Formation and Synthesis of Heavier Elements

Study Notes

Stars have a life cycle that spans millions to billions of years, influenced by their mass.
The mass determines the amount of gas that collapses to form a star, which serves as fuel for fusion.

Mass ranges from a minimum of about thirteen Jupiter masses to masses similar to the Sun.
Begins as a cloud of gas and dust, primarily composed of hydrogen and helium from the Big Bang.
When nuclear fusion initiates, a yellow or red main sequence star forms, emitting energy from collisions within.
The fusion process starts with proton fusion, creating deuterons, which subsequently fuse to form helium.
A low mass star remains stable for billions of years, fusing hydrogen into helium while maintaining size and temperature.
As hydrogen depletes, the core shrinks and heats, accelerating fusion and leading to outer layer expansion, transforming into a red giant star.
The red giant phase lasts around a billion years until the core becomes predominantly helium, reaching the Helium Flash stage.
In this phase, heavier elements like carbon and oxygen are produced through the triple alpha process.
The star then transitions through the horizontal branch, expanding and becoming hotter until helium is exhausted.
The core collapses, leading to the asymptotic giant branch, with the star swelling again until a final explosion ejects outer layers, leaving a white dwarf.

High mass stars are significantly more massive than the Sun and have a rapid and explosive demise.
Formation begins with a large gas cloud, resulting in strong gravitational forces leading to higher core temperatures.
High temperatures accelerate fusion rates, producing a larger, hotter, blue main sequence star.
Unlike low mass stars, high mass stars exhaust their fuel within about a hundred million years.
As hydrogen runs out, the core contracts, heats up, and expands into a giant star, capable of fusing heavier elements.
These stars produce a sequence of fusion up to iron, the heaviest element that can be formed through fusion in stars.
A high mass star ends its lifecycle with a supernova, a tremendous release of energy that also creates elements heavier than iron.

Atomic spectra, akin to fingerprints, allow for the identification of elements present in samples.
Isotopes have the same number of protons but different neutron counts.
Dmitri Mendeleev formulated the Periodic Law and developed an early version of the periodic table based on atomic weight.
Henry Moseley established the concept of atomic number, linking it to the number of protons through X-ray spectroscopy.
X-ray spectroscopy is a technique for characterizing materials based on X-ray excitation.

Synthetic elements with atomic numbers higher than uranium (Z > 92) are classified as transuranic.
Neptunium (Z = 93) was synthesized by E.M. MacMillan in 1940 using uranium and neutrons.
Plutonium (Z = 94) was produced through nuclear reactions involving neptunium and other isotopes.

Alchemy is the ancient study aiming to transmute basic substances into others, often relating to magic and astrology.
Practiced largely during the Middle Ages and Renaissance, it sought methods for transforming base metals into gold and discovering a universal solvent or elixir of life.
Scholars and practitioners of this field are referred to as alchemists.