1. Radiation Protection Course
Radiation Protection Service

2. Radiation Protection Course
Background Physics
Michael Watt

3. Contents Atomic Structure Types of Radiation Attenuation & Shielding
Activity & Half Life

4. Atomic Structure 1
Nucleus
Electrons
-ve charge

5. Atomic Structure 2
Proton +ve

6. Atomic Structure 3
Neutrons

7. no. protons and neutrons
Carbon 12
Atomic Mass -
no. protons and neutrons C 12 6
Atomic Number -
No. protons

8. Carbon 12

9. Definition of Isotope
Atom protons fixed – number of neutrons can vary to form different isotopes.
Example carbon has 2 stable isotopes 126C, 136C
To be stable number of N and P must be about equal

10. Stability Curve
p=n
No..of
Protons
No. of Neutrons

11. Definition of Radioactive Isotope
This occurs when the ratio of Neutrons to protons is too great or too small, and the atom spontaneously attempts to become stable
Example carbon has five radioactive isotopes
C-10, C-11, C-14, C-15, C-16

12. no. protons and neutrons
Carbon 14
Atomic Mass -
no. protons and neutrons C 14 6
Atomic Number -
No. protons

13. Ion An atom or molecule which has lost or gained one or more electrons
An ion will have a positive or negative electrical charge

14. Ionisation

15. Types of ionising radiation
Alpha
(2n+2p)
Smoke detectors
Beta
(electron or positron)
Biological work
Gamma &
X-ray
(electromagnetic radiation)
Some biological work (I-125) and Medical imaging
-VE or +VE

16. Sources of Ionising Radiation
Alpha
Americium 241 (& γ)
Radon 222
Polonium 210
Beta
Tritium (Hydrogen-3)
Carbon-14
Sulphur-35
Phosphorus-32/33
Gamma
Iodine-125
Cobalt-60 (& β)
Fluorine-18

17. X-Rays
Produced by accelerating electrons from a cathode onto an anode inside an evacuated glass tube. Less than 1 % of energy converted to x- rays, rest to heat.
X-rays have the same physical properties as gamma photons.

18. Attenuation
paper
perspex
lead

19. Energy of Ionising radiation
The energy of Alpha, Beta and Gamma radiations is measured in ELECTRON VOLTS eV, normally keV and MeV
1eV = 1.6 x J
Higher energy = more penetrating (for a given type of radiation)

20. Alpha Beta Gamma Americium 241 (& γ) 5.4 MeV Tritium (Hydrogen-3)
Carbon-14
Sulphur-35
Phosphorus-32
Phosphorus-33
18.6 keV
157 keV
167 keV
1710 keV
250 keV
Gamma
Iodine-125
Cobalt-60
Fluorine-18
36 keV
1.17 MeV & 1.33 MeV

21. Shielding Materials Alpha particles – Paper, dead layer of skin
Beta particles – 1 cm perspex or tissue
Gamma Photons – dense material such as lead or DU

22. Activity New Unit Old Unit Becquerel 1 disintegration per second.
Curie
Based on number of disintegrations from 1 g of radium x 1010 dps.

23. Measure of the activity per unit mass or volume
Specific Activity
Measure of the activity per unit mass or volume
Bq/g or Bq/ml

24. Half Life ( T1/2 )
Time
1 half life
1 half life
1 half life

25. Half Life Fluorine-18 110 min Phosphorus-32 14.3 d
Iodine d
Sulphur d
Cobalt y
Tritium (Hydrogen-3) y
Carbon y

26. Radiation Dose
Gray (Gy) – absorbed dose.
Defined as 1 Joule of energy absorbed per kilogramme of material.
Sievert (Sv)– Unit of equivalent dose and effective dose
100 rad = 1 Gray ( 100 rem = 1 Sv) 1mrad = 10 µGray ( 1 mrem = 10 µSv)

27. Next…
Short video:
Working Safely with Radioactivity