- Every atom has a positively charged nucleus at its centre that is ssurrounded by negatively charged particles called electrons.
- The nucleus of the atom is composed of protons and neutrons which have approximatety equal mass.
- Protons and electrons have fixed equal and opposite anounts of charge, and neutrons are uncharged.
- An uncharged atom has equal numbers of electrons and protons.
- Radioactive substances emit radiation because the nuclei of the atoms are unstable.
- The radiation from radioactive substances ionises substances it passes through.
- There are three types of radiation from radioactive substances
- alpha radiation which is stopped by paper and is strongly ionising
- beta radiation which is stopped by 2-3mm thickness of…