoracic airways and the skin may receive good dose, also low dose may receive to the kidney and bone marrow, while 222 Rn dissolved in drinking water may effect on the stomach. Many radionuclides in sediments transference are contributing to global collective doses [7,8]. Therefore, monitor of the pollution in sediments was used widespread and trace pollution sources. 222 Rn produced primarily in sediment by the decay of 226 Ra. A fraction of the radon which is produced in sediments will escape to the overlying water column, leaving a deficiency of radon in sediments, so that the activity ratio of radon to radium in less than one. Once radon is in water column, it is mixed vertically and will either decay there or escape to the atmosphere [9,10]. The measurement of radon flux from soil surface is a useful tool for the assessment of radon prone areas and monitoring of radon released from uranium mining, so it is necessary to study the transfer through porous soils Due to radon low concentration in the environment and its chemical inactivity, its activity concentration can be determined using some specialized equipment. This devices measures number of alpha-particles emitted from some kind of samples [11,12].
In measurements the radon monitor Alpha Guard (Saphymo, DE) was used. It determines radon specific activity concentration and, simultaneously, air temperature, pressure and humidity. It has optimal sensitivity coming to 5cpm at 100Bq/m 3 and linear response from 2-2 000 000Bq/m 3 . This set consists of the radon monitor and an air pump in the basic version [13]. The aim of the present work provides database about 226 Ra concentration and 222 Rn exhalation rate in terms of area and mass in sediments of Abian beach, Aden Gulf, Yemen using Alpha Guard Technique. This data can be used as a reference data for future studies and it may be useful for complete radioactivity mapping for Yemen republic. The map of studied area is shown in Figure 1.

Sampling and Samples Preparation
Twenty three sand beach sediment samples have been collected from predetermined undisturbed areas alongside the coast of Abian beach, Aden Gulf, Yemen during low-tide. At each of the sample sites, a sampling area of 1m 2 was considered, where five wet samples were taken, each weighing about 1kg. Four samples were taken from the corners of the site and the fifth was from the center. The sediment samples were taken at depth of 5cm from the surface; the samples were collected using Grab sample equipment. Then separated from the contamination materials and air-dried at room temperature for a week, then dried to 110 o C, milled and sieved through 0.2 mm sieve. The dried samples were put inside cylindrical can. The cans were sealed, gas-tight and stored for four weeks for secular equilibrium [14].

Measurement of Radon Gas Concentrations
Ionization chamber Alpha Guard PQ2000PRO along with the additional special equipment Aqua KIT was used for determining 222 Rn exhalation activity concentration in sand beach samples. The background of empty set-up was measured for a few minutes before every sample measuring. About 200g of sample was put into the degassing vessel. The Alpha pump was switched on with the flow rate 1dm 3 per minute and 10 min flow, so 222 Rn activity concentration will be recorded every 10 minute. The advantage of this system is that it is calibrated by the manufacturer and provided a 5-year warranty [15,16,13]. Schematic diagram showing the active setup used for the exhalation measurements of samples with Alpha Guard is given in Figure 2.
At equilibrium state, the final activity of exhaled radon inside that container is calculated as follows: Where λ is the decay constant of the radon nuclide and A 0 is the final value of the activity concentration, at t ≈ 7T 1/2 .

Calculation of Radon Exhalation Rate in Sand Beach Samples
The radon exhalation rate per unit area of the sample E A in (Bq·m −2 ·h −1 ) is calculated using the following formula: Where V is the volume of the emanation container (2400 × 10 −6 m 3 ) and F is the total surface area of the sample (0.0113m 2 ), which equals the cross-sectional area of the emanation container.
The radon exhalation rate in terms of mass E m in (Bq·kg −1 ·h −1 ) is calculated using the following formula: Where, m is the mass of the sample [16,17]. The effective radium content of the sand beach samples C Ra was calculated by using the following relation: Where C Ra (Bq.Kg -1 ) is the effective radium content of the sample, and E M is the radon exhalation rate per unit mass of the sample [17].
The annual effective dose E Rn was calculated using the following equation [18,20]: Where C Rn is the measured 222 Rn concentration (Bqm −3 ), (D f ) is the conversion factor (effective dose received by adults per unit 222 Rn activity per unit of air volume) of 9.0nSvh −1 per Bqm −3 , (E f ) is the equilibrium factor that equal to 0.4, (Q f ) is the indoor occupancy factor which equal to 0.8.

Result and Discussion
The activity concentrations of radon and the annual effective doses from sediment samples from Abian beach, Aden Gulf, Yemen are given in Table 1. The activity concentration of radon gas ranged from 64.84 to 166.93 Bq.m -3 with mean values 103.88±10.2 Bq.m -3 the mean value of the activity concentration of radon is lower than the worldwide value of 300Bq/m 3 , which is given in IAEA, 2018, and the annual effective dose ranged from 1.63 to 4.21mSvy -1 with mean value 2.62±1.621mSvy -1 . The annual effective dose was within the allowed limits if compared to the recommended effective annual dose by ICRP, 2007 which was 3-10mSv.y -1 for all samples and all regions that were selected in the present search [19,20]. The mean values of the annual effective dose in this study were 2.62mSvy -1 which it is lower than the permissible limits recommended by ICRP (2010). Figures 3 and 4 shows the variations of radon concentrations and annual effective doses at different sampling locations. It can be seen from the results that marine sediments radon concentration varies significantly among samples from the sampling location to another throughout the study area. The variation of radon concentration could be attributed to different types of activities for space and different concentration of radioactive material in earth's crust [21]. On the other hand, variation among the activity concentrations of radon of the collected samples from different locations may be due to the continuous wave action, where the high tide may lead to the deposition of radionuclides in sediments such as radium and uranium along the shoreline [22].
In general, the soil type and the characteristics of the surface sediment in this region are different from one site to another [23]. The range and mean values for the surface and mass radon exhalation rates, E A and E M , obtained in these measurements are shown in Table 2. The results show that the surface and mass exhalation rates of radon varies from 6.73 to 18.49 Bqm -2 h -1 with mean value 11.22 Bqm -2 h -1 and from 0.15 to 0.42Bqkg -1 h -1 with mean value 0.25Bq kg -1 h -1 , respectively in locations D 2 and D 8 . The highest values of surface and mass exhalation rates of radon of 18.49 Bqm -2 h -1 and 0.42Bqkg -1 h -1 , respectively. However average value for surface exhalation rates of radon are also quite below the world average of 57,600mBqm −2 h −1 and hence will not cause any health hazards to residents [22]. It is clear to see that the surface and mass exhalation rates vary from point to point as shown in Figures 5 and 6 and are strongly related to the radon concentration value of the study material. It seems that some of the most important parameters that determine the intensity of radon exhalation from the sediment samples are radium content of the sediment samples [24]. The radium content in the sediments ranged from 20.01 to 56.06Bqkg -1 with mean value 33.51Bqkg -1 . Figure 7 shows the variations of the radium content at different sampling locations. The values of radium content determined in sediment are within the permissible value 30Bqkg -1 , which is acceptable for safe use as recorded by the recommendation from the Organization for Economic Cooperation and Development "OECD" [25]. These results are given in Table 2. It was noticed that, surface exhalation rate E A , mass exhalation rate E M and radium content are increase with radon concentration. Thus, results show that the area is safe as far the health hazard effects are concerned. It is very important to notice that, this study is constitute the data baseline for the surface and mass exhalation rates in addition to the annual effective dose due to radon from marine sediment samples.        Table 3 compares the activity concentrations of radon in beach sediment samples with other studies in different beaches of the world [14,23]. The average value of the radon concentrations in sediment in our study is higher than that in Ras Tanura Saudi Arabia and Thailand, china and Egypt and lower than Saudi Arabia, Khor-Abdulla and Ra's Al-Besha, Iraq and Jordan. On the other hand, it is suitable to conclude that the recorded values are seen to be lower than the hazardous values when compared with other average values from other national and worldwide works.

Conclusions
The concentrations of radon in the marine sediment samples collected from the Abian beach have been measured directly; using Alpha guard technique and the radon annual effective doses E Rn (mSvy −1 ) have been calculated. The values of radon concentration, effective radium content and the annual effective dose were also determined. The recorded results of our study is representing, the activity concentration of radon in the sediments that range between 64.84 to 166.93±11.85Bq.m -3 with mean value 103.88±8.80Bq.m -3 .
The radium content in the sediments ranged from 20.01 to 56.06Bqkg -1 with mean value 33.51Bqkg -1 , while the area exhalation rate of 222 Rn ranged from 6.73 to 18.49Bqm -2 h -1 with mean value 11.22Bqm -2 h -1 also the mass exhalation rate of 222 Rn ranged from 0.151 to 0.424Bqkg -1 h -1 with mean value 0.253 Bqkg -1 h -1 , respectively.
The mean value of annual effective dose was 2.62mSv y -1 . The annual effective dose values were compared with the effective dose limit values recommended by the National Council on Radiation Protection and Measurements (from 1 to 5mSv/y). Results obtained from the current study show that the radon exhalation rates from marine sediments contribute less to the indoor radon. The observed values of effective radium content in sediment samples in the present study are less than the recommended safe according to OECD. The effective radium content and 222 Rn exhalation rate are within the average of the world. Thereby it is concluded that sediments of Abian beach, are radiological safe. The results for radon concentrations from the sediments of Abian beach were compared with other literature values and seem to be acceptable and concerning a health hazard for the inhabitant of the town. From these results, a radiological baseline map of the Abian beach can be extracted and used as information reference for the evaluation of any future changes in the radon concentration of the sands of the beach because of any changes in marine sediments.