Nuclear and Particle

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 aomts
• Some of them were deflected slightly (less than 90)
• A few of them were deflected backwards (greater than 90)

Question 5

What is thermionic emission?

Answer 5

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 happens 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

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 electgron in a magnetic field?

Answer 10

Force = Magnetic Flux Density x Charge x Velocity
F = Bqv

Question 11

If 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. Thisi 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

Cyclotron consists 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 cycltron 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 acclereated by a potential difference. This increases the speed of the beam, causing the radius of the path to increase. This process repeats every half cycle

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 = 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 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

State the composition of a baryon.

Answer 21

Baryons are made up of three quarks

Question 22

Describe the composition of a meson.

Answer 22

Mesons are made of a quark-antiquark pair

Question 23

Which categories of particles are classed as fundamental particles?

Answer 23

Leptons

Question 24

Give two examples of leptons.

Answer 24

Electron, Neutrinos, Muon

Question 25

What category of particles do pions belong in?

Answer 25

Mesons

Question 26

Give two examples of baryons.

Answer 26

Protons, 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. Baryon Number
2. Lepton Number
3. Charge
4. Mass / Energy

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

Describe how Chadwick found the existence of neutrons.

Answer 33

He fired alpha particles at Li atoms and noticed radiation was released but was not charged. He put a sheet of parafin in front and protons shoot out so the ‘thing’ needed to be heavy enough to cause protons to move, came up with the neutron

He used the conservation of momentum and energy to say they are uncharged and approximately the same mass of a proton

Question 34

What are the conclusions based on particles scattering?
- 0-10
- 10 -90
- 90+

Answer 34

• 0-10. Most particles pass straight through with little deviation, therefore most of the atom is empty space
• 10-90 Some particles deflected a large angle tells us there is a concentration of charge in one place
  -90+ few particles repelled back, so most of the mass and large concentration of charge in a tiny. central nucleus

Question 35

What was the model of the atom before the nuclear model?

Answer 35

The plum pudding model; a ball of a positive body with electrons scattered throughout

Question 36

As you progress through the periodic table, more neutrons are required for the atom to be stable, why?

Answer 36

More neutrons are generally needed to help bind the nucleus together as they exert a strong nuclear force on other electrons. They also act as a space buffer between mutually repelling protons. So as you go through the periodic table, atoms have more protons so more neutrons are required to buffer them

Question 37

What is the electronvolt?

Answer 37

The kinetic energy carried by an electron after it has been accelerated through a pd of 1v
1eV = 1.6 x10^-19 J

Question 38

What is a cathode ray?

Answer 38

A beam of electrons - you can use thermionic emission to produce electrons, apply an electric field to accelerate them to produce a fast-moving beam of electrons (cathode ray

Question 39

Give the de broglie wavelength equation?

Answer 39

lambda = h/mv
de broglie wavelength = planck’s constant / wavelength

Question 40

Why do the tubes in a linear acclerator have to get longer?

Answer 40

As particles leave one tube into the next, their speed increases, in order to keep accelerating the particles, the tubes need to be made longer so the particle spends the same time in each one

Question 41

How does a LINAC work?

Answer 41

It is a long, straight tube containing a series of electrodes. The charge on each electrode alternates along the tubes which allows the electron to move in a straight line as the electrodes are connected to opposite ends of an alternating pd so the electrodes are always switching firection allowing particles to accelerate

Question 42

What is found to happen as particles are accelerated close to the speed of light?

Answer 42

As particles were accelerated to what should have pushed them beyond the speed of light, their Ke and momentum continued to increase but their speed did not therefore the mass of the particle must increase

Question 43

How can you calculate the frequency of polarity switches in a cyclotron?

Answer 43

T = 2πr/v and r =mv/BQ
f= 1/T therefore
f= BQ/2πm