Nuclear Fission

    In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts (lighter nuclei), often producing free neutrons and protons (in the form of gamma rays), as well. Fission of heavy elements is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments. For fission to produce energy, the total binding energy of the resulting elements has to be higher than that of the starting element. Fission is a form of nuclear transmutation because the resulting fragments are not the same element as the original atom. 

    Nuclear fission produces energy for nuclear power and to drive the explosion of nuclear weapons. Both uses are made possible because certain substances called nuclear fuels undergo fission when struck by free neutrons and in turn generate neutrons when they break apart. This makes possible a self-sustaining chain reaction that releases energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon.

    The nuclear chain reactions can be classified into 2 categories:

• Controlled chain reaction: this type of reaction is present in nuclear power facilities. By all sorts of methods, the number of neutrons that bombard the target nucleus is controlled and kept under high observation. 
• Uncontrolled chain reaction: this type of reaction is present in nuclear bombs, where the number of neutrons is not controlled, therefore resulting an enormous quantity of energy released in a very small space in a very short time.

    The amount of free energy contained in nuclear fuel is millions of times the amount of free energy contained in a similar mass of chemical fuel such as gasoline, making nuclear fission a very tempting source of energy. The products of nuclear fission, however, are on average far more radioactive than the heavy elements which are normally fissioned as fuel, and remain so for significant amounts of time, giving rise to a nuclear waste problem.  

Atomic Nucleus

    The atomic nucleus was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. 

    The diameter of the nucleus is in the range of 1.6 fm (1.6×10−15 m) for hydrogen to about 15 fm for the heaviest atoms, such as uranium. These dimensions are much smaller than the diameter of the atom itself. 

    The branch of physics concerned with studying and understanding the atomic nucleus, including its composition and the forces which bind it together, is called nuclear physics.

    The nuclear force is highly attractive at very small distances, and this overwhelms the repulsion between protons which is due to the electromagnetic force, thus allowing nuclei to exist. However, because the residual strong force has a limited range because it decays quickly with distance, only nuclei smaller than a certain size can be completely stable. The largest known completely stable nucleus is lead-208 which contains a total of 208 nucleons (126 neutrons and 82 protons). 

    The nuclear radius (R) is considered to be one of the basic things that any model must explain. For stable nuclei the nuclear radius is roughly proportional to the cube root of the mass number (A) of the nucleus, and particularly in nuclei containing many nucleons, as they arrange in more spherical configurations. 

    In other words, packing protons and neutrons in the nucleus gives approximately the same total size result as packing hard spheres of a constant size (like marbles) into a tight spherical or semi-spherical bag. 

Short Introduction in Nuclear Physics

PHYSICS is a natural science that studies matter and the motion of matter in space-time. Since the beginning of mankind, we have tried to explain everything we see, hear, feel, making supernatural efforts to understand phenomena "unrolling under our noses". Mankind searched for answers to questions like: why are we here? or how it all began? or is there extraterrestrial life? and many more. These questions can be seen from a philosophical or a scientific point of view.

We now know that our Universe is made of tiny particles (when I say "tiny" I mean really really really small) held together by all sort of forces to form all the objects we recognize with our 5 senses. These particles were named ATOMS.

If objects are made out of atoms, what are atoms made of?

An atom is made of the NUCLEUS and the ELECTRONIC CLOUD.

If the atom is made of the nucleus and the electronic cloud, then what are these made of?

The electrons (as far as we know) have no inner structure. The nucleus on the other hand is made of PROTONS and NEUTRONS. Protons are pozitive-charged particles (whereas electrons are negative-charged particles); and neutrons (like the name suggests) are neutral from an electrical charge point of view. Almost the entire mass of an atom is concentrated in the nucleus, which is a lot more heavier that the electronic cloud. The atom is electrically stable, being composed of a pozitive nucleus and a negative electron cloud.

If we use the letter "Z" to express the number of electrons and "A" the number of particles in the nucleus, then "N" being equal to A-Z will be the number of neutrons. Keep in mind that the number of protons is equal to the number of electrons.

Imagine an atom similar to our solar system. The Sun being in the middle (it represents the pozitive nucleus) and the planets orbiting around it (they represent the negative electrons). This is the so-called Planetary Model of the Atom (I will cover this subject later).