Prevent the occurrence of the non-stochastic effect by restricting doses to individuals below the relevant thresholds.
Reduce induction of stochastic effect
Objectives of Radiation ProtectionObjectives of Radiation Protection
Justification of Practice
Optimization of Protection and Safety
Recommendations (Dose Limit)
Principles used in Radiation Principles used in Radiation Protection SystemsProtection Systems
Justification of PracticeJustification of Practice
No exposure is permissible unless there is benefit associated with exposure
Benefit may be to the exposed individuals or to society.
Optimization of Protection and Optimization of Protection and SafetySafety
Based on the principles of ALARA (As Low As Reasonably Achievable).
For any given radiation source within a practice, the magnitude of doses, the number of people exposed should be kept to as low as reasonably achievable.
DoseDose LimitLimit
Used to apply controls on each individual’s accumulation of dose.
Dose limits do not include medical exposures and natural background radiation.
Annual Dose Limits (ADL)There are different dose limits for :
radiation workers female pregnant workers members of the public
ADL for Occupational Exposure Whole body Whole body 5 rem 5 remEyeEye
15 rem 15 remPregnant Worker (Pregnant Worker (9 months9 months) 0.5 rem) 0.5 rem
ADL For Exposure of Members of PublicGeneral Public:General Public: 0.1 rem 0.1 remMinor (18 years): 0.1 remMinor (18 years): 0.1 rem
ALARA
ALWAYS KEEP RADIATION EXPOSURES AS LOW AS REASONABLY ACHIEVABLE
Can you think
of ways to do this?
TIME
• The exposure is to be kept as short as possible because the exposure is directly proportional to time.
TIME
Dose = Dose rate x Time of exposure
Example
A researcher stands in an area where a survey meter reads 50 mrem/hr for a period of six hours. What is their total exposure as a result?
50 mrem/hr X 6 hr = 300 mrem
DISTANCE
• Distance from the radiation source should be kept as great as possible
• Physical Law:
– Inverse Square Law
DISTANCE
DISTANCE Doubling distance from a point source of radiation
decreases dose rate to one quarter of what it was. The Inverse Square Law is:
D1 X r12 = D2 X r22
Example: The dose rate one feet away from a point
source is 100 mrem/hr. What is the dose rate after stepping back to a distance of two feet?
D2 = (100 mrem/hr) X (1 ft)2/(2 ft)2 = 25 mrem/hr
ShieldingShielding • Shielding takes into consideration :
– density and thickness of shielding materials, – type of radiation
• types of radiation and shielding required