4.2 - Atoms & 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 the name of the process in which an unstable nucleus gives out radiation to become more stable?

radioactive decay

Define the activity of an unstable nucleus.

The rate of decay of a source of unstable nuclei.

What is the unit of radioactive activity?

becquerel (Bq)

What is count-rate?

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

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

Geiger-Muller tube

State four types of nuclear radiation.

• Alpha particles

• Beta particles

• Gamma rays

• Neutrons

What are the constituents of an alpha particle?

• Two protons and two neutrons.

• It’s the same as a helium nucleus.

What is the range of an alpha particle through air?

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

What will stop beta radiation from passing through a point?

• A thin sheet of aluminum.

• Several meters of air.

What will stop gamma radiation from passing through a point?

• Several centimeters of lead.

• A few meters of concrete.

Which type of radiation is most ionizing?

alpha radiation

Which type of radiation is least ionizing?

gamma radiation

State any changes to mass or charge that occur due to the emission of a gamma ray.

Both mass and charge remain unchanged.

Describe the nature of radioactive decay.

• Random.

• Which nuclei decays and when is determined only by chance.

• It’s 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 irradiation?

• 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.