Radiation in Physics A reference booklet by Eli 1 But First, a recap of the atom The atom of any element is made up of a nucleus, containing protons and neutrons, and shells, containing electrons. Subatomic Particle Location Charge Mass Proton p + Nucleus 1+ 1 Neutron n 0 Nucleus 0 1 Electron e ¡ Shells 1- 'Negligible' or 1 2 000 Figure 1. Subatomic Particle Information Figure 2. Bohrian Model of the Atom So, put together: atoms have most of their mass concentrated in the nucleus, which contains +ve protons and neutral neutrons , around the nucleus, in shells , electrons orbit. Radiation in Physics - Eli 1 2 Types of Radiation There are 4 types of radiation, alpha ( a ), beta ( b ), gamma ( g ), and neutron ( n ). Each are different in their own ways and released for different reasons. 2.1 Why is radiation released? When nuclei are unstable, it is because there are too many or too few neutrons for how many protons it has. Whether there are too many or too few, certain radiation will be emitted to fix this. This is a random process. 2.2 a Alpha radiation is the release of 2 neutrons and 2 protons together, (equivalent to a Hydrogen nucleus). Represented as: 2 4 This means that when it is released, the Atomic Mass decreases by 4, and the Atomic Number decreases by 2 This is done when there are too few neutrons. a radiation has high ionising power, meaning it is dangerous to living cells, but can only travel less than 5 centimetres in air, and is stopped by skin or paper 2.3 b Beta radiation is when a neutron turns into a proton and releases an electron in the process. The electron is strongly repelled from the nucleus so is ejected at high speeds. Represented as: ¡ 1 0 or ¡ This means that when it is releases, the Atomic Mass stays the same, but the Atomic Number increases by 1 This is done when there are too many neutrons b radiation has low ionising power, meaning its not as dangerous, but can travel up to a metre in air, and is stopped by 3mm aluminum foil 2.4 g Gamma radiation is when a nucleus still has too much energy, or in layman's terms: is too hot. To counteract this, it releases a low electro-magnetic wave (essentially heat) to cool off or reduce its energy. This is represented as: 0 0 This means that when it is released, neither the Atomic Mass or Number changes. g radiation has the lowest ionising power, meaning it is very weak in small dosages, but can travel up to a kilometre in air, and is stopped by concrete or Lead (Pb) Radiation in Physics - Eli 2 2.5 n Rarely, a neutron can be emitted from a nucleus. This can occur naturally: such as cosmic rays entering the top layers of our atmosphere. Or artificially: such as Berillium atoms releasing neutrons when being hit with a particles. This is: 0 1 n This means that the Atomic Mass will decrease by 1, but the Atomic Number will stay the same. Type Symbol When Emitted Affect on Mass Affect on Atomic Number Ionising Strength Stopped By Travel a 2 4 Too few n -4 -2 Strong Paper <5cm b ¡ Too many n 0 +1 Weak 3mm Al <1m g 0 0 Cool off 0 0 Weakest Pb <1Km n 0 1 n Rare Events -1 0 Figure 3. Radiation Type Information 3 Half-Life Radiation is a random process ) Unable to predict decay ) Say when n: of unstable nuclei halves or count rate halves ? Count Rate = Decays per Second as recorded by a Geiger-Muller (GM) Tube Figure 4. Radioactivity Plotted against Time 3.1 Calculating isotopes remaining (Higher) Half-life ) 1 2 , Number of half-lives ) exponent , Outcome Starting Mass ) Remaining Mass Example Cobalt-60's half-life is 5 years. Presuming you started with 1Kg, how much is left after 15 years. 1 2 15 5 1 000 1 2 3 (1 000 ) 1 8 (1 000 ) , 125 g Radiation in Physics - Eli 3