Topic 11: Nuclear Radiation

Question 1

What is the definition of binding energy?

Answer 1

Binding energy is the energy required to separate a nucleus into individual constituents (protons and neutrons).

Question 2

How does binding energy change in either fission and fusion?

Answer 2

Total binding energy always increases as energy is always released during reaction.

Question 3

Why is the mass of a nucleus always lower than the mass of the mass of its constituents?

Answer 3

The mass ‘lost’ is converted into energy and released. Known as mass deficit.

Question 4

What is atomic mass unit?

Answer 4

Atomic mass unit is defined as 1/12 of the mass of a carbon-12 atom (1u = 1.661x10^27).

Question 5

What is a mass defect?

Answer 5

When the mass of the constituents is greater than the mass of the nucleus.

Question 6

Why does a mass defect occur?

Answer 6

A mass defect occurs because energy is required for nucleons to join together so the lost mass is converted into energy and released

Question 7

What is nuclear fission?

Answer 7

Nuclear fission is the splitting of a large nucleus into 2 daughter nuclei.

Question 8

When does nuclear fission usually occur?

Answer 8

In very large nuclei, which are unstable.

Question 9

Why is energy released during fission?

Answer 9

because the Smaller daughter nuclei have a higher binding energy per nucleon.

Question 10

What is nuclear fusion?

Answer 10

When two smaller nuclei join together forming one larger nucleus.

Question 11

Why is enegy released during fusion?

Answer 11

Because the larger nucleus has a much higher binding energy per nucleon.

Question 12

What is the binding energy per nucleon?

Answer 12

It is the binding energy of a nucleus divided by the number of nucleons in the nucleus.

Question 13

How can you tell whether an element undergoes fission or fusion?

Answer 13

On the graph of Binding energy/nucleon over no of nucleons,
- the elements that undergo fusion have less nucleons than iron
- the elements that undergo fission have more nucleons than iron

Question 14

What are the 2 conditions of nuclear fusion?

Answer 14

High Temperature
- Needed to overcome electrostatic repulsion between positively charged nuclei
High Density/Pressure
- Ensure nuclei are close together so increased rate of collision to maintain fusion reaction.

Question 15

What is background radiation?

Answer 15

Background radiation is the level of ionising radiation present in the environment.

Question 16

What is count rate?

Answer 16

No of decays recorded each second by GM tube

Question 17

How to calculate corrected count rate?

Answer 17

• Calculate background radiation count
• Calculate total count
• Take away background count from total count

Question 18

What is radiation?

Answer 18

Radiation is when an unstable nucleus emits energy in the form of EM waves or subatomic particles in order to become more stable.

Question 19

What can cause a nucleus to become unstable?

Answer 19

Unstable nuclei can be caused by
- too many neutrons
- too few neutrons
- too many nucleons (heavy)
- too much energy in the nucleus

Question 20

How does a nucleus decay?

Answer 20

By radioactive decay.
This is when a nucleus decays by releasing energy/particles until it is in a stable form.

Question 21

What are the 4 types of radiation?

Answer 21

Alpha - α - helium nucleus - 2 protons, 2 neutrons, +2 charge
Beta-minus - β, β- - electron
Beta-plus - β+ - positron
Gamma- Γ - short wavelength, high frequency EM wave

Question 22

What are the properties of alpha radiation?

Answer 22

Alpha has a:
- strong ionising ability
- slow speed
- Absorbed by paper or few cm of air

Question 23

What are the properties of a beta-minus?

Answer 23

Beta minus has a:
- Weak ionising ability
- Fast speed
- Absorbed by thin sheet of aluminium

Question 24

What are the properties of a gamma?

Answer 24

Gamma particles are:
- EM wave
- Infinte range; follows inverse square law
- Weak ionising ability
- Absorbed by metrrs of concrete or inches of lead

Question 25

List types of radiation from most ionising to least

Answer 25

Alpha
Beta
Gamma

Question 26

List types of radiation from most penetrative to least

Answer 26

Gamm
Beta
Alpha

Question 27

What is the nature of radioactive decay?

Answer 27

Random
-
Spontaneous
- Cannot influence when a nucleus will decay

Question 28

What is the decay constant?

Answer 28

Probability of a nucleus decaying per unit time
ΔN/Δt = -λN

Question 29

What is the half-life?

Answer 29

Time taken for the number of nuclei to halve

Question 30

How can you determine half-life from graph?

Answer 30

• Measure t for sample size to half.
• Complete multiple times
• Work out average half life

Plot lnN₀ against time; straight line
Gradient is decay constant λ
Use λ to calculate half life

Question 31

What is activity?

Answer 31

Activity is the number of nuclei that decay per second
A =λN

Question 32

What is ionising radiation?

Answer 32

Ionising radiation removes electrons from atoms/molecules

Question 33

What is not directly ionising but may still cause ionisation?

Answer 33

Presence of neutrons
Uncharged particles may not be directly ionising

Question 34

Why is radioactive count repeated?

Answer 34

Radioactive is random process so count for fixed time will vary
Repeated measurements allow for mean to be calculated

Question 35

What is the process of nuclear fusion? (2)

Answer 35

• Smaller mass nuclei come very close together
• So nuclei join and form a larger nucleus

Question 36

Explain conditions required to bring about and maintain nuclear fusion in stars

Answer 36

Very high temperature
- as nuclei have positive charge leading to electrostatic force of repulsion
- High temp increases KE to help overcome electrostatic force of repulsion
Very high density
- So nuclei are close enough to fuse
- So collision rate is high to maintain fusion