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Radiation Safety Course Radiation Monitoring Heath de la Giroday Dispensing Chemist Radiation Safety Officer.

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Presentation on theme: "Radiation Safety Course Radiation Monitoring Heath de la Giroday Dispensing Chemist Radiation Safety Officer."— Presentation transcript:

1 Radiation Safety Course Radiation 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 100cm 2 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 Master dial Battery Compartment Calibration dials (normally covered) Probe plug Reset Audible/mute Sampling rate F/S Display

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 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)

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