Module 4

• Nucleosynthesis - the study of nuclear processes responsible for the formation of the elements
• The first stage of element formation started in the Big Bang, and is thus called the Big Bang nucleosynthesis.
• All hydrogen and most of the helium in the universe were produced during the Big Bang nucleosynthesis.
• A small amount of lithium was also produced during the Big Bang nucleosynthesis.
• Element formation in our universe relies on nuclear fusion reactions.
• In nuclear fusion, smaller nuclei collide to make larger nuclei, and energy is released in the form of electromagnetic radiation.
• A star is a very hot ball of gas or a “nuclear fire”.
• Stars create elements by combining lighter nuclei into heavier nuclei via nuclear fusion reactions in their cores, in the process releasing energy in the form of electromagnetic radiation.
• Stars are natural nuclear reactors.
• Forming heavier nuclei from a cooler universe and larger space is difficult. This type of event happens only on supernovae, or stars that explode upon death.
• The elements are classified based on their atomic number, or the number of protons in their respective nuclei.
• Isotopes - atoms with the same number of protons but with a different number of neutrons.
• The number of nucleons affects the properties of the elements, most especially their abundance.
• The relative amounts of protons and neutrons in each element affect the element’s nuclear stability.
• The positioning and number of electrons in the element affect its chemical stability.
• Nuclear stability is defined as the ability of the element to retain its current nuclear state given a certain time interval.
• Nuclear stability is affected by the relative positions, or energy levels, of the nucleons.
• Belt stability - the relation of the relative number of protons and neutrons to the overall stability of the nucleus.
• Nucleosynthesis can be classified into two events:

  1. Big Bang nucleosynthesis
  2. Stellar nucleosynthesis
• Big Bang nucleosynthesis - the formation of lighter nuclei from the first moments of the universe
• Stellar nucleosynthesis - the formation of post-iron heavy nuclei from supernovae and nebular dusts
• The reactions that take place in nucleosynthesis require a very high temperature, which is characteristic of fusion reactions
• The events Big Bang nucleosynthesis and stellar synthesis are responsible for the existence and the current distribution of the chemical elements throughout the universe
• The elements are composed of three different subatomic particles:

  1. the proton
  2. the neutron
  3. the electron
• Neutrons - unstable, have half-life of 12 minutes
• Neutrons - decays to protons and electrons
• Hydrogen and helium were the only elements formed prior to star formation.
• Hydrogen - consists of 1 proton only
• Helium - results from the collisions between protons and neutrons
• Helium - consists of 2 protons and 2 neutrons
• When matter is made only of one kind of atom, it is called an element.
• Atomic number or the number of protons in the nuclei classify the elements.
• Atomic number - the identity of the element.
• Nucleon is the collective term for protons and neutrons.
• As the nucleus gets bigger, the higher the ignition temperature is required.
• Supernova nucleosynthesis - initial formation of the post-iron elements in the universe
• Nuclear reactions that create neutrons occur during a supernova.
• For elements of low atomic number, the ratio of protons and neutrons in stable nuclei is about 1:1.
• For elements of high atomic number, the ratio of protons and neutrons approaches 1:1.5.
• Bismuth - the stable nucleus with the highest number of neutrons and protons.