Edexcel P3 Radiation in Medicine,
Ionising radiation and Kinetic Theory
Physics
Pre exam presentation
By Mr Nesbo
Units!
You need to know the units for each value (or ANY
equation):
some tricky ones!
Intensity – W/m2 (Watts per meter square)
Power of a lense – D (dioptre)
Sin r and Cos r (or i) does not have units
Refractive index, n , does not have units
Energy of an electron/photon (small particle) – eV
(electron volt)
Charge – C (coulomb)
Momentum – Kg m/s (kilogram meters per second)
Temperature – K (kelvin) or ͦC (degrees Celsius)
Radiation for Diagnosis
Radiation
detected
How it forms an image
Where it is used
Visible light
Light reflects off features to form
an image
X-rays are absorbed by some
materials inside the body but not
others.
Positron annihilates with electrons
in the body producing 2 gamma
rays
High-frequency sound waves
reflect off features inside the
body.
Endoscopes
X-rays
Gamma rays
Ultrasound
X-ray photography and
CAT scanners
PET scanners
Ultrasound scanners
Higher
Intensity = power of incident radiation / area
I=P/A
Power measured in watts (W), area measured in
meters squared (m2) so intensity is measured in
watts per
square meter
(W/m2).
How the eye works
Iris controls the
amount of light
entering the eye.
Lenses
Key language:
Magnified means larger.
Diminished means
smaller.
A real image (on the
other side of the lens to
the object). A virtual
image (on the same side
of the lens as the
object).
Power of a Lens
1/f=1/u+1/v
u is the object distance, v is the image distance.
If the image is virtual then v is a negative
number.
Reflection and refraction
Snell’s law
sin I / sin r = nr / ni (a constant number)
focus on equation ‘i/r’ then ‘r/I’
X-ray machines uses an evacuated tube (so travelling
electrons don’t collide with air particles) with a negative
electrode (cathode). When heated thermionic emission
fires electrons towards a rotation positive electrode
(anode).
The electrons
collide with the
anode passing
energy to the
metal particles
which in turn
emit x-rays.
Equations for flowing particles
Higher
Flow of electrons equation:
I = N x q where I = current in amperes (A), N = number of
electrons flowing each second and q = charge of each
electron
Kinetic energy equation:
Ek = ½ m * v2 (m is mass in kg, v is velocity of the electron
in m/s).
Energy can be measured in eV (electron volts, electron
charge * 1 volt).
Fluoroscope:
2D image is taken to in
one direction. A camera
can be used to form a
real time video clip.
CAT scans:
2D image is formed from
several directions and can
be used to form a 3D
image.
Electron and positron radiation
6 protons
8 neutrons
7 protons
7 neutrons
Neutron changes into a
proton => emits an
electron (beta minus
decay). Atomic
number increases.
Higher
Down quark changes
to up quark.
Proton changes into a
neutron => emits a
positron (beta plus
decay). Atomic
number decreases.
Up quark changes to
down quark
6 protons
4 neutrons
5 protons
5 neutrons
Quarks:
Proton = u + d + u = p (total = +1e)
Neutron = d + u + d = n (total = 0)
Intensity – W/m2 (Watts per meter square)
Power of a lense – D (dioptre)
Sin r and Cos r (or i) does not have units
Refractive index, n , does not have units
Energy of an electron/photon (small particle) – eV
(electron volt)
Charge – C (coulomb)
Momentum – Kg m/s (kilogram meters per second)
Temperature – ͦK (degrees kelvin) or ͦC (degrees Celsius)
Radiation in hospitals
Palliative care help issues but does not cure them.
Beta emitters are used for internal radiotherapy.
Gamma sources and high-frequency X-rays are used
for external radiotherapy.
Tracers vary so that they will be absorbed by specific
parts of the body.
A tracer can be a radioactive isotope of the normal
substance which the body part absorbs. The tracer
must have a short half-life so that the body is not
exposed more than needs be. Due to this the
isotopes are made close by.
PET scans (positron emission
tomography)
PET scan uses
a positron
emitting tracer.
The positrons
annihilate with
electrons in
the body
producing two
gamma rays in
opposite
directions.
Circular Motion
The LHC (Large Hadron Collider)
is a particle accelerator.
It accelerates two beams of
protons or ions to high speed in
opposite directions eventually
causing them to collide.
Circular motion uses the concept of ‘resultant force’. The
momentum/velocity of an object wants to travel in a
straight line. The centripetal force acts at a right angle
towards the centre of a circular path. The result is a
motion between the two. As this continues the direction
of motion continues to turn towards the centre.
Cyclotrons
Cyclotrons are used to make the isotopes for
PET scans.
Collisions
Momentum is always conserved (involves direction).
Inelastic collision kinetic energy is not conserved.
Elastic collision kinetic energy is conserved.
Momentum equation:
Momentum of an object = mass * velocity
Total momentum before an interaction (collision or
explosion) = sum of momentum of all objects
(taking into account direction, choose one direction
to be +ve and the other –ve)
Kinetic Theory
Temperature is a measurement of the average
kinetic energy of the particles [in a gas].
Pressure is the force particles exert on a
surface/wall of a container when collide. Measured
in pascals (Pa) where 1 Pa = 1 N / m2.
Absolute zero is the lowest temperature (or
average kinetic energy) and occurs at -273 ͦC, also
known as 0 ͦK (zero degrees kelvin).
Changes in temperatures, volumes and
pressures
Under medium
temp. and pressure
the balloon has a
normal volume (A).
If the temp. inside
increases and/or
the pressure outside decreases the balloon, the
volume of the balloon increase (B).
The opposite applies if conditions are reversed.
Nuclear glossary
 alpha radiation – Positively charged particles made up of two protons and
two neutrons.
 background radiation – Constant low-level radiation from food and
environmental sources.
 beta radiation – High-energy electrons emitted by some radioactive
materials.
 gamma radiation – Short-wavelength electromagnetic radiation emitted
during radioactive decay.
 Geiger-Müller tube – A device used to detect and measure radiation from
radioactive materials.
 ionizing radiation – High-energy radiation capable of ionizing substances
through which it passes.
 radioactivity – The spontaneous emission of radiation from the nucleus of an
unstable atom.
Nuclear characteristics
Particles Symbol
Alpha
Beta
Gamma
α
β
ɣ
Structure
Helium nucleus
2x neutron 2x
proton
Electron
(high speed)
Light ray
(EM radiation)
Relative Penetrating
charge
The least
+2
-1
0
Stopped by
Paper
10cm – 1m of air
A lot
Aluminium
10m of air
The most
Lead
Not stopped by
air
30cm of concrete
Nuclear reactors
Safety:
Radioactive materials produce
dangerous radiation
Students frequently refer to
protective gear needing to be
worn when asked about safety HOWEVER this is
only one area of importance.
THERE ARE DANGERS AND SAFETY POINTS YOU CAN
DISCUSS!
Risks
Safety precautions
• different types of ionising radiation
produce different dangers
• protective clothing and handling
systems should be used
• energy from the ionising radiation can be
absorbed by the human body
• (prolonged) exposure to radiation can
cause {tissue / cell} damage and {mutation/
damage to DNA}
• increased risk due to long term exposure
to raised background levels of radiation
• minimise exposure to the ionising
radiation
• intensity of radiation decreases with
distance from the source
• personal radiation dose should be
monitored
• monitoring of background levels of
radiation