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
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