OSL Dosimeters

2/11/2011
General
General

General• Optically stimulated luminescence (OSL) is 

methodology that can be employed in persdosimetry to determine the “dose of record

It is an alternative to thermoluminescent do

• It is an alternative to thermoluminescent do

and film dosimetry.

• Materials suitable for OSL are similar to th

used in thermoluminescent dosimetry, i.e., crystalline solids. In many cases, the sammaterial can be used either as an OSL dosor a TLD.
General

General• Optically stimulated luminescence (OSL) 

thermoluminescence (TL) are very similar only difference is the manner in which the 

electrons are freed from their trapselectrons are freed from their traps.

• OSL dosimeters are of more recent vintag

thermoluminescent dosimeters (TLDs).
General

Basic Mechanism• Radiation energy deposited in the materia

promotes electrons from the valence band conduction band.

Th l t t t i th b d

• These electrons move to traps in the band 

• The greater the radiation energy absorbed 

the greater the number of trapped electro

• When it is time to assess the dose, the tra

electrons are freed by exposing the dosimlight. 
General

Basic Mechanism• When the electrons are freed, they fall to 

energy level and emit light photons.

• The intensity of the emitted light is measu

d t l l t th d

used to calculate the dose. 

• Not all the electrons are freed from their tr

the light output from the OSL dosimeter is analyzed over a short period of time, manelectrons will remain trapped. This means the dosimeter can be reread many times wa significant loss of signal. 
General

Advantages of OSL Dosimeters• OSL dosimeters can be read at room tem

This simplifies the design of the equipmen

• No need for nitrogen gas.• The use of OSL powders deposited in thin 

creates a two-dimensional detector with imcapabilities much like film.

• No correction factors are needed for indiv

elements.
General

Advantages of OSL Dosimeters• Unlike a TLD, OSL dosimeters can be rer

multiple times. Depending on the illumination conditions, 

will be a decrease of signal of less than opercent in a second reading.Used OSL badges are often archived for syears.

• No fading except in extreme temperatures• No annealing required.
General

Disadvantages of OSL Dosimeters• The OSL system is more expensive to use 

TLDs.

• Workers might wonder why doses are bei

reported with OSL dosimeters when no doreported with TL dosimeters.

• Uncertainties in background brings into qu

the validity of reporting doses of a few mre
Absorption and Trapping of 

Radiation Energy
CONDUCTION BAND

Absorption and Trapping of EnergyElectron in the valence band absorbs some radiation energy.

VALENCE BAND e e e e e e e e e 

Hole trapElectron trap

e
CONDUCTION BAND

Absorption and Trapping of EnergyElectron promoted to the conduction band. moves to a positively charged electron trap.

VALENCE BAND e + e e e e e e e 

Hole trap

Filled electron trap

e
CONDUCTION BAND

Absorption and Trapping of EnergyExtra electron at hole trap falls to fill newly chole in the valence band.

VALENCE BAND e + e e e e e e e 

Hole trap

Filled electron trap

e
CONDUCTION BAND

Absorption and Trapping of EnergyBoth the electron trap and the hole trap are filled. This represents trapped energy.

VALENCE BAND e e e e e e e e e 

Filled hole trap

Filled electron trap

+
Absorption and Trapping of Energy

• The net effect is that the electron originally 

hole trap has been promoted to the higheenergy level of the electron trap.

• The greater the radiation energy absorbed

greater the number of filled electron trapsgreater the number of filled electron traps
Optically Stimulated Light Emiss
CONDUCTION BAND

Optically Stimulated Light EmissionGreen light is used to free trapped electronVALENCE BAND e e e e e e e e e 

Filled hole trap

Filled 

+

Green Light
CONDUCTION BAND

Optically Stimulated Light EmissionElectron absorbs light energy, moves througconduction band to hole trap, and emits lighVALENCE BAND e e e e e e e e e 

hole trap

electron trap 

e

Light photon
or
CONDUCTION BAND

Optically Stimulated Light EmissionValence band electron absorbs light energy, moves to filled hole trap, leaving a hole in vaband. 

VALENCE BAND e e e + e e e e e 

hole trap

Filled electron trap

e

Green Light
CONDUCTION BAND

Optically Stimulated Light EmissionTrapped electron falls to fill vacancy in valencand emits light. 

VALENCE BAND e e e e e e e e e 

hole trap

electron trap

e

Light photon
Optically Stimulated Light Emission

The measured intensity of the emitted light (number of photons emitted) is used to estimdose.
Landauer OSL 

Dosimeters
Landauer OSL Dosimeters

General• At present, Landauer is the only company 

offers OSL dosimeters. 

• These dosimeters em

plo

y Al

2

O

3:C.

p y

2

• Meet NVLAP requirements for personnel 

dosimetry

• Landauer offers two versions of OSL dosi

systems:

• Luxel Dosimeter• InLight Dosimeter
Luxel OSL

Dosimeters
Landauer OSL Dosimeters

General• Landauer’s LUXEL dosimeters employ Al

2

as the OSL material. The Al

2

O

3:C is bonde

thin layer to a plastic substrate.

• Copper and tin filters are used to estimate 

energy of the radiation and correct for the over response at low photon energies.

• The imaging filter (perforated copper) in th

middle of the badge is used to qualitativelassess the exposure conditions.
Landauer OSL Dosimeters

Current Design

Old 

Beta Window

Layer of Al

2

O

3:C on 

plastic support

Badge

Imaging Filter

Copper Filter

Tin Filter
Landauer OSL Dosimeters

General• A circular window on the upper portion of 

badge allows a portion of the Al

2

O

3:C laye

respond to betas. 

• To provide a capability for neutron dosime

small sheet of CR-39 track etch plastic caincluded in the plastic pack.

• The Luxel dosimeters are sent to Landaue

the dose assessment and archiving.
Landauer OSL Dosimeters

Stimulating Light• Landauer’s stimulation source is a pulsed 

laser beam with a frequency (pulse rate) oHz. Each light pulse lasts 250 ns.

• The argon laser emits a green light at 514 • These pulses free some, but not all, of the 

electrons.

• The freed electrons will emit light as they 

lower energy level (see Appendix B and C more complete discussion).
Landauer OSL Dosimeters

Measuring the Emitted Light• Nine microseconds after a pulse, the 

measurement of the emitted light begins. measurement continues until the next ligh

from the laser (238 us)from the laser (238 us).

• An initial (test) reading is performed with a 

intensity laser beam. This involves 10 inteof 40 pulses (400 pulses total) and takes milliseconds. 
Landauer OSL Dosimeters

Measuring the Emitted Light• If the dose is <100 mrem, a second readin

performed with a high intensity beam. Thiconsists of ten integrations of 120 pulses 

pulses total) and takes 300 millisecondspulses total) and takes 300 milliseconds. 

• The reading with the low intensity beam o

burns up 1% or so of the usable signal.

• The reading with the high intensity bean b

up approximately 15% of the usable signa
Landauer OSL Dosimeters

Imaging Filter• An image is generated of the light emitted 

portion of the substrate covered by a grid “image filter”). 

• By analyzing this image it might be possi

By analyzing this image, it might be possi

determine if a seemingly high reading was contamination of the badge. 

• It can also be possible to distinguish acute 

term (static) exposures from continual (dyexposures. 
Landauer OSL Dosimeters

This shows the type of image seen when the badgexposure was at least partially due to badge conta- the formation of the hills only occurs in an isolateof the image.
Landauer OSL Dosimeters

Dynamic image ducontinual exposure and valleys not we

Static image due to shortterm exposure - peaks and valleys well defined.
Energy Response

Photons: 5 keV to in excess of 40 MBetas: 150 keV to in excess of 10 

Landauer OSL Dosimeters

Sensitivity

Photons: 1 mrem (10 uSv) to 1000 rem (Betas: 10 mrem (100 uSv) to 1000 rem 
InLight OSL 

Dosimeters
InLight OSL Dosimeters

General• Landauer’s InLight dosimeters, like their L

dosimeters, employ Al

2

O

3:C as the OSL m

•

A difference is that the InLi

ght s

ystem em

g y 

the OSL elements on a slide in a Panasonfour position dosimeter holder.

• Like the Panasonic TLD dosimeter, the In

dosimeter case employs aluminum, coppeplastic filters over the four elements.
InLight OSL Dosimeters

Case with filters

CR-39 for 

neutrons

Imaging 

filt

Slide with OSL elements 2D Barcode

er
InLight OSL Dosimeters

General• A barcode is used to identify both the dosi

case and the slide.
InLight OSL Dosimeters

Stimulating Light• The InLight system employs a bank of gre

(525 nm) in a continuous emission mode. the intensity is lower than that of the laser 

with the Luxel system longer read times awith the Luxel system, longer read times a

required.

• Use of LEDs eliminates laser safety issues
OSL micr

dosimete

InLight OSL Dosimeters

nanoDots
Energy Response

Photons: 5 keV to in excess of 20 MeV

Sensitivity

InLight OSL Dosimeters

Photons: 5 mrem (50 uSv) to 1000 rem (1
InLight OSL Dosimeters

nanoDot• Processed with inLight microStar reader.• Used to assess the dose at a single point. 

geared to applications in radiology.

• nanoDot carrier is approximately 1 cm x 1 

nanoDot carrier is approximately

1 cm

x

1 

• Employs a single OSL “element”• 2 D barcode on one side has serial numbe

sensitivity code.

• Alphanumeric serial number and sensitivit

on other side.
References
References

Akselrod, A. et al. Optically Stimulated LuminescencResponse of Al2O3 to Beta Radiation, Rad. Prot. Do

4):125-128; 1999.Botter-Jensen, L. Luminescence Techniques: Instrumentation and Methods Radiation Measureme

27(5/6):749-768, 1997.Botter-Jensen, L., Agersnap Larsen, N., Markey, B.GMcKeever, S.W.S. Al2O3:C as a Sensitive Dosemet

Rapid Assessment of Environmental Photon Dose RRadiation Measurements 27(2):295-298, 1997.
References

Bulur, E., and Goksu, H.Y. Pulsed Optically StimulaLuminescence from Al2O3:C using Green Light Emit

Diodes Radiation Measurements 27(3):479-488, 19McKeever, S.W.S. et al. Characterization of Al2O3 foThermally and Optically Stimulated Luminescence D

Rad Prot Dos 84 (1 4): 163 168; 1999Rad. Prot. Dos. 84 (1-4): 163-168; 1999.

McKeever, S.W.S. and Akselrod, M.S. Radiation DoUsing pulsed Optically Stimulated Luminescence of Rad. Prot. Dos. 84 (1-4): 317-320; 1999.McKeever, S.W.S. and Akselrod, M.S. Radiation DoUsing pulsed Optically Stimulated Luminescence of Rad. Prot. Dos. 84 (1-4): 317-320; 1999.
References

Nuclear Regulatory Commission NRC Broadens UsDosimeters to Reflect New Advances in Technology News No.00-157, October 11, 2000.Nuclear Regulatory Commission 10 CFR Parts 34, 3New Dosimetry Technology; Final Rule, Federal Re(206): 63750-63752. October 24, 2000.Summers, G.P. Thermoluminescence in Single CrysRad. Prot. Dos. 8 (1): 69-80: 1984.
References

Yoder, R.C. Optically Stimulated Luminescence DosUnpublished PresentationZelac, R.E. and R. Craig Optically Stimulated LumDosimetry in Radiation Instruments J. Higginbotham 

Summer School Proceedings 1996.
Appendix A:

Aluminum Oxide

(Al

2

O

3

)
Aluminum Oxide (Al

2

O

3

)

General• Aluminum oxide (Al

2

O

3) is the only materi

employed in OSL dosimeters.

• Little is known about the identity of the ele

traps in Al

2

O

3

• Much more is known about the recombina

centers and the hole traps.
Aluminum Oxide (Al

2

O

3

)

General• Aluminum oxide (Al

2

O

3) occurs naturally i

one form, corundum. Corundum is also kas alpha Al

2

O3.

• Ruby is corundum colored by chromium

Ruby is corundum colored by chromium. 

Sapphire is corundum colored with titaniuiron. 

• Al

2

O

3 is used in thermoluminescent dosim

and in optically stimulated luminescent dosimeters.
Al

O

O

Al

Arrangement of Ionsin Al2O3 Lattice

The oxygen atoms 

take on a distortedAluminum Oxide (Al2O3)

O 

Al

Al

O

take on a distorted

hexagonal arrangement within a sublattice.
Aluminum Oxide (Al

2

O

3

)

Advantages of Aluminum Oxide (Al

2

O

3:C)

• Extremely durable.• Available in a variety of forms: single c

powders, and thin layers bonded to a 

substrate.

• Extreme sensitivity.• Low fading at room temperatures.• Relatively low effective atomic number 

can reduce its energy dependence.

• Simple emission spectrum.• Light output is linearly related to dose.
Aluminum Oxide (Al

2

O

3

)

General - Al

2

O

3:C as a TLD

• Aluminum oxide activated with carbon (Al

was first used as a TL material in 1990 (Aet al.). 

Primary Advantage as a TLD • Extreme sensitivity: 40-60 times that of Li

100. This makes Al

2

O

3:C particularly suita

an environmental thermoluminescent dosand it is currently used for this purpose. 
Aluminum Oxide (Al

2

O

3

)

Primary Disadvantages as a TLD• Its TL output is heavily dependent on the 

(ramp) rate. 

• It is extremely light sensitive.
Aluminum Oxide (Al

2

O

3

)

General - Al

2

O

3:C as a OSL Dosimeter

• That Al

2

O

3:C was susceptible to light indu

fading, suggested the potential of this matoptically stimulated luminescence. 

I f t Al

O C h t iti it (li h

• In 

fac

t, Al

2

O

3:C

has grea

ter sensiti

vity (li

gh

output per unit dose) when used in the OSmode than in the TL mode.
12

10

8 sion (a.u.) OSL

Aluminum Oxide (Al2O3)Al2O3 Light Output as a Function of Dose

0 2 10 4 6 8

6420

Gamma Dose (uGy)

Light Emiss

TL
Aluminum Oxide (Al

2

O

3

)

Stimulating Light• The intensity of the emissions from Al

2

O

3:

greatest when stimulated by light with a wavelength of 500 nm. 

B th it li ht t 514 4

•

Because they emit li

ght a

t 514.4 nm, argo

lasers are the most common stimulating lisource used with Al

2

O

3:C. 
300

250

s200ion (a.u.)

Aluminum Oxide (Al

2

O

3

)

Al

2

O

3 OSL Light Output as a Function of 

Stimulation Wavelength

400 450 650 500 550 600

200150100

50

0

Stimulation Wavelength (nm)

OSL Light Emiss
100

on

Aluminum Oxide (Al2O3)Light Emission• After exposure to the stimulating source o

the light emission rapidly decreases (deca

0 20 100 40 60 80

80604020

0

Time (s)

OSL Light Emissio
Aluminum Oxide (Al

2

O

3

)

Heat Induced Fading• As can be seen from the following figure, 

of signal over time (fading) would be neglthe Al

2

O

3:C is maintained at room temper

Al

2

O

3:C. 

• However, storage at elevated temperature

even short periods of time can significant the OSL signal.
106

ssion

Aluminum Oxide (Al2O3)Al2O3 OSL Light Output as a Function of 

Storage Time at Various Temperatures

90 100 

0 60 240 120 180

105

104

Heating Time (minutes)

OSL Light Emi 110 

130 °C 120 
Appendix B: 

Recombination CentersRecombination Centers
CONDUCTION 

Recombination CentersAdditional imperfections/impurities called recombination centers might play a role in liemission. 

e e e e e e e e e e e e 

BAND

VALENCE 

BAND

hole trap

e

recombination

center

elec
CONDUCTION 

Recombination CentersRadiation energy is absorbed so that an elefrom the valence band moves to an electron 

e e e e e e e e e + e e 

BAND

VALENCE 

BAND

hole trap

e

recombination

center

filled e
CONDUCTION 

Recombination CentersThe electron in the empty hole trap falls to tvalence band, i.e., the hole moves up from tvalence band to fill the hole trap. 

e e e e e e e e e e e e 

BAND

VALENCE 

BAND

filled hole trap

+

recombination

center

filled e
CONDUCTION 

Recombination CentersThe electron trap and hole trap are now fille

e e e e e e e e e e e e 

BAND

VALENCE 

BAND

filled hole trap

+

recombination

center

filled e
CONDUCTION 

Recombination CentersOptically or thermally stimulated electron mofrom the valence band to the hole trap. 

e e e e e e e e e e e e 

BAND

VALENCE 

BAND

hole trap

Filled e

recombination

center

e
CONDUCTION 

Recombination CentersAn electron from the recombination center fvacancy in the valence band.

e e e e e e e e e e e e 

BAND

VALENCE 

BAND

hole trap

Filled e

+

recombination

center

e
CONDUCTION 

Recombination CentersOptically or thermally stimulated electron mofrom the electron trap to the conduction banthe positively charged recombination centercenter the electron is in an excited state.

e e e e e e e e e e e e 

BAND

VALENCE 

BAND

hole trap

elec

recombination

center

e

e
CONDUCTION 

Recombination CentersThe electron at the recombination center deand emits a photon. 

e e e e e e e e e e e e 

BAND

VALENCE 

BAND

hole trap

recombination

center

elec

e LIGHT P
Appendix C:

F Centers in Aluminum Oxide
F Centers in Al2O3

F+ (Recombination) Centers

• The recombination centers in aluminum ox

defects (not impurities) in the crystalline la

• Specifically a recombination center is a lo

Specifically, a recombination center is a lo

where an oxygen (O2+) ion is missing, i.e., 

oxygen vacancy.

• This recombination center is also known a

center. The F is for “farben”, the German wcolor - such sites can produce color.
F Centers in Al2O3

Types of F Centers• F centers: these have two trapped electr

the oxygen (O2+) vacancy. The two electro

result in charge cancellation – the site is n

The prevailing view is that these are hole The prevailing view is that these are hole 

• F+ centers: these have one trapped elec

the oxygen (O2+) vacancy. One electron d

result in charge cancellation – the site’s c+1. The prevailing view is that these are recombination centers.
F Centers in Al2O3

Energy States of F and F+ Centers

• Electrons at the F and F+ centers can pos

number of different energies.

• For simplicity only two energies are show

For simplicity, only two energies are show

each center: an excited state and a lower state. 
CONDUCTION 

BAND

F+ center * F center *

F Centers in Al2O3

Electron e

VALENCE 

BAND

F+ center

F center

e e e e e e e e e e e e e 

Recombination Hole t

center

Electron e

trap
F Centers in Al2O3

Production of F Centers• The Al2O3 crystals are grown in a reducing 

atmosphere in the presence of graphite (c

The reducing atmosphere results in a high

• The reducing atmosphere results in a high

concentration of oxygen ion vacancies.

• The use of graphite results in carbon ions 

replacing aluminum ions (Al3+). This incre

the number of F+ centers which increases 

OSL and TL sensitivity.
F Centers in Al2O3

Absorption of Radiation Energy • Radiation energy is absorbed by an electr

the valence band.
CONDUCTION BAND

F+ center * F t

e

F Centers in Al2O3An electron is promoted to the conduction bmoves to an electron trap (identity unknown

Electron

VALENCE 

BAND

F+ center

F center

F cente

F cente

e e e e e e e e + e e e 

Electron e

trap
F+ center * F+ e cente

F Centers in Al2O3An electron from the F center fills the vacancvalence band. This converts the F center to excited F+ center (F+*).

Electron

CONDUCTION BAND

VALENCE 

BAND

F+ center

F center

F+ cente

F cente

e e e e e e e e e e e e e 

Electron e

trap
CONDUCTION BAND

F+ center * F+ e cente

F Centers in Al2O3The excited F+ center (F+*) deexcites with the 

emission of a 330 nm photon.

Electron

VALENCE 

BAND

F+ center

F center

F+ cente

F cente

e e e e e e e e e e e e 

Electron e

trap 330 nm phot
F Centers in Al2O3

Freeing of Trapped Particles and Light E• A trapped electron is thermally or optically 
CONDUCTION BAND

F+ center *

e

F Centers in Al2O3The stimulated electron is promoted to the coband. It travels to an F+ center.

Electron F+ cente

VALENCE 

BAND

F+ center

F center

e e e e e e e e e e e e 

Electron

trap

F+ cente

F cente
CONDUCTION BAND

F+ e cente

F Centers in Al2O3This converts the F+ center into an excited F 

(F*).

Electron

VALENCE 

BAND

F centerF center *

F+ cente

F cente

e e e e e e e e e e e e 

Electron e

trap
CONDUCTION BAND

F+ e cente

F Centers in Al2O3The excited F center (F*) deexcites with the eof a 425 nm photon.

Electron

VALENCE 

BAND

F centerF center *

F+ cente

F cente

e e e e e e e e e e e e 

Electron e

trap

420 nm photon
CONDUCTION BAND

F+ cente

F Centers in Al2O3All the trapped energy has been released. Wnow back where we started. 

Electron

VALENCE 

BAND

F centerF center *

F+ cente

F cente

e e e e e e e e e e e e 

e

Electron

trap