6: Detection and Measurement Flashcards
As per section 31 of Nuclear Substances and Radiation Devices Regulations, every CEDO must use what 4 items at ALL TIMES?
- Survey meter
- DRD
- PAD
- Dosimeter issues by licensed dosimeter service - TLD/OSL
Survey meters and Geiger counters measure what?
Dose rate
A DRD measures what?
Exposure dose
A PAD measures what?
Dose rate and accumulated dose
A TLD & OSL measure what?
Accumulated dose
Define dose rate:
Measure of ionization of air per unit of time
Define exposure dose:
Quantity of radiation upon object
Define absorbed/accumulated dose:
Amount of energy deposited in matter in radiation field (in RAD or Gy)
Who must provide, maintain and calibrate all essential instruments (that you must have during every exposure)?
Licensee who authorizes you to use an exposure device
What are the 2 types of survey meters?
- Ionization Chamber
2. Geiger Muller Detector
Describe a ionization chamber survey meter:
Cylindrical container filled with gas (usually air) — ionization of gas molecules is able to detect
What does an ionization chamber survey meter contain?
Gas filled chamber with 2 electrodes, amplifier to amplify very small current from chamber, readout device - digital/analogue
What is the radiation scale on a ionization chamber survey meter?
1 to 100 mR/h
0.1 to 10 R/h
How is a Geiger Muller survey meters sensitivity compared to an ionization chamber?
Detects much lower dose, uses much high voltage and a gas (argon)
What does a Geiger Muller survey meter react with?
Ions coming in (instead of air).
A digital survey meter records dose rates as low as what?
0.01 mSv/h
A contamination detector is also called a what?
Pancake detector
What does a contamination detector read in?
Counts per minute (CPM)
What range of DRD’s are used in industrial radiography?
5 mSv (500 mR)
What is the low range of DRDs?
0-200 mR
0-500 mR
What is the middle range of DRDs?
0-1000 mR
2 R
0-5 R
0-20 R
What is the high range of DRDs?
0-100 R
0-200 R
0-600 R
What is the method of measurement used in a DRD?
Uses a conductive quartz fibre attached to collecting electrode (anode)
What 2 types of radiation do DRDs only measure?
X and gamma
When does a PAD go off?
2-5 mSv
Who supplies the TLD?
Bureau of Radiation and Medical Devices
When and to who must a TLD be returned?
To the licensee at end of 15 day period
What does a TLD contain?
Lithium fluoride chips of different thickness, shielded by metal foil which store energy until heated
What does an OSL contain?
Aluminum oxide and filters in water resistant blister pack.
What can TLD & OSL not be exposed to?
High temp, water or sunlight
Describe a Ring Dosimeter:
- Worn in dominant hand - monitors exposure to hands and fingers
- Contains lithium fluoride chips and determined the same way as TLD
* like TLD, can’t be shared with another*
As per CNSC regulations, what is the min range of survey meter?
20 microSv/h - 100 mSv/h
2 mR/h - 10 R/h
What is the principle of an ionization chamber?
- Based on ionization of air.
2. Ions created migrate toward an electrode of opposite polarity — causes current to measure
One disadvantage of the Geiger Muller which limits its use in field?
Can become saturated and inoperable for a short period of time.
What dosimeters keep your lifetime dose?
TLD & OSL
What are the 2 chips in the TLD used for?
One measures whole body, second measure dose to skin
How is radiation measured from TLD?
Chips heated, trapped electrons return to original position, visual light emitted, light read by photomultiplier tube.
How often must a DRD be read?
Minimum 2x daily
