icrp symposium on the international system of radiological ... dietze assessment of...22 biolog....
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ICRP Symposium on the International
System of Radiological Protection
October 24-26, 2011 – Bethesda, MD, USA
Günther Dietze
ICRP Committee 2
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Members of ICRP Task Group 67
D.T. Bartlett (UK) Comm. 2
D. A. Cool (US) Comm. 4
F. A . Cucinotta (US)
G. Dietze (DE), (chair) Comm. 2
J. Xianghong (CH)
I. McAulay (IR)
M. Pelliccioni (IT)
V. Petrov (RU)
G. Reitz (DE)
T. Sato (JP)
2
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Special situation for astronauts in space
extraordinary radiation field (high energies etc.)
specific environment with limited protection possibilities
only external radiation exposure
few number of astronauts are involved only
but high doses during missions (0.4 - 0.7 mSv/d)
strong interest in risk values of detriment
risk of deterministic effects
3
Assessment of radiation exposure of astronauts in space
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Components of the radiation field in space
galactic cosmic radiation (GCR) (protons, a-particles, heavy ions)
solar cosmic particles (low energy electrons and protons)
solar particle events (SPE) (electrons, protons, photons)
earth albedo (electrons, protons, neutrons)
secondary radiation in a spacecraft (photons, electrons, neutrons, charged particles)
4
Assessment of radiation exposure of astronauts in space
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5
Number of tracks for the same
absorbed dose in soft tissue
Protons 1000
C-12 ≈ 13
Fe-56 ≈ 1.3
Relative ion distribution of the galactic cosmic radiation (GCR)
Mean absorbed
dose, DT ?
Fe-56 H C-12
(Cucinotta et al., 2001)
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GCR fluence spectra at 380 km height (calculated with creme96/creme03)
Particle Energy in MeV/u
10-2
10-3
10-4
10-5
10-6
10-7
10-8
10-9
10-10
Flu
en
ce
rate
in
MeV
-1c
m-2
s-1
100 101 102 103 104 105 106
(Sato et al., 2010)
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Year
+10
+ 5
0
- 5
-10
-15
-20
-25
-30
-35
Rela
tive c
osm
icra
yfluence
rate
in
%
1960 1970 1980 1990 2000 2010
Relative cosmic ray fluence rate variation with time In the solar cycle of the heliocentric potential
(http://www.nmdb.eu/?q=node/138)
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8
Fp
>30 M
eV
in
cm
-2F
p>
100 M
eV
Fp
>80 M
eV
Date
Cycle 19 20 21 22 23
Fp
>30 M
eV
in
cm
-2F
p>
100 M
eV
Fp
>80 M
eV
Date
Cycle 19 20 21 22 23Cycle 19 Cycle 20 Cycle 21 Cycle 22 Cycle 23
1011
1010
109
108
107
1010
109
108
107
Integral proton fluence (Ep > 30 MeV, 100 MeV) of various solar particle events
(Myung-Hee et al., 2011)
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9
Neutron Energy (MeV)
10-810-610-410-21001021040.0
0.5
1.0
1.5
Fluence Rate per Lethargy E dN /dE (cm
-2 sec-1 ) 100 g/cm2 (16 km)
200 g/cm2 (12 km)
x 2.9
56 g/cm2 (20 km)
1030 g/cm2 (0 km)
on ground x 813
Neutron spectra measured with Bonner sphere spectrometer at different heights above ground
Neutrons from evaporation
Neutrons from proton collisions
(Goldhagen al., 2002)
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10
Particles fluence rates in trapped radiation zones – protons > 34 MeV and electrons > 0.5 MeV –
Proton belts E > 34 MeV (up to 700 MeV)
Electron belts
E > 0.5 MeV (up to 7 MeV)
Earth radius
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M
T
M
T DwH R F
T
F
T DwH R
Equivalent dose in an organ or tissue (ICRP 103)
Organ dose equivalent (ESA, NASA, …; NCRP )
m L
mLLDLQm
DQH dd)()(1
M
M
TT
M
T
m L
mLLDLQm
DQH dd)()(1
F
F
TT
F
T
TT HH ???
Mean weighted absorbed dose in an organ or tissue
)(5.0 FTM
T HHE
A single wR-value for each particle type except neutrons
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Human body averaged mean quality factors , QISO
for ISO exposure to GCR (data from Sato et al., 2009)
wR
T
TT
T
TTT
ISODw
DQw
Q
QIS
O
(Sato et al., 2010)
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0.00E+00
1.00E+03
2.00E+03
3.00E+03
4.00E+03
5.00E+03
Bo
ne
ma
rro
w
Bre
ast
Co
lon
Lung
Sto
ma
ch
Gonads
Liv
er
Oe
so
ph
ag
us
Th
yro
id
Bla
dd
er
Bo
ne
su
rfa
ce
Bra
in
Sa
liva
ry
Skin
Re
ma
ind
er
equivalent dose
dose equivalent
C-12
Equivalent dose and organ dose equivalent
from the GCR C-12 component (ISO exposure)
pSv
(Sato et al., 2010)
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0.00E+00
1.00E+03
2.00E+03
3.00E+03
4.00E+03
5.00E+03
6.00E+03
7.00E+03
8.00E+03
9.00E+03
Bo
ne
ma
rro
w
Bre
ast
Colo
n
Lung
Sto
ma
ch
Gonads
Liv
er
Oe
so
ph
ag
us
Th
yro
id
Bla
dder
Bo
ne
su
rfa
ce
Bra
in
Sa
liva
ry
Skin
Re
ma
ind
er
equivalent dose
dose equivalent Fe-56
pSv
Equivalent dose and organ dose equivalent
from the GCR Fe-56 component (ISO exposure)
(Sato et al., 2010)
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15
0.1000
1.0000
10.0000
100.0000
1000.0000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
103
102
101
100
10-1
effective d
ose, effective d
ose e
quiv
ale
nt ra
te
Z
Effective dose and effective dose equivalent rate
for ISO exposure to galactic cosmic radiation (GCR) (data from Sato et al., 2009)
(Sato et al., 2010)
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wR (ICRP 60) wR (ICRP 103)
qE
Radiation weighting for neutrons
(Sato et al., 2009)
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Measurements
Area monitoring (inside and outside of a space vehicle) provide information about the radiation field provide monitoring and warning capabilities Individual monitoring assessment of organ and tissue doses and effective dose equivalent Biodosimetry investigation of lymphocytes in blood samples
(problem of individual response and background)
17
Assessment of radiation exposure of astronauts in space
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Area monitoring: particle spectra, fluence rates, LET distributions development of special instrumentation for use in space, but mostly
using concepts also applied in dosimetry on Earth.
18
Area monitoring in space
Active devices can provide real-time access and warning capabilities
● Tissue-equivalent proportional counters D, D(L), LET-distributions., mean Q, H
(for all types of particles)
● Semiconductor devices Silicon diodes, multi-detector telescopes
charged particle energies and charges, LET-values and doses, directions of radiation incidence
● Specific electron detectors (for electrons < 1 MeV)
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Individual monitoring: assessment of individual exposure (risk assesment) and doses for the records
special devices measuring dose, LET, particle charges or specific
particles only.
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Individual monitoring in space
Active devices usually develloped for electron, photon and neutron fields can provide real-time access and warning capabilities
● Tissue-equivalent proportional counters (D, D, LET-distr., mean Q, H) (for all types of particles)
● Thermoluminescence and optically stimulated luminescence detectors
● Nuclear track detectors
● Superheated bubble detectors
● Combined detector systems
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idealactual
0
1
LET
10 keV/mm
TLD
1
0LET
10 keV/mm
ETD
idealactual
LDLLQDLDDH dd)(d ETDETDETDTLDTLDTDL
Combined detector system of thermoluminescence (TLD) and etched-track detector (ETD)
Detector response
L>10 keVmm L>10 keVmm L
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Human Phantom - MATROSHKA
Phantom torso + Poncho + Container outside ISS in space
HAMLET Project
DLR Deutsches Zentrum für
Luft und Raumfahrt e.V.
G. Reitz 2004 -2010 Some Missions at the ISS
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22
Biolog. Dose, RBED
in mGy
Individual dosem.
reading
Skin dose
equivalent
Effective dose
equivalent
Individual population
based calibration
mGy mSv mSv
19 Astronauts 10 - 134 15 - 130 20 - 36 56 - 115 47 - 99
Mean value 85 81 28,9 83,8 71,9
Biological dosimetry with astronauts
Mission doses of astronauts obtained by biological dosimetry and com-
pared to results from measurements with individual dosemeters (TLD) (Looking at total chromosomal exchanges, Cucinotta et al., 2008)
While the mean values agree very well, the variation and discrepancies of
individual doses are large.
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The primary radiation field in space with many charged particle types and
very high energies needs to be well known as a basis for a radiological
protection concept and particle transport calculations.
Depending on time and position in a spacecraft the radiation field varies
considerably and needs active radiation monitoring.
The relatively low number of astronauts involved in space missions and
the risk of higher doses to be achieved needs a more individually based
dose assessment than usual on Earth.
For planning of missions in space individual risk assessment is as
important as individual dose assessment which is needed for dose
recording.
The high contribution of various heavy ions to the exposure in space is
not sufficiently reflected by applying a single radiation weighting factor
wR = 20
23
Assessment of Radiation Exposure to Astronauts in Space
Conclusions (1)
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An assessment of doses to astronauts in space needs both measure-
ments with multidetector systems and radiation transport calculations.
Specific instrumentation is needed for separately assessing the dose
from low-penetrating radiation.
If the dose component from low-penetrating radiation can be separately
determined the measurement of the skin dose or dose near the surface of
the body may be appropriate for the assessment of effective dose or
organ doses.
Missions outside of a spacecraft needs careful consideration of the low-
energy electron and proton components for avoiding high exposures of
the skin and the lens of the eye.
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Assessment of Radiation Exposure to Astronauts in Space
Conclusions (2)
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