optically stimulated luminescence

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OPTICALLY STIMULATED

LUMINESCENCE A PRESENTATION

BY

MOHAMMAD AUN

SHAH

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INTRODUCTION TO OSL..

• IN PHYSICS, OPTICALLY STIMULATED LUMINESCENCE (OSL) IS A METHOD FOR MEASURING DOSES FROM IONIZING RADIATION.

• THE METHOD MAKES USE OF ELECTRONS TRAPPED BETWEEN THE VALENCE AND CONDUCTION BANDS IN THE CRYSTALLINE STRUCTURE OF CERTAIN TYPES OF MATTER (SUCH AS QUARTZ, FELDSPAR, AND ALUMINIUM OXIDE). THE TRAPPING SITES ARE IMPERFECTIONS OF THE LATTICE - IMPURITIES OR DEFECTS.

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PRINCIPLE

• IRRADIATION OF THE MATERIAL, STIMULATES SOME ELECTRONS INTO AN EXCITING STATE.

• DURING PROCESSING, LASER LIGHT STIMULATES THESE ELECTRONS, CAUSING THEM TO RETURN TO THERE GROUND STATE WITH THE EMISSION OF VISIBLE LIGHT.

• THE INTENSITY OF THE VISIBLE LIGHT EMISSION IS PROPORTIONAL TO THE RADIATION DOSE RECEIVED BY IT.

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INSIDE SIGHT..• THE PHENOMENOLOGICAL DESCRIPTION OF THE OSL AND THERMOLUMINESCENCE PROCESS ARE THE SAME.

• PURE CRYSTALLINE DIELECTRIC MATERIALS EITHER CONTAIN OR HAVE ADDED TRACE AMOUNTS OF CONTAMINANTS THAT FORM CRYSTAL-LATTICE IMPERFECTIONS.

• THESE IMPERFECTIONS ACT AS TRAPS FOR ELECTRONS OR HOLES AND ALSO CAN ACT AS LUMINESCENCE CENTERS, WHICH EMIT LIGHT WHEN ELECTRONS OR HOLES RECOMBINE NEAR THEM.

• AFTER IRRADIATION, FREE ELECTRONS AND HOLES ARE GENERATED THAT CAN BE TRAPPED.

• THE RECOMBINATION CENTERS IN AL2O3:C ARE MAINLY CREATED BY OXYGEN VACANCIES AND ARE CALLED F CENTERS .

• RADIATION GENERATED HOLES CAN BE TRAPPED AT THE RECOMBINATION CENTER, CREATING F+ CENTERS.

• WHEN THE CRYSTAL IS HEATED OR OPTICALLY STIMULATED, ELECTRONS CAN BE EJECTED OUT OF TRAPS AND RECOMBINE WITH HOLES AT THE F+ CENTER.

• THE RECOMBINATION ENERGY IS TRANSFERRED TO A LUMINESCENCE CENTER WHERE LIGHT IS EMITTED;

F++ELECTRON→F +420 NM LIGHT.

• IF THIS RECOMBINATION CASCADE IS INITIATED BY HEAT THEN IT IS CALLED THERMOLUMINESCENCE; IF IT IS INITIATED BY LIGHT THEN IT IS CALLED OPTICALLY STIMULATED LUMINESCENCE.

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OSL DOSIMETRY..

• THE OSL DOSIMETER PROVIDES A NEW DEGREE OF SENSITIVITY BY GIVING AN ACCURATE READING AS LOW AS 1 MREM FOR X-RAY AND GAMMA RAY PHOTONS WITH ENERGIES RANGING FROM 5 KEV TO GREATER THAN 40 MEV.

• THE OSL DOSIMETER'S MAXIMUM EQUIVALENT DOSE MEASUREMENT FOR X-RAY AND GAMMA RAY PHOTONS IS 1000 REM.

• IN DIAGNOSTIC IMAGING THE INCREASED SENSITIVITY OF THE OSL DOSIMETER MAKES IT IDEAL FOR MONITORING EMPLOYEES WORKING IN LOW-RADIATION ENVIRONMENTS AND FOR PREGNANT WORKERS.

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APPLICATION OF OSL..

• OSL IS USED IN AT LEAST TWO DIFFERENT APPLICATIONS:

• OPTICAL DATING OF ANCIENT MATERIALS

• RADIATION DOSIMETRY, WHICH IS THE MEASUREMENT OF ACCUMULATED RADIATION DOSE IN THE TISSUES OF HEALTH CARE, NUCLEAR, RESEARCH AND OTHER WORKERS, AS WELL AS IN BUILDING MATERIALS IN REGIONS OF NUCLEAR DISASTER

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OSL VS TLD..

THE OSL PROCESS IS NOT UNLIKE TLD. BOTH ARE BASED ON STIMULATED LUMINESCENCE. HOWEVER OSL HAS SEVERAL ADVANTAGES OVER TLD.

WITH A MINIMUM REPORTABLE DOSE OF 1 MREM, OSL IS MORE SENSITIVE THEN TLD.

OSL HAS PRECISION OF +-1 MREM, WHICH BEATS TLD.

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OTHER FEATURES OF OSL INCLUDES..NO HEATING CONTROLS FOR THE READER

NO NITROGEN REQUIRED

NO GLOW CURVE ANALYSIS REQUIRED

NO ANNEALING OVEN

SIMPLER AND MORE RELIABLE ANALYSIS INSTRUMENTATION

ROBUST AND DURABLE

MINIMAL FADE < 5% IN A YEAR.

INSENSITIVE TO ENVIRONMENTAL EFFECTS OF WATER, HEAT, PRESSURE AND CHEMICAL CONTAMINANTS

VARY LIGHT OUTPUT TO OPTIMIZE LOW-DOSE, HIGH-DOSE, OR BOTH.

FLEXIBLE OPERATING PARAMETERS.

BEAM CROSS-OVER.

SIMPLE, LONG-LIVED LED ILLUMINATION.

SYSTEM PROVIDES IMMEDIATE DOSE RESULT.

LESS MAINTENANCE AND EASE OF OPERABILITY THAN TLD READERS.

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CONCLUSION..• OSLDS EXHIBIT HIGH PRECISION AND ACCURACY IN MEASURING DOSE, ARE

SMALL IN SIZE, HAVE NO ENERGY DEPENDENCE, HAVE NO DEPENDENCE ON IRRADIATION ANGLE, AND CAN BE READ LONG AFTER IRRADIATION. OSLD CAN SUBSTITUTE FOR TLD AND DIODES FOR IN VIVO DOSIMETRY AND ROUTINE CLINICAL DOSE MEASUREMENTS. BECAUSE OF THEIR VERY LOW INTRINSIC BUILDUP OSLDS ARE IDEAL FOR MEASURING SURFACE DOSE. WITH PROPER HANDLING OSLDS CAN BE A PERMANENT RECORD OF MEASURED DOSE, THEY ARE REUSABLE, THE READOUT PROCESS IS LESS THAN 1 MIN, AND THE READOUT IS BY OPTICAL STIMULATION VERSUS HIGH TEMPERATURE SO THE DOSIMETER CAN BE MADE OUT OF INEXPENSIVE PLASTIC.

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LINKS..• RADIOLOGIC SCIENCE FOR TECHNOLOGIST, STEWART C.BUSHING, SEVENTH

EDITION, PAGE NO.544

• HTTP://EN.WIKIPEDIA.ORG/WIKI/OPTICALLY_STIMULATED_LUMINESCENCE

• HTTP://WWW.LANDAUERAUSTRALASIA.COM/SHOPPINGCART/PRODUCTINFO.ASPX?PRODUCTID=1

• SCREEN SHOTS FROM

HTTPS://WWW.AAPM.ORG/MEETINGS/09SS/DOCUMENTS/25CYGLER-OSL.PDF

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THANKYOU..