ICRP Symposium on the International

System of Radiological Protection

October 24-26, 2011 – Bethesda, MD, USA

Günther Dietze

ICRP Committee 2

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

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

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

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)

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)

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)

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)

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)

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

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

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)

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)

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)

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)

wR (ICRP 60) wR (ICRP 103)

qE

Radiation weighting for neutrons

(Sato et al., 2009)

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

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)

Individual monitoring: assessment of individual exposure (risk assesment) and doses for the records

special devices measuring dose, LET, particle charges or specific

particles only.

19

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

20

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

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

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.

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)

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.

24

Assessment of Radiation Exposure to Astronauts in Space

Conclusions (2)

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