Radiation Protection Course
Radiation Protection Service
Radiation Protection Course
Background Physics
Michael Watt
Contents
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Atomic Structure
Types of Radiation
Attenuation & Shielding
Activity & Half Life
Atomic Structure 1
Nucleus
Electrons
-ve charge
Atomic Structure 2
Proton +ve
Atomic Structure 3
Neutrons
Carbon 12
Atomic Mass no. protons and neutrons
12
6
Atomic Number No. protons
C
Carbon 12
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
Stability Curve
p=n
No..of
Protons
No. of Neutrons
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
Carbon 14
Atomic Mass no. protons and neutrons
14
6
Atomic Number No. protons
C
Ion
• An atom or molecule which has lost or
gained one or more electrons
• An ion will have a positive or negative
electrical charge
Ionisation
Types of ionising radiation
Alpha
Smoke detectors
(2n+2p)
Beta
(electron or positron)
Gamma &
X-ray
(electromagnetic
radiation)
Biological work
-VE
or
+VE
Some biological work
(I-125) and Medical
imaging
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
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.
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 10-19 J
Higher energy = more penetrating (for a given
type of radiation)
Alpha
Americium 241 (& γ)
5.4 MeV
Beta
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
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
Activity
New Unit
Becquerel
1 disintegration per second.
Old Unit
Curie
Based on number of disintegrations from 1 g
of radium-226. 3.7 x 1010 dps.
Specific Activity
Measure of the activity per unit mass or
volume
Bq/g or Bq/ml
Half Life ( T1/2 )
Time
1 half life
1 half life
1 half life
Half Life
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Fluorine-18
Phosphorus-32
Phosphorus-33
Iodine-125
Sulphur-35
Cobalt-60
Tritium (Hydrogen-3)
Carbon-14
110 min
14.3 d
25.6 d
59.9 d
87.5 d
5.3 y
12.3 y
5730 y
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)
Next…
• Short video:
– Working Safely with Radioactivity