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

Contributions to dose and dose equivalent

Proton

He

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

Shielding functions in the Service Module model

Results

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

Optics

Laser ： 635nmEmission ： 750nm

Objective 60x, 0.85NA

Heavy ion track in Crystal

Heavy ion track in Crystal

400 MeV/n Kr 400 MeV/n Ne

3D

Linearity of signal

Conclusions

Introduction of space radiation measurement Lack of information for short range recoils Introduction of Fluorescent nuclear track

detector