Topic 4: Atomic Structure Flashcards
4.1
Atoms and Isotopes
Give an approximation for the radius of an atom.
1 x 10(-10) metres
Give two ways that an atom’s electron arrangement can be changed.
- Absorbing electromagnetic radiation
- Emitting electromagnetic radiation
4.2
Atoms and Nuclear Radiation
Why do unstable nuclei give out radiation?
- Unstable nuclei undergo decay to become more stable
- As they release radiation their stability increases
What is count-rate?
The number of radioactive decays per second for a radioactive source.
Given an example of a detector that may be used to measure count-rate.
Geiger-Muller tube
What is the range of an alpha particle through air?
A few centimetres (normally in the range of 2-10 cm)
What will stop beta radiation from passing through a point?
- A thin sheet of aluminium
- Several metres of air
What will stop gamma radiation from passing through a point?
- Several centimetres of lead
- A few metres of concrete
Which type of radiation is most ionising?
Alpha radiation
Which type of radiation is least ionising?
Gamma radiation
Describe the nature of radioactive decay.
- Random
- Which nuclei decays and when is determined only by chance
- It is impossible to predict which nuclei will decay and when
Define the half-life of a radioactive isotope.
- 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
What is radioactive contamination?
The presence of unwanted radioactive nuclei on other materials.
What is irridation?
- The process of exposing a material to nuclear radiation
- The material does not become radioactive
Why is it important for the results of studies on the effects of radiation to be published and shared with other scientists?
- To allow the findings to be independently checked
- This is known as peer review
4.3
Hazards and Uses of Radioactive Emissions and Background Radiation (Physics Only)
Give 4 sources of background radiation.
- Rocks
- Cosmic rays from space
- Nuclear weapon testing
- Nuclear accidents
How should background radiation be dealt with in calculations?
The background count should be subtracted from any readings before calculations (half life etc.) are attempted.
Why might the radiation dosage that different people experience differ?
- 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
Why are isotopes with long half-lives particularly harmful?
- 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
State two uses of nuclear radiation in the field of medicine.
- Examining of internal organs
- Controlling and destroying unwanted tissue
Explain the process of radiotherapy.
- Gamma emitters direct gamma rays at the cancerous cells
- The cancerous cells absorb the radiation and are killed
How are medical tracers chosen?
- 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.
4.4
Nuclear Fission and Fusion (Physics Only)
What is nuclei fission?
The splitting of large, unstable nuclei to form smaller more stable nuclei (+ the emission of spare neutrons).
What usually needs to happen to induce fission?
- The unstable nuclei must absorb a neutron
- Spontaneous fission (where no neutron absorption occurs) is rare
What are the three main components of the core a nuclear reactor?
- Fuel rods
- Control rods
- Moderator
What is nuclear fusion?
The joining of two light nuclei to produce a heavier nuclei and release energy.
Which releases more energy, nuclear fission or nuclear fusion?
Nuclear fusion
Explain the difficulty of generating energy through nuclear fusion.
Fusion requires very high temperatures which in itself requires large quantities of energy and also requires casing which can withstand them.
Explain why nuclear fusion is currently not a viable way to produce energy on Earth.
With current equipment/techniques, the energy is required is greater than the energy produced, resulting in a net energy loss.
