The 2nd Japan Radiation Safety Management Association
Japan Health Physics Society Joint Conference
土壌から米への放射性セシウム吸収に及ぼす
隣接する田の性質の違いとその経年変化
Difference in properties among neighboring fields affecting
absorption of radiocesium from soil to rice
and their secular change
Hai Thanh NGUYEN1,2), Masaya TSUJIMOTO1,2), Sunao MIYASHITA2), Satoru NAKASHIMA1,2,3)
1) Radioactivity Environmental Protection Course, Phoenix Leader Education Program, Hiroshima University
2) Graduate School of Science, Hiroshima University
3) Natural Science Center for Basic Research and Development, Hiroshima University
Dec 5, 2019
Content
I. Purpose
II. Sampling and Method
III. Results and Discussion
IV. Conclusion
2
I. Purpose
• To investigate the depth dependence of 137Cs
concentration for the soil
• To investigate the oxidative/reductive atmosphere
in the paddy field
• To investigate the soil size distribution and
radioactivity
• To investigate the year dependence of
radiocesium in soil
3
II. Sampling and
Method
Fig.1.
Sample site: Fukushima City, Fukushima Prefecture
D
C
B
A
Pond
~60 km
Source: Google maps
4
II. Sampling and
Method
• Soil samples were collected Apr. 2014, and Mar. 2018
• Sampling by depth: 0-5 cm, 5-10 cm, 10-15 cm, 15-20 cm, 20-25 cm
and >25 cm
• We categorized the soil samples in accordance with the method of
classification of geomaterials for engineering purposes by The
Japanese Geotechnical Society (JGS0051).
• The surface soil samples (0-5 cm) were grouped into five by sieving
• X < 75 µm,
• 75 µm < X < 250 µm,
• 250 µm < X < 850 µm,
• 850 µm < X < 2 mm,
• and 2 mm < X
5
II. Sampling and
Method
•
Fe Mӧssbauer spectroscopic measurement was performed at
57
room temperature with a 57Co (Rh) radiation source moving in a
constant acceleration mode on Wissel MB-500.
• The Mӧssbauer parameters were obtained by least-squares fitting
to Lorentzian peaks.
• The spectra were calibrated by the six lines of α-Fe, the center of
which was taken as zero isomer shift.
• The radioactivity of Cs-134, Cs-137, and K-40 was measured by
using a p-type High-purity Germanium detector (GEM30-70,
ORTEC) with a 30% relative efficiency.
• Relative gamma-ray counting efficiency curve using a certified
mixed-radionuclide gamma-ray reference source (MX033U8PP,
Japan Radiation Association) containing Cd-109 (88 keV), Co-57 (122
and 136 keV), Ce-139 (166 keV), Cr-51 (320 keV), Sr-85 (514 keV),
Cs-137 (662 keV), Mn-54 (835 keV), Y-88 (898 and 1836 keV), and
Co-60 (1173 and 1332 keV).
• The activity concentration of Cs-134, Cs-137 and K-40 were
determined from the -ray energies of 796, 662 and 1460 keV,
respectively.
6
III. Results and
Discussion
1. The soil size distribution vs radioactivity (Fig.2.)
Cs-134 in 2018
1400
1200
1200
1000
Field A
800
Field B
600
Field C
400
Field D
Radioactivity (Bq/Kg)
Radioactivity (Bq/Kg)
Cs-134 in 2014
1400
200
1000
Field C
400
Field D
0
0-5 cm 5-10 cm 10-15 cm15-20 cm20-25 cm >25 cm
0-5 cm 5-10 cm 10-15 cm15-20 cm20-25 cm >25 cm
Cs-137 in 2014
Cs-137 in 2018
3500
3500
3000
3000
2500
Field A
2000
Field B
1500
Field C
1000
Field D
Radioactivity (Bq/Kg)
Radioactivity (Bq/Kg)
Field B
600
200
0
500
2500
Field A
2000
Field B
1500
Field C
1000
Field D
500
0
0
0-5 cm 5-10 cm 10-15 cm15-20 cm20-25 cm >25 cm
0-5 cm 5-10 cm 10-15 cm15-20 cm20-25 cm >25 cm
K-40 in 2014
K-40 in 2018
500
500
450
450
400
400
350
Field A
300
250
Field B
200
Field C
150
Field D
100
50
Radioactivity (Bq/Kg)
Radioactivity (Bq/Kg)
Field A
800
350
Field A
300
250
Field B
200
Field C
150
Field D
100
50
0
0
0-5 cm 5-10 cm 10-15 cm 15-20 cm 20-25 cm >25 cm
0-5 cm 5-10 cm 10-15 cm 15-20 cm 20-25 cm >25 cm
7
III. Results and
Discussion
2. Investigating the oxidative/reductive atmosphere in the paddy field
Relative Transmission
1.000
The spectrum consists of
divalent iron (Fe2+),
trivalent iron (Fe3+), and
hematite (a-Fe2O3)
0.995
0.990
0.985
0.980
0.975
0.970
-10
-5
0
5
10
Velocity/ (mm/s)
Ratio of Fe(II)/ %
Fig. 3. Typical 57Fe Mӧssbauer spectrum at room temperature.
20
15
10
5
0
A-1
A-2
A-3
B-1
B-4
C-4
C-5
D-1
D-2
D-3
Fig. 4. Ratio of Fe(II) to the sum of divalent and
trivalent iron. A-1 to D-3 show the sampling point.
8
III. Results and
Discussion
a. Iron amount depending on soil size of samples taken in April 2014
57Fe Mӧssbauer spectroscopy
0.99
1.000
black: < 75 m
blue: 75 m - 250 m
green: 250 m - 850 m
red: > 850 m
140426 A-3S 0-5 cm
RT
0.98
Relative Transmission
Relative Transmittance
1.00
0.995
0.990
0.985
black: < 75 m
blue: 75 m - 250 m
green: 250 m - 850 m
red: > 850 m
140426 B-3S 0-5 cm
RT
0.980
0.975
0.97
0.970
-10
-5
0
5
10
-10
-5
Velocity/ (mm/s)
black: < 75 m
blue: 75 m - 250 m
green: 250 m - 850 m
red: > 850 m
140426 C-3S 0-5 cm
RT
0.980
0.975
Relative Transmission
Relative Transmission
0.995
0.985
5
10
1.00
1.000
0.990
0
Velocity/ (mm/s)
0.99
black: < 75 m
blue: 75 m - 250 m
green: 250 m - 850 m
red: > 850 m
140426 D-3S 0-5 cm
RT
0.98
0.97
0.970
-10
-5
0
Velocity/ (mm/s)
5
10
-10
-5
0
5
10
Velocity/ (mm/s)
Fig. 5. Change of 57Fe Mӧssbauer absorption depending on the soil size.
9
III. Results and
Discussion
The change in minimum relative transmission depending on soil size of
samples taken in April 2014
The small sized soil
includes clay much
Relative Transmittance
0.990
0.985
0.980
●：Field A
〇：Field B
▲：Field C
△：Field D
The radioactive cesium is
adsorbed strongly to the clay
0.975
0.970
0.965
< 75 m
75 m - 250 m
250 m - 850 m
> 850 m
The amount of iron may affect
desorption of radioactive
cesium from large sized soil
Grain size
Fig. 6. The change in the least relative transmission depending on soil size (2014).
iron works as catalyst to
dissolve radioactive cesium
from soil
10
III. Results and
Discussion
b. Iron amount depending on soil size of samples taken in Mar 2018
57Fe Mӧssbauer spectroscopy
0.99
1.00
black: < 75 m
blue: 75 m - 250 m
green: 250 m - 850 m
red: > 850 m
180314 A-3S 0-5 cm
RT
0.98
0.97
Relative Transmission
Relative Transmission
1.00
0.99
180314 B-3S 0-5 cm
RT
0.98
0.97
-10
-5
0
5
-10
10
-5
Velocity/ (mm/s)
0
Velocity/ (mm/s)
5
10
1.000
1.00
0.995
0.99
black: < 75 m
blue: 75 m - 250 m
green: 250 m - 850 m
red: > 850 m
140426 C-3S 0-5 cm
RT
0.98
0.97
Relative Transmission
Relative Transmission
black: < 75 m
blue: 75 m - 250 m
green: 250 m - 850 m
red: > 850 m
0.990
0.985
black: < 75 m
blue: 75 m - 250 m
green: 250 m - 850 m
red: > 850 m
180314 D-3S 0-5 cm
RT
0.980
0.975
0.970
-10
-5
0
Velocity/ (mm/s)
5
10
-10
-5
0
5
10
Velocity/ (mm/s)
Fig. 7. Change of 57Fe Mӧssbauer absorption depending on the soil size.
11
III. Results and
Discussion
The change in minimum relative transmission depending on soil size of
samples taken in Mar 2018
Relative Transmittance
0.990
0.985
0.980
●：Field A
〇：Field B
▲：Field C
△：Field D
0.975
0.970
0.965
< 75 m
75 m - 250 m
250 m - 850 m
> 850 m
Grain size
Fig. 8. The change in the least relative transmission depending on soil size (2018).
12
IV. Conclusion
• 137Cs penetrated more in fallowed fields compared
with the cultivated fields.
• The oxidative atmosphere affects the features of
the field and induces the uptake of radioactive
cesium by rice plants.
• The amount of iron embedded in larger soil
particles may also affect the transfer of radioactive
cesium from soil to the rice body.
• There is a possibility that the iron works as catalyst
to dissolve radioactive cesium from soil.
• The fallowing effect was observed in the amount
of iron of soils larger than 850 micrometer.
13
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Thank you for your kind attention!