Determination of recovery efficiency of 137Cs in seawaterusing co-precipitation method

ergy Institute 
Determination of recovery efficiency of 
137
Cs in seawaterusing 
co-precipitation method 
Duong Duc Thang*, Vuong Thu Bac, Bui Dac Dung, Duong Van Thang, Doan Thuy Hau, 
Le Dinh Cuong, Nguyen Van Khanh, Nguyen Thi Thu Ha, Cao Duc Viet, 
Nguyen Huyen Trang, Nguyen Thi Oanh, Le Thị Hoa 
Institute for Nuclear Science and Technology, 179 Hoang Quoc Viet – Cau Giay – Hanoi 
* Email: ducthangb2k52@gmail.com, thangdd@vinatom.gov.vn 
(Received 16 December 2019, accepted 04 March 2020) 
Abstract: Recovery efficiency of 
137
Cs in seawater samples with different volumes of 40, 50, 60, 80 
and 100 liters using co-precipitation method by ferrocyanide compounds has been determined. 
134
Cs 
nuclide was used as a tracer to determine recovery efficiency. The results showed that the recovery 
efficiency of 
134
Cs ranged from 92.62% to 99.26% with mean value of (95.22 ± 2.61)% for different 
sample volumes. Average recovery efficiency for samples with a volume of 50 liters was (95.70 ± 
2.50)% and uncertainty when determining 
137
Cs in seawater samples were still less than 20%. 
Therefore, reducing the volume of sample to 50 liters still ensures reliability when determining 
137
Cs 
in seawater samples by co-precipitation method, thereby reducing the chemical and time when analyze 
a large number of samples. 
Keywords: Recovery efficiency of 
137
Cs, co-precipitation method, seawater, HPGe. 
I. INTRODUCTION 
Huge amounts of anthropogenic 
radionuclides have been introduced into marine 
environment as global fallout from large-scale 
atmospheric nuclear-weapon testing, discharge 
from nuclear facilities and ocean dumping of 
nuclear wastes [1]. Their radiological and 
ecological effects are still of world concern [2]. 
137
Cs is one of the most important 
anthropogenic radionuclides in the field of 
environmental radioactivity monitoring 
because of its long physical half-life of 30.02 
years. It is a major fission product (fission 
yield is about 6–7%) from both plutonium and 
uranium [1]. 
137
Cs in the ocean has been 
mainly derived from global fallout [1, 2, 3, 4, 
5], together with close-in fallout from the 
Pacific Proving Ground nuclear explosions [3, 
4], discharge of radioactive wastes from 
nuclear facilities and others [6, 7, 8]. 
The determination of activity 
concentration of radionuclides in seawater 
samples is a complicated issue, because 
their activity in seawater samples is very 
low, a large number of samples are required 
(about 200 - 400 liters) [9]. Currently, there 
are various processes in the world for 
preliminary enrichment of seawater samples 
on the field before laboratory analysis. A 
number of previous studies have 
successfully reduced seawater sample 
volume to 20 liters [10, 11] or 10 liters [12] 
to reduce chemical and sample processing 
time while still ensuring accuracy. 
This paper presents the survey results 
on the recovery efficiency of 
137
C in seawater 
samples by different volumes, determining 
the activity of 
137
C and uncertainty by co-
precipitation method in the field then 
analysis in the laboratory of Center for 
Environmental Radiation Monitoring and 
DUONG DUC THANG et al. 
41 
Impact Assessment (CERMIA), Institute for 
Nuclear Science and Technology (INST). 
Based on the results obtained, it is 
recommended to analyze 
137
C in seawater 
samples with optimal volumes. 
II. MATERIALS AND METHODS 
Sampling and sample processing 
The activity concentration of 
137
Cs 
currently in the East Sea is quite small. It 
ranges from (1.16 ± 0.06) Bq/m
3
 to (1.62 ± 
0.15) Bq/m
3
 [9], therefore, to determine 
137
Cs, 
the enrichment method must be applied prior to 
analysis in the laboratory. 
Seawater samples were taken on Co To 
island, Co To District, Quang Ninh province, 
the sampling locations are shown in Figure 1. 
Samples were taken at the time of high tide to 
avoid the influence from the mainland. In this 
study, we took samples of surface seawater 
with different volumes of 40, 50, 60, 80 and 
100 liters, pretreated by co-precipitation 
method in the field (Figure 2) according to the 
procedure presented as shown below. 
Fig. 1. Location of seawater sampling on Co To island. 
Fig. 2. Sample treatment. 
DETERMINATION OF RECOVERY EFFICIENCY OF 
137
Cs IN SEAWATERUSING  
42 
Result of analyzing seawater samples 
on Co To island in 2018 (State-level 
Scientific and Technological Program 
(KC.05.07/16-20)) shows that there is not 
134
Cs in seawater on Co To island. Because 
134
Cs and 
137
Cs have same chemical 
properties. So 
134
Cs is often used to 
determine the recovery efficiency for Cs in 
seawater samples. In this study, the 
134
Cs 
radioactive solution was used as a tracer to 
determine the recovery efficiency for 
137
Cs. 
For a 100-liter seawater sample, the 
following procedure has been applied [9]: 
- Pour the 100 L of seawater sample 
into the water tank, add (3.33 ± 0.05) Bq of 
134
Cs tracer. 
- Add 100ml of HCl (1:1) solution to 
adjust the pH to 2 ÷ 3. 
- Add 10ml of CsCl solution (100 
mg/ml), 15ml BaCl2 (100mg/ml), mix well. 
- Add 6 g of NiCl2, 40 g of CaCl2, 25 g 
of K4Fe(CN)6, mix well, leave for 3 hours. 
- Add to the sample 800 g NH4Cl, 400 g 
Na2CO3, mix well, leave for 2 hours. 
- Add to the sample 40 ml of FeCl3 15%, 
mix well, leave for 12 hours. 
- Discard the sample supernatant by 
siphon, pour the precipitated substance into 
5 L beaker. 
For the process of precipitation of seawater 
samples with a volume of 40, 50, 60 and 80 liters, 
the amount of chemicals as well as 
134
Cs to be 
used will increase or decrease proportionally to the 
volume of seawater samples. 
After pretreatment on the site, the 
precipitate is transferred to the laboratory. The 
precipitate was filtered thought paper filter, 
dried to dryness at 105
0
C and put into the 
measuring box. Typical gamma spectra of 
seawater samples are shown in Figures 3 and 4. 
Fig. 3. The gamma spectrum represents the peak of 604.7 keV of 
134
Cs. 
DUONG DUC THANG et al. 
43 
Fig. 4. The gamma spectrum represents the peak of 661.7 keV of 
137
Cs. 
The samples were measured on a low 
background gamma spectrometer with 
CANBERRA's HPGe GC5019 detector with 
energy resolution and relative efficiency at the 
peak of 1332.5 keV of 
60
Co of 1.8 keV and 
50%, respectively. The spectrometer is 
calibrated using the IAEA RGU-1, IAEA-
RGTh-1 and IAEA-soil 6 reference samples of 
comparable geometry. 
The activity of 
134
Cs and 
137
Cs in the 
precipitation samples were determined, 
respectively, through gamma rays of energy 
604.7 keV and 661.7 keV with a time of 
240000 seconds to ensure the counting 
statistical error below 10%. 
The recovery efficiency of 
134
Cs is 
determined by the formula 1: 
 (1) 
Where HS is recovery efficiency (%), 
 is the initial activity of 
134
Cs used as 
the tracer (Bq), is measured activity 
of 
134
Cs in precipitation (Bq). 
The recovery efficiency of 
134
Cs was 
used to determine 
137
Cs activity in seawater 
samples. The radioactivity concentration of 
137
Cs was calculated as follows (IAEA, 
International Atomic Energy Agency, 1989): 
= (2) 
Where is the activity 
concentration of 
137
Cs in seawater sample 
(Bq/m
3
), N is the net peak area in the sample 
spectrum, t is the live time of the sample 
spectrum collection in seconds, ε is the 
detector efficiency of the gamma-ray, γ is the 
emission probability of the gamma line 
corresponding to the peak energy, V is the 
volume of the measured sample (m
3
), HS is the 
recovery efficiency of 
134
Cs (%). 
III. RESULTS AND DISCUSSION 
10 water samples with the different 
volumes have been analyzed. The recovery 
efficiency of 
137
Cs in those samples were 
calculated and presented in the Table I. 
DETERMINATION OF RECOVERY EFFICIENCY OF 
137
Cs IN SEAWATERUSING  
44 
Table I. Recovery efficiency of 
137
Cs in seawater samples by different volumes. 
Sample Volume (L) Recovery efficiency (%) 
M1 40 92.62 ± 2.29 
M2 40 99.26 ± 2.47 
M3 50 98.50 ± 2.24 
M4 50 94.54 ± 2.17 
M5 50 93.15 ± 2.27 
M6 50 93.41 ± 2.25 
M7 50 98.92 ± 2.26 
M8 60 93.93 ± 2.03 
M9 80 93.39 ± 1.93 
M10 100 94.48 ± 3.25 
Table I shows that the recovery 
efficiency varies from (92.62 to 98.92)% 
with an average of (95.22 ± 2.61)%. In 
which, the recovery efficiency of 
137
Cs in 
different volumes of 40, 50, 60, 80 and 100 
liters are (95.94 ± 3.32)%, (95.70 ± 2.50)%, 
(93.93 ± 2.03)%, (93.39 ± 1.93 )%, (94.48 ± 
3.32)%, respectively. The recovery 
efficiency of 
137
Cs in different volume of 
seawater samples tends to decrease when the 
volume increases. 
The average recovery efficiency of the 
sample volumes of 40 and 50 liters are quite 
similar, but for our method, the volume of 50 
liters is optimal. Because the precipitates 
obtained from 40-liter samples are 
approximately the same as the amount to be 
measured, while the precipitation volume of 
50-liter samples is always greater than the 
amount to be measured. This makes the 
recovery efficiency of the sample volume of 50 
liters stable and has less uncertainty. 
Fig. 5. The recovery efficiency of 
137
Cs versus sample volume. 
DUONG DUC THANG et al. 
45 
Figure 5 and Table I shows that the 
recovery efficiency of 
137
Cs in seawater by 
different sample volumes is quite similar 
and greater than 90%. The recovery 
efficiency of the smaller volume seawater 
samples are greater a bit than those of the 
larger volume samples. 
Activity concentrations of 
137
Cs in 
different seawater samples with different 
volumes calculated by formula 2 are shown in 
Table II. 
Table II shows that the activity 
concentration of 
137
Cs are in the range of (1.12 
± 0.23) Bq/m
3 
to (1.69 ± 0.21) Bq/m
3
 with an 
average of (1.42 ± 0.22) Bq/m
3
, with 
uncertainty less than 20%. The activity 
concentration of 
137
Cs in different seawater 
volumes of this study is similar to previous 
publication [9]. 
Table III presents a comparison of the 
recovery efficiency of 
137
Cs in seawater in this 
study with some results published before. 
Table II. Activity concentration of 
137
Cs in seawater samples. 
Sample Volume, L Activity concentration 
137
Cs (Bq/m
3
) 
M1 40 1.12 ± 0.23 
M2 40 1.19 ± 0.19 
M3 50 1.68 ± 0.17 
M4 50 1.42 ± 0.28 
M5 50 1.46 ± 0.20 
M6 50 1.69 ± 0.21 
M7 50 1.14 ± 0.23 
M8 60 1.56 ± 0.23 
M9 80 1.61 ± 0.21 
M10 100 1.29 ± 0.19 
Table III. The comparison of the recovery efficiency. 
Volume, L Recovery efficiency (%) 
10 93 ± 3 K. Hirose [10] 
20 99 Nakano [11] 
20 90 ÷ 95 J. Kamenik [12] 
40 92.62 ÷ 99.26 This work 
50 93.15 ÷ 98.92 This work 
60 93.93 ± 2.03 This work 
80 93.39 ± 1.93 This work 
100 94.48 ± 3.25 This work 
From Table III, we find that the recovery 
efficiency of 
137
Cs in seawater in this study is quite 
good and as similar as results of other papers. 
IV. CONCLUSIONS 
In this study, we achieved the initial goal 
of determining the recovery efficiency of 
137
Cs 
DETERMINATION OF RECOVERY EFFICIENCY OF 
137
Cs IN SEAWATERUSING  
46 
in seawater with different volumes from 40, 50, 
60, 80 and 100 liters. The recovery efficiency of 
137
Cs in seawater samples varied from 92.62% 
to 99.26% with an average of (95.22 ± 2.61)% 
and relatively good repeatability. 
The average recovery efficiency for 
samples with a volume of 50 liters is (95.70 ± 
2.50)% and the uncertainty when determining 
the activity concentration of 
137
Cs is still less 
than 20%. Therefore, it is possible to reduce 
the sample volume to 50 liters while 
maintaining reliability when determining the 
activity concentration of 
137
Cs in seawater 
samples by the co-precipitation method, 
thereby reducing chemicals and time when 
analyzing many samples at the same time. 
ACKNOWLEDGMENTS 
The authors would like to thank Vietnam 
Atomic Energy Institute (VINATOM) under 
grant CS/19/04-05 and the State-level 
Scientific and Technological Program 
(KC.05.07/16-20) for funding this study. 
REFERENCE 
[1]. UNSCEAR. “Sources and Effects of Ionizing 
Radiation. United Nations”, New York, 2000. 
[2]. M.Aoyama∗, K.Hirose. “Radiometric 
determination of anthropogenic radionuclides 
in seawater”. Radioactivity in the 
environment, volume 11, 2008. 
[3]. Bowen, V.T., Noshkin, V.E., Livingston, H.D., 
Volchok, H.L. “Fallout radionuclides in the 
Pacific Ocean: vertical and horizontal 
distributions, largely from GEOSECS stations”. 
Earth Planet. Sci. Lett. 49, 411–434, 1980. 
 [4]. K. Hirose, Amano, H., Baxter, M.S., 
Chaykovskaya, E., Chumichev, V.B., Hong, 
G.H., Isogai, K., Kim, C.K., Kim, S.H., Miyao, 
T., Morimoto, T., Nikitin, A., Oda, K., 
Pettersson, H.B.L., Povinec, P.P., Seto, Y., 
Tkalin, A., Togawa, O., Veletova, N.K. 
“Anthropogenic radionuclides in seawater in 
the East Sea/Japan Sea: Results of the first-
stage Japanese–Korean–Russian expedition”. 
J. Environ. Radioact. 43, 1–13, 1999. 
[5]. Reiter, E.R. Atmospheric Transport Processes. 
“Part 4: Radioactive Tracers. Technical 
Information Center”, U.S. Department of 
Energy, Washington, DC, pp. 1–605, 1978. 
[6]. Livingston, H.D., Povinec, P.P. “A millennium 
perspective on the contribution of global 
fallout radionuclides to ocean science”. Health 
Phys. 82 (5), 656–668, 2002. 
[7]. Pentreath, R.J. “Sources of artificial 
radionuclides in the marine environment”. 
Radionuclides: A Tool for Oceanography. 
Elsevier, London, pp. 12–34, 1988. 
[8]. Sugiura, Y., Saruhashi, K., Miyake, Y.. 
“Evaluation on the disposal of radioactive 
wastes into the North Pacific”. Pap. Meteorol. 
Geophys. 27, 81–87, 1975. 
[9]. N. Q. Long, L. D. Cuong, T. V. Giap, D. V. 
Thang, D. D Thang, N. V. Khanh, D. X. Anh. 
“The dispersion of artificial radionuclides in 
seawater from the Fukushima nuclear 
accident to the Eastsea, Vietnam”. The 12th 
regional conference on nuclear science and 
technology, 2017. 
[10]. K. Hirose, M. Aoyama, Y. Igarashi, K. 
Komura. “Improvement of 137Cs analysis in 
small volume seawater samples using the 
Ogoya underground facility”. Journal of 
Radioanalytical and Nuclear Chemistry, Vol. 
276, No.3, 795–798, 2008. 
[11]. Masanao Nakano, Yuji Kokubun, Takeshi 
Sasaki, Minoru Takeishi. “Analytical Method 
of Gamma Emitters in Seawater Using 
Copercipitation with Nickel Hexacyanoferrate 
(II) and Iron (III) Hydroxide”. Radioisotopes, 
58, 61-69, 2009. 
[12]. J. Kameník, H. Dulaiova, K.O. Buesseler, S. 
M. Pike. “Cesium-134 and 137 activities in the 
central North Pacific Ocean after the 
Fukushima Dai-ichi Nuclear Power Plant 
accident”. Biogeosciences, 6045-6052, 2013.