Sunday, July 13, 2008
Thursday, July 3, 2008
Q & A SESSIONS 2 - PERSONAL DOSIMETRY
Q1. What thermoluminescent materials are used in a TLD badge ?
a. Most commonly lithium fluoride , dysprosium activated calcium sulphate may also be used
Q2. What is the principle of a TLD badge ?
a. It depends on the ability of certain crystalline materials to store energy on exposure to ionising radiation because of trapping of valence electrons in crystal lattice defects. Whan the crystals are heated under strictly controlled conditions the electrons return to their normal state, the stored energy being released in the form of light. Measurements of light by a photomultiplier device gives a measure of the initial radiation exposure, since the two are very nearly proportional.
Q3. What are the parts of a TLD badge ?
a. - Plastic cassette
- 3 filters : - metal filter made of 1 mm copper and aluminium each
for X & gamma rays
- 1.5 mm thick perspex - beta rays
- open window without filter - for reference dose
- TLD card : comprising of a Nickel plated aluminium holder with 3 TLD discs of thermoluminescent materials
Q4. To what temperatures are the discs heated ?
a. 300 - 400 C
Q5. What are the advantaged of a TLD badge ?
a. Chips can be reused, wide range of dose (0.1 - 2000mSv), suitable for finger dosimetry, energy independent , direct reading of personal dose, not affected by humidity/temperature/pressure,
Q6. What are the disadvantages of TLD badge ?
a. Greater initial cost than film badge, doesn't provide a permanent record, cannot distinguish radioactive contamination
Q7. What constitutes an electronic dosemeter ?
a. An EPD is a direct reading dosemeter consisting of two silicon photodiodes
Q8. What are the advantages of an EPD ?
a. Provides direct reading so that the worker can see when and where doses are being accrued ;
- is 50 - 200 times more sensitive than a TLD badge making it esp. useful in cases where individual doses are low and monthly dose limits ( eg in pregnant workers) are difficult to measure with a TLD/ film badge
- has a flat response from 20 keV to 10MeV
- can be zeroed by the wearer without removing the accumulative dose
- audible warning of high dose rates
Q9. What are the disadvantages of an EPD ?
a. High initial cost, battery to be renewed every year, heavier than a TLD badge
a. Most commonly lithium fluoride , dysprosium activated calcium sulphate may also be used
Q2. What is the principle of a TLD badge ?
a. It depends on the ability of certain crystalline materials to store energy on exposure to ionising radiation because of trapping of valence electrons in crystal lattice defects. Whan the crystals are heated under strictly controlled conditions the electrons return to their normal state, the stored energy being released in the form of light. Measurements of light by a photomultiplier device gives a measure of the initial radiation exposure, since the two are very nearly proportional.
Q3. What are the parts of a TLD badge ?
a. - Plastic cassette
- 3 filters : - metal filter made of 1 mm copper and aluminium each
for X & gamma rays
- 1.5 mm thick perspex - beta rays
- open window without filter - for reference dose
- TLD card : comprising of a Nickel plated aluminium holder with 3 TLD discs of thermoluminescent materials
Q4. To what temperatures are the discs heated ?
a. 300 - 400 C
Q5. What are the advantaged of a TLD badge ?
a. Chips can be reused, wide range of dose (0.1 - 2000mSv), suitable for finger dosimetry, energy independent , direct reading of personal dose, not affected by humidity/temperature/pressure,
Q6. What are the disadvantages of TLD badge ?
a. Greater initial cost than film badge, doesn't provide a permanent record, cannot distinguish radioactive contamination
Q7. What constitutes an electronic dosemeter ?
a. An EPD is a direct reading dosemeter consisting of two silicon photodiodes
Q8. What are the advantages of an EPD ?
a. Provides direct reading so that the worker can see when and where doses are being accrued ;
- is 50 - 200 times more sensitive than a TLD badge making it esp. useful in cases where individual doses are low and monthly dose limits ( eg in pregnant workers) are difficult to measure with a TLD/ film badge
- has a flat response from 20 keV to 10MeV
- can be zeroed by the wearer without removing the accumulative dose
- audible warning of high dose rates
Q9. What are the disadvantages of an EPD ?
a. High initial cost, battery to be renewed every year, heavier than a TLD badge
Thursday, May 29, 2008
Q & A SESSIONS 1 - PERSONAL DOSIMETRY – FILM BADGE
Q. What are the commonly used devices for personal dosimetry ?
A. Film badge, thermoluminescent dosimeter (TLD), electronic dosimeter
Q. What type of film is used in a film badge?
A. Double coated, about same size as dental film
Has 2 emulsions, one fast to detect occupational exposure ; second slow to detect accidental exposure
Q. What are the parts of a film badge ?
A. Consists of three parts : -
- plastic holder made of a material with low atomic number to filter low energy x rays
- assortment of filters / windows
- film packet and film
Q. What are the different filters/windows in a film badge and what are their uses?
A. Allow measurement of different types of radiation reaching the monitoring device eg,
Open window – measurement of xrays
Plastic ( grey colour) – beta rays
Cadmium (yellow) – slow neutrons
Thin copper (green) – diagnostic xrays
Thick copper (pink) – gamma rays
Lead (black) – fast neutrons and gamma rays
All filters except forthin copper are 1mm thick, thin copper is 0.25 mm
Q. What parameters can be assessed by processing the badge ?
A. a) Amount of radiation exposure –
Calibration films exposed to known quantities of radiation are used to generate density – dose graphs. Films worn by personnel are developed , densities are measured and the dose is then read from the density – dose graph
b) Different types of radiation – by use of different filters
c) Occupational/accidental exposure – using 2 different emulsions
d) Differentiating direct / scatter radiation – direct exposure has a sharp edge, scatter exposure ahs blurred edges, spots on intense blackening may result from a radioactive spill
Q. What are the advantages of film badges ?
A. Provides a permanent record
Inexpensive
Measure a wide range of exposure ( 0.2 – 1000 mSv)
Can differentiate btw diff types of radiation and accidental/occupational exposure, quantity and direction of radiation
Q. What are the disadvantages of film badges ?
A. Affected by heat, humidity, inadequate storage conditions
Requires dark room and wet processing
Have to changed on a monthly basis
Exposure cannot be determined on the day of occurrence
Accuracy +/- 20%
The next segment will deal with TLD badges and electronic dosemeters
A. Film badge, thermoluminescent dosimeter (TLD), electronic dosimeter
Q. What type of film is used in a film badge?
A. Double coated, about same size as dental film
Has 2 emulsions, one fast to detect occupational exposure ; second slow to detect accidental exposure
Q. What are the parts of a film badge ?
A. Consists of three parts : -
- plastic holder made of a material with low atomic number to filter low energy x rays
- assortment of filters / windows
- film packet and film
Q. What are the different filters/windows in a film badge and what are their uses?
A. Allow measurement of different types of radiation reaching the monitoring device eg,
Open window – measurement of xrays
Plastic ( grey colour) – beta rays
Cadmium (yellow) – slow neutrons
Thin copper (green) – diagnostic xrays
Thick copper (pink) – gamma rays
Lead (black) – fast neutrons and gamma rays
All filters except forthin copper are 1mm thick, thin copper is 0.25 mm
Q. What parameters can be assessed by processing the badge ?
A. a) Amount of radiation exposure –
Calibration films exposed to known quantities of radiation are used to generate density – dose graphs. Films worn by personnel are developed , densities are measured and the dose is then read from the density – dose graph
b) Different types of radiation – by use of different filters
c) Occupational/accidental exposure – using 2 different emulsions
d) Differentiating direct / scatter radiation – direct exposure has a sharp edge, scatter exposure ahs blurred edges, spots on intense blackening may result from a radioactive spill
Q. What are the advantages of film badges ?
A. Provides a permanent record
Inexpensive
Measure a wide range of exposure ( 0.2 – 1000 mSv)
Can differentiate btw diff types of radiation and accidental/occupational exposure, quantity and direction of radiation
Q. What are the disadvantages of film badges ?
A. Affected by heat, humidity, inadequate storage conditions
Requires dark room and wet processing
Have to changed on a monthly basis
Exposure cannot be determined on the day of occurrence
Accuracy +/- 20%
The next segment will deal with TLD badges and electronic dosemeters
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