1. Maximum Permissible Dose (MPD)

2. In This Lecture Revision
Radiation Protection Criteria & Exposure Limit
ALARA Principle
Radiation Protection Philosophy
Principles and 10 Commandments of Radiation Protection
Radiation warning signs
Maximum Permissible Dose (MPD)
Risk Factor

3. Ionizing Radiation Effects
STOCHASTIC EFFECTS
Probability of effect occurring is governed by laws of chance
Therefore, greater the dose the greater the probability of effect occurring.
No safe dose limit - ALL doses carries some risk
Severity of effect is not related to dose
Examples: Cancers & Genetic effects.
DETERMINISTIC EFFECTS
Severity increases with dose.
Usually threshold below which no effect occurs.
Examples: Erythema, Epilation & Cataract.

4. Radiation Protection Criteria & Exposure Limit
The objective of radiation protection is to balance the risks and benefits from activities that involve radiation.
Exposure guidelines keep risks of harm from radiation within the levels that society allows.
Specific radiation protection standard recommended by:
ICRP: International Commission on Radiological Protection.
NCRP: National Council on Radiation Protection and Measurements.
Different permissible exposure criteria are applied to different groups of persons:
Occupational or “on-site” standards for persons who work with radiation (18-60) years “Controlled exposure”.
Non-occupational or “off-site” guides for general public. Usually 10% of the allowable occupational values “In voluntary exposure”

5. How is ALARA used in the practice of radiation protection?
ALARA is a basic radiation protection concept or philosophy. It is an application of the "Linear No Threshold Hypothesis," which assumes that there is no "safe" dose of radiation. Under this assumption, the probability for harmful biological effects increases with increased radiation dose, no matter how small. Therefore, it is important to keep radiation doses to affected populations (for example, radiation workers, minors, visitors, students, members of the general public, etc.) As Low As Reasonably Achievable (ALARA).

6. Where are ALARA principles utilized?
ALARA principles can be utilized in an infinite number of situations. For example, the proper design of a nuclear facility depends on ALARA considerations (e.g., can the addition of more shielding to an area be justified in terms of the lower doses it will achieve?). In addition, designing an x-ray facility for medical applications requires consideration of the amount of shielding needed to ensure that individuals located near the facility (e.g., on the other side of the wall from the x-ray unit) do not receive any more dose than is really necessary during operation of the x-ray device.

7. ALARA Principles Source reduction “elimination”.
Controlling and containing the radioactivity.
Minimizing time in radiation field.
Maximizing the distance from radiation source.
Using proper shielding.
Optimization rule in radiation protection.

8. Principles of Radiation Protection
(Philosophy)
Justification: Radiation must not be used unless the benefit associated with that use outweighs the associated risks.
Optimization: As Low As Reasonably Achievable (ALARA)
The magnitude of individual doses, the number of people exposed, and the likelihood of incurring exposures from a justified application of radiation must be kept ALARA or As Low As Reasonably Achievable.
Dose Limits: no individual exposure is to exceed a predetermined regulatory limit, appropriate to the circumstances.
Do not define a fine line between safe and dangerous levels of exposure.

9. Principles and 10 Commandments of Radiation ProtectionNo
Principle
Commandment (familiar) 1.
Time
Hurry (but don't be hasty) 2.
Distance
Stay away from it or upwind of it 3.
Dispersal
Disperse it and dilute it 4.
Source Reduction
Make and use as little as possible 5.
Source Barrier
Keep it in 6.
Personal Barrier
Keep it out 7.
Decorporation (Internal & skin)
Get it out of you and off of you 8.
Effect Mitigation
Limit the damage 9.
Optimal Technology
Choose best technology
10.
Limitation of Other Exposures
Don’t compound risks (don’t smoke)

10. RADIATION WARNING SIGNS
As radiation is considered a hazard, it is important to make people aware of its presence since it can’t be seen, heard, smelled, or sensed by humans
International symbol indicating radioactive hazard in the black three foil on a yellow background

11. RADIATION WARNING SIGNS
Supplementary warning sing recently introduced by the IAEA (International Atomic Energy Agency)
Black on red background.

12. Maximum Permissible Dose
Government standards for radiation protection are established by the National Council on Radiation Protection and Measurement (NCRP) and its international counterpart, the International Commission on Radiological Protection (ICRP). Both of these organizations offer recommendations for the maximum permissible dose (MPD) of radiation to which people should be exposed, and those recommendations are generally adopted by various government regulatory agencies like (JAEC) as the maximum limits permitted by law.
Maximum permissible dose (MPD) is affected both by the size of each dose and the rate at which these doses are received.

13. Maximum Permissible Dose
History of Maximum permissible Dose
Date
Dose for General Public
(mSv)
Dose for Radiation Worker
1931 50
500
1936 30
300
1948 15
150
1958 5
1990 1 20

14. Exposure Limits from NCRP Report No. 116 and ICRP Publication 60
Criteria
NCRP-116
ICRP-60
Occupational Exposure
Effective Dose Annual
50 mSv
20 mSv
Effective Dose Cumulative
10 mSv × age (y)
100 mSv in 5 years
Equivalent Dose Annual
150 mSv lens of eye; 500 mSv skin, hands, feet
Pregnant
5 mSv
2 mSv
Public Exposure
1 mSv if continuous
5 mSv if infrequent
1 mSv; higher if needed, provided 5-y annual average ≤ 1 mSv
15 mSv lens of eye;
50 mSv skin, hands, feet

15. Maximum Permissible Dose
Example:
A radiation worker is 31 years of age. What is his cumulative effective-dose limit in mSv according to:
(a) the NCRP?
(b) the ICRP?
Answer:
(a) NCRP :
31 × 10mSv = 310 mSv
(b) ICRP :
(31-18) × 20mSv = 260 mSv

16. Risk Factor
Units: Sv-1

17. Risk Factor Tissue (T) Risk Coefficient *WT Gonads
40 × 10-4 Sv-1 ( 40 × 10-4 rem-1 )
0.25
Breast
25 × 10-4 Sv-1 ( 25 × 10-4 rem-1 )
0.15
Red bone marrow
20 × 10-4 Sv-1 ( 20 × 10-4 rem-1 )
0.12
Lung
Thyroid
5 × 10-4 Sv-1 ( 5 × 10-4 rem-1 )
0.03
Bone surface
Remainder
50 × 10-4 Sv-1 ( 50 × 10-4 rem-1 )
0.30
Total
165 × 10-4 Sv-1 ( 165 × 10-4 rem-1 )
1.00
Calculated from data in 1CRP # 26
* These "weighting factors" are simply the fractions of the overall risk, i.e. entries in column # 2 divided by 165 x 10-4 “Total Risk”.

18. Risk Factor 20×10-4 × (1×106) = 2000 cases Answer:
Example:
The Risk factor for radiation-induced leukemia is estimated to be 20×10-4 Sv-1 , if each member of a population of 1 million receives a 1 Sv dose how many leukemia's will occur?
Answer:
20×10-4 × (1×106) = 2000 cases
1 Sv ≈ 50,000 chest X-rays

19. Applicable Body Organ or Tissue
Annual Recommended Dose Limits & Reference values for diagnostic x-ray examinations
Applicable Body Organ or Tissue
Radiation Workers
Public
Whole body
20 mSv
1 mSv
Lens of the eye
150 mSv
15 mSv
Skin
500 mSv
50 mSv
Hands
All other organs