Topic 4: Atomic Structure - Subtopic 2: Atoms & Nuclear Radiation

Question 1

Why are some atomic nuclei unstable?

Answer 1

Imbalance in the forces within the nucleus, often caused by having too many or too few neutrons.

Question 2

What is the difference between carbon-12 and carbon-14?

Answer 2

Carbon-12 is stable, while carbon-14 is unstable because it has two extra neutrons.

Question 3

What is radioactive decay?

Answer 3

It is the process by which unstable nuclei emit radiation (particles or waves) to become more stable.

Question 4

Is radioactive decay a predictable process?

Answer 4

No, it is random. Scientists cannot predict exactly when a particular nucleus will decay.

Question 5

What is radiation?

Answer 5

Radiation refers to the high-energy particles or waves emitted from an unstable nucleus during radioactive decay.

Question 6

What is activity in radioactive decay?

Answer 6

Activity is the rate at which unstable nuclei decay, measured in Becquerels (Bq).

Question 6

How many nuclei decay per second in a source with an activity of 2000 Bq?

Answer 6

2000 nuclei decay per second.

Question 7

How do you calculate the number of decays over a time period?

Answer 7

Multiply the activity (Bq) by the time period in seconds.

Question 8

What is a Geiger-Muller tube used for?

Answer 8

It is used to detect radiation by counting the ions created when radiation passes through it.

Question 9

What is count rate?

Answer 9

Count rate is the number of decays detected per second by a device like a Geiger-Muller tube.

Question 10

How do you calculate count rate?

Answer 10

Divide the total number of decays by the time period in seconds.

Question 11

What is the difference between activity and count rate?

Answer 11

Activity measures the rate of decay of unstable nuclei, while count rate measures the rate of detected radioactive emissions.

Question 12

What happens to the energy of a nucleus during radioactive decay?

Answer 12

The energy of the nucleus decreases as radiation is emitted, making the nucleus more stable.

Question 13

What is the unit of activity?

Answer 13

The unit of activity is the Becquerel (Bq), where 1 Bq = 1 decay per second.

Question 14

How does photographic film detect radiation?

Answer 14

It changes color when exposed to radiation.

Question 15

What is nuclear radiation?

Answer 15

When an unstable nuclei decays and emits radiation

Question 16

What is an alpha particle?

Answer 16

• The symbol for alpha is α
• An alpha particle is the same as a helium nucleus
• Consist of two neutrons and two protons
• Alpha particles have a charge of +2
• Can be affected by an electric field

Question 17

What is a beta particle?

Answer 17

• The symbol for beta is β
• Beta particles are fast-moving electrons
• Produced in nuclei when a neutron changes into a proton and an electron
• Beta particles have a charge of -1
• Can be affected by an electric field

Question 18

What are gamma rays?

Answer 18

• The symbol for gamma is γ
• Gamma rays are electromagnetic waves
• Have the highest energy of the different types of electromagnetic waves
• Have no charge

Question 19

What are neutrons?

Answer 19

• The symbol for a neutron is n
• Neutrons are one of the two particles found in the nucleus of atoms
• Neutral, Have no charge

Question 20

What is the range in air for the radiation particles?

Answer 20

Alpha - Few cm
Beta - Few 10’s of cm
Gamma - Infinite

Question 21

What is the penetration for the radiation particles?

Answer 21

Alpha - Stopped by paper
Beta - Stopped by few mm Aluminium
Gamma - reduced by few mm Lead

Question 22

What is the ionisation for the radiation particles?

Answer 22

Alpha - High
Beta - Medium
Gamma - Low

Question 23

What is radiation used for?

Answer 23

• Producing electricity through nuclear fission
• Medical procedures including diagnosis and treatment
• Testing material
• Determining the age of ancient artefacts
• Checking the thickness of materials
• Smoke detectors

Question 24

How are alpha particles used in smoke detectors?

Answer 24

- The alpha radiation will normally ionise the air within the detector, creating a current - The alpha emitter is blocked when smoke enters the detector - The alarm is triggered by a microchip when the sensor no longer detects alpha

Question 25

What happens during alpha decay?

Answer 25

- Alpha particle is emitted from an unstable nucleus - Completely new element is formed in process

Question 26

What happens during beta decay?

Answer 26

- Neutron changes into a proton and an electron - Electron is emitted, proton remains in nuclei - Completely new element is formed as atomic number changes

Question 27

What happens in gamma decay?

Answer 27

- Gamma ray is emitted from unstable nucleus - Nucleus becomes less energetic but doesn't change structure

Question 28

Describe the gamma ray emitted during gamma decay

Answer 28

Ray emitted has a lot of energy, but no mass or charge

Question 29

What can be inferred due to the random process of radioactive decay?

Answer 29

- There is an equal probability of any nucleus decaying - It cannot be known which particular nucleus will decay next - It cannot be known at what time a particular nucleus will decay - The rate of decay is unaffected by the surrounding conditions - It is only possible to estimate the probability of a nuclei decaying in a given time period

Question 30

What is half-life?

Answer 30

The time it takes for the number of nuclei of a sample of radioactive isotopes to decrease by half

Question 31

How do you calculate half-life of a sample?

Answer 31

- To calculate the half-life of a sample, the procedure is: > Measure the initial activity, A0, of the sample > Determine the half-life of this original activity > Measure how the activity changes with time - The time taken for the activity to decrease to half its original value is the half-life

Question 32

What is contamination?

Answer 32

The unwanted presence of materials containing radioactive atoms on other materials

Question 33

How is a substance radioactive?

Answer 33

- Contains radioactive atoms that emit radiation

Question 34

When does contamination occur?

Answer 34

When a radioactive isotope gets onto a material where it should not be

Question 35

What is irradiation?

Answer 35

The process of exposing a material to alpha, beta or gamma radiation

Question 36

What does irradiation do?

Answer 36

- Does not make material radioactive - Can kill living cells

Question 37

What is irradiation used for?

Answer 37

- Used as method of sterilisation

Question 38

Why is contamination dangerous?

Answer 38

- Can get into human body - Internal organs will be irradiated as source emits radiation as it moves through body

Question 39

What causes more harm: irradiation or contamination?

Answer 39

Contamination - Continuous exposure to radiation it will produce

Question 40

What is used to absorb radiation?

Answer 40

Shielding

Question 41

What type of shielding is used to prevent irradiation?

Answer 41

- Lead lined suits are used to reduce irradiation for people working with radioactive materials - The lead absorbs most of the radiation that would otherwise hit the person

Question 42

What is used to prevent contamination?

Answer 42

Airtight suit - Prevents radioactive atoms getting inside person - Used in areas with radiation leak