recent advances in optically stimulated luminescence dosimetry

Oklahoma State University

WRMISS: Oxford Univ., Sept. 2006WRMISS: Oxford Univ., Sept. 2006

Passive Space Radiation Dosimetry Passive Space Radiation Dosimetry using Optically and Thermally using Optically and Thermally

Stimulated LuminescenceStimulated Luminescence

Stephen W.S. McKeever

Department of Physics, Oklahoma State University


AcknowledgementsAcknowledgements

All original data shown in this presentation have been gathered at Oklahoma State University, unless otherwise indicated.

Thanks are due especially to:Dr. Eduardo YukiharaDr. Ramona Gaza

andGabriel Sawakuchi


Background:Background:

• Two luminescence dosimetry methods for measurement of absorbed radiation dose– Thermoluminescence (TL)– Optically Stimulated Luminescence (OSL)

• TL– Stored energy from the radiation released from the dosimetry

material by thermal stimulation. Energy release in form of luminescence

• OSL– Stored energy from the radiation released from the dosimetry

material by optical stimulation. Energy release in form of luminescence

• Methods can reveal the absorbed dose, even years after exposure; contains information about radiation quality


TL and OSL Principles:TL and OSL Principles:

PMTLaser or LEDs

(CW, ramped or pulsed)

Detection filters

TLD or OSLD Detector

OSL, or TL

Heat


TLD and OSLD Materials:TLD and OSLD Materials:

Commercial TLDs Commercial OSLDs

• LiF:Mg,Ti (TLD-100/600/700)

• LiF:Mg,Cu,P (TLD-100H)

• CaF2:Mn (TLD-400)

• CaF2:Dy

• CaF2:Tm, (TLD-300)

• CaSO4:Dy

• CaSO4:Tm

• …….and many others

• Al2O3:C • BaFCl:Eu•……plus several experimental materials


Typical TL and OSL Signals:Typical TL and OSL Signals:

100 200 300 4000.0

0.2

0.4

0.6

0.8

1.0

1.2

TLD-100

TL (n

orm

aliz

ed)

Temperature (ºC)

TLt

T TLD-500

0 100 200 300 400 500 6000

100

200

300

400

constant

CW

-OS

L (a

rbitr

atry

uni

ts)

Time (s)

CW-OSL

0.0 0.5 1.0 1.5 2.00.0

0.5

1.0

1.5

2.0

2.5

POSL

pulsed

PO

SL

(arb

itrat

ry u

nits

)Time (s)

POSL


CWCW--OSL and POSL:OSL and POSL:

Continuous stimulation (CW-OSL)

Pulsed stimulation (POSL)

0.0 0.5 1.0 1.5 2.00.0

0.5

1.0

1.5

2.0

2.5 (c)

POSL

PO

SL

(arb

itrat

ry u

nits

)

Time (s)

Ligh

t Int

ensi

ty

Time

0 100 200 300 400 500 6000

100

200

300

400(b)

CW

-OS

L (a

rbitr

atry

uni

ts)

Time (s)

Ligh

t Int

ensi

ty

Time


A Brief Tutorial:A Brief Tutorial:

Conduction Band

Valence Band



Conduction Band

Valence Band

Before irradiation



Conduction Band

Valence Band

After irradiation



Conduction Band

Valence Band

Stimulation



Conduction Band

Valence Band


Conduction Band

CW-OSL

Valence Band



Conduction Band

0 100 200 300 400 500 6000

100

200

300

400(b)

CW

-OS

L (a

rbitr

atry

uni

ts)

Time (s)

Ligh

t Int

ensi

ty

Time

Valence Band

Continuous stimulation anddepletion

CW-OSL



Conduction Band

Valence Band


A Brief Tutorial:

Conduction Band

Valence Band

Lifetime (“delay”)in excited state

A Brief Tutorial:



Conduction Band

Lifetime (“delay”)in excited state

Valence Band


A Brief Tutorial:

Conduction Band

Valence Band

relaxation

POSL

A Brief Tutorial:

Detect OSL after stimulation pulse removed


The Pulsed OSL (POSL) Technique:The Pulsed OSL (POSL) Technique:

Pulsed OSL (POSL)Measures OSL emission between stimulation pulses, not during the pulse. Better separation between the signal and the stimulation light.

Stimulate Measure OSL

Akselrod and McKeever, Radiat. Prot. Dosim. 81, 167-176 (1999)


An OSL advantage:An OSL advantage:

Possibility of Possibility of ReRe--estimation estimation

of dosesof doses

Can re-read the OSLsignal, if the signal is strong enough. (No need to deplete the

signal in order to measure it.)

Akselrod and McKeever, Radiat. Prot. Dosim. 81, 167-176 (1999)


Some OSL and TL comparisons:Some OSL and TL comparisons:

• Both have adequate sensitivity for space dosimetry• Both have stable signal (no fading)• All-optical method for OSL; lends itself to multiple configurations and

devices• Re-read of OSL signal (period dose plus total dose)• Re-setting of OSL signal by bleaching; TL signal by heating• Faster readout for OSL• Lower (electrical) power requirements for OSL• Various on-board readout configurations• Thin OSL powder dosimeters (e.g. LuxelTM) for reliability and

ease of use • Potential for integration with microelectronics • Can combine OSLD/TLD/PNTD badges• Can combine OSLD/TLD readers• Both TL and OSL contain information about LET spectrum


OSL/TL and the LET Spectrum:OSL/TL and the LET Spectrum:

OSL and TL have different efficiencies for different HCPs (LETs)

0.1 1 10 1000.0

0.2

0.4

0.6

0.8

1.0

1.2

β

FeSi

C

He

Al2O3 single crystal dosimeters

Integrated CW-OSLInitial CW-OSL intensityTL peak height

Effi

cien

cy

LET (keV/ µm H2O)

0.1 1 10 1000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

β

FeSi

C

He

Al2 O3 :C LuxelTM dosimeters

POSLIntegrated CW-OSLInitial CW-OSL intensity

Effi

cien

cy

LET (keV/µm H2 O)

(1) Sensitivity to HCP of LET > 10 keV/µm (up to Fe56)(2) Sensitivity depends on:

method of readout; material; material type (chip, powder); annealing; emission wavelength


1 10 100

1

10

100

Al2O3:C

Three different samplesof Al2O3; OSL vs. Dose

Lum

ines

cenc

e S

igna

l (no

rmal

ized

)

Beta Dose (Gy)


Sensitivity decrease with LET due to loss of sensitivity at high dosesSupralinearity causes increase in efficiency with LET



Charged particle track within the dosimeter - non-uniform spatial distribution of dose

Dose

DistanceOSL/TL

Net OSL/TL due to contributions from regions of different dose, over a wide dose range

Dose


Dose Distributions:Dose Distributions:

Possibility of extracting dose due to low LET from dose due to high LET

100 mGy beta 100 mGy He

10 100Dose,Gy

10 100Dose, Gy

0

5

10

g

10 100 10000

1

2

3

g

100 mGy C

Dose distributionsextracted from deconvolutions ofOSL decay curves

10000

5

10

g

0

5

10

g

Dose,Gy10 100 1000

1000

100 mGy Fe

Dose,Gy

Courtesy: Dr. Eduardo Yukihara


An An ““LET MeterLET Meter””::

Use two or more parts of the TL or OSL signal that have different efficiencies with respect to LET.

Examples:TLD-100 “HTR” method

HTR

HT signal

Main “peak 5”signal

100 200 300 4000.0

0.2

0.4

0.6

0.8

1.0

TL (n

orm

aliz

ed)

Temperature (ºC)1 10 100

0

2

4

6

8

LET (keV/ µm H20)

He

C

SiFe




Examples:

β irradiationHe 150MeV/nC 400MeV/nSi 190MeV/n

0 50 100 150 200 250 3000.0

0.2

0.4

0.6

0.8

1.0

Fe 500MeV/n

OS

L (n

orm

aliz

ed)

1 10 100

1.0

1.2

1.4

1.6

1.8Fe

SiC

He

β

Rat

io

OSL Peak intensity/Area Ratio

LET (keV/ µm in water)Time (s)




Examples:

300 350 400 4500

2

4

6

8Channel B (signal between laser pulses)Channel A (signal during laser pulses)

Wavelength (nm)

OS

L (a

rb. u

nits

)

OSL emission Wavelengths; Time-resolved Using POSL

0.1 1 10 100 1000

0.5

0.6

0.7

0.8

0.9

1.0

SU

V/ S

blue

LET in water (keV/µm)



Can we use these measurements to determine a “mean” or “effective” LET for space radiation (unknown mixed radiation field)?

∑∑ ==i i

i

ii

DDD

ηγ ,

• Absorbed dose

Uncorrected OSL/TL dose

effective

DD

ηγ=• ‘Effective’ efficiency

?Corrected OSL/TL dose

then

H =QeffectiveD• Dose equivalent



1 10 100 10000.10.20.30.40.50.60.70.80.91.01.11.2

ηeffective

28Si

Effi

cien

cy,η

LET (keV/µm in water)

4He

12C

56Fe

20Ne

LET effective

1 10 100

1.0

1.2

1.4

1.6

1.8

Fe

SiC

He

β

Rat

io

LET (keV/ µm in water)

Measure Ratio and estimate effective LET

LETeffective

Use effective LET to estimate effective efficiency

Then, Corrected Dose = Measured Dose/effective efficiency


How well does it work? Absorbed Dose:How well does it work? Absorbed Dose:

25.025.4 ± 1.320.8 ± 0.2Unknown #5single high-LET particle

10.211.2 ± 1.08.4 ± 0.1Unknown #4mixed field-strong high-LET component

12.612.5 ± 0.213.4 ± 0.0Unknown #3mixed field-strong low-LET component

25.025.3 ± 0.426.2 ± 0.0Unknown #2single low-LET particle

27.828.5 ± 0.331.0 ± 0.2Unknown #1single low-LET particle

Actual dose (mGy)

Corrected dose (mGy)

Uncorrected dose (mGy)

‘Unknown-ion’exposure


How well does it work? Dose Equivalent:How well does it work? Dose Equivalent:

‘Unknown-ion’ exposureDose

equivalent H(Sv)

Corrected dose equivalent

(Sv)

Unknown #1single low-LET particle 27.8 28.5 ± 0.3

Unknown #2single low-LET particle 25.0 25.3 ± 0.4

Unknown #3mixed field-strong low-LET component

20.4 12.5 ± 0.2

Unknown #4mixed field-strong high-LET component

64.9 35.7 ± 1.0

Unknown #5single high-LET particle 33.0 25.4 ± 1.3


How well does it work? How well does it work?

Measured doses (before efficiency correction) using • TL or OSL• TLD-100 or TLD-500 or Luxel, etc.

will all be different.

This is caused by the different efficiency curves for each.

Must correct using particular efficiency curve measured in specific lab.

Correcting for the efficiency curves works for:• Single particle irradiation• Mixed field dominated by Low LET

However, does not work for high LET radiation dominated mixed fields.OSL/TL cannot measure dose from high LET component of space radiation because of low sensitivity.


Space DosimetrySpace Dosimetry

To measure dose from full spectrum, use TLD and/or OSLD in conjunction with PNTDs.

NCRP 142, 2002 Recommendation 11:

∫+= dLLDDD PNTDTLDOSLD )(/

Join together OSLD/TLD data and PNTD data (method of Benton & Benton)

∑=

−< −=

mkeV

mkeVi

CRi

TLOSLi

TLOSLdUncorrecte

TLOSLmkeV DDD

µ

µµ η

/1500

/5

39////5

∑=

−< +≅mkeV

mkeVi

CRiTLOSL

effective

TLOSLmkeV

Total DD

Dµ

µ

µ

η

/1500

/5

39/

//5


Dose & Dose Equivalent Dose & Dose Equivalent

For Dose (Gy)

Can use EITHER:

Dcorrected = Duncorrected/ηeffective

OR:

∑=

−< −=

mkeV

mkeVi

CRi

TLOSLi

TLOSLdUncorrecte

TLOSLmkeV DDD

µ

µµ η

/1500

/5

39////5

∑=

−< +≅mkeV

mkeVi

CRiTLOSL

effective

TLOSLmkeV

Total DD

Dµ

µ

µ

η

/1500

/5

39/

//5

For Dose Equivalent (Sv)

Must use:

∑=

−< +≅mkeV

mkeVi

CRiiTLOSL

effective

TLOSLmkeV

Total DQH

Hµ

µ

µ

η

/1500

/5

39/

//5

Cannot use:

H =QeffectiveDcorrected



On-Board OSLD reader:• OSL personal dosimeter readout capability for long-

duration missions (ISS, CEV, Moon, Mars)• Design and build a functioning prototype OSL reader

for on-board use (light source, light transducer, associated electronics, software)

• Design an astronaut personal dosimeter badge including capability for PNTD and TLD

• Design interface to the reader



Requirements• Sensitivity < 0.01 mGy• Days to years of accumulated dose (up to 3 year

missions)• Fast and easy readout• Dosimeter – easy to wear, use, handle, read• Light-weight, low power, etc.


Summary:Summary:

1. Uncorrected doses determined by OSL or TL will be different, depending upon the readout method, material, annealing conditions, etc., etc.

2. Corrected doses, using the concept of “effective” efficiency and “effective LET”, will be the same, independent of readout method, material, etc., etc.

3. Therefore, OSL/TL provide simple and reliable methods for determining Dose (Gy) - expressed as gamma dose equivalent in a reference material (water)

4. However, since TL/OSL sensitive to low LET only, cannot use corrected OSL or TL doses to calculate Dose Equivalent (Sv)

5. Must use TLDs/OSLDs in combination with PNTDs to evaluate Dose Equivalent.

6. Possibility of versatile on-board readers for long-duration flights

recent advances in optically stimulated luminescence dosimetry

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