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Space radiation dosimetry and the fluorescent nuclear track detector
Nakahiro Yasuda
National Institute of Radiological Sciences
Contents
Space Radiation Monitoring (Passive dosimeter)
- Requirements to be measured (ICRP 1991)
- Technique for personal dosimetry for astronauts
- Recent experiments and topics Fluorescent nuclear track detector
Radiation of Space
Sources:- GCR (Protons~87%, He~11%, HZE~1%) with large scale of energy range- Solar particles (Dominated by protons) with the energy of ~ 100 MeV (300@ max)- Trapped protons (Dominated by protons) with the energy of below 250 MeV
Characteristics:- Mixed radiation field- Fluctuations (time and space)
Track traversal frequency for biological cell nucleus (~100m2)- Proton / every few days- He ion / every month- Fe ion / every 100 years = one Fe ion is hitting the surface of body for every second
Space craft walls Secondary
Elemental Abundance of the Galactic Cosmic Rays
0 8 16 24 32 40 48 56 64 72 80 88
Atomic Number (Z)
10-3
10-2
10-1
100
101
102
103
104
105
106
107
108
109
1010
Rel
ativ
e A
bund
ance
(S
i = 1
06)
Abundance
Fe
Pb
PtBaZr
H He
C OSi
Individual Elements Even Z Elements Element Groups
Galactic Cosmic Ray Energy Spectra
101 102 103 104 105 106
Energy MeV/amu
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
101
Flu
ence
(m
2 s
r se
c M
eV
/am
u)-
1 Solar MaximumSolar Minimum
protons
Helium
Oxy gen
Iron
Radiation of Space
Sources:- GCR (Protons~87%, He~11%, HZE~1%) with large scale of energy range- Solar particles (Dominated by protons) with the energy of ~ 100 MeV (300@max)- Trapped protons (Dominated by protons) with the energy of below 250 MeV
Characteristics:- Mixed radiation field- Fluctuations (time and space)
Track traversal frequency for biological cell nucleus (~100m2)- Proton / every few days- He ion / every month- Fe ion / every 100 years = one Fe ion is hitting the surface of body for every second
Space craft walls Secondary
Quantifying Space Radiation Exposure
Dose is the amount of energy deposited per unit mass:
D = E/m; 1 Gy = 1 Joule/kg
• F is the Fluence, the number of incident particles per unit area, usually in particles/cm2,
• LET (dE/dx) is the amount of energy deposited per unit distance by the particle as it traverses matter often in unit of keV/m (unit used in radiation protection),
-91.602 10 F LETD
=
Conventional method for assessing radiation risk
Evaluation of the risk of cancer mortality has been to estimate the dose equivalent at points in the various organ or tissue of interest within the individual.
Assumption:Same dose equivalent for each radiation type results in the same risk
Quality Factor (Q)- Universal function of particle LET (keV/m)- Defined under the assumption that the same radiological effectiveness is obtained for different particle with the same LET at the point of interest
Dosimetric values and Quality factor
dE/dx ~ LET (keV/m) conventional assumption = 1 g/cm3 (water)
Dose Equivalent is expressed in
Sieverts 1 Sv = Q(LET) 1 Gy.
Fe
Requirements for radiation monitoring for astronauts
- Large dynamic range (0.1~1,000 keV/m)- Real time (area monitor) and personal dosimetry
R-16 (IC)
DB-8 (Si)
Shuttle TEPC
CPDS (Si stack)
Passive dosimeters
- Photogenic (nuclear) emulsion * No charge resolution to heavy ions (up to Fe) * Sensitive to MIP- Thermoluminescence Detectors (TLD) - Optically Stimulated Luminescence Detectors (OSLD) * Measures total absorbed Dose (Gy) * No LET information, so can’t be used by itself to determine Dose Equivalent (Sv)- CR-39 plastic nuclear track detector * High charge resolution, but no sensitivity to lower LET particles (below 5 keV/m)
Operation of TLD and OSLD
e-
Conduction Band
stimulate withthermal energy (TL)
photon of visiblelight is emitted
(a) (b)
e-
e-
p+
trappedelectron
electron trap inforbidden gap
stimulate withvisible light (OSL)
or
Valence Band
En
ergy
Fermi(forbidden)
Gap
Passive dosimeters
350 MeV/n 84Kr424.5 keV/m
422 MeV/n 56Fe202 keV/m
450 MeV/n 40Ar93.7 keV/m
438 MeV/n 28Si57.4 keV/m
370 MeV/n 20Ne31.8 keV/m
270 MeV/n 12C13.6 keV/m
Combine method with CR-39 an TLD or OSLD
Combine method using TLD and CR-39
Dtotal = DTLD – k D>5keV/m + D<5 keV/m = DTLD + (1-k) DCR-39
H<5keV/m = DTLD – k D>5 keV/m = DTLD – k DCR-39
Htotal = H>5keV/m + H<5keV/m = DTLD – k DCR-39 + HCR-39
T. Doke et al., Radiat Meas.24(1995)74.
CR-39TLD
- TLD for low LET particles (0.1 – 5 or 10 keV/m) - CR-39 for High LET particles (~5 or 10 keV/m – 1,000 keV/m)
BRADOS phase-2 experiment in the ISS (Russian Service Module )
Phase-2- Spacial distributions of dose (rate) at 5 locations - Intercomparison for dosimeters of NIRS and IBMP- Exposure duration: 268.5 days
Locations of BRADOS boxes and exposed durations
Box #(Panel #)
Location Exposure duration (days)
A46(P#443)
Starboard side 91.5
A41(P#445)
Starboard side 268.5
A42(P#240)
Port side 268.5
A43(P#111)
Floor, Starboard side
268.5
A44(P#445)
Starboard side 268.5
A45(P#326)
Ceiling near the R-16, port side
268.5
Typical Radiation Exposures
Limit: Annual Public 1 mSv
Limit: Annual Radiation Worker 50 mSv
Average yearly exposure to natural background 2.4 mSv
Living 1 year in Japan * 2.3 mSv
Living 1 year in Kerala, India 13 mSv
STS-57 (473 km, 28.5) 19.1 mSv
STS-60 (352 km, 57) 4 mSv
270 day mission on ISS (400 km, 51.56) ~50 mSv
*Excluding exposure to Natural Background
Sample of target fragmentation event in nuclear emulsion
290 MeV/u Carbon Nuclear emulsion (H, C, N, O, Br, Ag)
50m
Target fragment
P148
Fluorescent nuclear track detector
Ideal detector for space radiation measurement as personal dosimeter
- Large dynamic range (0.1 – 1,000 keV/m)- No fading- No chemical treatment- Able to readout on board- (mobile, no electricity)
Characteristics of luminescence detectors
0 200 400 600 0 200 400 600
0 200 400 6000
100
200
300
400
0 200 400 600
Exposed dose (mGy)
0 200 400 600
0 200 400 6000
100
200
300
400
Mea
sure
d do
se (m
Gy)
OSL (Luxel) Glass (FD-P33-7) Glass (FD-P8.5-7)
TLD-100 (LiF) TLD (MSO-S) TLD (MSO-5D)
~ 500mGy
Ideasaturate
Fact :Signal will be saturated when the exposed dose becomes high
Can be explained by overlapping tracks
Individual tracks?
Low High
Luminescence detector response to heavy ion
0.1 1 10 100 10000
0.2
0.4
0.6
0.8
1
1.2
1.4
Rel
ativ
e ef
ficie
ncy
0.1 1 10 100 10000
0.2
0.4
0.6
0.8
1
1.2
1.4
0.1 1 10 100 10000
0.2
0.4
0.6
0.8
1
1.2
1.4
0.1 1 10 100 10000
0.2
0.4
0.6
0.8
1
1.2
1.4
0.1 1 10 100 10000
0.2
0.4
0.6
0.8
1
1.2
1.4
LET in water (keV/m)0.1 1 10 100 1000
0
0.2
0.4
0.6
0.8
1
1.2
1.4
OSL (Luxel) Glass (FD-P33-7) Glass (FD-P8.5-7)
TLD-100 (LiF) TLD (MSO-S) TLD (MSO-5D)
0.1 1 10 100 10000
0.2
0.4
0.6
0.8
1
1.2
1.4
Rel
ativ
e ef
ficie
ncy
0.1 1 10 100 10000
0.2
0.4
0.6
0.8
1
1.2
1.4
0.1 1 10 100 10000
0.2
0.4
0.6
0.8
1
1.2
1.4
0.1 1 10 100 10000
0.2
0.4
0.6
0.8
1
1.2
1.4
0.1 1 10 100 10000
0.2
0.4
0.6
0.8
1
1.2
1.4
LET in water (keV/m)0.1 1 10 100 1000
0
0.2
0.4
0.6
0.8
1
1.2
1.4
OSL (Luxel) Glass (FD-P33-7) Glass (FD-P8.5-7)
TLD-100 (LiF) TLD (MSO-S) TLD (MSO-5D)
Material developed by Landauer Inc.Al2O3:C, Mg single crystalTrapping center ~ 104-105/m3
Stable ~ 600℃No fading