What happens to radioactive substances when they decay?


To understand what happens to radioactive substances when they decay we need to understand the structure of the atoms from which they are made.

" to explain how the Rutherford and Marsden scattering experiment led to the plum pudding model of the atom being replaced by the nuclear model.


All atoms are made of just 3 particles. This is what you need to know about them.

  particle charge mass location and ...

electron negative very light in orbit around nucleus In a neutral atom there is as many of these as there are protons.
If an atom loses electrons it becomes a positive ion.
If an atom gains electrons it becomes a negative ion.
proton positive heavy inside nucleus All atoms of the same element have the same number of protons, e.g. all carbon a toms have 6 protons.
This is called its Atomic Number.
neutron neutral heavy inside nucleus Atoms of the same element may have different numbers of neutrons. (Isotopes)
The number of protons + neutrons is called the Mass Number.

In an atom the number of electrons is equal to the number of protons in the nucleus. The atom has no net electrical charge.

Atoms may lose or gain electrons to form charged particles called ions.
 

All atoms of a particular element have the same number of protons.
Atoms of different elements have different numbers of protons.
Atoms of the same element which have different numbers of neutrons are called isotopes.


The total number of protons in an atom is called its atomic number.
The total number of protons and neutrons in an atom is called its mass number.


The effect of alpha and beta decay on radioactive nuclei.

Alpha Decay

An alpha particle is made up of 2 protons and 2 neutrons. If an atom emits an alpha particle from its nucleus its atomic number will go down by 2 and its mass number will go down by 4.

 

e.g. this isotope of Uranium decays by giving off an alpha particle
Beta Decay

A beta particle is a very fast moving electron which comes from the nucleus. A neutron inside the nucleus changes into a proton and a beta particle is emitted. The atomic number increases by 1 but the mass number stays the same.

e.g. the isotope of carbon 14C decays by giving off a beta particle.

14C   →   14N   +   β-


The origins of background radiation.

There are small amounts of radioactive substances all around us.

Living things are made mostly of carbon and some of these are the radioactive isotope carbon 14. We can find out how old some things are by carbon dating them.
 		 Rocks contain small amounts of radioactive isotopes. We know how old the Earth is by measuring the amount of radiation given off by rocks.
 

There are radioactive atoms in the air. This comes from the ground and can reach dangerous levels in some parts of the country.

 

 The Sun give off huge amounts of radiation most of which is stopped by the atmosphere and deflected by the Earth's magnetic field. It can be a big problem for astronauts though.