THE BASICS OF IRRADIATION

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THE BASICS OF IRRADIATION

• Dr. Harry Farrar IV
• Chairman, ASTM Subcommittee E10.01 Dosimetry for
  Radiation Processing
• Bell Canyon, California 91307, USA

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OVERVIEW

• ABSORBED DOSE
• RADIATION SOURCES
• DOSE DISTRIBUTION UNIFORMITY
• EXAMPLES OF IRRADIATORS
• DOSIMETERS DOSE MAPPING
• PERSPECTIVE CONCLUSIONS
• TEST

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ABSORBED DOSE

• ABSORBED DOSE IS THE MAJOR PARAMETER
• RADIATION DOSE IS THE AMOUNT OF ENERGY ABSORBED
  (4000 GY 1 C)
• DOSE CAN BE GIVEN BY
• - GAMMA RAYS (COBALT-60 or CESIUM-137)
• - ELECTRONS (DIRECT) or
• - X-RAYS (BREMSSTRAHLUNG)
• IT MAKES NO DIFFERENCE WHICH TYPE OF SOURCE IS
  USED BECAUSE IT IS THE ELECTRONS THAT CREATE ALL
  THE EFFECTS

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SOURCES FOR RADIATION PROCESSING
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X-RAYS ON TOTE
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NEED FOR ACCURATE DOSIMETRY

• EFFECTIVENESS OF THE PROCESS DEPENDS ON
• PROPER APPLICATION OF THE DOSE
• ACCURATE MEASUREMENT OF DOSE
• ALL LOCATIONS IN THE PRODUCT MUST BE CONSIDERED
• LOWER LIMIT MUST BE HIGH ENOUGH TO ACCOMPLISH
  DESIRED EFFECT
• UPPER LIMIT NO QUALITY EFFECTS

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Hidden Slide JS900
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Hidden Slide E-Beam Carrier
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Hidden Slide - Ebeam Vert
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GRAYSTAR GENESIS
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DOSE CONSIDERATIONS

• MINIMUM DOSE
• MUST ACCOMPLISH THE DESIRED EFFECT
• DETERMINED BY RESEARCH
• USUALLY DICTATED BY REGULATIONS
• MAXIMUM DOSE
• QUALITY EFFECTS START TO APPEAR
• DETERMINED BY RESEARCH
• OFTEN LIMITED BY REGULATIONS
• GOAL
• ALL PRODUCT GETS BETWEEN MAX MIN DOSE
• IDEALLY
• ALL PRODUCT GETS SAME DOSE (MAX/MIN RATIO 1)

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DOSIMETER

• A device that, when irradiated, exhibits a
  quantifiable change in some property of the
  device which can be related to absorbed dose in a
  given material using appropriate analytical
  instrumentation and techniques.

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DOSE MEASUREMENT

• DOSIMETERS MEASURE DOSE ACCURATELY
• REQUIRE INSTRUMENT TO READ
• KNOWN ENVIRONMENTAL SENSITIVITY
• CAN BE CALIBRATED ACCURATELY
• LABEL DOSIMETERS NOT YET AVAILABLE
• RADIATION-SENSITIVE INDICATORS CANNOT BE USED TO
  ASSURE MINIMUM DOSE
• CALLED GO/NO GO INDICATORS
• INDICATE SOME IRRADIATION HAS OCCURRED
• NOT CALIBRATABLE
• SENSITIVE TO ENVIRONMENT

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DOSE MAPPING
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PERSPECTIVE

• HUNDREDS OF BIG IRRADIATORS (BOTH GAMMA AND
  E-BEAM) ARE USED ROUTINELY FOR OTHER APPLICATIONS
• NO PUBLIC DEMONSTRATIONS OR FUSS
• 55 OF US EUROPEAN MEDICAL DEVICES (IMPLANTS,
  SYRINGES, BANDAGES) STERILIZED BY RADIATION
• FDA RELIES ON DOSIMETRY FOR STERILITY ASSURANCE
• MILLIONS OF STERILE FRUIT FLIES AND OTHER INSECTS
  ARE ROUTINELY RELEASED IN USA
• APHIS RELIES ON DOSIMETRY FOR STERILITY ASSURANCE
• IDENTICAL PROCEDURES ARE APPLICABLE FOR
  QUARANTINE TREATMENT
• RELIANCE ON DOSIMETRY IS NOTHING NEW

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OVERALL EFFECTS OF RADIATION (1)

• DOSE (GRAYS) OBJECTIVE EXAMPLES
• 0.0001 chest X-ray humans
• 5 Lethal dose (D50) humans
• 15-50 inactivate lymphocytes blood
• 30-150 inhibit sprouting potatoes
• 50-150 sterilize insects fruit flies
• 60-500 inhibit opening mushrooms
• 150-250 stop adult emergence fruit flies
• 300-1000 eliminate trichinella pork
• 250-2000 retard ripening mango
• 500-10k extend shelf life fish
• 500-10k control vibrio cholerae frogs legs

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OVERALL EFFECTS OF RADIATION (2)

• DOSE (GRAYS) OBJECTIVE EXAMPLES
• 1000-2200 reduce pathogens fish products
• 1500-3000 inhibit mold strawberries
• 1500-3000 reduce spoilage meat
• 3000-7000 reduce salmonella chicken
• 2000-25,000 eliminate salmonella poultry feed
• 10,000-20,000 reduce cooking time old beans
• 10,000-30,000 reduce pathogens spices
• 20,000-25,000 sterilize equipment health care
• 25,000-50,000 destroy all bacteria shelf stable
  
• 50,000 oligosaccharide breakdown beans

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CONCLUSIONS

• DOSE IS THE CRITICAL VARIABLE
• FACILITY TYPE IS AN ECONOMIC CONSIDERATION
• PROTOCOL SHOULD OPTIMIZE DOSE UNIFORMITY
• SELECT OPTIMUM DOSIMETRY SYSTEM
• RIGOROUSLY FOLLOW PUBLISHED STANDARDS
• THE TECHNOLOGY TO RELEASE PRODUCT ON THE BASIS OF
  DOSIMETRY,WHEN COMBINED WITH A PROPER QA/QC
  PROGRAM IS PROVEN, RELIABLE, AND ROUTINE.

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TEST

• QUESTION
• HOW MANY GRAYS OF RADIATION ARE REQUIRED TO RAISE
  A WATER-EQUIVALENT MATERIAL, SUCH AS AN ORANGE,
  BY 1 CENTIGRADE DEGREE ?

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ANSWER

• 4000 GRAYS 1 CENTIGRADE DEGREE