A Level Pearson Edexcel Physics Topic 8 Nuclear & Particle Physics

What is the nucleon number

The sum of the number of protons and neutrons in the nucleus
(mass number)

What is the atomic (proton) number

The total number of protons in the nucleus

Outline Rutherford's alpha scattering experiment

High speed alpha particles were fired at a very thin sheet of gold foil. The deflections of the particle's were measured and conclusions were drawn

What was observed in the Alpha scattering experiment

-Most alpha particles passed straight through the gold atoms
-Some were deflected
-A few of them were deflected backwards

What is thermionic emission

Thermionic emissions is the release of electrons due to heating

Explain why electrons are released from a heated filament

As the filament heats up , free electrons inside the metal gain kinetic energy. When the surface electrons gain sufficient energy, they are released from the surface

What will happen to a beam of electrons if it passed through a potential difference

The beam of the electrons will be accelerated since work is done by the potential difference

How do we calculate the energy transferred to an electron, when it is accelerated across potential difference

Energy = Charge * Potential Difference
E = eV

What happens when a beam of electrons is directed into a magnetic field

The electron beam will be deflected, since magnetic fields apply forces on moving charges.

What is the magnitude of the force experienced by a moving electron in a magnetic field

Force = Magnetic Flux density Charge Velocity
F = BeV

If the electrons are moving perpendicular to the field lines, which direction will the magnetic force act

The force will act perpendicular to both the electron and field directions

Describe the shape of the path of a beam of electrons passing through a magnetic field

The beam will produce a circular path since the magnetic force always acts perpendicular to the electrons motion. This means it acts as centripetal force and produces a circular path

What are the two kinds of particle accelerators

-Linear accelerator (LINAC)
-Circular accelerators

What is a Linear accelerator (LINAC)

It is a particle accelerator that is used to accelerate charged particles (such as electrons or protons) along a straight path using alternating electric fields

Describe the composition of a Linear accelerator (LINAC)

• LINAC consists of several cylindrical electrodes called drift tubes, arranged in a series, with increasing lengths along the path

• These electrodes are connected to alternating voltages, which create electric fields between them

• There is a particle source at the beginning of the accelerator where the particles are released

How does a Linear accelerator (LINAC) work

Charged particles are released from a source and accelerated toward the first electrode.
Alternating electric fields between the electrodes accelerate the particles each time they pass through a gap.
The polarity of the electric field switches at the right moment, ensuring the particles continue accelerating through the successive gaps.
This process repeats until the particles reach the desired speed as they exit the accelerator.

What does a Linear accelerator (LINAC) use

Uses an alternating electric field

What are two kind of circular particle accelerators

• Cyclotrons

• Synchrotrons

What is a Cyclotron

Is a particle accelerator that uses magnetic fields to accelerate particles in circular paths. This allows higher speeds to be reached, without the limitations of the accelerator's length.

Describe the composition of a Cyclotron

• Cyclotrons consist of two D-shaped paths which are separated by a small gap

• An alternating potential difference is applied across the gap

How does a Cyclotron work

An electron beam(particle) is passed into the cyclotron, where it is deflected into a circular path by a perpendicular magnetic field.
When the beam(particle) reaches the gap, it's accelerated by a potential difference.
This increases the speed of the beam, causing the radius of the path to increase.
This process repeats every half circle.

What does a Cyclotron use

Uses a magnetic field and an alternating electric field

What is the force like that is exerted by a magnetic field on a charged particle

The exerted force must be perpendicular to its motion of travel

State the equation used to calculate the circular radius of an electron beam deflected in a magnetic field

Radius = mv/BQ

What two equations must be used if you want to derive Radius = mv/BQ (the radius equation)

• Centripetal force = mv^2 / r

• Magnetic field = BQv

Derive Radius = mv/BQ (the radius equation)

Centripetal force = Magnetic field
mv^2 / r = BQv
Rearange:
mv^2/BQv = r
Cancel v:
mv/BQ = r

Why do we use r = mv/BQ

To find the radius of curvature of tracks

Why do we find the radius of curvature of tracks

This allows us to find out certain characteristics of particles that are being observed

How can you simply r = mv/BQ further by using the fact that p =mv

r = mv/BQ
So p =mv hence substitute it in:
r = p/BQ

What are the three properties that must always be conserved during particle interactions

• Charge

• Energy

• Momentum

What are ways we can view charged particles

By using a particle track

What are two kinds of particle tracks

• Bubble chamber

• Cloud chamber

What is a bubble chamber

A tank filled with superheated liquid hydrogen.
Forms bubbles around ionized particles from the movement of charged particles.

How does a bubble chamber work

By observing the path created by visible bubbles, you can see the path taken by moving, charged particles.
The tank is placed in a magnetic field, causing charged particles to take circular paths.

What is a cloud chamber

A cloud chamber is a device used to visualise ionising radiation. It contains supersaturated alcohol vapor that forms visible tracks when charged particles pass through and ionize the vapor. These trails reveal the paths of subatomic particles.

How does a cloud chamber work

Alcohol vapour supersaturated into chamber and cooled
Particle interacts with alcohol vapour
This results in "clouds" being seen

What must you always do when investigating an object

Must use waves with wavelengths similar in size

How to find wavelengths

Use de Broglie relation (λ = h/p)

de Broglie relation

λ = h / p

λ is Broglie wavelength
h is planks constant
p is the momentum of a particle

What can we see by using de Broglie relation

The smaller the de Broglie wavelength needed, the higher energy (/momentum) of the particle is required

State the mass-energy equation

E = mc^2
m = mass
c = speed of light

What is matter

Anything that has mass and takes up space

What is antimatter

Has exactly the same mass as the normal particle
Has opposite charges (if the normal particle is charged)

What happens when antimatter and matter meet

Annihilation

What is pair production

Where a photon is converted into an equal amount of matter a and antimatter

What is Annihilation

When a particle and its corresponding antiparticle collide.
This results in their masses being converted into energy. This releases two photons into opposite directions

Why must the mass be converted into energy during annihilation

This is to conserve momentum

What happens to a photon in Particle production

photon -> electron + positron

How is a photon created in Particle annihilation

electron + positron -> photon(s)

What does eV stand

electron Volt

What is eV

1 eV, is the kinetic energy of an electron accelerated across a potential difference of 1V

What is 1 eV into joules

1 eV = 1.6 * 10^-19 J

What does MeV stand for

Mega electron Volts

What does GeV stand for

Giga electron Volts

In a quark-lepton model, what are the four main categories of a particle

• Baryons

• Mesons

• Leptons

• Photons

What is the quark composition of a baryon

Baryons are made up of three quarks

What is the quark composition of a meson

Mesons are made up of a quark and a antiquark pair

Which category of particles are classed as fundamental particles

Leptons

Give two examples of leptons

• Electrons

• Neutrinos

What category do pions belong to

Mesons

Give two examples of baryons

• Protons

• Neutrons

What did the symmetry of the quark-lepton model predict the existence off

The top quark

What is a antiparticle

An antiparticle is one that has the same mass but opposite charge and conservation numbers to its corresponding particle

What is the antiparticle of a proton

An antiproton

What is the antiparticle of a electron

A positron

Name four things that are always conserved in a particle interaction

• Mass/Energy

• Baryon number

• Lepton

• Charge

Describe the conservation of lepton number

The lepton number for each specific type of lepton must be the same before and after the interaction