Radiation can cause damage to cells and DNA which may lead to cancer or genetic mutations. The main dangers of ionising radiation are killing healthy cells, stimulating cancer growth, and causing mutations to DNA that can be passed down generations. Radiation exposure is measured in dosage, and dosimeters are used to monitor the dose received by individuals. Protective measures include increasing distance from sources of radiation, limiting exposure time, and using shielding such as lead to absorb radiation.

1. P3
Topic 1 Applications of Physics

2. P3.1 Radiation in Medicine
Keywords
• Ionising Radiation – radiation that can cause charged
particles by knocking electrons from the atom. Causes
tissue damage and may cause mutations.
• Intensity – the strength of a wave defined as power of
incident radiation/area.
• Diagnosis – identifying a medical condition by its signs and
symptoms or from a medical imaging scan
• Non-ionising radiation– radiation that does not cause
formation of charged particles.
• Incident radiation– falling of striking of radiation on
something.
Facts:
• Intensity is an example of a compound
measure (its units are determined by the
units used in the calculation)
• Standard units = W/m2
• Visible light - example of radiation
(energy carried by waves from a
source)
• Different types used to identify and
treat medical problems.
• Produce images that show features
inside the body.
• Non-ionising = lasers used in eye
surgery; ultrasound to treat swelling.
• Intensity decreases with distance
from source. (Different tumours
treated with different intensities)
• Denser medium to move through =
weaker radiation.
Visible light Light reflects to form an image Endoscopes
X-ray Absorbed by some material but not others. Negative image
produced
X-ray photography and CAT
scanners
Gamma Rays Movement of a substance producing Gamma rays is detecting and
observed
PET scanners
Ultrasound High frequency sounds waves reflect off internal features Ultrasound scanners
Intensity (I) = power of incident radiation in Watts (P)
W/m2 area in Metres squared (A)

3. P3.2 – How eyes work
Eye structure diagram
• Constricted pupil – small to reduce light entering
• Dilated pupil – larger to allow more light to enter
Image formation
• Light converges on the retina
• Path of rays is changed by the eye by refraction (carried out by cornea and lens)
• Ciliary muscles change the shape of the lens to keep image focussed on retina if the distance alters.
– Contracted ciliary muscles = loose ligament = lens more rounded = focus on nearby objects
– Relaxed ciliary muscles = taut ligaments = lens flattened = focus on distant objects
• No limit to how far away you can focus – far point is at infinity
• You near point is approx. 25cms – nearer and image is blurred.
Accommodation/ Focussing

4. P3.3 –Sight problems
Keywords
• Short Sight– cannot focus on distant objects as light rays focus on a point in front of the retina
• Long Sight – cannot focus on near objects as light rays focussed to a point behind the retina
• Diverging Lenses – spreads out light rays
• Converging Lenses – brings light rays together
Short and long sightedness
• Near objects = lens is shorter and fatter
• Distant object = lens is thinner
Short sighted
• Eyeball too long or cornea curved too sharply
• Rays focussing in front of retina
• Distant objects are blurred
Long sighted
• Eyeball too short or lens not thick /curved
enough.
• Taut ciliary muscles still cannot bend the light
enough
• Near objects are blurred
Correcting vision
• Short sight corrected by glasses with diverging
lenses
– Bends light apart to focus correctly on
retina
• Long sight corrected by glasses with converging
lenses
– Refracts the light more to meet on the
retina.
Laser Correction
• Uses a laser beam to reshape the front of the
cornea
• Lasers make precise incisions without
damaging surrounding areas
• Changes the way light is refracted by the
cornea

6. P3.5 Different lenses
Keywords
• Dioptres – Unit for measuring the power of a lens
• Real Image – An image that can be projected onto a
screen
• Virtual Image – An image that cannot be projected
onto a screen
 Converging lens – parallel rays refracted
and meet at focal point
 Lens to focal point = focal length
 Diverging lens – focal point is point rays
seem to coming from
 Focal point to lens = focal length
Power of a lens = 1
(dioptre, D) Focal length(metre, m)
Lens Equation – links the object distance (u), the image distance (v) and the focal length (f)
1 = 1 + 1
F u v

7. P3.5 Different lenses
Lens Equation – links the object distance (u), the image distance (v) and the focal
length (f)
1 = 1 + 1
f u v

8. Incident angle i
Reflected angle r
Reflected ray
Incident ray
P3.6 Reflection and P3.9
Critical Angle
Reflection
• Law of reflection states:
Angle of incidence = Angle of reflection
• Both are measured from the ‘normal’
• Can predict the path of a particular
reflected ray
Key word
• Normal – line at right angle to a surface
Total Internal Reflection
• Critical angle = the smallest angle of
incidence at which the angle of refraction is
90° or total internal reflection occurs.
• Greater the refractive index = the smaller the
critical angle
• Calculation of the critical angle
Sin c nr
=
Sin r ni
• Light can travel along the boundary
between the different mediums in some
exceptional situations.
• Automatic windscreen wipers sense
refraction of light when water is on the
windscreen changing the medium from
glass alone.

9. Snell’s Law
• Links the angles of incidence and
refraction when waves travel from
one medium to another.
• The constant is related to the
refractive index (n) of each
material
Refraction
• In a denser medium the waves travels
slower
• Wave changes direction = refraction
• If slowed down – refract towards the
normal
• If travelling faster = refract away from
normal
P3.6 Refraction
Refractive index = speed of light in air
speed of light in substance
image
actual location
normal
Angle of
incidence
Angle of
refraction
Sin i nr
=
Sin r ni
nr - refractive index of medium ray is travelling into
ni - refractive index of medium ray is travelling from

10. P3.10 – Using reflection and refraction
Optical Fibre
Light ray travelling is consistently reflected back as it is
at an angle greater than the critical one.
The edge is acting like a mirror and laws of reflection
are obeyed.
Endoscope – look inside a patient.
 Flexible rod of optical fibres.
 Light reflected off the inside of the body is
gathered and focussed to form an image.
Ultrasound – higher frequency than human hearing
 Travel through solid objects being partly reflected when the medium changes
 Medical scan transmit and receive the waves
 At the interface between tissues reflection occurs.
 Reflected rays converted into an image
 Used in diagnosis and treatment
 Used to locate hard deposits like kidney stones
 e.g. high intensity ultrasound can break down kidney stones
 Treat injured muscles (easy to target the correct area

11. P3
Topic 2 X-rays and ECG

12. Facts
• Ionising radiation – turns atoms to ions
• More energy the x-ray has = more ionising
• Higher frequency x-ray = more energyX-ray machine
• Evacuated tube containing 2
electrodes
• Cathode (negative) 9s a wire
filament. When heated it emits
electrons (electron gun). This is
called thermionic emission.
• Anode (positive) made of metal. If
there is a large potential
difference the electrons are
accelerated to the anode. Most
kinetic energy is transferred to
thermal energy but some is
transformed into x-rays.
• Higher potential difference = x-rays
with greater energy
• Tube is evacuated to prevent
electrons colliding with other
particles.
Comparing currents
• Charged particles from cathode to anode
completing the circuit.
• Increase temperature = increase the electrons
emitted = increases the X-rays produced.
Measuring current in X-ray machine
I = current in amperes
N = number of particles flowing each second
q = charge on each particle in coulombs
I = N x q
P3.11 – X-rays
Kinetic energy
m = mass of an electron in kg
v = velocity of the electron in m/s
e = charge on the electron
V = potential difference in volts
KE = 1/2mv2 = e x V

13. P3.12 – Using X rays
Absorption of X-rays
• Different materials absorb different amounts of x-rays
• Denser material = more absorption = looks lighter on the x-ray photo
Fluoroscopes
• Show organs working
• Detect blocked vessels
• Consist of x-ray source and detector on digital video camera
CAT Scans
• X-ray source moves in circle around patient
• Detectors opposite the source
• Many cross-sectional images that can build up 3D image
• Tumours detected with areas of brightness or dark patches
Keyword
Inverse Square Law– the value of a physical property is inversely
proportional to the square of the distance from the source.
Benefits
 Painless and non invasive
 Can eliminate the need for biopsy to decide on treatment.
Risks
 Both give a dose of radiation equivalent to 10 yrs background radiation
 Increased risk of cancer so not recommended on children or pregnant females.

14. P3.13 – ECGs and Pulse Oximetry
Pulse Oximetry
• 2 LEDs – one red light and the other infrared radiation
• A detector to see the peaks in absorbance which gives a pulse rate
• Oxygenated blood absorbs more infrared so machine can compare absorbency of each LED to work
out oxygen in blood.
Pacemakers
– If action potentials do not spread across heart properly the pacemaker amplifies and transmits
them so chambers contract correctly.
Action potential – change in voltage across a nerve
cell (neurone) or cardiac muscle when and electrical
impulse travels along it.
1. Action potential is sent to each muscle cells to
tell it to contract.
2. Starts in Atria (top chambers)
3. Body has a high proportion of water and salts
so conducts electricity
4. Action potentials will travel through the skin
and can produce an ECG picture of the heart
electrical signals.
5. Heart has a regular pattern
6. Frequency of heartbeat in beats/seconds
Frequency, F (Hz) = 1
time period, T (second)

15. P3
Topic 3 Production, uses and risks of
ionising radiation from radioactive
sources.

16. P3 Topic 3: P3.14 Beta and Positron radiation
• Atom – an atom consists of a small nucleus containing protons and neutrons and with
electrons around it.
• Nucleons – protons and neutrons are known as nucleons.
• Atomic number – same as proton number which is the number of protons in the atom
• Mass number – same as nucleon number, which is the number of protons and neutrons in
an atom.
• Beta particles – electrons (Beta-minus) or positrons (Beta-plus)
What is beta decay?
Beta minus decay – In beta minus decay, a neutron
becomes a proton plus an electron. Beta minus radiation is
made up of a stream of high energy electrons. They can
penetrate paper but not thin sheets of metal. The particles
are ionising. Beta-minus decay increases the atomic
number by 1 but mass number is unaffected.
Beta plus decay – In positron or beta-
plus decay, a proton becomes a neutron
plus a positron. Positron decay decreases
the atomic number by 1 but mass number
remains unchanged.
The diagram shows how ionising radiation can
be used as part of the system for controlling
the thickness of paper produced in a paper
mill.

17. P3.15 Alpha and gamma radiation
• Radioactive emissions – there are three types,
alpha, beta and gamma.
• Alpha radiation – alpha particles are each made
up of 2 protons and 2 neutrons. They are not very
penetrating but are very ionising.
• Alpha decay – results in the atomic number
decreasing by 2 and mass number decreasing by 4.
• Gamma radiation – are a type of electromagnetic
radiation, it has no mass and causes no change to
the atomic number or mass number. Gamma rays
are very penetrating but not very ionising.
• Neutron radiation – sometimes in radioactive
decay, a neutron is emitted. Neutrons have no
charge, but they are as penetrating as gamma
rays.
• Nuclear Reactions – Shows the reactants and
products in a nuclear reaction. This reaction has
to be balanced in terms of the total atomic mass
number and total mass number which must be the
same on both sides.
What are alpha and gamma decay? Alpha decay
Beta decay
Gamma decay

18. P3.15 Alpha and gamma radiation
Smoke detectors found in people’s
homes use an alpha source such as
americium. Alpha particles are capable
of ionising particles in the air, breaking
them up into positive and negative
ions.
Uses of alpha radiation – A smoke detector
Remember!!! – In nuclear reactions:
An alpha (α) particle has two protons, two neutrons and no electrons. It is
therefore a helium nucleus and is shown as
A β− particle is an electron and has a mass number of zero. It has the opposite
charge to a proton so it has an atomic number of –1 (i.e. opposite to a proton)
and is shown as
A β+ particle is a positron. It has a mass number of 0 and a positive charge so
is shown as having an atomic number of +1:
A gamma ray has no mass and no charge and so is shown as

19. P3.16 The Stability Curve
• Isotopes - of an element have the same number of protons but
different number of neutrons.
• Stable isotopes – isotopes which stay in their arrangement
indefinitely
• Unstable isotopes – isotopes which decay by emitting
radioactivity.
• N = Number of Neutrons
• Z = Number of protons
How is the N-Z curve used?
Stability Curve or N-Z curve
The stability curve is important as it shows the patterns in the way
that different isotopes behave. It compares different isotopes with
regard to the numbers of protons and neutrons they have, and shows
whether they are stable or not and, if not, what kind of emissions they
release.
• Each grey dot on the graph represents an isotope
• The black dots represent stable isotopes
• The other isotopes are unstable.
• The straight black line is the N = Z line. Any isotope on that line
has the same number of protons and neutrons in its nucleus.
Carbon-12 is an example of this.
• Heavier elements (those with a more massive nucleus) are nearer
the top of the graph. They are not close to the N = Z line

20. P3.17 Quarks
• Quark – a particle from which
protons and neutrons are made.
Protons and Neutrons contain 3
quarks.
What is the role of quarks in beta decay?
Quark compositions in a proton and
a neutron
Quarks
Quarks exist within larger particles called hadrons (which
include protons and neutrons). The two types of quarks
we will consider are ‘UP’ and ‘DOWN’ quarks.
• A Proton – consists of two UP quarks and one DOWN
quark
• A Neutron – consists of two DOWN quarks and one UP
quark
• Quarks can change from one into another – this
explains how a proton can change into a neutron and
vice-versa.
• Beta plus decay – when an UP quark changes into a
DOWN quark.
• Beta minus decay – when a DOWN quark changes into
an UP quark.
What are quarks?
Charges on Quarks
Up quarks have an electrical charge of +⅔.
Down quarks have an electrical charge of -⅓.
This explains why protons have a positive
charge and neutrons have no charge
Quark Up Down
Mass 1/3 1/3
Charge +2/3 -1/3
Mass and Charge of Quarks

21. P3.18 Dangers of ionising radiation
What are the dangers of ionising radiation?
• Mutations – changes in the structure of the DNA, which may
then copied over to new cells.
• Dosage – in radiation exposure, it is the total amount of
radiation absorbed by the person exposed to it.
• Dosimeter – is a film badge, developing the film reveals the dose
of radiation received by the wearer.
Increase in radiation levels can:
• Kill healthy cells – risk of damage to their
DNA.
• Stimulate the growth of cancers
• Cause mutations – the structure of the
DNA in cells can cause cancers or harmful
changes to the function of genes, which
are passed down to the next generation.
• Cause radiation burns – beta burns are
mainly surface burns, gamma burns go
deeper into the tissue and organs inside
the body.
Protecting people from over-exposure
• Increase the distance that medical staff
work from the source.
• Shielding the containment of the
radioactive source
• Minimise the time spent in the presence
of sources
• Controlling the dosage of the radioactive
material used in patients for diagnosis or
treatments
• Wear a dosimeter to monitor the levels of
exposure and dose received by the wearer

22. P3.19 Radiation in hospitals
How are radioactive substances used in hospitals?
• Radiotherapy – Use of ionising radiation to treat cancer by killing cancer cells or to reduce the size of
a tumour with
• Internal radiotherapy – where the radioactive source is placed inside the body, e.g. placing iodine-
131 next to the tumour in the patient
• External radiotherapy – where a gamma source or X-ray tube is used to apply a dose to the patient.
• Palliative care = a condition that cannot be cured, but allows the patient to be in less pain to enjoy a
better quality of life.
• Tracer – a radioactive substance that is injected into the body and emits gamma rays that can be
detected outside of the body to monitor how a part of the body is functioning.
• PET Scans – Positron emission tomography – uses principle of positron-electron annihilation shows
the active areas of parts of the body that take up more of the injected tracer (more detail found in
Topic 4: PET Scans slide).
Radiotherapy is used to treat cancers by killing cancer cells. It may also be used in palliative
care. Cancers can be diagnosed using a tracer. Tracers will concentrate in particular organs
or diseased or cancerous tissues and tumours. They usually have a short half-life, i.e. it will
lose its radioactivity very quickly so other parts of the body are affected minimally.
In a PET scan, the tracer emits a positron, this then interacts with an electron (annihilates)
releasing two gamma rays in opposite directions. The PET camera then detects the gamma
rays.

23. P3
Topic 4 Motion of particles

24. P3 Topic 4: P3.20 Collaboration and Circular Motion
• Particle physics – is the study of the nature and properties of sub-atomic particles and
fundamental particles and their interactions.
• Circular Motion – motion of an object in a circle which requires centripetal force.
• Centripetal Force – A resultant force acting inwards along the radius of the circle.
What are particle accelerators used for?
Circular Motion
To keep the bucket moving in a circle, a resultant force
acts inwards towards the centre of the circle along the
radius. In the above example, the centripetal force is
provided by the tension in the string in both diagrams
above. If the bucket or rock are released, there is no
longer any centripetal force and therefore no tension.
The object will travel in a straight line at a tangent to
the circular path it has been following.
Theories and models of particles are tested
over time as other scientists repeat
experiments and critically evaluate the work
published in Scientific papers and journals.
LHC – Large Hadron Collider – is a particle
accelerator. It can accelerate beams of
protons or ions to very high speeds in
opposite directions to allow head-on
collisions. Scientists then study the particles
created in the collisions and may discover new
particles.

25. P3.20 Cyclotrons
Cyclotron - A cyclotron is a particle accelerator. The
particles start at the centre and follow a spiral path. The
particles are accelerated to greater and greater speeds until
they hit a target at the edge of the cyclotron.
Positive ions produced at the centre of the cyclotron enter a
uniform magnetic field created by D-shaped magnets or
‘dees’. The magnetic field deflects the ions into a circular
path. Each time the ions cross the gap between the dees
they are accelerated by the voltage. As the ions gain speed
they follow a spiral path until they leave the cyclotron and
undergo a collision with the particles in the target.
Artificial radioactive isotopes can be produced when a
beam of accelerated protons from a cyclotron is collided
with the nucleus of a stable element. The nucleus of this
element gains a proton and is changed into an unstable
nucleus of a different element. Small cyclotrons are now
used in hospitals to produce the short-lived isotopes
needed in PET scanners.
• Cyclotrons – are particle accelerators in which moving charged particles are bent into circular or spiral
paths (as in the LHC – Large Hadron Collider)
• Radioactive Isotope – An unstable isotope that emits radiation, such as alpha, beta or gamma
radiation.
How a cyclotron works

26. P3.22 Collisions
How is an elastic collision different to an inelastic collision?
• Inelastic collision – a collision where kinetic energy (KE) is not conserved, some of the KE
is transferred to its surroundings, e.g. as sound or heat.
• Elastic collision – a collision where there is conservation of kinetic energy.
• Momentum – Mass x velocity of a moving object. The units are kg m/s. It is a vector
quantity which has both size and direction.
• Conservation of Energy – states that energy cannot be created or destroyed.
• Conservation of momentum – states that the total momentum before and after collision
remains unchanged.
Colliding objects have energy and momentum. Momentum is conserved in all collisions. In
elastic collisions, kinetic energy is conserved but in inelastic collisions, kinetic energy is not
conserved. The diagrams above show examples of elastic and inelastic collisions. In an elastic
collision, the balls m1 and m2 collide and then carry on moving at speeds, v1 and v2. In an
inelastic collision, the red and blue ball stick together and move at a speed of v.
Inelastic Collision
Elastic Collision

27. P3.22 Momentum Calculations
Solving problems using momentum conservation
Two trolleys collide and stick together.
From the data below, calculate the
velocity of the trolleys after the
collision.
trolley A trolley B
mass = 3kg mass = 5kg
velocity = 8m/s velocity = -4m/s
momentum = 24kgm/s (3 x 8) momentum = -20kgm/s (5 x -4)
total momentum before collision = 4kgm/s (24 + -20)
mass after collision = 8kg (3 + 5)
momentum after collision = 4kgm/s
velocity after collision = momentum / mass = 0.5 m/s

28. P3.23 PET Scanners
Why do the radioisotopes used in PET scans produce pairs of gamma rays?
• Antimatter – is matter that has particles of the same mass and properties as their counterparts. E.g.
the anti-matter of an electron is a positron.
• Positron – is the anti-mater of an electron which has the same mass as an electron but carries a
positive charge.
• Annihilation – when an electron and a positron collide, they annihilate each other and produce 2
gamma rays photons which move away in opposite directions.
• Mass-energy equivalence – occurs when the masses of the annihilated electron and positron are
converted into an equivalent amount of energy.
PET Scans - To produce a PET scan, a radioactive isotope that emits positrons and has a short half-life is
injected into the patient’s blood. This isotope accumulates in various tissues of the body. The positrons
from the decaying isotope meet electrons in the tissue surrounding the isotope. When this happens, a pair
of gamma rays is produced moving in opposite directions. The gamma rays are detected by pairs of gamma
ray sensors positioned around the person. Through analysing where the gamma ray pairs originate within
the tissue, a picture of the internal organs can be produced.
PET ScannerElectron-Positron annihilation

29. P3
Topic 5 Kinetic Theory and Gases

30. P3 Topic 5: P3.24 Kinetic Theory
• Kinetic theory – states that everything is made up of tiny
particles that are atoms or molecules.
• Kinetic energy – the energy a particle has due to its
movement. Calculated using the equation K.E. = 1/2mv2, unit
of K.E. is Joules (J).
• Pressure – is force per unit area and is measured in Pascals
(Pa) where 1 Pa = 1 N/m2.
• Absolute zero – is a temperature of -273oC which is the
temperature at which the pressure of a gas would be zero and
the particles would NOT be moving.
• Kelvin temperature scale – measures the temperatures
relative to absolute zero. The units are kelvin (K) and 1K is the
same temperature interval as 1oC.
What is Absolute Zero? Absolute zero = 0K = -273oC
• A graph to show how the pressure of a fixed volume of gas
changes with temperature.
• Temperatures are easily converted:
• From Kelvin to Celsius – subtract 273 degrees
• From Celsius to Kelvin – add 273 degrees

31. P3.24 Kinetic Theory
Particle movement in the three
states of matter
Kinetic Theory
1. Gases are compressible (easily
squashed) and expand to fill up a
container.
2. The temperature of a gas is a
measure of the average kinetic
energy of the particles in the gas.
3. The faster the average speed, the
higher the temperature
4. Heating a gas increases the kinetic
energy of particles so they move
faster and temperature rises.
Particles and Pressure & Absolute Zero
1. The pressure of a gas is caused by the forces of moving particles on the walls of a
container. The faster the movement, the higher the number of collisions and more force
will be exerted.

32. P3.27 Calculating volumes and pressures
How can we calculate the pressure or volume of a gas?
Volume and Pressure
• If the volume of a gas increases at a constant temperature,
the pressure decreases.
• Volume and pressure are inversely proportional
• Volume and pressure are related by this equation:
V1P1 = V2P2
V1 and V2 are volumes in m3 and P1 and P2 are pressures
in Pa.
Volume and Temperature
If the temperature of a gas is increased at a constant pressure,
the volume increases.
Volume and temperature are directly proportional and are
related by this equation:
𝑽 𝟏=
𝑽 𝟐 𝑻 𝟏
𝑻 𝟐
V1 and V2 are volumes in m3 and T1 and T2 are temperatures in
K.
• V = Volume in m3
• P = Pressure in Pa
• T = Temperature in K
Combining the equations
The two equations on the
left can be combined to
give the one above
You will need to be able to select and use these
relationships to calculate either P, V or T