2. Radiation Detection Systems
Laboratory Radiation
Surveillance

3. Direct Survey Meters Geiger-Mueller Scintillation Counter
Measure surfaces directly
Main use for contamination control

4. Radiation Survey Meters Maintenance
Per use:
Battery power
Check source
Check background
Calibration:
Yearly
After maintenance or repairs

6. Geiger-Meuller Tube

8. Low Energy Gamma Scintillator (LEGS)

9. Survey Instrument Comparison
Geiger-Muller
Detection through window
Detects rays (photons)
Detects a few particles
Shields allow differentiation between particles & photons
Designed to measure activity
Can be less sensitive to low counts
Scintillation Counter
Much more sensitive than Geiger-Muller
Widespread detection

10. Indirect Survey Methods
Liquid Scintillation Counter
Gamma Counter
Wipe of surfaces
Detect contamination on wipes

11. No internal radioactive
Gamma Counter
No internal radioactive
standard.
May generate small,
negative numbers when
counting low activity
samples: ie wipe tests.
Wipe test criterion of
100 cpm above bkgnd
still applies!

13. Scintillation Counter
Distintegrations Per Minute = Counts Per Minute / % Efficiency

14. Scintillation Counter
Distintegrations Per Minute = Counts Per Minute / % Efficiency
Sample 123
1000 cpm
Eff=50%
Sample 124
800 cpm
Eff=39%

15. Activity / Calibration
A ~ 2.22 MBq
Activity / Calibration
Detector
Counter N
Amp
N = Activity x (Efficiency x Geometry Factor)
A ~ 2.22x106 dps
Efficiency ~ 50 %
GF ~ 0.5
N =

16. Activity / Calibration
If you detect 555,000 cps, is the activity of the source 2.22 MBq?
Consider other contributing factors :

17. Radiation Sources in the Workplace
9. Radiation Protection Principles

18. Radiation
Transfer of energy, in the form of waves or particles, from one point in space to another point in space.

19. Time
Distance
Shielding
Contamination Control

20. Time Minimize the time spent in a radiation field. Example:
You are working in front of a fume hood where the field is 18 Sv/h.
What is the dose you would receive after 90 minutes?
after 10 minutes?

21. Distance Inverse Square Law
The radiation intensity, I, is proportional to one over the distance squared:
The source is assumed to be small compared to the distance.

22. Inverse-Square Law 9 4 1 1 2 3

23. What is the intensity at twice the distance?
If I α 1
(D)2
What is the intensity at twice the distance?
I1 = (D2)2
I (D1)2
I2 = I1 (D1)2 / (D2)2 OR
Let D2 = 2D1
I2 = I1/(D1)2 / (2D1)2
I2 = I1 / 4

24. Distance Example
At 10 cm you measure the field intensity to be 160 μSv/ h.
What is the field intensity at 1 m?
I1 = D1 =
I2 = D2 =

25. Shielding
Material 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 thickness
Radiation type: α, β, γ, or x-ray
Radiation energy

26. Half-value Layer
20 Sv/hr

27. Half-value Layer
Sv/hr

28. Half-value Layer
Sv/hr

29. Half-value Layer
Sv/hr

30. Recommended Shielding
32 P mm Plexiglas
14 C Glass container Plexiglas
125 I 1 mm Lead sheet
99m Tc 12 mm Lead

31. Contamination Control
Purpose is to ensure that all work and non-work surfaces do not pose a risk to health
Survey Meter
Wipe Test
Combination

32. Wipe 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 fluorescence
not from radioactive source.
Be suspect of zeroes!

34. END DAY 1