Nuclear Physics

Nuclear Physics

1. Radioactivity

   • Nuclear Reactions
     • Isotopes of an element are atoms with the same number of protons but with different numbers of neutrons. Therefore they have the same atomic number but different mass numbers.
     • Alpha Decay
       • Changes in the nucleus - Nucleus loses 2 protons and 2 neutrons
       • Particles emitted - 2 protons and 2 neurons emmitted as an alpha particle
       • X = Y + alpha
     • Beta Decay
       • X = Y + beta
       • Changes in the nucleus - A neutron in the nucleus changes into a proton
       • Particle emitted - An electron is created in the nucleus and instantly emmitted
   • Atoms and Radiation
     • A radioactive substance contains unstable nuclei that become stable by emitting radiation
     • There are three main types of radiation
       • Alpha
       • Beta
       • Gamma
     • Radioactive decay is a random event - we cannot predict or influence when it will happen
     • Background radiation is mostly from radioactive substances occurring naturally in rocks or in space or in man made sources such as nuclear fallout
   • Half life
     • The half life of a radioactive isotope is the average time it takes for the number of nuclei of the isotope in a sample to halve
     • The count rate of a Geiger counter due to a radioactive source decreases as the activity of the source decreases.
     • The number of atoms of a radioactive isotope and the count rate both decrease by half every half life.

2. Nuclear Fission

   • Nuclear fission is the spiltting of an atomic nucleus into two smaller nuclei and the release of two or three neutrons and energy.
   • Nuclear fission occurs when a neutron is absorbed by a uranium-235 nucleus or a plutonium-239 nucleus and a nucleus splits.
   • A Chain Reaction occurs in a nuclear reactor when each fission event causes further fission events.
   • In a nuclear reactor, control rods absorb fission neutrons to ensure that, on average only one neutron per fission goes on to produce further fission.

3. Nuclear Issues

   • Radon gas is an alpha emmittin g isotope that seeps into houses in certain areas through the ground
   • There are thousands of fission reactors in the world. None of them is the same type as the Chernobyl reactors that exploded
     • Chernobyl nuclear disaster
   • Nuclear waste is stored in safe and secure conditions for many years after unused uranium and plutonium (to be used in the future) are removed from it

4. Nuclear Fussion

   • Nuclear fusion is the process of forcing two atomic nuclei close enough together so that they form a single larger nucleus.
   • Nuclear fusion can be brought about by making two light nuclei collide at very high speed
   • Energy is released when two light nuclei are fused together. Nuclear fusion in the Sun's core releases energy
   • A fusion reactor needs to be at a very high temperature before nuclear fusion can take place. The nuclei to be fused are difficult to contain