NUCLEAR AND PARTICLE PHYSICS

Question 1

Nucleon number (Mass number)

Answer 1

Total number or protons and neutrons in an atom or nucleus.

Question 2

Thermionic emission

Answer 2

When a metal is heated, electrons can gain enough energy to be released from the surface of a metal.

Question 3

Rest mass energy

Answer 3

E= mc2 is the energy associated with an object’s mass. ‘Rest mass’ means the mass of the object when it is not travelling at relativistic speeds. At relativistic speeds, the mass of the particle increases, as does its particle lifetime.

Question 4

Geiger Marsden experiment:

Answer 4

1. Most of the alpha particles were undeflected–> the atom is mostly empty space – most alpha particles did not get near enough to matter to be deflected.
2. A few alpha particles were deflected by small angles –> the charge is concentrated in the centre of the atom – most alpha particles did not get near enough to a sufficiently large charge to be affected.
3. A very small proportion of alpha particles were deflected through more than 90 degrees –> The nucleus must contain a high mass in order to cause this deflection because the mass of the atom is concentrated in a very small space relative to the size of the atom.

Question 5

Standard model

Answer 5

1. All matter is made of two types of fundamental particles – quarks and leptons.
2. Hadrons are particles made from quarks. These consist of baryons (3 quarks – eg. protons and neutrons ) and mesons (quark and antiquark – eg pions).
3. Leptons are electrons, muons, taons and neutrinos. There are six quarks. Every particle has a corresponding antiparticle that has opposite charge, baryon number, lepton number and the same mass.
4. The symmetry of the model predicted the top quark.

Question 6

What happens to momentum in particle interactions?

Answer 6

In particle interactions, baryon number, lepton number, charge, mass-energy and momentum are all conserved.

Question 7

Compare the properties of antiparticles to particles

Answer 7

1. Same mass as the original particle.
2. Opposite charge to the original particle.
3. Opposite value of the baryon/lepton number and strangeness.

Question 8

Name the antiparticle to the electron and write its symbol

Answer 8

The positron can be written as e^+ or e line on top or a beta plus particle.

Question 9

Name the antiparticles to the proton and electron neutrino.

Answer 9

The antiparticle to the proton is the anti-proton. The antiparticle to the electron neutrino is the antielectron neutrino.

Question 10

Describe what is meant by annihilation and explain why photons are produced when particle annihilate

Answer 10

Annihilation is when a particle meets an antiparticle and produces two photons. Two photons are formed as energy and momentum have to be conserved.

Question 11

Define ‘rest mass’

Answer 11

The mass of a subatomic particle when it is stationary ‘at rest’.

Question 12

Define ‘rest energy’

Answer 12

E=mc^2 where:
E= is the energy
m= the rest mass
c^2= speed of light squared

Question 13

List all six examples of leptons and what is special about antiparticles, stating the charge.

Answer 13

1. Electron (-1)
2. Muon (-1)
3. Tau (-1)
4. Tau neutrino (0)
5. Muon neutrino (0)
6. Electron neutrino (0)

They all have their own antiparticles

Question 14

State the lepton number of all leptons

Answer 14

1

Question 15

State the lepton number of all anti-leptons

Answer 15

-1

Question 16

Name the two types of hadrons

Answer 16

Baryons and mesons

Question 17

Explain why baryons are not classed as fundamental particles

Answer 17

Fundamental particles are not composed of other particles baryons however are.

Question 18

Name the only stable baryon

Answer 18

Proton

Question 19

Explain what happens to the neutron when it is outside the nucleus and write an equation for this process, naming each symbol you write

Answer 19

Outside of the nucleus, a neutron has a half-life af about 13 minutes and decays to produce a proton, an electron and an electron neutrino.

Question 20

Name five mesons and write their charge and their antiparticles

Answer 20

1. pion + = +1
2. pion 0 = 0
3. kaon + = +1
4. kaon 0 = 0
5. eta = 0

For antiparticles see sheet

Question 21

State what all hadrons are made from

Answer 21

All hadrons are made from quarks

Question 22

State the number of quarks that baryons are made from

Answer 22

3 quarks

Question 23

Describe what mesons are made from

Answer 23

A quark and anti-quark

Question 24

What does it mean to say ‘quarks have not been observed in isolation’?

Answer 24

They have always been found within hadrons.

Question 25

State the baryon number of a quark and antiquark

Answer 25

1. quark: 1/3

2. anti-quark: -1/3

Question 26

State the lepton number of a quark

Answer 26

zero

Question 27

Explain why the baryon number of a baryon is 1

Answer 27

There is one baryon in a baryon so the number is 1.

Question 28

Explain why the baryon number of a meson is 0

Answer 28

Baryons don’t consist of mesons so the baryon number is zero.

Question 29

Explain the lepton number of a baryon. List the names of all 6 quarks

Answer 29

1. up
2. down
3. strange
4. charm
5. top
6. bottom

The lepton number of a baryon is zero as no lepton consists of baryons

Question 30

Draw the summary of particle classification on paper

Answer 30

See particle physics notes

Question 31

Draw the symbols for quarks and their antiquarks

Answer 31

See particle physics notes

Question 32

Draw the symbols for mesons and their antiparticles

Answer 32

See particle physics notes

Question 33

Draw the symbols for leptons and their antiparticles

Answer 33

See particle physics notes

Question 34

Define binding energy

Answer 34

1. The energy released when a nucleus is formed from its constituent nucleons.
2. The energy required to split a nucleus into its constituent nucleons.

Question 35

Explain why energy is required to split a nucleus up into its separate protons and neutrons

Answer 35

The protons and neutrons are held together by the strong nuclear force so it would require energy to split them.

Question 36

Define binding energy per nucleon

Answer 36

The total binding energy/total number of nucleons

Question 37

Explain why a high binding energy per nucleon would indicate a high degree of stability

Answer 37

A high binding energy means a lot of energy is required to break the nuclei apart.

Question 38

Explain why energy is always given out in radioactive decay

Answer 38

The nucleus decays to form a more stable nucleus so energy is always given out.

Question 39

Define mass defect

Answer 39

The mass defect of a nucleus is the difference between the mass of the nucleus and the mass of its nucleons.

Question 40

State the equation for mass defect

Answer 40

Mass of nucleus- Mass of particles

Question 41

Explain what is meant by a ‘chain reaction’

Answer 41

The neutrons produced from nuclear fission collide with other atoms causing them to also undergo fission hence the chain.

Question 42

List the environmental hazards of nuclear reactors

Answer 42

1. Radiocatve dust or gases can escape and be absorbed by humans/ animals via food, air, water.
2. If the chain reaction is not controlled the reactor may act as a bomb.

Question 43

List the environmental benefits of nuclear fission

Answer 43

1. No gaseous products produced.

Question 44

Describe the process of nuclear fusion

Answer 44

Two light nuclei combine to form one heavy nucleus and energy and neutrons are also produced.

Question 45

List the potential benefits of nuclear fusion

Answer 45

1. The raw materials can be obtained from seawater.
2. Waste products are not radioactive.
3. Uncontrolled chain reaction cannot develop.

Question 46

What is radioactivity?

Answer 46

The spontaneous mission of an alpha or beta particle from the nucleus of an atom.

Question 47

List the constituents, range and ionising properties of beta radiation

Answer 47

Constituents: Fast electrons

Range: up to a few meters in air ( can be stopped by a few mm of aluminum)

Ionising properties: less than alpha

Question 48

List the constituents, range and ionising properties of alpha radiation

Answer 48

Constituents: helium nuclei ( 2 protons and 2 neutrons)

Range: 5cm in air ( cane be stopped by a thick sheet of paper)

Ionising properties: highly ionising

Question 49

List the constituents, range and ionising properties of gamma radiation

Answer 49

Constituents: very high frequency/energy electromagnetic waves

Range: significantly reduced by several cm of lead or meters of concrete.

Ionising properties: very weak - much less than beta

Question 50

Define the term nucleon

Answer 50

proton or neutron

Question 51

Which part of the nucleus is involved in radioactivity?

Answer 51

unknown

Question 52

Define the term isotope

Answer 52

Isotopes of an element have the same proton number but different nucleon numbers.

Question 53

State what is meant by the nucleon number

Answer 53

The mass number ( number of protons and neutrons)

Question 54

State what is meant by the atomic number

Answer 54

The proton number - it tells you the number of protons.

Question 55

List four sources of background radiation

Answer 55

1. rocks (e.g granite)
2. radon gas ( formed from the ground)
3. cosmic rays which come from space
4. artificially produced radioisotopes

Question 56

Describe the effect of alpha decay on the nucleus.

Answer 56

1. Alpha decay removes 2 protons and 2 neutrons from the nucleus.
2. So Z, the proton number, decreases by 2, 3. A the nucleon number decreases by 4.

Question 57

Describe the effect of beta decay on the nucleus

Answer 57

1. In beta decay, a neutron in the nucleus emits an electron and changes to a proton.
2. So Z increases by 1 and A stays the same

Question 58

Describe the rules for the A and Z values.

Answer 58

A – the nucleon number (or mass number)

Z – the proton number (or atomic number)

Question 59

Describe what is meant by a ‘radioactive decay series

Answer 59

in some cases, the atom produced is also radioactive so that will decay too until an atom that is not radioactive and doesn’t decay is produced.

Question 60

Describe what is meant by the phrase ‘radioactive decay is a random process

Answer 60

You cannot predict whether an atom will decay or not

Question 61

Define activity and state its unit

Answer 61

The number of decays per second of a sample is called its activity, and is measured in bequerels

Question 62

Describe the effect of gamma radiation on the A and Z number

Answer 62

Gamma radiation only involves the emission of energy, and so does not change either A or Z.

Question 63

Explain what is meant by the equation ‘A = lambda N’

Answer 63

The number of atoms decaying over a given period is proportional to the number remaining.

Where:

1. A = activity,
2. lambda = decay constant ( the probability of any given atom of that element decaying in one second)
3. N = no. of undecayed atoms

Question 64

State the key features of the exponential decay curve for activity

Answer 64

1. Activity never decreases to zero
2. There is a constant half life – for a given radioactive element, the time taken for the activity to halve will always be the same.
3. The half-life in seconds is given by T½ = 0.69/lambda Where: lambda is the decay constant.

Question 65

List the safety precautions when handling radioactive sources

Answer 65

1. Always lift with forceps
2. Hold so that the open end is directed away from the body
3. Never bring close to the eyes

Question 66

Define ‘corrected count rate’ and describe how it should be determined

Answer 66

1. The corrected count rate is the count rate due to the source alone.
2. It is determined by measuring and taking an average of the background radiation and subtracting it from all the readings to get the count rate from the source alone.

Question 67

Describe the relationship between the intensity of gamma radiation and the distance from the source

Answer 67

Their intensity is inversely proportional to the square of the distance from the source .

I = K/d^2 where k is a constant.

Question 68

Explain how radioactivity can be used to determine the age of wooden objects from antiquity. Describe an assumption made in the method.

Answer 68

By measuring the residual activity, it is possible
to estimate how many half-lives there have been since the plant died,
and how long ago it lived.

The assumption is that the proportion of carbon-14 in the atmosphere has stayed the same.

Question 69

Describe what is meant by a radioactive tracer and why a gamma source would not be a suitable choice as a tracer.

Answer 69

Radioactive tracers are used to follow the path of a compound in a system e.g ( human body or pipelines).

For example, a radioactive tracer can
be used to detect a leak in a pipe, since the count-rate will increase
where the leak occurs as the pipe will block alpha and beta emissions.
A gamma emitter would not be suitable, since the pipe would not block this.

Question 70

Explain how radioactive sources can be used in cancer treatment

Answer 70

Radiotherapy uses gamma sources to attack cancer cells as cancer cells are more affected by radiation than normal ones. Normal cells however are affected too.