Linear Accelerator Radiation Safety Training Seminar

1
Linear Accelerator Radiation Safety Training
Seminar

• By
• Stephen Simpson
• Health Physicist
• Iowa State University
• Environmental Health and Safety

2
Radiation
What is it?
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Radiation

• Dictionary Definition
• the emission or diffusion of rays
• Examples
• Light
• Heat
• Ionizing Radiation

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Sources Of Ionizing Radiation
Natural and Man-Made
Cosmic 26.9
Med X-ray 10.9
Misc 0.5
NDI 4.0
Consumer Prod. 3.0
Radon 54.7
Miscellaneous - Fallout from weapons testing and
other misc.
Reference NCRP 93, September 1987
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Ionizing Radiation

• Radiation with sufficient energy to remove
  orbital electrons from the atoms through which it
  passes
• Major types
• Alpha
• Beta
• GammaX-ray

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Alpha Particles

• A large particle with a 2 charge
• Where do we run into alpha particles?
• Uranium and Thorium in the soil
• Radium (Radon)

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Beta Particles

• Identical to an electron
• negative one charge
• Range in air depends upon energy of emission
• Ability to penetrate depends upon energy of
  emission

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Gamma X-rays

• Photon of energy, not a particle
• Identical to each other except in origin
• Very penetrating radiation

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Penetrability by Type of Radiation
Gamma X-ray
High Energy Beta
Alpha Low Energy Beta
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Diagram of the Accelerator
Klystron
Bending Magnet
Gun
Horn
Beam Port
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Fundamentals of the Linear Accelerator

• Duel Mode Accelerator
• Electron Beam
• X-ray Beam
• NO Radioactive Materials as the Source

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Electron Beam

• Identical to a beta particle
• negative one charge
• different origins
• High energy electrons
• accelerated to near the speed of light
• very penetrating radiation

e-
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X-ray Beam

• Bremsstahlung Radiation
• slowing of electrons
• very penetrating radiation

e-
TARGET
X-rays generated
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Diagram of the Accelerator
Klystron
Bending Magnet
Gun
Horn
Beam Port
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Keeping exposures ALARA

• Fundamental tenet of radiation safety
• Personal protective measures shall be implemented
  to keep doses As Low As Reasonably Achievable
• Its the law!

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Dosimetry Units

• Exposure
• Ability of photons to ionize air
• 1 roentgen (R) 2.58 e-4 Coul./kg in air
• Absorbed Dose (RAD)
• Energy actually deposited by mass
• 1 rad 100 ergs/gram
• 1 gray (Gy) 100 rad -- SI units

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Dose Equivalent - REM

• Takes into account the relative biological effect
  for different radiations
• 1 rem 1rad x QF
• QF Quality Factor
• Beta 1
• Gamma X-ray 1
• 1 seivert (Sv) 100 rem -- SI units

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Routes of Exposure

• External Exposure
• Radiation with energy capable of penetrating the
  dead layer of skin
• E-beam, X-rays
• NO Internal hazard
• No radioactive material produced

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Biological Effects

• Chronic Exposure
• dose spread over years of exposure
• very slight increase in chance of cancers and
  genetic effects
• Example - Sun Tanning while Golfing

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Biological Effects

• Acute Effects
• A large dose imparted in a short time, within 24
  hours
• Radiation Syndrome
• beta burns, vomiting, DEATH
• Example - Sun Burn

21
Personal Protection Techniques - External

• Time
• reduce time spent in front of source
• Distance
• increase distance from source
• Shielding
• place shielding between you and source

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Shielding

• Approximately 8 to 10 feet of concrete.
• Facility dose rates are background outside of the
  concrete maze.
• Four 90 turns in each maze

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Safety Features

• Controlled Access Areas
• Control Room
• Product Handling Area
• Authorized (Restricted) Access Areas
• Processing Room
• Machine Room

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Safety Features

• Lighted Entrance Signs
• machine room entrance
• processing maze area entrance
• Timed Entry and Start-up Procedures

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Safety Features

• Unauthorized Door or Gate Openings
• Pressure Mat Detection
• Photo Cell Detection
• Pull Cords
• Emergency Shut-down Buttons

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Important Notes

• When the linear accelerator is off, there is NO
  radioactive hazard.
• NO radioactive materials are used in the
  production of the electron beam.
• The product that has been irradiated is not
  radioactive.

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Regulatory Control
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Iowa Department of Public Health

• ISU's regulatory agency
• Iowa Public Administrative Code (136C)
• Regulation for ISU
• Radioactive Materials
• Radiation Producing Devices
• Linear Accelerator is registered with IDPH

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Regulatory Dose Limits

• Annual occupational limits
• Lens Dose Equivalent (LDE)
  15 rem
• Shallow Dose Equivalent (SDE) , whole-body 50
  rem
• Shallow Dose Equivalent (SDE) , extremity
  50 rem
• Total Effective Dose Equivalent (TEDE)
  5 rem
• Total Organ Dose Equivalent (TODE)
  50 rem

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Dosimetry Program at ISU

• Issue film badges
• Linear Accelerator Staff must be monitored
• Required to maintain records for everyone who has
  ever been monitored at ISU
• Pocket Alarming Dosimeters
• Hand-held Survey Instrument