Chapter 25 - Radioactivity (UNFINISHED) Flashcards
Define radioactive decay.
The process by which unstable nuclei split, or decay, by emitting ionising radiation.
Describe the spontaneous & random nature of decay.
Spontaneous: occurs without external influence.
Random: cannot predict when a nucleus will decay.
What is an alpha particle?
A helium nucleus (two protons & two neutrons).
What is a beta particle?
A fast-moving electron.
What is a gamma ray?
High energy photons of wavelength <10¹³.
What is the range of alpha radiation?
Short, absorbed by a few cm of air or by a sheet of paper.
What is the range of beta radiation?
~1m in air and 1-3mm in aluminium.
What is needed to absorb gamma radiation?
A few cm of lead or several m of concrete.
Arrange alpha, beta & gamma radiation from most to least ionising.
Alpha, beta, gamma.
Define activity of a source.
The rate at which nuclei decay or disintegrate in a radioactive source, measured in becquerels (Bq) or decays per second.
Define decay constant.
The probability of decay of an individual nucleus per unit time.
Describe the process of carbon dating.
-The ratio of carbon 12 to 14 atoms for a dead sample of material is compared to that of a living one.
-A material with more carbon 12 atoms is older.
State some limitations of carbon dating.
-Assumes ratio of carbon 12 to 14 in the atmosphere has remained constant, though it may have changed due to volcanic eruptions, burning fossil fuels etc.
-Tiny amounts of carbon 14 in organisms are difficult to measure accurately.
-Cannot be used to date rocks.
