4. IONISING RADIATION: MEASUREMENTS AND STANDARDS

Question 1

1. What is necessary to have when using Ionising Radiation?

Answer 1

• a method for detecting and recording its presence

Question 2

2. Can ionisation be identified directly?

Answer 2

• NO
• we need the radiation to interact with another material
• this produce an effect
• this effect can be detected

Question 3

3. Who is the Father of Radiology?

Answer 3

• Wilhelm Conrad Röntgen
• he is a mechanical engineer and physicist

Question 4

4. When did Wilhelm discover X-Rays?

Answer 4

• in 1895
• on the 8th of November
• he did this accidentally

Question 5

5. What did Henri Becquerel discover in 1896?

Answer 5

• he discovered radioactivity
• he did this when he accidentally detected radiation

Question 6

6. What two methods did Becquerel use to detect ionising radiation?

Answer 6

1. Film
2. Electroscope

NB:
- both cases involve the interaction of radiation with
another material
- this allows for it to be detected

NB:
- both are still commonly used today

Question 7

7. Why do we need to be able to calculate Dose Rate immediately?

Answer 7

• this allows us to calculate the accumulated dose
• this gives us a warning if the dose rate becomes very
  high

Question 8

8. What is a Dosimeter?

Answer 8

• this is an instrument that measures ionising radiation

Question 9

9. What does a Dosimeter comprise of?

Answer 9

• it comprises of a measuring assembly
  (this is often referred to as an electrometer)
• it has one or more detector assemblies
  (these may or may not be an integral part of the
  measuring assembly)

Question 10

10. What are Monitoring equipments often calibrated in?

Answer 10

• they are calibrated in terms of:
  
  • mrad/h
  • μGy/h
  • centigrade / hour

Question 11

11. How are low levels of dose rate measured?

Answer 11

• using a Geiger-Muller (G-M) tube
• using Scintillation Counters

Question 12

12. What is an Ionisation Chamber?

Answer 12

• this is another way of measuring Dose Rates
• it is more accurate
• it is less affected by Radiation Energy

Question 13

13. What is another advantage of the Ionisation Chamber systems?

Answer 13

• they can measure high dose rates
• this would saturate other monitors

Question 14

14. What is the standard instruments for measuring dose rates?

Answer 14

• it is usually the Ionisation Chamber System

Question 15

15. Why is it desirable to be able to monitor dose and dose rate with an instrument which can be worn on the body?

Answer 15

• we can use them to measure the ionising radiation
  received by different doses in different parts of our
  body

Question 16

16. Name two examples of measuring methods that can be worn on the body.

Answer 16

1. Pocket Dosimeters
2. G-M Tube Instruments with a dose rate alarm

Question 17

17. Why are Solid-State detectors and Scintillation Counter Systems not suitable for routine dose measurements?

Answer 17

• they are relatively expensive

Question 18

18. What is currently the cheapest and most commonly used way to measure Radiation dose?

Answer 18

• personal monitors
• these use Thermoluminescent Dosimetry (TLD)

Question 19

19. What is slowly replacing Thermoluminescent Dosimeters (TLDs)?

Answer 19

• Ionisation Chamber Dosimeters
• this is because TLDs are passive dosimeters
• they cannot provide direct measurements of ionising
  radiation

Question 20

20. What is the safety hazard with Dosimeters?

Answer 20

• they offer no active protection or mitigation from
  harmful radiation
• they do not alert individuals when they are exposed to
  high doses
• they are not radioactive themselves

Question 21

21. List the 4 Advantages of Film Dosimeters.

Answer 21

1. A FILM BADGE
   
   • that acts as a personal monitoring device
   • is very simple
   • it is not expensive
2. A FILM BADGE
   
   • provides a permanent record
3. FILM BADGE DOSIMETERS
   
   • are very reliable
4. A FILM BADGE IS USED TO:
   
   • measure and record radiation exposure
   • this radiation exposure is due to Gamma Rays, X-
     Rays and Beta Particles

Question 22

22. List the 3 disadvantages of Film Dosimeters.

Answer 22

1. FILM DOSIMETERS USUALLY CANNOT BE READ ON
   SITE
   
   • they have to be sent away for developing
2. FILM DOSIMETERS ARE FOR ONE TIME USE ONLY
   
   • they cannot be reused
3. EXPOSURES OF LESS THAN 0.2 mSv OF GAMMA
   RADIATION
   
   • this is 20 millirem of Gamma Radiation
   • this cannot be actively measured

Question 23

23. List the 4 Advantages of TLD Dosimeters?

Answer 23

1. TLDs
   
   • are able to measure a greater range of doses in
     comparison with film badges
2. DOSES FROM TLDs
   
   • can be easily obtained
3. TLDs CAN BE READ ON SITE
   
   • they usually do not have to be sent away for
     developing
4. TLDs
   
   • are easily reusable

Question 24

24. List the 2 disadvantages of TLDs?

Answer 24

1. EACH DOSE
   - cannot be read out more than once
2. THE READOUT PROCESS
   • effectively zeroes the TLD

Question 25

25. What is an Electronic Personal Dosimeter?

Answer 25

• it is a high range dosimeter
• it is alarming
• it is active

Question 26

26. What was an Electronic Personal Dosimeter designed for?

Answer 26

• it was designed to be worn by occupational Radiation
  Workers in planned exposure situations
• it is meant to measure personal dose equivalence for
  regulatory compliance

Question 27

27. In which 2 settings are Electronic Personal Dosimeters used?

Answer 27

1. Industrial
2. Medical

Question 28

28. What does the Electronic Personal Dosimeter display?

Answer 28

• it displays dose and dose rate
• this is because it has a high level of Radiation
  sensitivity