Nuclear Physics

• The mass number is the total number of protons and neutrons
• Thomson's model of the atom was a semipermeable sphere of positive charge with negative electrons embedded in it.
• Rutherford's model of the atom was a positive nucleus with a negative electron cloud. He believed the nucleus was at the centre of the atom due to the majority of alpha particles going straight through the gold foil. The nucleus was thought to have been positively charged, as some of the alpha particles deflected at different angles. The nucleus was thought to be very dense as a few of the alpha particles "bounced back" from the gold foil.
• There are three types of radioactivity: alpha particles, beta particles and gamma rays
• Alpha particles are positively charged particles made up of 2 protons and 2 neutrons, the same as a He nucleus. They travel at 0.1*the speed of light and only travel a few cms. They are not very penetrating and are stopped by paper.
• Beta particles are negatively charged particles, as they are electrons from the nucleus. They travel at 0.9*the speed of light and can travel a few metres. They are quite penetrating and are stopped by aluminium.
• Gamma rays are high energy electromagnetic rays that have no charge or mass. They travel at the speed of light and are very penetrating although they are stopped by thick lead or cement.
• The term half-life is used to describe how long it takes the radioactivity of the halve or the time taken for half the sample to decay into something else.
• Radiocarbon dating is used to determine the age of fossils and artefacts. This is done by measuring the ratio of carbon (-12) to carbon (-14).
• Nuclear Fission occurs when one large nuclei separates into two smaller nuclei. The most common example is when uranium separates into barium and krypton.
• Nuclear fusion occurs when two small nuclei join together to form a larger nucleus. It releases more energy because there is less mass left over.
• Conservation of charge means that the total atomic numbers on one side of the equation will equal the total atomic numbers on the other side.
• Conservation of nucleon number means that the total mass number on one side of the equation will equal the total mass number on the other side of the equation.