Chapter 1 - Matter and Radiation

Question 1

State the quark composition of a meson.

Answer 1

a quark and an antiquark.

Question 2

Name two mesons

Answer 2

The pion and the kaon for example.

Question 3

Name the quarks making up a proton

Answer 3

Two up quarks and a down quark.

Question 4

What’s the baryon number of a down quark?

Answer 4

A third - all quarks have a baryon number of 1/3.

Question 5

A baryon is made of two strange quarks and an up quark. Give the charge and strange number of this baryon.

Answer 5

Charge = zero ( two -1/3 and a 2/3)
Strangeness = -2.

Question 6

What’s the difference between a hadron and a lepton?

Answer 6

A hardon is made of quarks, a non-fundamental particle. Leptons are fundamental particles.
Hardons experience the strong nuclear force. Leptons don’t.

Question 7

Give similarities and differences between a muon and an electron.

Answer 7

Same charge - minus one, same lepton number, 1. Both experience three forces, weak force, electromagnetic force and gravity.
Different mass or rest energy - muons are heavy electrons.

Question 8

Name 2 Baryons.

Answer 8

Proton and neutron for example.

Question 9

State the baryon number of the K minus meson.

Answer 9

Zero - it is not a baryon, but is a hadron.

Question 10

What is the quark composition of the K minus meson?

Answer 10

An anti up, charge -2/3 and a strange, charge -1/3.

Remember that kaons have strangeness.

Question 11

Describe the interaction responsible for the decay of a strange quark to an up quark.

Answer 11

The weak interaction ( a W- Boson is formed which is the exchange particle for this interaction). Strange quark has -1/3 charge and an up quark has 2/3 charge.

Question 12

Other than energy and momentum, state two quantities that are conserved when a W minus particle is produced due to a strange quark decaying to an up quark and one quantity that is not.

Answer 12

Conserved : charge and lepton number.

Not conserved : strangeness ( this does not have to be in weak interactions, only in strong)

Question 13

What is meant by nucleon number?

Answer 13

The number of protons and neutrons in a nucleus.

Question 14

State the units for specific charge.

Answer 14

C Kg-1

Question 15

How do you calculate the specific charge of a carbon nucleus with a mass number of 12 and an atomic number of 6?

Answer 15

Specific charge = charge / mass
Charge = 6 X 1.6 X 10-19
Mass = 12 X 1.67 X 10-27
Divide these two values. The answer is large!

Question 16

What is meant by the term isotope?

Answer 16

An atom with the same proton number as another but a different mass number (number of neutrons)

Question 17

Protons and neutrons can interact through three fundamental interactions. Name them and give the exchange particles responsible for 2 or these 3 interactions.

Answer 17

Gravity or gravitational force
Electromagnetic force - photon
Weak force - bosons ( W plus, minus or Z zero)

Question 18

What is meant by electron capture?

Answer 18

A shell electron interacts with a proton in a nucleus and a neutron is formed OR an u quark changes to a d quark.

Question 19

State the quark structure of an antineutron.

Answer 19

Anti u anti d anti d

Question 20

Give one property of an antiparticle that is the same as a particle and one difference.

Answer 20

Same : mass

Different : charge and baryon/lepton number.

Question 21

What is specific charge?

Answer 21

Ratio of charge to mass of the nucleus.

Question 22

What is the specific charge of an atom?

Answer 22

Zero, as it has the same number of protons as electrons.

Question 23

Describe the process of pair production.

Answer 23

A photon interacts with an electron/nucleus/atom
Energy of the photon is used to create a particle and anti particle
Momentum is conserved as photon interacts with the electron/nucleus/atom.

Question 24

Describe what occurs to a nucleus as a result of alpha decay.

Answer 24

The nucleus emits 2 protons and 2 neutrons. The mass lost is 4 units and 2 units of charge.

Question 25

Why is an alpha particle unaffected by the strong force once outside the nucleus?

Answer 25

The strong force only acts over very short distances, up to 3 femto metres. It has a very short range. Beyond this there is no interaction.

Question 26

Which sub atomic particle has the largest specific charge?

Answer 26

The electron, same charge as a proton but a much smaller mass.

Question 27

Describe the changes that occur to a nucleus during beta minus decay.

Answer 27

A neutron changes to a proton and a W- Boson is formed. This decays into an electron and an electron antineutrino. The nucleus does not change in mass number, but the atomic number increases by one.

Question 28

What is the quark structure of the K + kaon, which has a strangeness of +1?

Answer 28

An anti strange quark and an up quark.

Question 29

A K+ kaon with a strangeness of 1 can decay into a muon neutrino and an anti muon. Other than charge, energy and momentum, show another quantity that is conserved and one quantity that is not conserved.

Answer 29

Lepton number zero on left hand side and 1 -1 = zero on right hand side. Strangeness not conserved +1 on left hand side, zero on the right. Must be decaying through the weak interaction.

Question 30

A K+ particle can decay to form a positive pion and one other particle. Suggest which particle this is based on the laws of conservation.

Answer 30

Charge must balance and so it must be a neutral particle. Lepton number must be conserved and so it can't be a lepton such as a neutrino. It must be a neutral meson, e.g. A pion-zero.

Question 31

Two nuclei, one with 7 protons and 14 nucleons and the other with 9 protons and 19 nucleons. Which nucleus has the smallest specific charge?

Answer 31

The one with a nucleon number of 19 as this has a smaller proton to mass number ratio 9/19 as a fraction is less than 7/14.

Question 32

Describe how the strong nuclear force between a neutron and a proton varies with the separation of the two particles.

Answer 32

Between 3fm and 0.5 fm, the particles attract each other through the strong interaction. Above 3fm there is no force between particles at all. Below 0.5fm the force becomes repulsive, increasingly so as the separation becomes smaller.

Question 33

Other than the strong force, give another interaction between two protons in a nucleus and name the exchange particle responsible for this interaction.

Answer 33

Electromagnetic | (virtual) Photon

Question 34

Name a constituent of an atom which, when removed leaves a different isotope of that atom.

Answer 34

The neutron

Question 35

It is possible for a photon to be converted into an electron and a positron. What is this process called and why can't a single particle be produced?

Answer 35

Pair production | Both particles must be produced so that charge and momentum are conserved.

Question 36

If a photon has more energy than needed to create an electron and positron pair what happens to this excess energy?

Answer 36

This goes into the kinetic energy of the positron and electron.

Question 37

What is likely to happen to a positron that has been created through pair production?

Answer 37

It will collide with an electron and the two particles will annihilate to form 2 photons.

Question 38

There are two groups of hadrons. Name them.

Answer 38

Baryons and mesons

Question 39

Give two properties that distinguish hadrons from leptons.

Answer 39

Hadrons are non- fundamental particles, made of quarks. Leptons are fundamental particles. Hadrons experience the strong interaction, leptons don't. Hadrons eventually decay to a proton.

Question 40

State the charge in coulombs of a magnesium atom after losing 2 electrons.

Answer 40

The ion will have a 2+ charge and so has 2 more protons than electrons. Charge in coulombs = 2 X 1.6 x 10-19.

Question 41

A magnesium ion with 12 protons and 24 nucleons loses 2 electrons. Calculate the specific on the ion formed.

Answer 41

Specific charge = charge / mass Charge = 2x 1.6 X 10-19 Mass = 24 X 1.66 X 10-27 + 10 X 9.11 X 10-31 Specific charge = 8.03 X 10+6 C Kg-1

Question 42

Give two differences between the exchange particles boson and a photon.

Answer 42

Boson W- or W+ are charged, photon is not. Bosons have a rest mass, photons do not. Photon has an infinite range, bosons do not.