12. RADIATION HEALTH EFFECTS: DIFFERENT TYPES OF DOSES

Question 1

1. What is the largest man-made source of radiation exposure to the general population?

Answer 1

• the radiation exposure from diagnostic X-Rays

Question 2

2. How much does man-made radiation exposure contribute to the total annual exposure from all sources?

Answer 2

• 14%

Question 3

3. What is the downfall to diagnostic X-Rays?

Answer 3

• they provide many benefits
• the use of them does involve a small risk of developing
  cancer
• the more exposure one receives makes this probability
  higher

Question 4

4. What was the traditional method of measuring the amount of Ionisation in the air?

Answer 4

• Exposure
• this measured the ratio of the total charge produced in
  a small volume of air
• the total charge was usually in reference to the
  electrons

Question 5

5. What is the Unit of Exposure for air?

Answer 5

• Coulombs per kilogram of air
• Charge/ kilogram
• C/kg

NB:
- the new unit is the Röntgen
- 1R = 2.58 x 10⎺⁴ C/kg

Question 6

6. What does the method of Exposure only apply to?

Answer 6

• X Radiation (Photons)
• Y Radiation (Gamma Photons)

Question 7

7. Which concept is now used more widely as a measure of Radiation damage rather than Exposure?

Answer 7

• the concept of an Absorbed Dose
• this is related to the Equivalent and the Effective Dose

Question 8

8. What is the SI Unit for the Absorbed Dose?

Answer 8

• the Gray
• Gy
• this is the equivalent to the absorption of one joule of
  energy in a kilogram of a substance
• ionising energy is absorbed in this case

Question 9

9. The Gray is a large unit, what are the more common subunits to use for normal radiation protection purposes?

Answer 9

1. Microgray
   
   • µGy
   • this is one millionth of a Gray
   • Gy x 10⎺⁶
2. Milligray
   
   • mGY
   • this is one thousandth of a Gray
   • Gy x 10⎺³

Question 10

10. What happens when a photon beam reacts with a Medium?

Answer 10

• the photon interactions release electrons with Kinetic
  Energy
• they release them into the medium
• this is known as KERMA

Question 11

11. What is KERMA?

Answer 11

• this is an acronym for:
  Kinetic Energy Released In Medium
  (per unit mass)

Question 12

12. What happens with the energy that is deposited by these released electrons?

Answer 12

• the energy deposited by these electrons per unit mass is the Absorbed Dose

Question 13

13. What is the Unit for Kerma?

Answer 13

• the Joule Per Kilogram
• the Gray (Gy)
• this is the same as for the Absorbed Dose

Question 14

14. How is the KERMA dose different than the absorbed dose?

Answer 14

• it is different at high energies
• this includes energies up to 1 MeV
• the KERMA and the Absorbed doses are roughly equal
  at low energies

Question 15

15. What is the Vital difference between KERMA and the Absorbed Dose?

Answer 15

KERMA
- this is the energy released

THE ABSORBED DOSE
- this is the energy absorbed

Question 16

16. What is the Equivalent dose?

Answer 16

• this is the dose that allows for the effect of Radiation
  Exposure on human tissue to be determined

Question 17

17. What does the Equivalent Dose relate?

Answer 17

• it relates the Absorbed Dose in human tissue
  TO THE Effective Biological Damage of the Radiation

Question 18

18. What can be said about the relation between Radiation and biological Effects?

Answer 18

• different types of radiation have different biological
  effects
• even if they have the same amount of absorbed dose

Question 19

19. What is the SI Unit of the Equivalent Dose?

Answer 19

• the Sievert (Sv)
• it represents the Stochastic Biological Effect
• EG: cancer

Question 20

20. The Sievert is a large unit, what other modifications of it do we use for Normal radiation Protection levels?

Answer 20

1. MicroSievert
   - µSv
   - this is one millionth of a Sievert
   - Sv x 10⎺⁶
2. MilliSievert
   - mSv
   - this is one thousandth of a Sievert
   - Sv x 10⎺³

Question 21

21. How do you determine the Equivalent Dose?

Answer 21

• we multiply the Absorbed Dose (Gy)
  BY a Radiation Weighting Factor (WR)
• this weighting factor is unique to the type Radiation

Question 22

22. What does the Weighting Factor (WR) take into account?

Answer 22

• some kinds of radiation are more dangerous to
  biological tissue

Question 23

23. How do we determine the dose in Sieverts (Sv) from the dose in Grays (Gy)?

Answer 23

• we multiple by the Wr
• the Wr approximates what would be a very
  complicated calculation
• the values for Wr will change periodically according to
  the ICRP

Question 24

24. What affects the intensity of the Exposure?

Answer 24

• the more Sieverts that are absorbed in a unit of time
  will increase the intensity of the exposure

Question 25

25. How do we express Exposure?

Answer 25

• we express it as an amount over a specific time period
• this is also known as the Dose Rate
• EG: 5 mSv per year

Question 26

26. What does the Probability of a harmful effect from Radiation Exposure depend on?

Answer 26

• it depends on the part/parts of the body that are
  exposed to the radiation
• this is because some organs are more sensitive to
  radiation than others
• a tissue weighting factor is used to take this into
  account

Question 27

27. What is more dense: skin or bone marrow?

Answer 27

• Bone Marrow
• it will sustain more damage from Radiation Exposure

Question 28

28. How do we find out the Effective Dose of an organ?

Answer 28

• we multiply the Equivalent Dose of an organ
  BY THE tissue weighting factor for that organ

Question 29

29. What is the SI unit for the Effective Dose?

Answer 29

• the Sievert (Sv)

Question 30

30. Does this diagram make sense?

Answer 30

• yes

NB:
- the higher the number:
the more sensitive the bone/muscle/organ are

Question 31

31. Does this summary make sense?

Answer 31

• yes