Dosimetry of wild organisms
and their natural dose
Y. Ohtsuka, T. Iyogi, N. Okabe, Y. Takaku, S. Hisamatsu
Institute for Environmental Sciences, Department of Radioecology
4Oct.2016
1
Outline
1.
2.
3.
4.
Motivation
Target organisms
Voxel phantoms
Dose rate calculation
(Internal/External/Rn inhalation/Cosmic rays)
5．Summary
2
1. Motivation
ü To protect ecosystems from radiation, precise assessment of the
radiation dose to wild organisms is important and necessary.
However, the precise radiation dosimetry method has not yet
been established for the wild organisms.
ü In addition, though the background radiation dose rate in a
contaminated environment is of fundamental importance for
evaluating the effects of radiation on wild organisms living there,
very few studies have evaluated it.
ü The natural background radiation dose of the wild organisms in
Rokkasho Village is important in relation with public acceptance
of the JNFL nuclear fuel reprocessing plant.
We have developed the precise radiation dosimetry
method for terrestrial mammalians and aquatic
organisms and calculated their background dose rates.
3
2. Target organisms
4
Terrestrial mammalians
Mouse
(Apodemus argenteus)
Shrew mole
(Urotrichus talpoides)
Small-sized
Mouse(ヒメネズミ)
Red fox
(Vulpes vulpes japonica)
Raccoon dog
(Nyctereutes procyonoides viverrinus)
Middle-sized
5
3. Voxel phantoms
6
Development of voxel phantoms
(Mouse / Shrew mole)
• Voxel phantoms of a male and
female of mouse were based on
the Digimouse (1, 2) developed by
University of Southern California.
• Intestine parts were newly
produced. Ovaries were
incorporated instead of testes for a
female phantom.
• The mouse phantom was also
used for shrew mole with some
adjustment of body size and
weight.
Digimouse
1)B.Dogdas,D.Stout,A.Chatziioannou,andR.M.Leahy,2007
2)D.Stout,P.Chow,R.Silverman,R.M.Leahy,X.Lewis,S.Gambhir,A.Chatziioannou,2002.
7
Development of voxel phantoms
(Red fox)
• A red fox voxel phantom was
constructed on the basis of
tomographic images by
magnetic resonance imaging
technique (MRI) for a female
fox caught in 2009.
• The phantom was also used
for raccoon dog.
8
Dimensions and voxel sizes of our phantoms
Phantom
Mouse
(male/female)
Shrew mole
(male/female)
Red fox
(female)
Body
length
(cm)
Weight
(g-wet)
Voxel size(mm)
7.1
13.4
0.087 0.087 0.080 2.2×1010
8.1
16.7
0.091 0.091 0.091 2.2×1010
76.6
3.58×103
X
0.78
Y
0.78
Z
2.0
No. of
voxels
2.8×106
9
4. Dose rate calculation
• Internal radiation
– Distribution of radionuclides in body (ex. 210Po, 40K)
– Dose rate of each organ
– Comparison (Our results / ERICA-tool)
• External radiation
– On ground and in burrows
– Cosmic rays
• Radon (Inhalation)
– On ground and in burrows
10
Mean concentration of radionuclides
in terrestrial mammalians
Mean concentration(Bq g-1)
1E+0
Mouse
Shrew mole
Red fox
Raccoon dog
1E-1
1E-2
1E-3
1E-4
1E-5
1E-6
210Pb 210Po
Pb
Po
40K
K
137Cs 226Ra 228Ra 228Th 232Th 238U
Cs
Ra
Ra
Th
Th
U
78Rb
Rb
14C
Cs11
1000
Mouse
Shrew mole
Red fox
Raccoon dog
750
500
250
NS
NS NS
Error bars indicate standard deviations.
NS means no sample.
n=19 – 20 (mice), 16(shrew mole), 2 (female red fox and raccoon dog).
Whole
Carcass
Overies
Testes
Gastric contents
GI tract
Thyroid
Hair
Skin
Vertebra
Muscles
Eyes
Brain
Skeleton
Heart
Liver
Spleen
Kidneys
0
Lungs
210Po
concentration (mBq g-1)
Mean 210Po concentration in organs of
mouse, shrew mole, red fox and raccoon dog.
12
Internal radiation dose rate calculation
1. Their radiation dose rates were calculated by the Monte
Carlo code (EGS4) using each voxel phantom and
concentration of elements and radionuclides measured in
organs.
2. Relative biological effectiveness (RBE) of alphaparticles is assumed to be “1”.
3. Our whole body doses were compared with those by
ERICA-tool.
Using ERICA-tool, an ellipsoid as body shape and homogeneous
distribution of radionuclides in the body are assumed.
13
80
60
40
20
Internal dose rate (nGy h-1)
100
Mouse
0
Lungs
Kidneys
Spleen
Liver
Heart
Skeleton
Brain
GI tract
Ovaries
Carcass
Whole
Lungs
Kidneys
Spleen
Liver
Heart
Skeleton
Brain
GI tract
Ovaries
Carcass
Whole
Internal dose rate (nGy h-1)
Internal dose rates of the female mouse and shrew mole
2000
Shrew mole
1500
1000
Others*
226Ra
Ra
40K
K
210Po
Po
500
0
* Sum of 14C, 87Rb, 137Cs, 210Pb, 228Ra, 228+232Th and 234+238U
14
400
300
200
100
0
Internal dose rate (nGy h-1)
500
Red fox
Lung
Kidneys
Spleen
Liver
Heart
Skeleton
Brain
Eyes
Carcass
Skin
Thyroid
GI tract
Overies
Lung
Kidneys
Spleen
Liver
Heart
Skeleton
Brain
Eyes
Carcass
Skin
Thyroid
GI tract
Overies
Internal dose rate (nGy h-1)
Internal dose rates of the female red fox and raccoon dog
1500
Raccoon dog
Others*
226Ra
Ra
1000
40K
K
210Po
Po
500
0
* Sum of 14C, 87Rb, 137Cs, 210Pb, 228Ra, 228+232Th and 234+238U
15
Comparison of our whole body dose rates with those by
ERICA-tool
Internal dose rate (nGy h-1)
500
Others*
400
40K
K
300
210Po
Po
200
100
0
IES
ERICA
Mouse
IES
ERICA
Shrew mole
Small-sized mammalian
IES
ERICA
Red fox
IES
ERICA
Raccoon dog
Middle-sized mammalian
* Sum of 14C, 87Rb, 137Cs, 210Pb, 226,228Ra, 228,232Th and 234+238U.
Values of ERICA are evaluated from whole body concentration of each radionuclide and DCCs by
ERICA-tool.
16
External radiation dose rate calculation
1. Soil horizons of a litter layer and two soil layers were assumed.
2. Dimensions of a burrow for the small-sized mammalian were
cited from a literature (Higuchi et al., 1981).
3. Dimensions of a burrow for middle-sized mammalians were
decided from mean sizes of six burrows found in Rokkasho.
4. External dose rate on ground and in the burrow were calculated
by the Monte Carlo code based on UCPIXEL using these voxel
phantoms.
5. Radiation from alpha-particles was not considered.
6. Concentrations of 14 elements and radionuclides including
137Cs were analyzed in litters and soils collected in the forests
and around burrows for middle-sized mammalians in Rokkasho.
17
Radiation on ground
Cosmic rays 27 nGy h-1
-3 cm
Litter
3 cm
0 cm
Soil layer1
3 cm
3 cm
Soil layer2
27 cm
Red fox 11 nGy h-1
Mouse
21 nGy h-1
Shrew mole 20 nGy h-1
30 cm
18
External radiation doses for the mouse
and shrew mole in the burrow
1m
Cosmic rays 27 nGy h-1
-3 cm
Litter
0 cm
1.25 cm
3.5 cm
Soil layer1
3 cm
Mouse
24 nGy h-1
Shrew mole 23 nGy h-1
Soil layer2
30 cm
Dimensions of a burrow for a small-sized mammalian were
cited from a literature (Higuchi et al., 1981).
19
External radiation dose for the red fox in the burrow
250cm
φ=30cm
34°
20°
184cm
29 nGy h-1
Dimensions of a burrow for middle-sized mammalians were
defined from the mean shape of six burrows found in Rokkasho.
20
Radiation from radon in air to these mammals
Mammalian
Mouse
Shrew mole
Red fox
Raccoon dog
Location
Mean 222Rn
concentration
(Bq m-3)
Equilibrium
factor
On ground
6.5
0.27
In a burrow
2.7×102
0.27
On ground
5.5
0.27
In a burrow
8.6×102
0.30
Dose conversion
(nGy h-1)(Bq m-3)-1
Lungs
Bronchus
2.85 1)
3.88 1,2,3)
0.92 4)
1.48 4)
References
1) Morken et al. (1966)
2) Strong and Baker (1996)
3) Hofmann et al. (2006)
4) Harley et al. (1992)
150 cm
50 cm
5 cm
RADUET
RSF(Rn)
Glass dosimeter
21
Natural radiation dose rates
Dose rate (nGy h-1)
Radiation source
Internal
External 1)
222Rn2)
Mouse
Shrew mole
Red fox
Raccoon dog
37
4.0×102
50
2.3×102
46 – 51
47 – 50
29 – 38
Lungs
5.0 – 2.1×102
1.4 –2.4×102
Bronchus
6.8 – 2.8×102
2.2 –3.8×102
1) Including dose rate from cosmic rays.
2) Evaluation from concentration of 222Rn and its progenies on ground in forests and in burrows.
22
5. Summary
1. Voxel phantoms of 3 species terrestrial mammalians (a male and
female of each mouse and shrew mole, a female red fox) were
constructed for their internal and external dose rate calculation of
each organs.
2. Their background dose rates were also calculated from
concentrations of radionuclides in organs of each mammalian and
environmental samples collected around their inhabit in Rokkasho.
3. Polonium-210 and 40K in their body is an important radionuclide
because of its high contribution to their internal radiation dose. The
radiation dose to each organs significantly varied depending mainly
on 210Po.
4. Radiation dose rates from radon in air to terrestrial mammalians are
especially high when they are in a burrow.
5. ERICA-tool gave a reasonable estimation for whole body internal
dose by natural radionuclides.
23
Acknowledgement
• This study was performed under a contract with the Government of Aomori
Prefecture, Japan.
24