2.1 Particles

Question 1

What are the main constituents of an atom?

Answer 1

● Proton
● Neutron
● Electron

Question 2

What is meant by specific charge?

Answer 2

The charge to mass ratio:
Specific charge = charge / mass
Units C/kg.

Question 3

What is the specific charge of a proton?

Answer 3

= 9.58 x 10^7 C/kg

Question 4

What is the letter associated with a
proton number?

Answer 4

Z.

Question 5

What is a nucleon?

Answer 5

A constituent of the nucleus: a proton or a neutron.

Question 6

What letter represents nucleon number?

Answer 6

A.

Question 7

What is an isotope?

Answer 7

A version of an element with the same number of protons but a
different number
of neutrons.

Question 8

State a use of radioactive isotopes.

Answer 8

Carbon dating - the proportion of carbon-14 in a
material can be used to estimate its age

Question 9

What is the strong nuclear force?

Answer 9

The fundamental force that keeps the nucleus stable
by counteracting the electrostatic force of repulsion between protons

Question 10

Describe the range of the strong force?

Answer 10

● Repulsive up to 0.5fm
● Attractive from 0.5-3fm
● Negligible past 3fm

Question 11

What makes a nucleus unstable?

Answer 11

Nuclei which have too many of either protons or
neutrons or both.

Question 12

How do nuclei with too many nucleons decay?

Answer 12

Alpha decay (emission of a helium nucleus formed of 2 protons and 2 neutrons)

Question 13

How do nuclei with too many neutrons decay?

Answer 13

Beta minus decay in which a neutron decays to a
proton by the weak interaction (quark character has
changed from udd to uud).

Question 14

How was the existence of the neutrino hypothesised?

Answer 14

The energy of particles after beta decay was lower than before, a particle with 0 charge (to conserve charge) and negligible mass must carry away this excess energy, this particle is the neutrino.

Question 15

What is meant by beta minus decay?

Answer 15

When a neutron turns into a proton, the atom releases an electron and an anti-electron neutrino.

Question 16

What is an alpha particle?

Answer 16

A particle contains two protons and two neutrons, the same as a helium nucleus.

Question 17

What is an antiparticle?

Answer 17

For each particle there is an antiparticle with the
same rest energy and mass but all other properties
are the opposite of its respective particle

Question 18

True or false:
‘Every particle has a antiparticle’

Answer 18

True.

Question 19

What is the name of the antiparticle of an electron?

Answer 19

Positron.

Question 20

What is the antiparticle of π0 (pion with 0 charge) ?

Answer 20

π0, its antiparticle is itself.

Question 21

What occurs when a particle and
antiparticle meet?

Answer 21

Annihilation

Question 22

what is annihilation

Answer 22

The mass of the particle and antiparticle is converted back to
energy in the form of 2 gamma ray photons which go in
opposite directions to conserve momentum.

Question 23

What is pair production?

Answer 23

A gamma ray photon is converted into a particle-antiparticle pair

Question 24

What is the minimum energy of a photon required to make a proton-antiproton pair?

Answer 24

2 x proton rest energy
2 x 938.257 = 1876.514 MeV

Question 25

Name the 4 fundamental forces?

Answer 25

● Gravity
● Electromagnetic
● Weak nuclear
● Strong nuclear

Question 26

The virtual photon is the exchange
particle of which force?

Answer 26

The electromagnetic force

Question 27

What type of particles are affected by the strong nuclear force?

Answer 27

Hadrons.

Question 28

What is the exchange particle of the
weak nuclear force?

Answer 28

The W boson (W+ or W-).

Question 29

What does the electromagnetic force act on?

Answer 29

It acts on charged objects,

Question 30

When does weak nuclear interaction occur?

Answer 30

When quark character changes (a quark changes into another quark), it affects all types of particles.

Question 31

Which properties must be conserved in particle interactions?

Answer 31

● Energy
● Charge
● Baryon number
● Lepton number
● Momentum
● Strangeness (only for strong interactions)

Question 32

What is a hadron?

Answer 32

Both baryons and mesons are hadrons, hadrons are made of 2 or more quarks held together by the strong nuclear force.

Question 33

What are the classes of hadrons?

Answer 33

● Baryons (three quarks)
● Mesons (1 quark, 1 antiquark)

Question 34

The pion and kaon are both examples of
which class of particle?

Answer 34

Mesons.

Question 35

The pion can be an exchange particle for
which force?

Answer 35

The strong nuclear force.

Question 36

What particle does a kaon decay into?

Answer 36

A kaon decays into a pion

Question 37

Give some examples of baryons?

Answer 37

● Proton - uud
● Neutron - ddu

Question 38

What is significant about a proton?

Answer 38

● It is the only stable baryon
● All baryons will eventually decay into protons

Question 39

What are some example of leptons?

Answer 39

● Electron
● Muon
● Neutrino
● (the antiparticles of the above)

Question 40

What does a muon decay into?

Answer 40

An electron and two types of neutrino.

Question 41

What is the strangeness value of a
strange quark?

Answer 41

-1

Question 42

True or false:
‘Strangeness is always conserved in a weak interaction’

Answer 42

False.
Strangeness is only conserved in the strong
interaction, in weak interactions it can change by
0, -1 and +1.

Question 43

Complete the sentence:
Strange particles are produced through the
_____________ and decay through the ___________

Answer 43

Strange particles as particles that are produced through the
strong interaction and decay through the weak interaction.