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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

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space radiation dosimetry and the fluorescent nuclear track detector

Space radiation dosimetry and the fluorescent nuclear track detector

Nakahiro Yasuda

National Institute of Radiological Sciences

contents
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
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 (~100mm2)
  • 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

radiation of space6
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 (~100mm2)
  • 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
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/mm (unit used in radiation protection),
conventional method for assessing radiation risk
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/mm)

- 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
Dosimetric values and Quality factor

Fe

dE/dx ~ LET (keV/mm)

conventional assumption

r = 1 g/cm3 (water)

Dose Equivalent is expressed in

Sieverts 1 Sv = Q(LET)  1 Gy.

requirements for radiation monitoring for astronauts
Requirements for radiation monitoring for astronauts
  • - Large dynamic range (0.1~1,000 keV/mm)
  • Real time (area monitor) and personal dosimetry

CPDS (Si stack)

DB-8 (Si)

R-16 (IC)

Shuttle TEPC

passive dosimeters
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/mm)
combine method with cr 39 an tld or osld
Combine method with CR-39 an TLD or OSLD
  • Combine method using TLD and CR-39
  • TLD for low LET particles (0.1 – 5 or 10 keV/mm)
  • CR-39 for High LET particles (~5 or 10 keV/mm – 1,000 keV/mm)

Dtotal = DTLD– k D>5keV/mm + D<5 keV/mm

= DTLD + (1-k) DCR-39

H<5keV/mm = DTLD– k D>5 keV/mm

= DTLD– k DCR-39

Htotal = H>5keV/mm + H<5keV/mm

= DTLD– k DCR-39 + HCR-39

CR-39

TLD

T. Doke et al., Radiat Meas.24(1995)74.

brados phase 2 experiment in the iss russian service module
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

sample of target fragmentation event in nuclear emulsion

Target fragment

Sample of target fragmentation event in nuclear emulsion

P148

290 MeV/u Carbon

Nuclear emulsion (H, C, N, O, Br, Ag)

50mm

fluorescent nuclear track detector
Fluorescent nuclear track detector
  • Ideal detector for space radiation measurement as personal dosimeter
  • Large dynamic range (0.1 – 1,000 keV/mm)
  • No fading
  • No chemical treatment
  • Able to readout on board
  • (mobile, no electricity)
slide25
Idea

saturate

Fact :

Signal will be saturated

when the exposed dose becomes high

Can be explained by overlapping tracks

Individual tracks?

High

Low

material developed by landauer inc
Material developed by Landauer Inc.

Al2O3:C, Mg single crystal

Trapping center ~ 104-105/mm3

Stable ~600℃

No fading

optics
Optics

Laser:635nm

Emission:750nm

Objective 60x, 0.85NA

heavy ion track in crystal30
Heavy ion track in Crystal

400 MeV/n Ne

400 MeV/n Kr

conclusions
Conclusions
  • Introduction of space radiation measurement
  • Lack of information for short range recoils
  • Introduction of Fluorescent nuclear track detector