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Radiation Detection Systems. Laboratory Radiation Surveillance. Direct Survey Meters. Geiger-Mueller Scintillation Counter Measure surfaces directly Main use for contamination control. Radiation Survey Meters Maintenance. Per use: Battery power Check source Check background

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Presentation Transcript
slide2

Radiation Detection Systems

  • Laboratory Radiation
  • Surveillance
direct survey meters
Direct Survey Meters
  • Geiger-Mueller
  • Scintillation Counter
  • Measure surfaces directly
  • Main use for contamination control
radiation survey meters maintenance
Radiation Survey Meters Maintenance
  • Per use:
    • Battery power
    • Check source
    • Check background
  • Calibration:
    • Yearly
    • After maintenance or repairs
survey instrument comparison
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
indirect survey methods
Indirect Survey Methods
  • Liquid Scintillation Counter
  • Gamma Counter
  • Wipe of surfaces
  • Detect contamination on wipes
gamma counter
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!

slide13

Scintillation Counter

Distintegrations Per Minute = Counts Per Minute / % Efficiency

slide14

Scintillation Counter

Sample 124

800 cpm

Eff=39%

Sample 123

1000 cpm

Eff=50%

Distintegrations Per Minute = Counts Per Minute / % Efficiency

activity calibration
Activity / Calibration

A ~ 2.22 MBq

Detector

Counter N

Amp

N = Activity x (Efficiency x Geometry Factor)

  • A ~ 2.22x106 dps
  • Efficiency ~ 50 %
  • GF ~ 0.5

N =

activity calibration16
Activity / Calibration

If you detect 555,000 cps, is the activity of the source 2.22 MBq?

  • Consider other contributing factors :
slide17

Radiation Sources in the Workplace

9. Radiation Protection Principles

radiation
Radiation

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

slide19
Time

Distance

Shielding

Contamination Control

slide20
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?

distance
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.

slide23

I2 = I1 (D1)2 / (D2)2

OR

If I α1

(D)2

What is the intensity at twice the distance?

I1= (D2)2

I2 (D1)2

Let D2 = 2D1

I2 = I1/(D1)2 / (2D1)2

I2 = I1 / 4

distance example
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 =

shielding
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
slide26

Half-value Layer

20 Sv/hr

recommended shielding
Recommended Shielding

32 P 12 mm Plexiglas

14 C Glass container Plexiglas

125 I 1 mm Lead sheet

99m Tc 12 mm Lead

slide31

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

slide32

Wipe tests

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!