08 - Nuclear And Particle Physics

Question 1

What is nucleon number?

Answer 1

The sum of the number of protons and neutrons in the nucleus.

Question 2

What is atomic number?

Answer 2

The total number of protons in the nucleus.

Question 3

Outline Rutherford’s alpha scattering experiment.

Answer 3

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

Question 4

What was observed in the Alpha scattering experiment?

Answer 4

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

Question 5

What is thermionic emission?

Answer 5

Thermionic emission is the release of electrons due to heating.

Question 6

Explain why electrons are released from a heated filament.

Answer 6

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.

Question 7

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

Answer 7

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

Question 8

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

Answer 8

Energy = Charge x Potential Difference
Energy = eV

Question 9

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

Answer 9

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

Question 10

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

Answer 10

Force = Magnetic Flux Density × Charge
× Velocity
F = Bev

Question 11

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

Answer 11

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

Question 12

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

Answer 12

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

Question 13

What is a cyclotron?

Answer 13

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 limitation of the accelerator’s length.

Question 14

Describe the basic composition of a cyclotron.

Answer 14

Cyclotrons consist of two D-shaped paths which are separated by a small gap. An alternating potential difference is applied across the gap.

Question 15

How does a cyclotron work?

Answer 15

An electron beam is passed into the cyclotron, where it is deflected into a circular path by a perpendicular magnetic field. When the beam reaches the gap, it is 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.

Question 16

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

Answer 16

Radius =mV / BQ

Question 17

What two equations must you combine to derive the radius equation?

Answer 17

1. Centripetal Force = mv^2/r
2. Magnetic Force = BQv
   Centripetal Force = Magnetic Force

Question 18

State the mass-energy equation.

Answer 18

E = mc^2

Question 19

What is 1 MeV in joules?

Answer 19

(1.6×10^-19) × 10^6 = 1.6 x10^-13 J

Question 20

In the quark-lepton model, what are the four main categories of particles?

Answer 20

1. Baryons
2. Mesons
3. Leptons
4. Photons

Question 21

Describe the quark composition of a baryon.

Answer 21

Baryons are made up of three quarks.

Question 22

Describe the quark composition of a meson.

Answer 22

Mesons are made up of a quark and antiquark pair.

Question 23

Which category of particles are classed as fundamental particles?

Answer 23

Leptons

Question 24

Give two examples of leptons.

Answer 24

1. Electrons
2. Neutrinos

Question 25

What category of particles do pions belong in?

Answer 25

Mesons.

Question 26

Give two examples of baryons.

Answer 26

1. Protons
2. Neutrons

Question 27

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

Answer 27

The top quark.

Question 28

What is an antiparticle?

Answer 28

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

Question 29

What is the antiparticle of a proton?

Answer 29

An antiproton.

Question 30

What is the antiparticle of an electron?

Answer 30

A positron.

Question 31

Name four things that are always conserved in a particle interaction.

Answer 31

1. Mass/Energy
2. Baryon Number
3. Lepton Number
4. Charge

Question 32

Describe the conservation of lepton number.

Answer 32

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

Question 33

what was concluded from Rutherford’s gold foil experiment

Answer 33

atom is mostly empty space
mass is concentrated in a very small dense nucleus (concluded as most went through)
could tell nucleus was positive as some reflected

Question 34

why does a cathode ray tube have to be in a vaccum

Answer 34

as otherwise te electrons would lose eneergy and ionise atoms in the air and the electron beam would not be produced

Question 35

what is relativistic mass

Answer 35

as velocity increases mass increases at a certain point

Question 36

explain how a cyclotron produces a high energy proton beam

Answer 36

• alternating p.d/electric field
• the electric field between the 2 dees causes the acceleration of the protons across the gap (between the 2 dees). alays accelerating across the gap as charge of 2 dees keeps flipping
• magnetic field is perpendicular to pare of dees
• proton path is curved by the magnetic field
• as velocity of proton increases, radius of path in dees increases
• therefore the time for which a proton is in a dee remains constant

Question 37

how does a bubble chamber detector work?

Answer 37

As particles enter the chamber, a piston suddenly decreases its pressure, and the liquid enters into a superheated(maintained just below boiling). as the particle passes through the liquid it ionises particles in the liquid knocking of electrons leaving an ionised track, around which the liquid vaporizes, forming microscopic bubbles as these th electrons dissipate energy into the surrounding liquid causing localised boiling. Bubble density around a track is proportional to a particle’s energy loss.

Question 38

how does a geiger muller tube work

Answer 38

wall of tube is a cathode as is a conducting material
anode carrying wire
radial electric field between the wall and the wire
gas is ionised by radiation causing an electron to be repelled by the cathode
leaving charged particles which gain energy so they ionise other gas atoms causing an ionising avalanche

Question 39

describe the set up of a Linear particle accelerator (LINAC)

Answer 39

set of metal drift tubes in a line
electrons accelerated by electrc field between drift tubes
acceleration between gaps
adjacent tubes connected to opposite terminals of a power supply and opposite charge
charge of particle is opposite to the first drift tube charge
p.d / electric field is alternating so that the next tube is of opposite charge to particle so its accelerated
time spent in each tube must be the same so as the electron accelerates, tubes must be longer

Question 40

explain how a cloud chamber works

Answer 40

It consists of a sealed container filled with a supersaturated vapour, typically a mixture of alcohol and water. When a charged particle passes through the vapour, it ionizes the molecules along its path, causing them to release electrons.. the ionised gas particles align surrounding alcoholk particles, condensing them into doplets
the greater the charge, the thicker the trial.

Question 41

what is a quark

Answer 41

an elementary particle and a fundamental particle consistent of matter. quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons