3-3 Radioactive Decay (Sec 10.3 pg 284-289)

Some isotopes are more stable than others - some can last billions of years, others only a few seconds. The nuclei of some isotopes are unstable and emit radiation (they’re called ‘radioisotopes’). Radioisotopes undergo radioactive decay.

There are three main types of radioactive decay – alpha, beta, gamma. Please note new symbols and notation used in radioactive decay (Table 1 p.284): Type of decay Radiation Radiation symbol Electric charge Mass (e = 1) What is it? Characteristics Alpha decay Alpha particle α +2 7000 A helium nucleus: Slow moving Penetrates paper Beta decay Beta particle β -1 1 An electron: Can penetrate few sheets of Al foil Gamma radiation Gamma rays ᵞ Energetic light: Can pass through a human.

Each type of decay can be written as a nuclear equation. The two rules for writing nuclear equations is: (1) the mass numbers on each side of the arrow have to add up, and (2) all the atomic numbers on each side of the arrow have to add up. This employs the same concept as balancing chemical reactions.

Alpha decay is when a radioactive atom emits an alpha particle, α. An α particle consists of 2 protons and 2 neutrons – it is identical to the nucleus of a helium atom. The release of an α particle causes the ‘parent nucleus’ to change – it loses two protons and therefore becomes an entirely new element (the ‘daughter nucleus’). GOOD CLIP: http://www.youtube.com/watch?v=CwExbnOzc4o

Beta Decay is when the nucleus emits a beta particle, β, which is actually an electron. Although e and protons are quite stable, neutrons are relatively unstable. Neutrons in an unstable nucleus can decay into a proton, an e and something called a neutrino (often emitted from equations). β decay involves the decay of a neutron into a proton and electron. The proton stays in the nucleus which changes the atomic number but not the atomic mass. The electron comes flying out as beta radiation. GOOD CLIP: http://www.youtube.com/watch?v=uqAA_D9Mi_I

Gamma decay occurs when the nucleus emits a gamma ray, , which is very high electromagnetic radiation. After emitting α or β particles, nuclei may have surplus energy, and release it in the form of a ray (excited atoms denoted with an asterisk ‘*’). Gamma decay doesn’t change the type of isotope, just changes the isotope’s energy.

Pg 289 # 5,7,9-14