Simple Radiometric Determination of Strontium-90 in Seawater Using. Measurement of Yttrium-90 Decay Time Following Iron-Barium Co-

Transcription

1 Original Papers Simple Radiometric Determination of Strontium-0 in Seawater Using Measurement of Yttrium-0 Decay Time Following Iron-Barium Co- precipitation Mitsuyuki KONNO, and Yoshitaka TAKAGAI, Faculty of Symbiotic Systems Science, Cluster of Science and Technology, Fukushima University, Kanayagawa, Fukushima 0-, Japan 0 Environmental Radiation Monitoring Centre, Fukushima Prefecture, - Sukakeba, Kaibama, Haramachi, Minamisoma, Fukushima -00, Japan Institute of Environmental Radioactivity, Fukushima University, Kanayagawa, Fukushima, 0-, Japan To whom correspondence should be addressed. s0@ipc.fukushima-u.ac.jp

2 Abstract 0 A radiometric quantitative methodology of 0 Sr in seawater was developed using the measurement of 0 Y decay time following iron-barium co-precipitation. With calculations of its decay time, the radioactivity of 0 Sr can be indirectly determined under the conditional environmental samples. In addition, to avoid the interference of other radionuclide, the prepared samples were measured using germanium semi-conductivity detector, then the deposited radioactivity was subtracted from the actual measurement values of beta-ray counting. In this paper, the sea water samples were collected within km around Fukushima Daiichi Nuclear Power Plants at the term from October 0 to March 0. This method showed the good linearity between 0 Sr concentration and total beta counting following the proposed method, with a correlation coefficient of 0. in seawater sample analysis. Any interference which was caused by other radionuclides such as radioactive cesium was not observed in the quantification of 0 Sr. The whole process need hours to quantify 0 Sr and the time is /0 shorter than traditional milking-low background gas-flow counting method. The lower limit of detection (average value; n=0) of the 0 Sr radioactivity was shown as 0.0 Bq/L (uncertainty:.%). Keywords: radioactive strontium, iron-barium co-precipitation, yttrium-0, simple radiometric determination, seawater. 0

3 Introduction Radioactive strontium ( Sr (half-life (HLT): 0. d ) or 0 Sr (HLT:. y )) is one of β-ray emitting radionuclides and is widely known as a representative fission product of U and Pu. Sr is an element belonging to the same family as Ca, known to form deposit in the bone when incorporated into the body,, and cause long-term internal exposure, for which it is one of the most important monitoring radionuclides in nuclear disasters. Amongst environmental samples, seawater monitoring is very important not only for environmental protection but also for international influence. 0 In the accident at TEPCO's Fukushima Daiichi Nuclear Power Plants (NPP), which occurred on March 0, various artificial radionuclides were released into the environment, and many agencies are monitoring the released radionuclides,. Detailed nuclide analysis can be carried out in a short time by monitoring the γ-ray emitting radionuclides with a Ge semiconductor detection device. However, in the case of analyzing pure β-ray emitting radionuclides such as Sr or 0 Sr, especially in the case of the conventional method (Milking- Low Background Gas-Flow Counting Method (LBC)), it takes about weeks to month to obtain the results of measurement. For this reason, monitoring of pure β-ray emitting radionuclides is time-consuming in comparison with the determination of γ-ray emitting radionuclides and shortening of the measurement is desirable. 0 As methods for analyzing radioactive Sr in a short time, quantitative analysis by inductively coupled plasma mass spectrometry (ICP-MS) and solid phase material, obtained by selective extraction of Sr 0, are the subject of studies. However, in these analytical methods, the lower limit of quantification is about 0. to.0 Bq/L, and interference is caused in the case of a sample containing elements of high concentration in a matrix.,

4 0 0 Alternatively, the measurement of total β radioactivity is also well known as the analytical means. In this method, β-rays emitted from a sample are counted without energy division, and the radioactivity is determined by comparison with a standard sample. Since total β radioactivity does not measure α-rays and γ-rays, the difference in quantitative values is small as compared with the measurement method of milking-lbc, and it is excellent as a simple monitoring method of pure β-ray emitting radionuclides. Many samples such as airborne dust, drinking water, rainwater, seawater etc. are being analyzed due to this convenience. Amongst them, regarding in particular the method for analyzing the total β radioactivity of seawater, it is known that total β radioactivity can be measured with a comparatively simple operation via co-precipitating metallic elements. By using the cobalt sulfide co-precipitation method, Fe, 0 Co, Zn, 0 Ru, and the like, can be co-precipitated efficiently. Furthermore, the iron-barium co-precipitation method is an efficient method for co-precipitation of 0 Y (HLT:.0 h ) and m Ba (HLT:.min ) by applying a basic NHCl NH mixture to a mixed solution of Fe(III)-Ba(II) ions. Authors consider that it is possible to efficiently perform the measurement of total β radioactivity with proper use of the chemical coprecipitation method, as described above. Since, however, in total β radioactivity analysis the calculated values are obtained without energy division of β rays emitted from a sample, the quantitative determination of a specific β-ray emitting nuclide proved difficult. Due of this disadvantage, although the total β-radioactivity analysis is a simple means for measuring radioactivity, even if 0 Y as a daughter nuclide of 0 Sr can be iron-barium co-precipitated, the method can be hardly used for quantitative determination of 0 Sr due to co-precipitation with other β-emitting radionuclides. On the other hand, Bau reported that by adjusting the ph from. to., in the presence of iron, an Fe(III) hydroxide precipitate is formed, and thereby rare earth elements can be scavenged. This report relates to verification with stable isotopes, and it does not assume

5 0 fission products occurring in an actual nuclear power plant. Table S in supporting information shows a part of radionuclides assumed to be fission products among rare earths and Y (REY). In the total β radioactivity analysis, the radioactivity of pure β-ray emitting radionuclides can be calculated by subtracting the contribution of γ-ray emitting radionuclides as measured by a Ge semiconductor detector. Otherwise, if radionuclides having short halflife time such as Pb and Bi, and radionuclides reaching transient equilibrium such as 0 Ba and 0 La are detected in γ-ray spectrum, the interferences of those radionuclides need to subtract from the measurement value of LBC. In addition, other β emitter radionuclide P (. MeV) was considered as an inhibitor of the measurement using LBC; however, the P was able to be separated by Fe-Ba co-precipitation (the stable P isotopes were distributed into water-phase). 0 The authors concluded that most of the co-precipitated radionuclides are radionuclides with a half-life of month or longer and focused on the facts that (), only 0 Y has short HLT (. h), (), has large β-ray energy (. MeV) and (), is a pure β-ray emitting nuclide. It is conceivable that this could be applied to low concentration environmental radioactivity analysis, especially seawater analysis, derived from nuclear disasters satisfying fixed conditions. Here, the fixed conditions include: (a) two weeks and more have passed since a nuclear disaster, and (b) the total radioactivity concentration is sufficiently low to the environmental level. In addition, to avoid the interference of other radionuclide, we considered that the prepared samples were measured using germanium semi-conductivity detector, and then the deposited radioactivity was subtracted from the actual measurement values of beta-ray counting. Therefore, in this study, we applied Fe-Ba co-precipitation to seawater, and the precipitated 0 Y was identified by measuring time-intensity measurement (decay curve) by beta counter. With calculations, we indirectly determined the radioactivity of 0 Sr in seawater.

6 Experiments Equipment For β-ray measurement, a low background gas-flow counter LBC-0 (Hitachi ALOKA Medical Co., Ltd., Tokyo, Japan) was used. The detector was a GM counter, which was equipped with an anti-coincidence calculation function with a center counter and a guard counter. This detector was shielded with 00 mm lead, and a thin polyethylene terephthalate film with gold vapor deposit which was attached to the β-ray detection part of the detector. For quenching, a mixed gas of helium % - isobutane % was used. 0 For γ-ray measurement, a GC00 type germanium semiconductor detector (manufactured by Canberra Japan, Tokyo, Japan) was used. The resolution was. kev, a relative efficiency of % was used. Self-absorption correction function and sum peak correction function were employed. ELAN DRC-II inductively coupled plasma mass spectrometer (PerkinElmer, Inc., Shelton, CT, USA) was employed with ultrapure CH (>.%) a reaction gas in a collision- reaction cell (the dynamic reaction cell (DRC) to measure the concentration of multielement. 0 Reagents and preparation In this research, unless specified otherwise, special grade reagents of Wako Pure Chemical Industries, Ltd. were used. For the iron carrier,. g of Fe(III)Cl HO was dissolved in 0 to 0 ml of M HCl. This solution was transferred to a volumetric flask and filled up to 0 ml with distilled water. For the Ba carrier,. g of BaCl HO was dissolved in ion exchanged water and made up to 000 ml to prepare a concentration of 0

7 0 mg Ba + /ml. A certified 0 Sr solution was used 0. Bq/g (relative expansion uncertainty:.%) and manufactured by Japan Isotope Association. The standard solution of radioactive Cs was prepared as following. The radioactive Cs was extracted from the soil sample ( Cs: and Cs: 0 Bq/g; : 00 June, 0) collected at a location about km southwest of the Fukushima Daiichi NPP by the following procedure. 00 g of soil was extracted to L of conc. HCl with heating. This was filtered with glass fiber filter paper (manufactured by ADVANTEC, GA-00). Next, NaOH (granitic solid) was gradually added to this solution to adjust the ph to 0 or more, then 00 g of NaCO was added and stirred. After the precipitate was sufficiently settled, the supernatant was separated by decantation and the volume was made up to a constant volume. After quantitative analysis with the Ge semiconductor detector, this was used as a standard radioactive Cs solution and diluted with ultrapure water as the case requires for use. 0 Fe-Ba co-precipitation and LBC analysis The 0 mg of each Fe + (carrier) and Ba + (carrier) were added to L of seawater sample and stirred thoroughly. g of NHCl was added and dissolved completely while heating with a gas burner. Heating was continued, and when the sample solution reached approximately 0 C, aqueous NH was added slowly. When aqueous NH was added slowly, the white-turbid solution arose and then the solution was colored the reddish brown by the addition of more excess of NH. Dropwise addition of aqueous NH was continued until a dark brown precipitate was formed in the sample solution, and then the sample solution was boiled once. The ph of this solution was adjusted at the range from.0 to.. After boiling, the sample solution was kept at about 0 C for 0 min to let the precipitate grow. Then, the sample solution was allowed to cool to room temperature. The original whole sample solution ( L) was filtered using a paper filter (φ mm, B) and the precipitate was collected.

8 The precipitate was washed with % NHCl and ethanol, heated and dried with an infrared lamp, and then β-rays were measured using LBC. The background count rate was subtracted from data in each measurement 0 0 Counting efficiency in LBC analysis The counting efficiency in the total β radioactivity analysis is usually determined using UO or KCl standards. This standard radiation source has a structure in which the above- mentioned reference material is applied to a sample dish and its surface is covered with a plastic film or the like, and in most cases the shape and the base material are different from the actual measurement sample. When quantifying the result of 0 Sr from the result of total β radioactivity as in this study, we considered that the difference in counting efficiency due to the difference in sample shape remarkably affects the result. Although the solvent for dissolving reference material is desired to be same as the sample solvent, the pure water was used as a solvent to dissolving reference material in this study. Therefore, this time, exchanged ion water, containing a fixed amount of 0 Sr standard solution, was prepared and β-rays were measured by the above-mentioned method described in the section of Treatment of Fe-Ba co-precipitation and LBC analysis to determine the counting efficiency. The measurement time is 0 min and the counting rate is 0. cpm for gain of Bq The counting efficiency was calculated according to the following equation. ee (%) = NN ss NN bb tt RR ssssss 00 where e (%) represents the counting efficiency, Ns (counts) and Nb (counts) are count values of the standard sample and the background, respectively, t (sec) is the measurement time, Rstd (Bq) indicates the amount added of 0 Sr standard substance. Accordingly, the

9 obtained counting efficiency was 0. % and this value was used to calculate the β-rays radioactivity in this study Sr analysis of seawater by the official method of Japan (milking process-lbc) Radioactive Sr in sea water was analyzed according to the official method in Japan. A 0 L of seawater sample was filtered with a paper filter (A), 0 ml of HCl was added and the solution was passed through a column (φ00mm, L=0 mm) packed with anion exchange resin (Dowex 0W-X manufactured by Muromachi Technos Co., Ltd.). Next, Sr was isolated by flowing 000 ml of a : mixture of M aqueous CHCOONH solution and methanol and then 000 ml of M HCl, in that order. NaOH (granular solid) was gradually added to M HCl fraction and adjust the ph to 0 or more, then 00 g of NaCO was added; the mixture was thoroughly stirred and then heated. After allowing it to cool, the precipitate formed was separated by centrifugation (,000 rpm, 0 min) and dissolved with HCl. This solution was heated on a hot plate for full evaporation, 00 ml of 0. M HCl was added and the solid matter was completely dissolved. This sample solution was passed through a column (φ0mm, L=0 mm) filled with an anion exchange resin (Dowex 0W-X manufactured by Muromachi Technos Co., Ltd.) at a flow rate of 0 ml/min. Next, 000 ml of a : mixture of M aqueous CHCOONH solution and methanol was flowed through the ion-exchange resin holding the adsorbed sample, Ca was eluted, and the Sr was isolated by passing 00 ml of M aqueous CHCOONH solution. The flow rate at this time was 0 ml/min. The sample solution with isolated Sr was heated to evaporate the liquid and then a small amount of nitric acid was added to form SrNO. Thereafter, this sample was dissolved in ion exchanged water and an appropriate amount of a saturated (NH)CO solution was added to precipitate Sr(CO). After filtration immediately, through a glass filter (φ0mm, 0~μm), the precipitate was dissolved in diluted HCl. Fe carrier

10 (Fe + ) and Y carrier (Y + ) were added, and the mixture was kept in a sealed state for at least weeks waiting for radiation equilibrium between 0 Y and 0 Sr. Two weeks later, NHCl and aqueous NH were added to the sample solution, and 0 Y was co-precipitated with iron. The time to be precipitate was recorded and the decay correction of 0 Y time was calculated using the time. This precipitate was filtered with a paper filter (φ mm, C), dried, and β-rays were measured using LBC. The background count rate was subtracted from data in each measurement. 0 0 Sampling Seawater samples collected at locations around the Fukushima Daiichi NPP were used (Table and Fig. show sampling locations). The sample volume was approximately 00 L and the collection was carried out from a ship (Hatsukaze #, -ton) using a pump from a depth of m. The salinities of collected seawaters were measured using IC-00 series ion-chromatograph (TOSOH Corporation, Tokyo) following Japanese Industrial Standard (JIS 00-.) and consequently, the concentration range of Cl - was from 000 to 000 mg/l. Those concentrations depended on the sampling locations. After sampling, the concentrated HCl was added into the seawaters (the 0. v/v% HCl aq. sol. was prepared). The seawater was allowed to stand for at least hours, and after precipitation of impurities such as sand and seaweed, the supernatant was used as a sample. The collection period was 0 months from June 0 to March 0, the sampling frequency was to times/month, and the total number of samples was 0. [Note] The typical radioactivity concentrations of 0 Sr in seawater near and around Fukushima Dai-ichi NPP at April, 0 were the range from 0. to. mbq/l. Results and discussion 0

11 0 0 Relationship between total β radioactivity treated by Fe-Ba co-precipitation method and 0 Sr radioactivity Fig. shows the relationship between 0 Sr and the total β radioactivity (after treatment of the proposed method) of seawater (collected around the Fukushima Daiichi NPP) with presented method. The 0 Sr concentration in seawater was determined by public authorized analytical method which was described in the section of 0 Sr analysis of seawater by the official method of Japan (milking process-lbc), and the total β radioactivity means the measurement values using LBC after the treatment of Fe-Ba co-precipitate. As a result, good correlation (R = 0.) was found between the total β radioactivity and 0 Sr radioactivity. Plotted each points mean the different seawater samples which were collected at different location around the Fukushima Daiichi NPP. Generally, in the total β radioactivity measurement, about 0% of 0 Sr and % of the rare earth 0 Y are believed to co-precipitate with iron ions, and it was considered that the slope of 0 Sr to the total β radioactivity should be or larger. Plausible causes of the constant of proportionality becoming smaller than, include loss of precipitate at the time of preparing the measurement sample, decrease in recovery rate, due to insufficient co-precipitation of 0 Y in the co-precipitation operation with iron ions, and inhomogeneity of the sample. The certain precipitation rate of Sr was approx. only 0% in this study and the mere quarter of the energy of 0 Sr was counted among of the only 0% precipitation; therefore, it was considered that the interference of other radionuclides were difficult to be found. For other confirmation, the total β radioactivity in a standard sample (after the treatment of this method) obtained by adding a fixed amount of 0 Sr standard solution to the ion exchanged water was measured, and the plotted results are shown in Fig.. In this graph, the ordinate represents the total β radioactivity concentration and the abscissa represents the addition amount of the 0 Sr standard solution. According to this graph, the constant of proportionality of the total β radioactivity to 0 Sr concentration was

12 0 almost with a correlation coefficient of.00, consistent with the constant of proportionality of the seawater sample shown in Fig.. This suggests that sedimentation loss, during test sample preparation and counting error of the measuring device, do not have remarkable impact. Next, to check whether 0 Y co-precipitates with Fe ions at the theoretical value, a certain amount of Y was added as a tracer to the sample, and the Y concentration contained in the supernatant, when the settled precipitate was formed by the analytical procedure described above, was measured by ICP-MS and the recovery rate was determined. Table summarizes the results. In all samples, the recovery rate of Y was %, thus Y coprecipitated according to the theoretical value. Furthermore, to confirm the interference by other radionuclides, similar tests were performed on samples intentionally added with excessive amount of radioactive Cs, but also in that case, no change was observed in the recovery rate of Y. These results confirmed that Y, in the sample, was recovered in its entirety, and the likelihood of insufficient co-precipitation of Y with iron ions could be denied. From those results, it is considered that pure β-emitting radionuclide in co-precipitate is almost 0 Y. The 0 Sr was not able to detect due to the lower β-ray energy than 0 Y (approx. %) and the abundance is quite low in co-precipitate. This consideration was indicated as same as the results using 0Sr reference materials. 0 The identification of radionuclides using decay time Since the traditional total β radioactivity measurement method is a simplified means to estimate all β-ray emitting radionuclides, identification of radionuclides is difficult. Therefore, the authors tried to identify radionuclides (after the treatment of presented method) by measuring decay time to prevent false recognition of the target nuclide. Using the short halflife of 0 Y (HLT: hours ), identification was attempted by checking the attenuation of β-

13 rays emitted from the sample. Fig. (A) shows the time course of total β radioactivity of seawater samples. Here, to clearly confirm the attenuation of the sample, the results of samples with comparatively large count value were used. Samples were then taken at the same location with different collection dates and the measurement interval was hours. As a result, it was confirmed that the count values decreased at a fixed rate over time in all measured values. In addition, the data was converted to the equation of the radioactive decay due to the identification of the nuclide as follows; AA = AA 0 exp ( λλλλ) 0 where, the A and A0 represents the current and initial radioactivity, respectively; the t and T are elapsed time and the half life time (HLT) of radionuclide, respectively. Here, so we aim to make the precipitate of 0 Y using Fe-Ba co-precipitate reaction, and the HLT of 0 Y is hours. The equation can be changed as follows; AA AA 0 = exp( λλλλ) ln AA AA 0 = λλλλ =.0 0 tt The data of the Ln (A/A0) vs. time was plotted as shown in Fig. (B). The slopes of both samples were corresponded with [h - ]; thus the radiation source from the precipitate was found to be 0 Y. 0 Moreover, we checked whether this attenuation was due to 0 Y. For other radionuclides present in the test sample, with highly probability and natural radionuclides, the attenuation of the count value was calculated at the same time and plotted as shown in Fig..

14 As a result, the measured value of the sample agreed with the theoretical value calculated for attenuation of 0 Y. The actual measurement value s plots were described on the theoretical decay curve of 0 Y until 0 h. After 0 h, the plotted slightly shifted from the theoretical line. It was suggested that trace amounts of long-lived radionuclide survived in the precipitate. However, the trace nuclides were little affected on the proposed method (the approx. 0 h measurements). In addition, the overshoot of the counting value due to the mixture of the short half-life nuclides was not observed. The decays of the natural radionuclides, e.g. Pb (HLT: 0. h) was obviously different from the measurement dots. 0 From the above, in the total β radioactivity analysis, by the Fe-Ba co-precipitation method, by measuring the change over time of the sample we were able to achieve the identification of the nuclide, which is a weak point of this analytical method. Furthermore, as the nuclide identification became possible in this way, false identification of the nuclide can be prevented, and it seems that this analytical method can be very useful in screening tests in case of emergency. Impact to radioactive Cs on this method 0 We investigated the influence of other radionuclides contained in samples in the environment on total β radioactivity. An excess amount of radioactive Cs ( Cs + Cs = 00 Bq) was added to distilled water containing with the 0 Sr standard solution, and the total β radioactivity (after the treatment of this method) was measured. The results are shown in Fig.. Even in the sample to which radioactive Cs was added, similarly to the correlation between 0 Sr and the total β radioactivity illustrated in Fig., very good correlation (R =.000) was found and also the calibration was substantially prepared. The graph also revealed that there

15 was no change in the value of total β radioactivity even in the presence of excessive amount of radioactive Cs. This demonstrates that the method is effective for easily analyzing 0 Sr even when a large amount of radioactive Cs is released as in the case of this accident. From these results, the actual Fukushima Daiichi nuclear accident the amount of radioactive Cs emitted into the environment was more than 0 times higher than that of radioactive Sr and this method can use in the actual monitoring. As a result, it was found that the presence of radio Cs in the concentration range of several Bq/L in seawater did not influence on the 0 Sr quantification using the presented method. 0 Furthermore, the detection limit (DL; average value; n=0) of the 0 Sr radioactivity was 0.0 Bq/L (uncertainty:.%) in this presented method. The time required for analysis was hours at maximum speed, which was /0 compared to analysis by the milking-lbc method. In addition, the DL was 0 to 00-fold lower than other method such as ICP-MS., Conclusion 0 We investigated whether 0 Sr contained in seawater can be quantified by the total β Fe-Ba co-precipitation method. As a result, correlation (correlation coefficient R =0.) was found between the data of total β radioactivity analysis method treated after Fe-Ba coprecipitation method of seawater collected in the waters surrounding the Fukushima Daiichi NPP, Tokyo Electric Power Co., Inc. and the values of 0 Sr concentration obtained by milking-lbc method. Furthermore, by measuring the decay time (in the measurement time was limited range from 0 to 0 h, typically 0 h), 0 Y was identified, thus it was possible to avoid false recognition regarding 0 Sr and other radionuclides. This method could expect to use as an alternative radiometric quantification for radioactive Sr in limited environmental

16 conditions; (a) two weeks and more have passed since a nuclear disaster, and (b) the total radioactivity concentration is sufficiently low to the environmental level. Acknowledgments 0 The authors gratefully acknowledge funding by the Ministry of Education, Culture, Sports, Science & Technology in Japan (MEXT), Human Resource Development and Research Program for Decommissioning of Fukushima Daiichi Nuclear Power Station. In addition, we thank Mr. Makoto Matsueda (Japan Atomic Energy Agency), Mr. Hiroaki Ogata and Ms. Mizuki Odashima (Fukushima University) for experimental cooperation and useful discussions. References. R. B. Firestone and V. S. Shirley, Table of Isotopes (CD-ROM ver),, th ed., John Wiley & Sons Inc.. Ministry of Health Labour and Welfare (Japan), Inspection of Radiomaterials in Tap water, Kenkoukyoku/0_houshasei_0_m.pdf. 0. Fukushima prefecture Government, Results of Environmental Radioactivity Monitoring, Japan Atomic Energy Agency, Database for Radioactive Substance Monitoring Data,

17 . MEXT, Research and Development Bureau, Atomic Energy Division. Analytical methods of the radioactive strontium, No., Japan, Y. Takagai, M. Furukawa, Y. Kameo, and K. Suzuki, Anal. Methods, 0,,.. M. Furukawa and Y. Takagai, Anal. Chem., 0,,.. A. Ayala and Y. Takagai, Anal. Sci., 0,,.. M. Furukawa, M. Matsueda, and Y. Takagai, Anal. Sci., 0,,. 0. S. Scarpitta, J. Odin-McCabe, R. Gaschott, A. Meier, and E. Klug, Health Phys.,,. 0. Y. Takagai, M. Furukawa, Y. Kameo, M. Matsueda, and K. Suzuki, Bunseki kagaku, 0,,.. M. Furukawa, M. Matsueda, and Y. Takagai, Bunseki kagaku, 0,,.. C. Dueñas, M. C. Fernández, E. Gordo, S. Cañete, and M. Pérez, Atmos. Environ., 0,, 0.. D. Zapata-García, M. Llauradó, and G. Rauret, Appl. Radiat. Isot., 00,,.. M. Palomo, M. Villa, N. Casacuberta, A. Peñalver, F. Borrull, and C. Aguilar, Appl. Radiat. Isot., 0,,.. P. Thakur and G. P. Mulholland, Appl. Radiat. Isot., 0,, 0.. S. Wisser, E. Frenzel, and M. Dittmer, Appl. Radiat. Isot., 00,,.. R. I. Kleinschmidt, Appl. Radiat. Isot., 00,,. 0. M. Bau, Geochim. Cosmochim. Acta,,,.

18 0. C. Liu, Sci. China Ser. D, 00,,.. Ching-kuo Daniel Hsi and D. Langmuir, Geochim. Cosmochim. Acta,,,.. Nuclear Regulation Authority, Radioactivity Concentration in the Seawater Near and Around Fukushima Dai-ichi NPP, 00.pdf.

19 Table Sampling locations No. GPS coordinate a) Latitude -N Longitude -E Direction or location from Fukushima NPP Air radiation dose rate b) / µsv h - A.00.0 NPP cooling water outlet 0. B NPP cooling water outlet 0.0 C..0 NPP cooling water inlet 0.0 D..00 East 0.0 E.00.0 South-east 0.0 F Nouth-east 0.0 a) Geographical coordinate values were based on the World Geodetic System (WGS- ) datum. b) Air radiation dose rates were measured at m above the on ground. The values were calculated as the dose rate of July 0. Air radiation dose rates were measured using NaI (Tl) scintillation survey meter.

20 Table Recovery of yttrium in sea water samples sample No. Composition 0 Sr / Bq Y / ppm Cs / Bq Y μg/l Recovery of Y, % RSD, % blank blank

21 Figure Captions Fig. The map of locations for seawater samples. The detail information was shown in Table. Center of circle in this figure is the intermediate point between plant and of Fukushima nuclear power plant: latitude -N:., longitude -E:.00. Fig. The relationship of 0 Sr radioactivity in seawater samples between Fe-Ba coprecipitation method (proposed method) and public authorized analytical method. The public authorized analytical method for 0 Sr in seawater is the low background gas-flow counting measurement with milling process. Fig. The spike of 0 Sr and its detection test using ion exchanged water (solid line). The dotted line was theoretical detection line. Fig. Time course curve of beta ray count rate values (A) and the correlation line between the radioactivity ratio vs. time (B). The sample # and # were seawater samples collected at Oct. 0th, 0 and March 0th, 0, respectively. Fig. The typical radionuclides of decay curves which were released to nature, and the correlation of the measurement values obtained by the proposed method. The sample was seawater samples collected at Oct. 0th, 0. The two of L of samples were treated by proposed method and measured as n =. Fig. The 0 Sr detection in the presence of 00 Bq of radio Cs. The Cs radioactivity was total radioactivity of Cs and Cs.

22 Fig. The map of locations for seawater samples. The detail information was shown in Table. Center of circumference in this figure: Latitude -N:., Longitude - E:.0.

23 Fig. The relationship of 0 Sr radioactivity in seawater samples between Fe-Ba coprecipitation method (proposed method) and public authorized analytical method. The public authorized analytical method for 0 Sr in seawater is the low background gas-flow counting measurement with milling process.

24 Fig. The spike of 0 Sr and its detection test using ion exchanged water (solid line). The dotted line was theoretical detection line.

25 Fig. Time course curve of beta ray count rate values (A) and the correlation line between the radioactivity ratio vs. time (B). The sample # and # were seawater samples collected at Oct. 0th, 0 and March 0th, 0, respectively.

26 Fig. The typical radionuclides of decay curves which were released to nature, and the correlation of the measurement values obtained by the proposed method. The sample was seawater samples collected at Oct. 0th, 0. The two of L of samples were treated by proposed method and measured as n =.

27 Fig. The 0 Sr detection in the presence of 00 Bq of radio Cs. The Cs radioactivity was total radioactivity of Cs and Cs.