Particles and Radiation

• Specific Charge is the charge/mass ratio
• The specific charge of electrons is greater than protons
• The strong nuclear force keeps the nuclei stable by counteracting the electrostatic force of repulsion between protons in the nucleus (as they have the same charge). It only acts on nucleons and has a very short range - attractive force from 3-4fm but repulsive force that acts to prevent neutrons and protons being pushed into each other below separations of 0.5fm.
• Unstable nuclei are those which have too many of either protons, neutrons or both causing the SNF to not be enough to keep them stable, therefore these nuclei will decay in order to become stable. The type of decay the nuclei will experience depends on the amount of each nucleon in them.
• Annihilation occurs when a particle and corresponding antiparticle meet and their mass is converted into radiation energy. Two photons are produced in this process (as a single photon cannot ensure a total momentum of zero after the collision). Minimum energy of each photon produced = hfmin = Eo
• Pair production is when a photon creates a particle and a corresponding antiparticle, and vanishes in the process. Minimum energy of photon needed = hfmin = 2Eo
• Alpha particles are helium nuclei that consist of two protons and two neutrons. Alpha particles are positively charged and have a large rest mass compared to other types of radiation. Due to their size, alpha particles interact strongly with matter and so do not penetrate far. However, they can cause significant damage if absorbed by living tissue.
• Gamma rays can ionise atoms as well as penetrate matter due to its high frequency and low wavelength. They also travel at the speed of light.
• Beta minus emission involves an electron emitted from the nucleus of an unstable atom. This results in a decrease in atomic number by one unit as well as a decrease in mass number by one unit. Beta minus emitters are usually radioactive isotopes of elements found near the end of a period in the periodic table.
• Gamma rays are high frequency electromagnetic waves that travel at the speed of light. They are produced during certain types of radioactive decay processes such as beta plus decay and gamma ray emissions. Gamma rays carry no electric charge and have no mass, making them highly penetrating and difficult to shield against.