Atomic Physics
Isotopes are varieties of the same element. They have the same chemical properties but different physical properties influencing how they behave in nuclear reactions. They have the same number of protons but different numbers of neutrons, therefore they have different atomic masses. For example, Carbon-12 has 6 protons and 6 neutrons, while Carbon-14 has 6 protons and 8 neutrons.
Hydrogen occurs in three isotopes Hydrogen-1 (most abundant), Hydrogen-2 (Deuterium) and Hydrogen-3 (Tritium).
Nuclear force is the force that keeps nuclei together. This force is independent of the charge. Unstable (radioactive) nuclides tend to disintegrate causing the formation of different nuclides and the release of radiation.
The original element, (before the disintegration) is called the parent nuclide and the newly formed elements are called daughter nuclides. Elements may transform into different elements when they disintegrate. This process is called Transmutation.
Three types of radiation have been described
radioactive elements contain large numbers of nuclei that do not all decay at the same time. A decay curve is a measure of how much time it takes for the amount of radioactive compound to be reduced by 50%. This amount of time can also be called 'half-life'. An element's half-life is always a uniform interval of time.
If we have 10 g of carbon-14 when an organism dies, after 5,730 years, we will have 5 g, and after another 5,730 years, we will have 2.5g. The age of a material can be determined using radioactive dating using the equation:
Where N is the amount of parent nuclide remaining. N0 is the original amount of parental nuclide. n is the number of half-lives that have passed.
Nuclear fission involves 'splitting' an atom into smaller nuclides to release nuclear energy. Nuclear fission is used in nuclear power generation with Uranium as the most common source of this power. The emitted neutrons strike more uranium atoms causing them to undergo fission. Heavy water (containing deuterium) acts as a moderator by slowing down neutrons to the correct speed to cause a fission chain reaction. Many safety mechanisms for example, neutron absorbing control rods are used to prevent the reactors from overheating. There is high release of gamma radiation released during nuclear fission, so thick shielding is required. Even the spent fuel still contains fission products that are highly radioactive and can remain reactive for over 10,000 years.
Nuclear fission is also used to create nuclear bombs.
Fusion is the reverse of Fission. It is the process that results in the formation of atoms. For example, two nuclide with extremely high energy collide to form a bigger nuclide.
The mass of a nucleus is always less than the mass of all the separate nucleons (protons and neutrons). This difference in mass is called the Mass Defect (Δm). According to Einstein's theory of relativity, mass and energy are interchangeable as described by the equation:
With ΔE as change in Energy (J), Δm as change in mass and c2 as the speed of light.
Around the 1930s, Paul Dirac, Werner Heisenberg, and Max Born established the foundations of quantum field theory. This theory involves mediating particles, which cause forces to act over a distance. These particles have not yet been observed, they are virtual particles so energy, momentum and mass are not relevant as they are for real particles. When applied to electric force, quantum field theory predicts that virtual photons are exchanged between charges.
By 1960, experiments with high energy colliders and cloud chambers led to the discovery of a large number of new subatomic particles. Most of them were unstable and quickly decayed into other particles.
In cloud chambers, moving charges cause condensation of gas, showing the path of the particle.
In bubble chambers charged particles traveling through liquefied helium or hydrogen cause visible bubbles to form.
Pair Production: A high energy photon causes the production of an electron and an antielectron i.e., positron). When matter and antimatter meet, they are converted back to energy.
Some examples of subatomic particles include Leptons, Hadrons, Fermions and Bosons.
Later in 1963, it was proposed that the many seemingly elementary particles might be made up of simpler, even more elementary particles. These are now called Quarks. They are inside subatomic particles, Therefore they have fractional charges. Quarks have either one third or two thirds of the elementary charge. For example, protons are made up of two up quarks and one down quark (uud) with the net charge at 1+. Neutrons are made up of one up quark and two down quarks.