13+-+Atoms+and+Radioactivity

**Nuclear Binding Energy:** Is the energy required to split a nucleus of an atom into its component parts. The component parts are neutrons and protons, which are collectively called nucleons. If the binding energy for the products is higher than the reactants the process (either fission or fusion) will result in a release of the extra binding energy.
 * Atoms and Radioactivity **

The mass of an atom's nucleus is always less than the sum of the individual masses of the constituent protons and neutrons. This difference is a measure of the nuclear binding energy. When a nucleus forms, energy goes into the forces holding it together. The missing mass (in the formed nucleus) is now present in the form of energy, holding the nucleons together. This same energy (the mass deficit) is released (in the form of photons/gamma rays/kinetic energy of particles) when the nucleus splits up. Total mass (and energy) is conserved throughout the process, it simply changes form/carrier.
 * Mass Deficit: **

**Nuclear Force:**  Electrons and nuclei are kept together by electric attraction (negative attracts positive). The force of electric attraction does not hold nuclei together, because all protons carry a positive charge and repel each other. the nuclear force, holds nuclei together. The nuclear force must be stronger than the electric repulsion at short distances, but weaker far away, or else different nuclei might tend to clump together. Therefore it has short-range characteristics. An analogy to the nuclear force is the force between two small magnets: magnets are very difficult to separate when stuck together, but once pulled a short distance apart, the force between them drops almost to zero.

**Fission and Fusion: ** Nuclear energy is released by the splitting (fission) or merging together (fusion) of the nuclei of atom(s). The conversion of nuclear mass-energy to a form of energy which can remove some mass when the energy is removed, is consistent with the mass-energy equivalence formula //ΔE// = //Δmc//², in which //ΔE// = energy release, //Δm// = mass deficit, and //c// = the speed of light in a vacuum (a physical constant). When this equation is used in this way, the mass "changes" only because it is removed from the system, not because it is converted or destroyed (the removed binding energy retains and accounts for the missing mass, which is a conserved quantity).

**The Binding Energy Curve:**

In the periodic table, the light elements from hydrogen up to sodium exhibit generally increasing binding energy per nucleon as the atomic mass increases. This increase is generated by increasing forces per nucleon in the nucleus, as each additional nucleon is attracted by other nearby nucleons, and thus more tightly bound to the whole.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 120%;">The region of increasing binding energy is followed by a region of relative stability (from magnesium through xenon). In this region, the nucleus has become large enough that nuclear forces no longer completely extend efficiently across its width. Attractive nuclear forces in this region, as atomic mass increases, are nearly balanced by repellent electromagnetic forces between protons, as the atomic number increases.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 120%;">At the peak of binding energy, <span class="wiki_link_ext">nickel-62 is the most tightly bound nucleus (per nucleon), followed by <span class="wiki_link_ext">iron-58 and <span class="wiki_link_ext">iron-56. This is the approximate basic reason why iron and nickel are very common metals in planetary cores.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 120%;">Finally, in elements heavier than xenon, there is a decrease in binding energy per nucleon as atomic number increases. In this region of nuclear size, electromagnetic repulsive forces are beginning to overcome the strong nuclear force attraction.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 140%;">**Class Slides:**