5. Atomic Physics

• Almost all the mass of an atom is concentrated in the nucleus.
• The nucleus consists of protons and neutrons.
• Total number of protons and neutrons is called the nucleon number.
• Isotopes are atoms of certain elements with the same proton numbers but different nucleon numbers (difference in number of neutrons).
• Isotopes have the same chemical properties but different physical properties (e.g., molecular mass, density).
• Protons can be thought of as atomic DNA.
• Ions are formed when an atom gains or loses electrons.
• Alpha particles are positively charged particles.
• Scattering of alpha particles by gold foil refers to the deflection of alpha particles when they collide with the atoms of a gold foil.
• An experiment was performed by Ernest Rutherford in 1909 to determine the structure of the atom. The results of the experiment showed that most of the mass of an atom is concentrated in a small, dense nucleus. A few alpha particles were deflected at large angles, indicating that they had encountered something massive in the gold foil. This led Rutherford to propose that the atom consists of a positively charged nucleus surrounded by electrons. The experiment helped to confirm the atomic model with a central nucleus and electrons in orbit around it.
• The 3 findings from the scattering of alpha particles by gold foil experiment:

  1. The majority of alpha particles passed through the foil without being deflected.
  2. Some alpha particles were slightly deflected, suggesting the existence of empty spaces within the foil.
  3. A small number of alpha particles were greatly deflected or completely bounced back, suggesting the presence of dense, positively charged objects within the foil.
• Nuclear fission involves the splitting of a heavy nucleus into two or more smaller nuclei.
• The nucleus is typically bombarded by a neutron, causing the nucleus to become unstable. This instability leads to the nucleus splitting into two or more smaller nuclei.
• When the nucleus splits, it also releases a large amount of energy and additional free neutrons. The free neutrons can then go on to collide with other nuclei, leading to a chain reaction. This chain reaction can be harnessed to produce nuclear energy or used in nuclear weapons.
• Nuclear fusion involves the joining of two or more lighter nuclei to form a heavier nucleus.
• Nuclear fusion requires high temperatures and pressures to overcome the repulsive forces between the positively charged nuclei. When the nuclei are joined, they form a single, heavier nucleus. The process releases a large amount of energy, which can also be harnessed to produce energy or used in weapons.
• During the process of fusion, a small amount of mass is transformed into a large amount of energy, according to the famous equation: $E=$$mc^2$

  This equation states that energy (E) is equal to mass (m) times the speed of light (c) squared.
• In the process of fusion, the total mass of the system decreases, but the total energy released is much greater.
• Determine which of the following emissions are alpha, beta and gamma emissions.

  A) Alpha

  B) Gamma

  C) Beta

  
• Radioactivity refers to the spontaneous emission of radioactive particles from an unstable nucleus.
• Radioactive emission is a way for the nucleus to become more stable by reducing its energy.
• There are three types of radioactive emission: alpha, beta and gamma.
• Alpha emission involves the release of alpha particles, which are helium nuclei.
• Beta emission involves the release of beta particles, which are high-energy electrons.
• Gamma emission involves the release of gamma rays, which are high-energy photons.
• The instability of a nucleus can be due to an imbalance of protons and neutrons, known as isotopes.
• The process of radioactivity can result in the nucleus changing into another element through a decay process.
• The nucleus of an unstable isotope emits nuclear radiation, including alpha, beta, and gamma rays, to become stable.
• The process of emitting nuclear radiation is called radioactive decay.
• Radioactive decay occurs spontaneously and randomly.
• The unstable nucleus before decay is called the parent nuclide.
• The stable nucleus produced after decay is called the daughter nuclide.
• During an alpha decay, a radioactive atom X decay and emits an alpha particle.
• A beta particle is an electron emitted from a nucleus.
• Beta particles are very small and move with very high speed.
• During a beta decay, a radioactive atom X decay and emits a beta particle.
• In beta decay, one of the neutron is disintegrated to become proton and electron. The electron is emitted out from the nucleus whereas the proton stay in the nucleus. Hence, the proton number goes up by 1 while the nucleon number remains unchanged.
• Gamma emission causes no change in nucleon or proton number. This is because gamma ray is an electromagnetic radiation and not a particle.
• In gamma decay:

  • Unstable nucleus undergoes radioactive decay

  • Daughter nucleus may still be unstable

  • Daughter nuclide undergoes another radioactive decay

  • Process continues until stable nuclide is reached

  • This is called series decay
• Radioactive decay occurs randomly and spontaneously, transforming an unstable nucleus into a more stable one.