Radiation Safety Course Radiation Monitoring

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Radiation Safety CourseRadiation Monitoring

• Heath de la Giroday
• Dispensing Chemist
• Radiation Safety Officer

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RADIATION MONITORING

• Dose rate instruments
• Personal dosimetry TLDs
• Survey meters
• Contamination instruments
• Liquid scintillation counter
• Survey meters

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Dose Rate Instruments

• Personal dosimetry
• Thermoluminescent dosimeters (TLDs)
• ß, ? and x-ray
• Landauer

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Dose Rate Instruments

• TLD proper use and care
• Wear badge inside or outside lab coat at chest
  level
• Wear ring on dominant hand with text facing
  radioactive material
• Best practice to wear on inside of gloves to
  match actual exposure and prevent contamination
• Be careful not to contaminate TLDs
• Return TLDs to storage box after use

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Dose Rate Instruments

• Dose rate meters
• Displays µSv/hr or mR/h
• Can be used to calculate dose
• RSO uses dose rate meters when receiving
  radioisotopes to measure radiation field

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Liquid Scintillation Counter

• Uses
• Alpha, beta, and gamma
• Only method able to detect H-3
• Only detect loose surface contamination
• Extremely sensitive

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Liquid Scintillation Counter

• Principles of operation
• Sample added to vial of liquid scintillation
  cocktail
• Particle or photon energy is transferred to a
  solvent molecule, causing it to enter an excited
  state
• Energy is eventually transferred to a fluor
  molecule
• Fluor decays to ground state with emission of
  photon
• Light is detected by photomultiplier tube
• Photomultiplier tube generates electrical signal

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Liquid Scintillation Counter

• LSC operation, e.g. wipe test
• Map wipe spots
• Wet absorbent wipe, e.g. filter paper soaked
  w/ethanol
• Wipe 100cm2 area
• Label all vials and include a control vial
• Fill vials with scintillation cocktail to cover
  wipes

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Liquid Scintillation Counter

• Technical issues
• Chemiluminescence
• Chemical reactions generate photon emissions
• Photoluminescence
• Excitation of fluors by ambient like results in
  photon emission
• Quenching
• Molecules absorb energy, preventing photon
  emissions
• Give false readings

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Liquid Scintillation Counter

• Heat adapting37C for 1-2 hours
• Speeds chemical reactions
• Dark adaptingPut in dark for 5-10 minutes
• Stops absorption of external photons
• Quenchingaddress if it becomes a problem

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Contamination Instruments

• Survey meters
• Ludlum model 3 survey meter detector
• Geiger-Mueller probe
• Thin end window or pancake
• NaI probe

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Survey Meters

• Geiger-Mueller probe
• Thin end window or pancake
• Principles of operation
• Particle causes ionization of gas inside tube
• Potential causes ion to accelerate to inner wire
  or outer wall
• Succession of ionizations occur
• This causes meter to register a count

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Survey Meters

• Geiger-Mueller probe
• Use
• Nearly all beta emitters
• Including beta/gamma emitters
• Not H-3 because the beta particles do not have
  sufficient energy to penetrate the window
• Some pure gamma emitters
• Does not detect low-energy gamma rays (I-125)
  efficiently
• Does not detect low-energy x-rays efficiently
• Both CPM and mR/h scales are calibrated

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Survey Meters

• NaI probe
• Solid scintillator
• Principles of operation
• Particle or photon interacts with a NaI crystal
• A solid crystal is better than a gas-filled tube
  at absorbing low-energy gamma rays and x-rays
  (density)
• Light is emitted by crystal
• Emitted light falls on photomultiplier tube
• Photomultiplier tube generates a signal

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Survey Probe

• NaI probe
• Use
• Low-energy gamma radiation (e.g. I-125)
• Low-energy x-rays (e.g., Bramsstrahlung)
• CPM scale is calibrated
• Dose rate (mR/h) scale is not calibrated

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Survey Meters-Ludlum Model 3

• Audio always on
• F for rapid monitoring
• S for accurate monitoring
• Always start at most sensitive

Display
Sampling rate F/S
Probe plug
Audible/mute
Calibration dials (normally covered)
Reset
Master dial
Battery Compartment
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Ludlum Pre-Operation Checks

• Four Checks
• Calibration
• Verify calibration from sticker
• 1 year in Canada
• Battery
• Rotate master knob from Off to Bat
• Verify needle is in Bat Test region of scale
• Background count rate
• Check source (if available)

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Survey Meter Operation

• Scanning for contamination
• Move at a steady pace and be systematic-1/s
• If a hot spot is found ,use a spiral pattern to
  find the edges of a hot spot

Monitoring surface
Finding edges of contamination
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Ludlum Operation

• Contamination Check
• If meter chirp rate increases above background
  rate, find location of highest count rate
• If necessary, slowly rotate master knob
  counterclockwise until needle is on-scale
• Push reset button to speed equilibration after
  switching to lower sensitivity
• When site of contamination is located, flip
  response fast/slow switch to slow for more
  accurate readings

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Keep in Mind

• CPM and dose rate of survey meters is variable
  between radioisotopes
• Detection efficiency
• Do not contaminate the probe or meter

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Survey Meter Operation-Summary

1. Check calibration sticker
2. Ensure unit is in good condition
3. Turn unit on and check battery
4. Turn switch to lowest multiplication scale
5. Check background
6. Perform positive check
7. Measure radioactivity
8. Note highest count rate in CPM
9. Turn unit off when finished (Be green-use less
   batteries)