Nuclear Reactions

1. Nuclear Reactions Nuclear reactions Radiation Fission Fusion

2. Nuclear Reactions • In a chemical reaction bonds between atoms are broken or made. This is essentially the swapping of electrons in and out of electron shells • Nuclear reactions are different. They involve changes occurring in the nucleus of an atom. A nucleus contains protons and neutrons, so any event that adds or removes these nucleons is called a nuclear reaction • When a nuclear reaction occurs all the mass numbers and atomic numbers on both sides must balance. The one below does not balance The reaction to the left shows chlorine’s nucleus changing. What has it lost?

3. Radiation • It takes a huge amount of energy to break the nucleons (protons and neutron) apart and to force them together. As these events occur often particles are emitted form the nucleus at great speed. These particles are known as nuclear radiation and they come in three forms: • Alpha particles (a) • Beta particle (b) • Gamma rays (g) • These particles are made of specific components and therefore they have specific properties

4. Alpha Particles (a) • An alpha particle is a fast moving Helium nucleus ( ) • Because of their mass they can be stopped something the thickness of paper • Of the three types of radiation it travels the slowest Here is a nuclear reaction that shows the emission of an alpha particle. Note that the mass (top) and atomic (bottom) number balance on both sides of the equation

5. Beta Particles (b) • Beta particle are fast moving electrons ( ) • They have little mass so they can pass 10cm into wood before being stopped • They move fast • They are created by a neutron emitting an electron, turning it into a proton Note: The mass number stays the same because the electron it loses has no mass. One neutron has changed however, it has turned into a proton therefore increasing the mass number

6. Gamma Rays (g) • Gamma rays are just high energy electromagnetic radiation (sort of like light, UV rays, X-rays etc) • It has no charge and no mass therefore when it is emitted from a nucleus there are no changes to the nucleus. It is a way of removing excess energy • They are extremely fast (moving at the speed of light) • They can penetrate solids very well. About 60cm of lead will stop gamma rays

7. Other Particles • Some other particles my be emitted during a nuclear reaction: • Protons ( ) • Neutrons ( ) • Positrons (positive electrons) ( )

8. Half-Life • Some isotopes are stable, some are not. An unstable isotope will lose bits of it’s nucleus until it reaches a stable configuration • The amount of time it takes for half of the mass of an unstable isotope to break down is called its half-life. For example cobalt-60 (cobalt with a mass number of 60) has a half life of 5.26 years. So after 5.26 years 100g of 60Co will decay into 50g of 60Co. Then after another 5.26 years that 50g of 60Co will decay into 25g (half the original mass)…an so on.

9. Fission • Nuclear fission is the term given to any nuclear reaction where a large nucleus is broken down into smaller ones. • This is the process used to produce nuclear power because of the heat energy given off during the reaction • As can be seen in the reaction above a uranium atom has been bombarded by a neutron which causes a split into two nuclei and the production of 3 more neutrons to keep the reaction happening

10. Nuclear Fusion • A nuclear reaction that involves to smaller nuclei combining to form on larger one is called nuclear fusion • This is the process that fuels our Sun as it converts hydrogen into helium