Topic 4: Atomic Structure

Question 1

4.1

Answer 1

Atoms and Isotopes

Question 2

Give an approximation for the radius of an atom.

Answer 2

1 x 10(-10) metres

Question 3

Give two ways that an atom’s electron arrangement can be changed.

Answer 3

1. Absorbing electromagnetic radiation
2. Emitting electromagnetic radiation

Question 4

4.2

Answer 4

Atoms and Nuclear Radiation

Question 5

Why do unstable nuclei give out radiation?

Answer 5

• Unstable nuclei undergo decay to become more stable
• As they release radiation their stability increases

Question 6

What is count-rate?

Answer 6

The number of radioactive decays per second for a radioactive source.

Question 7

Given an example of a detector that may be used to measure count-rate.

Answer 7

Geiger-Muller tube

Question 8

What is the range of an alpha particle through air?

Answer 8

A few centimetres (normally in the range of 2-10 cm)

Question 9

What will stop beta radiation from passing through a point?

Answer 9

• A thin sheet of aluminium
• Several metres of air

Question 10

What will stop gamma radiation from passing through a point?

Answer 10

• Several centimetres of lead
• A few metres of concrete

Question 11

Which type of radiation is most ionising?

Answer 11

Alpha radiation

Question 12

Which type of radiation is least ionising?

Answer 12

Gamma radiation

Question 13

Describe the nature of radioactive decay.

Answer 13

• Random
• Which nuclei decays and when is determined only by chance
• It is impossible to predict which nuclei will decay and when

Question 14

Define the half-life of a radioactive isotope.

Answer 14

• The time it takes for the number of unstable nuclei in a substance to halve
• The time it takes for the count rate from a sample to fall to half its initial level

Question 15

What is radioactive contamination?

Answer 15

The presence of unwanted radioactive nuclei on other materials.

Question 16

What is irridation?

Answer 16

• The process of exposing a material to nuclear radiation
• The material does not become radioactive

Question 17

Why is it important for the results of studies on the effects of radiation to be published and shared with other scientists?

Answer 17

• To allow the findings to be independently checked
• This is known as peer review

Question 18

4.3

Answer 18

Hazards and Uses of Radioactive Emissions and Background Radiation (Physics Only)

Question 19

Give 4 sources of background radiation.

Answer 19

1. Rocks
2. Cosmic rays from space
3. Nuclear weapon testing
4. Nuclear accidents

Question 20

How should background radiation be dealt with in calculations?

Answer 20

The background count should be subtracted from any readings before calculations (half life etc.) are attempted.

Question 21

Why might the radiation dosage that different people experience differ?

Answer 21

• Some occupations involve working with radiation
• Background radiation differs with location due to things such as the locality of nuclear power stations or radiation related testing

Question 22

Why are isotopes with long half-lives particularly harmful?

Answer 22

• They remain radioactive for much longer periods of time
• They must be stored in specific ways to avoid humans and the environment from being exposed to radiation for too long

Question 23

State two uses of nuclear radiation in the field of medicine.

Answer 23

1. Examining of internal organs
2. Controlling and destroying unwanted tissue

Question 24

Explain the process of radiotherapy.

Answer 24

• Gamma emitters direct gamma rays at the cancerous cells
• The cancerous cells absorb the radiation and are killed

Question 25

How are medical tracers chosen?

Answer 25

• They should have a short half life and decay into a stable isotope which can be excreted.
• They should only release gamma radiation since it is weakly ionising and can easily pass through body tissue without damaging it.

Question 26

4.4

Answer 26

Nuclear Fission and Fusion (Physics Only)

Question 27

What is nuclei fission?

Answer 27

The splitting of large, unstable nuclei to form smaller more stable nuclei (+ the emission of spare neutrons).

Question 28

What usually needs to happen to induce fission?

Answer 28

• The unstable nuclei must absorb a neutron
• Spontaneous fission (where no neutron absorption occurs) is rare

Question 29

What are the three main components of the core a nuclear reactor?

Answer 29

1. Fuel rods
2. Control rods
3. Moderator

Question 30

What is nuclear fusion?

Answer 30

The joining of two light nuclei to produce a heavier nuclei and release energy.

Question 31

Which releases more energy, nuclear fission or nuclear fusion?

Answer 31

Nuclear fusion

Question 32

Explain the difficulty of generating energy through nuclear fusion.

Answer 32

Fusion requires very high temperatures which in itself requires large quantities of energy and also requires casing which can withstand them.

Question 33

Explain why nuclear fusion is currently not a viable way to produce energy on Earth.

Answer 33

With current equipment/techniques, the energy is required is greater than the energy produced, resulting in a net energy loss.