Radiation Safety Course Radiation Monitoring

1. Radiation Safety CourseRadiation Monitoring Heath de la Giroday Dispensing Chemist Radiation Safety Officer

2. RADIATION MONITORING • Dose rate instruments • Personal dosimetry TLDs • Survey meters • Contamination instruments • Liquid scintillation counter • Survey meters

3. Dose Rate Instruments • Personal dosimetry • Thermoluminescent dosimeters (TLDs) • β, γ and x-ray • Landauer

4. 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

5. 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

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

7. 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

8. 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

9. 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

10. Liquid Scintillation Counter • Heat adapting—37C for 1-2 hours • Speeds chemical reactions • Dark adapting—Put in dark for 5-10 minutes • Stops absorption of external photons • Quenching—address if it becomes a problem

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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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)

18. 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

19. 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

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

21. Survey Meter Operation-Summary • Check calibration sticker • Ensure unit is in good condition • Turn unit on and check battery • Turn switch to lowest multiplication scale • Check background • Perform positive check • Measure radioactivity • Note highest count rate in CPM • Turn unit off when finished (Be green-use less batteries)