Radiation Protection Dosimetry (2008), Vol. 130, No. 3, pp Advance Access publication 12 March 2008

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1 Radiation Protection Dosimetry (2008), Vol. 130, No. 3, pp Advance Access publication 12 March 2008 doi: /rpd/ncn064 NATURAL RADIOACTIVITY AND EXTERNAL GAMMA RADIATION EXPOSURE AT THE COASTAL RED SEA IN EGYPT S. Harb* Department of Physics, Faculty of Science, South Valley University, Qena 83523, Egypt Received September , revised January , accepted February Radionuclides which present in different beach sands are sources of external exposure that contribute to the total radiation exposure of human. In this work, superficial samples of beach sand were collected from the Red Sea coastline (Ras Gharib, Hurghada, Safaga, Qusier and Marsa Alam areas) and at 20 km on Qena-Safaga road. The distribution of natural radionuclides in sand beach samples was studied by gamma spectrometry. The activity concentrations of primordial and artificial radionuclides in samples that are collected from the coastal environment of the Red Sea were Bqkg 21 for 210 Pb, Bqkg 21 for 226 Ra, Bqkg 21 for 238 U, Bq kg 21 for 235 U, Bqkg 21 for 228 Ra, Bqkg 21 for 228 Th, Bqkg 21 for 232 Th, Bq kg 21 for 40 K and Bq kg 21 for 137 Cs. The mean external gamma-dose rate was nsv h 21, ngy h 21 Ra equivalent activity (Ra eq ) was Bq kg 21, Bq kg 21 for representative level index (I g ) and effective dose rate was msv y 21 in beach sand red sea, in air due to naturally occurring radionuclides. INTRODUCTION Natural background radiation is the combined radiation field produced by the primordial and cosmogenic radioactive materials that are around us plus cosmic radiation from space. Everyone is exposed to this background radiation throughout their lives, at levels that depend on the ambient concentration of those radioactive materials and the altitude at which we live. This background radiation is the major source of radiation exposure to humans. Natural background dose rates are frequently used as a standard of comparison for doses from various man-made sources of radiation and also from the production, testing and use of nuclear weapons. There are few areas in the world such as Brazil, China, India, Austria, France and Iran (1 4), where the background radiation levels were found to be high, varying over an order of magnitude depending upon the site-specific terrestrial radioactivity. An attempt is made in this paper to determine the activity concentration of 210 Pb, 226 Ra, 238 U, 235 U, 228 Ra, 228 Th, 232 Th, 40 K and 137 Cs in beach sand samples collected from Red seashore using hyperpure germanium (HPGe) gamma-ray spectrometer and to compute the total absorbed gamma-dose rate in air due to the presence of 238 U series, 232 Th series and 40 K in the samples. *Corresponding author: s_r_m_h_10@yahoo.com, s.harb@web.de MATERIALS AND METHODS Sample collection and preparation Twenty beach sand samples were collected from the seashore (0 30 cm depth) of Red sea covering these cities (Ras Gharib N, E, Hurghada N, E, Safaga N, E, Qusier N, E and Marsa Alam N, E) and 20 km Qena-Safaga road are shown in Figure 1. After collection, each sample was air-dried (in summer, 458C in Qena) for several days. Then the soil samples placed in an oven at 1008C for 72 h, sieved through a 2-mm mesh-sized sieve to remove stone, pebbles and other macro-impurities. The homogenised sample was placed in a 250-ml bottle airtight container. The container was closed tightly with cap kept aside for about a month to ensure secular equilibrium between 226 Ra and its decay products and 228 Ra and its decay products before being taken for gamma-spectrometric analysis. Gamma spectrometry Detector The samples were measured using a high-resolution HPGe gamma-ray spectrometer system consisting of a p-type intrinsic germanium coaxial detector (model: GX3018) mounted vertically and coupled to 8 K multichannel analyser (Canberra). The detector # The Author Published by Oxford University Press. All rights reserved. For Permissions, please journals.permissions@oxfordjournals.org

2 NATURAL RADIOACTIVITY AND EXTERNAL GAMMA RADIATION EXPOSURE (radiological concentration) for each of the detected nuclides are calculated. The specific activity (in Bq kg 21 ), A s, is given by A s ¼ N s;n=t s N 0;n =t 0 I g 1m ð1þ Figure 1. Map of the sampling sites (*) of beach sand at the Red Sea coast. was housed inside a lead shield to reduce the background of the system. The gamma-ray spectrometry analysis of the sand samples was carried out using an HPGe coaxial detector with a relative efficiency of 35% and a resolution of 1.78 kev for the gamma emission of the 1333 kev of 60 Co. The gamma-ray spectra were analysed by means of the software associated with the detector. Since there was a low activity concentration in the samples, the counting time was long (18 24 h) so that the minimum detectable concentrations were sufficiently low as to be capable of measuring the low concentrations in the sand samples. Efficiency calibration For efficiency calibration of the detector, mixed radionuclide gamma-ray reference standards QCY48 and QCY40 (obtained from Physikalisch-Technische Bundesanstalt PTB, Germany) were used with 10 gamma-ray emitters in the energy range from to 1836 kev. Efficiency calibration was carried out by a certified standard solution containing 210 Pb, 57 Co, 60 Co, 85 Sr, 88 Y, 109 Cd, 113 Sn, 139 Ce, 137 Cs, 241 Am. The detector was calibrated in an absolute efficiency using a 10-nuclide gamma standard in the same geometry as the measurement sand samples (5). Primordial radionuclides in beach sand Following the spectrum analysis, count rates for each detected photo peak and activity per mass unit where N s,n is the net number of counts in a given peak area for the sample and t s the counting live times for the sample. Since there was a low activity concentration in the samples, the counting time was from 18 to 24 h to get a statistically small, N 0,n the net number of counts in a given peak area for background, t 0 the counting live times for background (72 h), 1 the detection efficiency, I g the number of gammas per disintegration and m the mass in kg of the measured sample. On the basis of the measured gamma-ray photopeaks, emitted by specific radionuclides in the 232 Th and 238 U decay series, 40 K and in 137 Cs, their radiological concentrations in samples collected were determined. Calculations relied on the establishment of secular equilibrium in the samples, due to the much smaller lifetime of daughter radionuclides in the decay series of 232 Th and 238 U. More specifically, the 232 Th concentration was determined from the average concentrations of 212 Pb and 228 Ac in the samples, and that of 238 U was determined from the average concentrations of the 214 Pb and 214 Bi decay products. Thus, an accurate measurement of 232 Th and 238 U radiological concentrations was made, whereas a true measurement of 40 K concentration was achieved. The 238 U activity concentration was calculated from the mean value of gamma transitions obtained from the photo peaks of 234 Th (63.28, kev), 226 Ra activity concentration calculated from the mean value of 214 Pb (295.22, kev), 214 Bi (609.31, 1120 kev) and 210 Pb (46.54 kev). Each tabulated value for the 232 Th series concentration was an average of three values obtained from 228 Ac the photo peaks of the 212 Pb ( kev), (209.25, , 911.2, kev) and 208 Tl ( kev). The 1461 kev gamma of 40 K was used to determine the concentration of 40 K in different samples and artificial nuclide 137 Cs (661.6 kev). The specific activity of 235 U is calculated using the equation 235 U ¼ 238 U/21.7. To estimate the uncertainty using the ISO standard (6 7), testing laboratories are obliged of the measurement results such as efficiency and activity of radionuclides in beach sand. The total uncertainty value (Table 1) is composed of the random and systematic errors in all of the factors involved in producing the final nuclide 377

3 S. HARB Table 1. Activity concentration (in Bq per kg dry weight) of 238 U, 235 U, 226 Ra, 210 Pb, 28 Ra, 228 Th, 232 Th, 40 K, and 137 Cs in bulk sand samples collected from Read Sea coast in Egypt. Sites 238 U 235 U 226 Ra 210 Pb 228 Th 228 Ra 232 Th 40 K 137 Cs Marsa-Alam MA MA MA MA E v Qusier QU QU QU QU E v Safaga SA SA SA SA E v Hurghada HU HU HU HU E v Ras Gharib RG1 v RG RG RG E v Qena Safaga QE1 E v for all samples GSD Min Max Median concentration result. The error is written as u 2 ða s Þ A 2 s ¼ u2 ðnpþ ðnpþ 2 þ u2 ðt c Þ t 2 þ u2 I g ðe g Þ c I 2 g ðe gþ þ u2 1ðE g Þ 1 2 ðe g Þ þ u2 ðmþ M 2 Where is the uncertainty from the spectra evaluation NP ¼ NP þ N 0 þ N 0 ð2þ NP is the net count t c is the counting time and N 0 is the counting of background. Gamma radiation dose Estimation of the absorbed dose rate The conversion factors (8) are used to compute the absorbed dose rate in air per unit of specific activity concentration in soil for 40 K, 226 Ra and 232 Th. The conversion factor for photon equivalent dose rate in 378

4 NATURAL RADIOACTIVITY AND EXTERNAL GAMMA RADIATION EXPOSURE Table 2. Specific activity ratios of 210 Pb/ 226 Ra, 232 Th/ 238 U, 232 Th/ 40 K, 238 U/ 40 K and 228 Ra/ 228 Th in sand beach samples Red Sea coast. Sites Sample 210 Pb/ 226 Ra 232 Th/ 238 U 232 Th/ 40 K 238 U/ 40 K 228 Ra/ 228 Th Marsa MA Alam MA MA MA Qusier QU QU QU QU Safaga SA SA SA SA Hurghada HU HU HU Ras Gharib Qena- Safaga HU RG RG RG RG QE air kerma (9) is 1.15 Sv Gy 21 in Equation (3): DðnGy h 1 Þ¼0:0417A K þ 0:462A Ra þ 0:604A Th DðmSv h 1 Þ¼ð0:0417A K þ 0:462A Ra þ 0:604A Th Þ1:15 ð3þ ð4þ where A Ra, A Th and A K are the specific activities of 226 Ra, 232 Th and 40 KinBqkg 21, respectively. Gamma-ray radiation hazard indexes The natural radioactivity of building materials is usually determined from 226 Ra, 232 Th and 40 K contents. As 98.5% of the radiological effects of the uranium series are produced by radium and its daughter products, the contribution from the 238 U has been replaced with the decay product 226 Ra (10). Since sand beach can be used in industries and building constructions, the gamma-ray radiation hazards due to the specified radionuclides were assessed by three different indexes. Radium equivalent activity is an index that has been introduced to represent the specific activities of 226 Ra, 232 Th and 40 K by a single quantity, which takes into account the radiation hazards associated with them. The first index can be calculated (11) as Ra eq ¼ C Ra þ 10 7 C Th þ C K ð5þ where C Ra, C Th and C K are the specific activities of 226 Ra, 232 Th and 40 K inbq kg 21, respectively. Another radiation hazard index called the representative level index (I g ) is defined as follows NEW- OECD (12). I gr ¼ C Ra þ C Th þ C K ð6þ All parameters were defined as mentioned before. To estimate the annual effective dose rates, the conversion coefficient from absorbed dose in air to effective dose (0.7 Sv Gy 21 ) and outdoor occupancy factor (0.2) proposed by (UNSCEAR) (13) were used. The effective dose rate in units of msv y 21 was calculated by the following formula: Effective dose rate ¼ Energy dose rateðngy h 1 Þ 8760 h 0:2 0:7 Sv Gy ð7þ The results obtained for the gamma radiation dose rate in air and the comparative results for background radiation areas of the world are presented in Table

5 RESULTS AND DISCUSSION Natural and artificial radionuclides in Red Sea shore Measurements of environmental radioactivity have been the objective of several investigations (14 19). This work achieved, by means of gamma spectrometric techniques, the activities of the majority of all natural radionuclides 210 Pb, 226 Ra, 238 U, 235 U, 228 Ra, 228 Th, 232 Th, 40 K and 137 Cs present in beach sand samples. From north to south along the length of the Red Sea coastline, 21 sand samples were collected (Figure 1). The radioactivity in the beach sand is due to radionuclides belonging to natural families of 238 Uand 232 Th, besides other primordial nuclides such as 40 K; the presence of small amounts of 137 Cs is due to the radioactive fallout from atmospheric nuclear weapon testing. From Table 1. the following can be noticed. (1) The 238 U series ( 238 U, 226 Ra and 210 Pb) The activities of concentration in beach sand were to , to , to , to and to Bq kg 21 for 238 U, to , to , to , to , to Bq kg 21 for 226 Ra and to , to , to , to , to Bq kg 21 for 210 Pb observed in sand samples collected from Marsa-Alam, Qusier, Safaga, Hurghada, Ras Gharib, respectively. Activity of 238 U, 226 Ra and 210 Pb in beach sand samples collected from different beach locations of the coastal environment of Red Sea coastal that were the average of , and Bq kg 21, respectively. The concentrations for 238 U, 226 Ra and 210 Pb are similar to the average activity of each of the radionuclides in the beach sand from Alexandria and el Arish on the Mediterranean sea coast of Egypt (18 19), and from some other areas of the world (20), whereas the average concentration of 210 Pb is low. Generally, beach sand from Safaga area display higher concentrations of 226 Ra and 210 Pb relative to those collected from Hurghada. The concentrations of all radionuclides of uranium series of the coastal sediments are generally comparable with those in Safaga city lays (60 km) south Hurghada, which is 60 km south of Hurghada. (2) The 232 Th series ( 228 Ra, 228 Th and 232 Th) The results of g-spectrometric analyses are presented in Table 1. Beach sands show the high activity concentrations of 232 Th found in sample HU3 from Hurghada Bq kg 21 and lower activity in sample MA2 was Bq kg 21, concentrations of 228 Th of ranged from to S. HARB Bq kg 21 and activity concentrations of 228 Th of about to Bq kg 21. The values obtained for 232 Th series in beach sand are in good agreement with those reported by other authors (4, 21, 22). It is clear from these data that thorium concentrations in these materials are similar to the worldwide average concentrations in beach sand. (3) 235 U, 40 K and 137 Cs The results of g-spectrometric analyses presented in Table 1 show activity concentrations of 235 U of about to Bq kg 21 for beach sands. The expectation value of activities of concentration for 40 K in beach sand was from Marsa-Alam, from Qusier, from Safaga, from Hurghada, Bq kg 2l from Ras Gharib. A range of 40 K activity was observed in beach sand samples (from to Bq kg 21 ) with mean value of Bq kg 21. As regards artificial radioactivity, the anthropogenic radionuclide 137 Cs is also considered in this study in order to ascertain whether there has been any fallout of 137 Cs in the Red Sea coastal. The presence of 137 Cs in the sediment was evident; its activity ranged from to Bq kg 2l dry weight with a mean value of Bq kg 2l. When the sediments are compared location-wise with respect to 137 Cs content, those collected from Safaga beach show relatively high values. 137 Cs levels in the soil from nationwide survey vary from 0.1 to 4.26 Bq kg 2l with an average value of 0.49 Bq kg 21, which is in a good agreement with the average value found in sediments (17). From the results, it was found that the highest activity of 232 Th and 238 U series was found in surface sand at a distance of 10 m away from the waterline. This may be due to the continuous wave action, as the waves reaches up to about 10 m from the waterline during high tide and results in the fresh deposition of heavy minerals along the seashore. According to UNSCEAR (13), the world s average activity concentrations in beach sand from areas of normal radioactivity are 25, 25 and 370 Bq kg 21 for 232 Th, 238 U and 40 K, respectively. Table 1 lists the statistical data [expectation values (EV), geometric standard deviation (GSD), min., max. and median] for these radionuclides in the beach sand samples. Among the natural radionuclides series and 137 Cs studied in the sand samples, the mean concentration observed was the highest for 40 K (930 Bq kg 21 ), followed by 238 U ( Bqkg 21 ) and the lowest value activity was observed for 232 Th ( Bq kg 21 ).

6 381 Table 3. Comparison of activity concentrations of 238 U, 232 Th, 40 Kand 137 Cs external gamma-dose rate, radium equivalent activity (Ra eq ), representative level index (I g ) and effective dose rate (msv y 21 ) in beach sand samples of Red sea coast, Egypt and other studies in different beaches of the world. Locations 238 UBqkg Th Bq kg KBqkg Cs Bq kg 21 Dose rate (ngyh 21 ) Ra eq (Bq kg 21 ) I g r (Bq kg 21 ) Eff. D (msv y 21 ) References Marsa-Alam Present work Qusier Safaga Hurghada Ras Gharib Bangladesh (24) Bangladesh (25) Sudan (16) India (3) (26,27) Egypt Roseta (18) Al-Arish (14,17,19) Safaga Alexandria The Netherlands (28) Brazil (29) NATURAL RADIOACTIVITY AND EXTERNAL GAMMA RADIATION EXPOSURE

7 Correlation between naturally occurring radionuclides Table 2 shows the specific activity ratios of 210 Pb/ 226 Ra, 232 Th/ 238 U, 232 Th/ 40 K, 238 U/ 40 K and 228 Ra/ 228 Th in sand beach samples of Red Sea coast and the correlation between 210 Pb and 226 Ra, 232 Th and 238 U, 238 U and 40 K, 232 Th and 40 K and 228 Ra and 228 Th computed from the results of the concentration of naturally occurring radionuclides given in Table 1 (0.8069, , , and , respectively). The correlation between 238 U and 40 K is very weak with a correlation coefficient of The correlation coefficient of 232 Th and 40 K is (Figure 2b). A good correlation between 228 Ra and 228 Th is shown in Figure 2a. The correlation coefficient between 210 Pb and 226 Ra is shown in Figure 2c. The ratios for 228 Ra/ 228 Th indicate that for some samples the activities of 228 Ra and 228 Th deviate slightly from secular equilibrium, but the value approaches unity for most of the samples. The ratios for 210 Pb/ 226 Ra indicate that for some samples the activities of 226 Ra and 210 Pb deviate slightly from secular equilibrium. Anderson (23) suggested that particulate authigenic uranium is primarily formed in surface seawater, but is rapidly re-mineralised in deep water. Therefore, the 232 Th/ 238 U ratios in surface marine sediments should be representative of that in detrital phases. S. HARB Gamma radiation exposure External gamma dose rate, Ra equivalent activity (Ra eq ), representative level index (I g ) and effective dose rate (msv y 21 ) in beach Red sea were estimated, and the values being shown in Table 3. The activity concentrations of 238 U, 232 Th, 40 K and 137 Cs, and external gamma dose rate, radium equivalent activity (Ra eq ), representative level index (I g ) and effective dose rate (msv y 21 ) for coastal environmental beach sand samples of different beaches of the world for comparison are shown in Table 3. The mean values of the gamma dose rate for the five studied beaches were ngy h 21 for Ras Gharib, ngy h 21 for Hurghada, ngy h 21 for Safaga, ngy h 21 for Qusier, ngy h 21 for Marsa Alam and ngy h 21 for 20 km Qena-Safaga road. The higher values of gamma dose rates found at Safaga and Hurghada beach are due to 226 Ra, 232 Th and 40 K radionuclides. The values of gamma dose rates found in all beaches studied in this work are higher than those found by Gonzalez-Chornet and Gonzalez-Labajo (30) ranged from 12.1 to 19.8 ngyh 21. The average values of the radium equivalent activities were evaluated and found to be in Ras Gharib, in Hurghada, Figure 2. Correlations between the activity concentration of (a) 228 Ra and 228 Th, (b) 232 Th and 40 K and (c) 210 Pb and 226 Ra in Safaga, in Qusier, in Marsa Alam and in 20 km Qena-Safaga road. The world average for 382

8 NATURAL RADIOACTIVITY AND EXTERNAL GAMMA RADIATION EXPOSURE ACKNOWLEDGEMENTS The author thank Prof. R. Michel, Director of Centre for Radiation Protection and Radioecology (ZSR), Hannover University, Germany, for his encouragement and support. Ra eq and I g r value being and 0.66 Bq kg 21, mean gamma-dose rate in air at 1 m above the ground surface is 0.39 mgy y 21 UNSCEAR (21). The annual external effective dose rates varied from to msv y 21. With an average value, the annual external effective doses ( , , , , and msv y 21 Marsa-Alam, Qusier, Safaga, Hurghada, Ras Gharib and Qena-Safaga road, respectively) of Red Sea shore are less than the worldwide average normal background doses received from radionuclides of terrestrial origin. On the basis of lower levels of natural radioactivity and gamma absorbed dose rates, the Red Sea beach region can be considered as a less natural background radiation area. CONCLUSION The expectation values of activities concentrations were for 210 Pb, for 226 Ra, for 238 U, for 235 U, for 228 Ra, for 228 Th, for 232 Th, for 40 K and kg 21 for 137 Cs and concentrations of these radionuclides in beach sand in Marsa-Alam, Qusier, Safaga, Hurghada, Ras Gharib were obtained. The lowest concentration of 238 U (3+ 1Bqkg 21 ) was observed in Qusier (QU1) and the highest (41 + 3Bqkg 21 ) was seen in Safaga (SA2). Similarly, the lowest concentration of 235 U was found in Qusier (QU1) ( Bq kg 21 ), 226 Ra in Marsa-Alam (MA2) (5 + 2Bqkg 21 ), 210 Pb in Ras Gharib (RG2) ( Bq kg 21 ), 228 Th in Marsa-Alam (MA2) ( Bqkg 21 ), 228 Ra in Marsa-Alam (MA2) (4 + 1Bqkg 21 ), 232 Th in Marsa-Alam (MA2) ( Bqkg 21 ), 40 K in Ras Gharib (RG2) ( Bqkg 21 ) and 137 Cs in Qusier (QU1) ( Bq kg 21 ), and highest concentration of 235 U, 226 Ra, 210 Pb, 228 Th, 228 Ra, 232 Th, 40 K and 137 Cs ( , , , , , , and Bq kg 21, respectively) were found in SA2, SA2, HU3, HU3, HU3, HU3, HU2 and SA2 sand samples, respectively. External gamma-dose rate ranged from to , Ra equivalent activity (Ra eq ) ranged from to , representative level index (I g ) ranged from to and effective dose rate (msv y 21 ) ranged from to in beach Red sea. The activities of 238 U and 232 Th series in the sand samples of Coastal Safaga and Hurghada are lower, whereas those of 40 K are on the higher side compared with the worldwide average value. The correlation between 238 U and 40 K and 232 Th and 40 K are poor, but the individual results of 228 Ra and 228 Th is a good predictor of each other. 383 FUNDING Funding is by a research grant from the Egyptian government. REFERENCES 1. Alencar, A. S. and Freitas, A. C. Reference levels of natural radioactivity for the beach sands in a Brazilian southeastern coastal region. Radiat. Meas. 40(1), (2005). 2. Wei, L. and Sugahara, T. An introductory overview of the epidemiological study on the population at the high background radiation areas in Yangjiang. China. J. Radiat. Res. 41, 1 7 (2000). 3. Narayana, Y., Somashekarappa, H. M., Radhakrishna, A. P., Balakk Rishna, K. M. and Siddappa, K. External gamma radiation dose rates in coastal Karnataka. J. Radiol. Prot. 14(3), (1994). 4. United National Scientific Committee on the Effects of Atomic Radiation. Report to General Assembly, with Scientific Annexes, Sources and Effects of Ionizing Radiation. Table 9 (New York: UNSCEAR), P. 65 (1993). 5. Harb, S. On the human radiation exposure as derived from the analysis of natural and man-made radionuclides in soils. Ph.D. thesis, Germany, ZSR, Hannover University (2004). 6. International Standards Organization. General requirements for the competence of testing and calibration laboratories (ISO/IEC 17025:1999) (Brussels ISO: European Committee for Standardization) (1999). 7. Michel, R. Quality assurance of nuclear analytical techniques based on Bayesian characteristic limits. J. Radioanal. Nucl. Chem. 245(1), (2000). 8. International Commission on Radiation Units and Measurements. Gamma-ray spectrometry in the environment. ICRU Report 53 (ICRU) (1994). 9. Kemski, J., Klingel, R. and Siehl, A. Die terrestrische Strahlung durch natürlich radioaktive Elemente in Gesteinen und Böden. Siehl, A.Ed. (Umweltradioaktivität: Ernst und Sohn Verlag) (1996). 10. Veiga, R. et al. Measurement of natural radioactivity in Brazilian beach sands. Radiat. Meas. 41, (2006). 11. Beretka, J. and Mathew, P. J. Natural radioactivity of Australian building materials, industrial wastes and by products. Health Phys. 48, (1985). 12. Nuclear Energy Agency. Exposure to radiation from natural radioactivity in building materials. Report by NEA Group of Experts OECD (Paris: NEA-OECD) (1979). 13. UNSCEAR United National Scientific Committee on the Effects of Atomic Radiation. Report to General Assembly, with Scientific Annexes, Sources and Effects of Ionizing Radiation (New York: UNSCEAR) (2000).

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