We have studied the structure of an atompreviously and we know about the three mainsubatomic particles: protons, neutrons andelectrons.What makes the protons and electrons staytogether in an atom?A force called the strong force opposes andovercomes the force of repulsion between theprotons and holds the nucleus together. Theenergy associated with the strong force iscalled the binding energy. The electrons arekept in orbit around the nucleus because thereis an electromagnetic field of attractionbetween the positive charge of the protons andthe negative charge of the electrons.
In most cases, elements like to have an equal numberof protons and neutrons because this makes themthe most stable. Stable atoms have a binding energythat is strong enough to hold the protons andneutrons together.However, an additional neutron or twomay upset the binding energy and causethe atom to become unstable. In anunstable atom, the nucleus changes bygiving off a neutron to get back to abalanced state. As the unstable nucleuschanges, it gives off radiation and is saidto be radioactive.
All elements with atomic numbers greater than 83 are radioisotopesmeaning that these elements have unstable nuclei and are radioactive.Elements with atomic numbers of 83 and less, have isotopes (stablenucleus) and most have at least one radioisotope (unstable nucleus).Examples of chemical elements with radioactive atoms includeuranium, plutonium & radium. As atoms give out particles or rays theychange into atoms of simpler elements. For example, uranium changesto thorium. This change is called radioactive decay. When there is achange in the nucleus and an element changes into anotherelement, it is called transmutation. It happens at different speeds orrates for different radioactive elements. changes toRadioactivity can be dangerous since it harms living things. But undercontrolled conditions it is very useful in medicine and scientificresearch.
When alpha or beta particles (radiation) are emitted by a radioisotope, theycollide with surrounding atoms and make them move faster. In otherwords, the temperature rises as nuclear energy is transformed into thermalenergy (heat).The diagram shows what can happenif a neutron strikes and penetrates anucleus of uranium-235. The nucleusbecomes highly unstable and splitsinto two lighter nuclei. This splittingprocess is called nuclear fission. Ifemitted neutrons go on to split othernuclei, the result is a chain reaction.Whenever particles penetrate andchange a nucleus, this is callednuclear reaction.
During the process of fission, bits ofmatter cease to exist and become vastquantities of energy instead. The energyproduced is given by ΔE = Δmc 2 whereΔm is the lost mass in kg and c is thespeed of light in m/s.Albert Einstein postulated this theorythat mass could be converted intoenergy.
A nuclear reactor is a device or a furnacewhere controlled fission chain reaction iscarried out and the energy released is usedto generate electricity.The reactor uses Uranium rods as fuel, andthe heat is generated by nuclearfission: neutrons smash into the nucleusof the uranium atoms, which split roughlyin half and release energy in the form ofheat. In nuclear reactions, the energy released per atom is around a million timesgreater than that from a chemical change such as burning.Carbon dioxide gas or water is pumped through the reactor to take the heataway, this then heats water to make steam. The steam drives turbines whichdrive generators. Modern nuclear power stations use the same typeof turbines and generators as conventional power stations.
The Sun and other stars are mostlymade of Hydrogen. At the centre ofthe Sun, tremendous temperaturesand pressures make the hydrogennuclei collide at such high speedsthat they join together (fuse) to formhelium nuclei. As this happens, hugeamounts of energy are released asheat and light. The energy travels upto the Sun’s glowing surface andthen passes through space to reachEarth.