atoms & radiation

• an atom can have an unstable nucleus which can become more stable over time by spontaneously emitting ionising radiation - radioactive decay
• substances that decay radioactively are 'radioactive substances'
• we cannot predict when an individual atom will emit ionising radiation
• these are 3 primary ways of detecting radioactivity
• geiger counter (geiger-muller tube): ionising radiation enters a tube full of low pressure gases and ionises the atoms in the gas, knocking electrons out of the atoms. the gas can now conduct electricity and completes an electric circuit and current flows between electrodes. the current produces a clicking noise and the count-rate is the number of decays recorded each second
• photographic film: ionising radiation has the same effect on photographic film as light. a bright spot appears wherever the ionising radiation hits the film
• cloud chamber: a cloud chamber is a container full of air containing alcohol vapour. ionising radiation enters the air and leaves a trail of ionised air molecules, making the alcohol condense on the ionised air molecules, showing the trail of radiation
• alpha, beta and gamma radiation all have different properties
• each alpha particle contains 2 protons and 2 neutrons, and because of this, alpha particles have a relative mass of 4.
• because the particles are big and heavy, alpha radiation is strongly ionising and does a lot of damage, but is stopped by a small amount of matter - like paper
• beta radiation is made up of high-energy electrons and is more ionising than gamma radiation, but less ionising than alpha radiation
• beta radiation can pass trough paper, but is stopped by aluminium foil
• gamma radiation is weakly ionising and does less damage than beta or alpha radiation, but is stopped only be metres of lead or concrete
• more strongly ionising radiation is less able to penetrate materials as it interacts with materials much more, so comes to a stop sooner
• during alpha, beta, and gamma radioactive decay, an unstable nucleus becomes more stable
• in alpha decay, a nucleus loses an alpha particle and because 2 protons have been lost, we now have a new element
• in beta decay, a neutron in the nucleus decays to form a proton and electron, which is then ejected from the nucleus
• in gamma decay, the composition of the nucleus is unchanged and the nucleus is said to be 'relaxing' from one state into another state with lower energy
• we can use alpha, beta, and gamma radiation for many practical purposes
• alpha radiation is used in smoke detectors: a radioactive material fires alpha particles at a smoke detector, if there is smoke between the radioactive material and the smoke detector, then less alpha particles will reach the detector, setting off the smoke alarm
• beta radiation is used in paper production: we can fire beta particles through paper in a factory to make sure that the paper being produced is the right thickness. if the thickness of the paper changes, more or less beta particles will reach the detector, stopping production
• gamma radiation is used in exploring internal organs: if we put a gamma-emitting isotope into a patient's body, we can trace the radiation's movement around the body, and the radiation can also leave the body without creating too much damage
• gamma radiation has a short half-life, meaning that radiation vanishes quickly
• gamma radiation can also be used in sterilisation: we can use gamma radiation to sterilise medical equipment in hospitals, which kills bacteria and viruses
• when writing nuclear equations, atomic number and mass number must be the same on each side: the sum of the atomic numbers on one side must equal the sum of atomic numbers on the other side, same with mass numbers
• the half-life is the average time taken for the number of radioactive nuclei to halve, radioactivity being measured in becquerels (Bq)
• the radioactive decay of an individual atom is random and unpredictable, however large groups of nuclei do normally behave in predictable ways
• the half-life is for any one isotope of an element is constant
• alpha, beta and gamma radiation are all ionising radiation, which can break molecules into small particles called ions
• ions are particles that become charged by gaining or losing electrons
• ions can react in unusual ways to ionising radiation, which can damage cells and complex chemical structures, such as dna
• the cell damage from ionising radiation can cause mutations, which can lead to cancer
• ionising radiation can damage cells, cause mutations that lead to cancer and possibly organ failure. because of this, we should follow safety precautions to reduce our exposure to radioactive materials
• radioactive sources should be stored in lead-lined boxes and locked in steel cabinets away from people
• radioactive sources should not be handled directly and should only be used for the shortest time possible. we should use rubber gloves when handling and wash our hands thoroughly after use
• we should not eat or drink when using a radioactive source, and should be kept at arm's length and we should not put them in our pockets
• we should minimise our exposure to sources, use shielding and maximise the distance between the user and the source