Formation And Synthesis of Heavier Elements PDF

FORMATION AND SYNTHESIS OF HEAVIER ELEMENTS STAR CYCLE The life cycle of any star from birth to death, and all stages in between, will span millions or billions of years. The path to be followed by a particular star depends mainly o...

FORMATION AND SYNTHESIS OF HEAVIER ELEMENTS STAR CYCLE The life cycle of any star from birth to death, and all stages in between, will span millions or billions of years. The path to be followed by a particular star depends mainly on its mass, or how much gas is collected and collapsed to form a star, because that material will serve as a star’s fuel. STAR CYCLE LOW MASS OR AVERAGE STAR  This would range from the smallest that stars can be, meaning the smallest amount of material that can sufficiently trigger nuclear fusion to qualify as a star, which is about thirteen Jupiter masses, to a star somewhere in the ballpark of our sun’s mass.  As we already know, any star will begin as a cloud of gas and dust at least a few light years across.  In the earliest era of star formation, this material was almost exclusively hydrogen and helium, as this was the remains after the brief seventeen minutes of nucleosynthesis soon after the Big Bang.  When nuclear fusion begins, it establishes equilibrium, and it generates a yellow or red main sequence star that glows with all energy released from the collision happening inside.  The fusion reaction begins with two protons fusing, followed by subsequent beta decay, to get proton and neutron, and we call it deuteron, which is a nucleus of heavy hydrogen. Then deuterons are involved in reactions that make helium, which has two protons and two neutrons.  Such a star will continue in this manner for a billions of years, slowly fusing all of the hydrogen in its core into helium and maintaining a relatively the same size, temperature and luminosity as it does so, until almost all the hydrogen is gone.  The core of the star will shrink and get hotter, which make the remaining hydrogen burn even faster and all that extra energy being generated will be radiated outward and push the outer layer away from the core.   As the outer layers expand, they cool and thus become more and more red, and the star become of what we called the red giant star. The star can maintain this new status for around a billion years but after all the hydrogen is gone, the core will get smaller and even hotter.  A phase called Helium Flash makes things so hot that the stars can fuse heavier helium nuclei into larger nuclei like carbon and oxygen through something called the triple alpha process, which means that the star has whole new source of fuel.  The stars begin pulsating as it runs through its final energy reserve entering the horizontal branch and at this time, it becomes smaller, hotter and bluer until all helium fused into larger nuclei.  Once the core is predominantly carbon and oxygen, it will collapse, and the star enters the asymptomatic giant branch. This means it will grow rapidly and become a giant star again, until the last burst of energy ejects to the outer layer, leaving only a tiny very hot bare core behind about the size of the Earth.  This will gradually cool and will contract further until we are left with a white dwarf star.  HIGH MASS STAR High mass star is one that is much more massive than the sun, and their demise will not be so quiet  Things start out normally with gas collecting cloud under the influence of gravity. This means that this cloud will be much larger than that of low mass stars, so it will contain much more mass.  More mass means more gravity, which means the force pushing inward is much stronger and star gets much hotter.  A hotter temperature means faster fusion which generates greater outward pressure to counteract the greater inward pull of gravity  It will result in a main sequence star that is hot, big, bright, and blue.  Low mass stars take billions of years to use up their fuel, while high mass stars are much hotter and can use up all their fuel in a hundred million years only.  As the fuel starts running out, the core contracts and heats up producing more energy so that the star will swell up into a giant star just like in a low mass star.  But while the core of a high mass star continues to compress, it gets much hotter, and it becomes able to fuse helium nuclei to form carbon and then oxygen, neon, silicon each heavier nucleus being relegated to a smaller and smaller region of the core that is hot enough to fuse it. All the way at the center sits the heaviest element that can be fused within a star, iron.  As this occurs in the different layers, the star is left with a core of iron nuclei that are so stable that further fusion can release no more energy.  One of the violent and energetic phenomena in the universe is called supernova.  A supernova generates an unbelievable burst of energy.  In this brief moment, dozens of elements heavier than iron can also be synthesized such as nickel, copper, zinc, silver and gold.  Any element with an atomic number greater than 26 is made either in a supernova or a rare event like a collision of two neutron star or a neutron star collide with black hole. SYNTHESIS OF ELEMENTS  Atomic spectra can help us identify elements like fingerprints to identify people.  It serves as a characteristic property for each element, which allows scientists to identify the elements present in sample.  An isotope of an element has the same number of protons but a different number of neutrons in the nucleus of the atom.  Dmitri Ivanovich Mendeleev was a DMITRI Russian chemist and inventor. MENDELEEV  He was best remembered for formulating the Periodic Law and creating a farsighted version of the periodic table of elements.  He created a classification of elements based on their atomic weight.  He found that organizing the elements by their calculated weight demonstrated a periodic pattern of both physical and chemical properties, such as luster, physical state, reactivity to water and others.  Henry Gwyn Jeffreys Moseley was an HENRY MOSELEY English physicist, whose contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic number. This stemmed from his development of Moseley's law in X-ray spectra. The experimental evidence he gave to an existing hypothesis: that the elements’ atomic number, or place in the periodic table, was uniquely tied to their “positive charge”, or the number of protons they had. His method of identifying elements by shooting electrons and looking at x-rays became a very useful tool in characterizing elements, and is now called x-ray spectroscopy. X-ray spectroscopy is a general term for several spectroscopic techniques for characterization of materials by using x-ray excitation.  The invention of the device called cyclotron paved the way for transmuting one element into another artificially. The high-energy particles SYNTHESIS OF that are produced from the cyclotron upon hitting heavy target nuclei produce heavier ELEMENTS nuclei.  The bombarding of Molybdenum with deuteron formed technetium which is the first artificially made element. Its name is derived from the Greek word technetos which means artificial. THE TRANSURANIC  Transuranic elements are ELEMENTS synthetic elements with atomic numbers higher than that of Uranium(Z = 92).  Neptunium (Z = 93) – synthesized by E.M. MacMillan in 1940 23892U + 10n —> 23993Np + 0-1ß  Plutonium (Z = 94) 23892U + 21H —> 23893Np + 210n 23893Np —> 23894Np+ 0-1ß  THE SUPERHEAVY Superheavy elements are elements ELEMENTS with atomic numbers beyond 103. These are produced by bombarding heavy nuclear targets with accelerated heavy projectiles. Bohrium (Z = 107) – projectile used was Cr 20983Bi + 5424Cr —> 261107Bh + 210n   Alchemy is the very old study and philosophy of how to change basic substances (such as metals) into other ALCHEMY substances.  It also studied how substances (and how they are changed into other substances) were related to magic and astrology.  It was practiced in the Middle Ages and the Renaissance and concerned principally with discovering methods for transmuting baser metals into gold and with finding a universal solvent and an elixir of life.  Alchemists – refer to people who studied alchemy.