9Survey Instrument Comparison Geiger-MullerDetection through windowDetects rays (photons)Detects a few particlesShields allow differentiation between particles & photonsDesigned to measure activityCan be less sensitive to low countsScintillation CounterMuch more sensitive than Geiger-MullerWidespread detection
10Indirect Survey Methods Liquid Scintillation CounterGamma CounterWipe of surfacesDetect contamination on wipes
23What is the intensity at twice the distance? If I α 1(D)2What is the intensity at twice the distance?I1 = (D2)2I (D1)2I2 = I1 (D1)2 / (D2)2ORLet D2 = 2D1I2 = I1/(D1)2 / (2D1)2I2 = I1 / 4
24Distance ExampleAt 10 cm you measure the field intensity to be 160 μSv/ h.What is the field intensity at 1 m?I1 = D1 =I2 = D2 =
25ShieldingMaterial placed between yourself and the source will reduce your exposure to radiation.The amount of reduction will depend upon the material and the radiation.Material density and thicknessRadiation type: α, β, γ, or x-rayRadiation energy
30Recommended Shielding 32 P mm Plexiglas14 C Glass container Plexiglas125 I 1 mm Lead sheet99m Tc 12 mm Lead
31Contamination Control Purpose is to ensure that all work and non-work surfaces do not pose a risk to healthSurvey MeterWipe TestCombination
32Wipe tests Be suspect of zeroes! Use filter paper/tissue etc. Wet with appropriate solvent.Standard surface area to cover is 100 cm2 for each wipe.Place in vial with scintillation cocktail, count.Always include a background.Action level for contamination is 100 cpm above bkgnd.Spurious counts may be due to static, or fluorescencenot from radioactive source.Be suspect of zeroes!