11 Nuclear Radiation

Question 1

What two processes can cause electrons to change energy levels?

Answer 1

Excitation and lonisation

Question 2

What are the four scenarios in which an atom may become unstable?

Answer 2

1. The atom having too many neutrons.
2. The atom having too few neutrons.
3. The atom having too much mass.
4. The atom having too much energy.

Question 3

How do unstable nuclei become more stable?

Answer 3

Unstable nuclei are radioactive, so emit radiation in order to become more stable.
The type of radiation they emit depends on what makes them unstable.

Question 4

What are the constituents of an alpha particle?

Answer 4

Two protons and two neutrons.

Question 5

What are penetration capabilities of alpha radiation?

Answer 5

Alpha particles are weakly penetrating and so are stopped by a few centimetres of air or a sheet of paper.

Question 6

What does beta-minus radiation consist of?

Answer 6

High-energy electrons

Question 7

What does beta-plus radiation consist of?

Answer 7

High-energy positrons

Question 8

What are the penetration capabilities of beta-minus radiation?

Answer 8

Beta-minus radiation has medium penetrative capabilities and is stopped by a few mm of aluminium or around 1 m
of air.

Question 9

What are the penetration capabilities of beta-plus radiation?

Answer 9

Beta-plus radiation is almost instantaneously annihilated by electrons and so has virtually zero range.

Question 10

What is gamma radiation?

Answer 10

Gamma radiation is a form of high-energy electromagnetic radiation.

Question 11

What charge do gamma rays have?

Answer 11

Gamma rays are a form of
electromagnetic radiation and so don’t have a charge.

Question 12

Which type of radiation is most ionising?

Answer 12

Alpha radiation.

Question 13

Which type of radiation is most weakly ionising?

Answer 13

Gamma

Question 14

Why type of radiation travels the fastest and at what speed?

Answer 14

Gamma radiation travels the fastest since it is a type of electromagnetic radiation and so travels at the speed of light.

Question 15

Under what circumstance is alpha radiation emitted?

Answer 15

When a nucleus has too much mass.

Question 16

Under what circumstance is beta minus radiation emitted?

Answer 16

Beta-minus radiation is emitted when a nucleus has too many neutrons.

Question 17

Under what circumstance is beta plus radiation emitted?

Answer 17

Beta-plus radiation is emitted when a nucleus has too many protons.

Question 18

Under what circumstance is gamma radiation emitted?

Answer 18

Gamma radiation is emitted when a nucleus has too much energy.

Question 19

What are the penetrative capabilities of gamma radiation?

Answer 19

Gamma radiation is highly penetrative but is absorbed by several inches of lead or several metres of concrete.

Question 20

Explain the process of beta minus decay.

Answer 20

Beta-minus decay is where a neutron in the nucleus turns into a proton, and releases an electron and an electron antineutrino.

Question 21

Explain the process of beta plus decay.

Answer 21

Beta-plus decay is where a proton in the nucleus turns into a neutron, and releases a positron and an electron neutrino.

Question 22

How does the mass of a nucleus compare to the sum of the individual masses of its constituents?

Answer 22

The mass of the nucleus is always less the sum of the individual masses of its constituents.

Question 23

What is the name given to the difference in the mass of a nucleus and its individual constituents?

Answer 23

The mass defect.

Question 24

Explain why there is a mass defect in nuclei

Answer 24

The mass defect is a result of some of the mass being converted into energy used to hold the nucleus together.

Question 25

What is the name for the value of the energy required to hold a nucleus together?

Answer 25

Binding energy.

Question 26

How can the mass defect be used to calculate the binding energy of a nucleus?

Answer 26

By substituting the mass defect into Einstein's mass energy equation.

Question 27

Why isn't it useful to compare binding energies for different nuclei?

Answer 27

Different nuclei have different numbers of nucleons.

Question 28

What is a more useful measure used to compare the binding energies of different nuclei?

Answer 28

The binding energy per nucleon.

Question 29

State the equation used to calculate the binding energy per nucleon of a nucleus.

Answer 29

Binding energy ———————————- = binding energy per nucleon Number of nucleons

Question 30

What is the relationship between the stability of a nucleus and its binding energy per nucleon?

Answer 30

The larger the binding energy per nucleon, the more stable the nucleus will be.

Question 31

What is the most stable nucleus?

Answer 31

Iron

Question 32

Name two nuclear procesees that can be used to generate energy.

Answer 32

1. Nuclear Fission 2. Nuclear Fusion

Question 33

What are the two types of fission?

Answer 33

1. Spontaneous fission 2. Induced fission

Question 34

Explain the basic process of induced fission.

Answer 34

A large nucleus absorbs a thermal neutron causing it to split into two smaller nuclei, releasing energy and at least one neutron.

Question 35

Explain the basic process of nuclear fusion.

Answer 35

Two smaller nuclei join together to form a larger one, and releases energy in the process.

Question 36

Why is nuclear fusion is not currently a feasible method of energy production?

Answer 36

Nuclear fusion requires very high temperatures in order to overcome the electrostatic force between the nuclei. This makes it hard to contain and means more energy must be inputted to heat the nuclei than is generated.

Question 37

Which decay has the shortest range and why

Answer 37

A positron has the shortest range as it’s a type of anti-matter so it annihilates immediately. When it annihilates, it produces 2 gamma rays in pair production

Question 38

What is the equation for activity

Answer 38

A = -λN λ = decay constant - the probability or chance that an individual nucleus will decay per second measured in s^-1 or h^-1 A = activity measured in Bq N = sample of N undecayed nuclei

Question 39

What is half life

Answer 39

Time or activity to decrease by half

Question 40

What is the half life equation

Answer 40

T1/2 = ln2 / λ T1/2 = half life λ = decay constant

Question 41

What is the atomic mass unit and what is it’s value

Answer 41

Atomic mass unit (amu / u) is a convenient unit of nuclear mass 1u = 1/12 the lass of a neutral carbon atom = 1.66x10^-27

Question 42

Where does the mass go when split up

Answer 42

To separate the particles, they must be pulled apart against the strong nuclear force. They thus have potential energy when they are separated. When the particles come together to form the nucleus, their potential energy decreases so energy must be put in to seperate the nucleons of the nucleus. This energy is known as the binding energy.

Question 43

What is binding energy simply

Answer 43

Tells us how much energy is required to pull the nucleus apart. Hence why the higher binding energy the the more stable the nucleus

Question 44

Explain the conditions required to bring about and maintain nuclear fusion.

Answer 44

- (very) high temperature and (very) high density - (Very) high temperature to provide enough energy to overcome the (electrostatic) repulsive force between nuclei - (Very) high density to give big enough collision rate to maintain reaction

Question 45

Why do u need high density for fusion

Answer 45

To ensure ions are close enough to each other to maintain collision rate to maintain fusion

Question 46

What does it mean by radiation being random and spontaneous

Answer 46

Random nature of radioactivity is indicated by the fluctuation of the count-rate. Whereas, spontaneous means that the process of radioactivity is not dependent upon any external environmental conditions like temperature, pressure, magnetic/electric field.