Radioactivity (general)

What is proton / atomic number and nucleon / mass number respectively?

Proton → no. of protons in an atom

Nucleon → total no. of neutrons and protons in the nucleus of an atom

Define nuclides

Atoms of a specific no. of neutrons and protons

Define isotopes

Atoms of the same element that have the same number of protons but different number of neutrons

Define nuclear / radioactive decay

A random process by which an unstable atomic nucleus loses its energy by emission of electromagnetic radiation or particles

• Radiation is spontaneous and random in direction

How does an atomic nucleus become unstable?

Nuclear forces within the nuclei are unable to bind the nucleons together

What factors remain the same before and after nuclear reaction?

• Total no. of protons and neutrons

• Total relative charge

What is alpha decay?

• Nucleus emits an alpha particle identical to helium nucleus 4/2 He

• The nucleon number decreases by 4 and the proton number decreases by 2

What is beta decay?

• Nucleus emits a beta particle (electron)

• Nucleon number remains the same and proton number increases by 1

What is gamma radiation?

When a nuclei undergo alpha or beta decay, gamma radiation is also emitted

Define ionisation

The ability of an atom to eject electrons from atoms to form ions

What is the nature of alpha particles?

• 2 protons and 2 neutrons tightly bound together

• Identical to a helium nucleus

What is the relative ionizing effect and relative penetrating ability of alpha particles?

• Ionizing effect → highest

• Penetrating ability → least

  • They are easily absorbed by a piece of paper

What is the nature of beta particles?

A fast-moving electron ejected from radioactive nucleus

What is the relative ionizing effect and relative penetrating ability of beta particles?

Ionizing effect → medium

Penetrating ability → medium

• Absorbed by aluminium a few meters away

What are gamma rays?

Electromagnetic radiation emitted by a radioactive nucleus with excess energy

What is the relative ionizing effect and relative penetrating ability of gamma rays?

• Ionizing effect → lowest

• Penetrating ability → highest

  • Pass through most materials easily 

  • Absorbed by lead that is a few cm thick or very thick concrete

Define background radiation

Nuclear radiation in an environment where no radioactive source is deliberately introduced

What are natural and artificial sources of radiation?

• Artificial

  • Medical rays

  • Building materials

  • Waste products from nuclear power stations

• Natural

  • Rocks

  • Radon gas in the air

  • Food and drink with radioactive elements

Define ionizing radiation

Radiation with high energies that can knock off electrons from atoms to form ions e.g. UV rays, X rays, gamma rays

Where can non-ionizing radiation be found?

• Visible light and infra-red radiation from the sun

• Microwaves and radio waves in communication systems

How can background radiation be measured?

• Using a GM (Geiger-Muller) counter

• SI: Bq (Becquerel) / rate of counts per unit time / count rate

1. Remove all radioactive sources

2. Start the counter and stopwatch

3. Stop the counter after 10min and record counts per minute

*BG radiation should be first measured then subtracted from measurements

Define half-life of a radioactive nuclide

Time taken for half the nuclei of the sample to decay

Define nuclear fission

A process in which the nucleus of an atom splits and releases a huge amount of energy

What is nuclear fuel?

A material used in nuclear power stations that undergoes nuclear reactions to release energy

What happens during nuclear fission?

1. Parent nucleus decays to form daughter nuclei which may decay or be stable

2. Neutrons produced will go on to split more nuclei in a self-sustaining chain reaction controlled in a nuclear reactor

Where is energy from the nuclear store of the unstable nucleus transferred to during nuclear fusion?

• Kinetic, internal and nuclear stores of the daughter nuclei / bigger nucleus

• Internal store of the surrounding media

  • Used to heat water so that in changes into steam

  • Can be used in the electrical power generation process

Define nuclear fusion

A process in which 2 light atomic nuclei combine to form one heavier atomic nucleus and release a huge amount of energy

Why is a lot of work done during nuclear fusion?

• Nuclei of atoms are positively charged and it is difficult for 2 nuclei to combine as like charges repel

• A lot of work is done to overcome the repulsive forces between nuclei

• Requires very high temperature and pressures

*Once combined, the nuclear forces hold the nucleus together

Where is energy from the nuclear

• 2 nuclei ca