- 3580 - ELEMENTS - Created in the 1st 3 Minutes? Einstein’s theory of Relativity specifies the expansion rate of the Universe. Run these equations backwards to the Big Bang. To within 3 minutes Nuclear physics and Quantum Mechanics equations are used to specify the temperature and density of each moment of cosmic history from 0.01 seconds to 3 minutes. Past 0.01 seconds these equations do not work. But, up to 3 minutes they do. We think.
--------------------- 3580- ELEMENTS - Created in the 1st 3 Minutes?
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- So what happened in the first 3 minutes? At 2 trillion Kelvin the Universe was cool enough to coalesce protons and neutrons a millionth of a second after the Big Bang. After 1 second fusion reactions can begin but this window lasts only for 3 minutes. After 3 minutes the Universe has expanded and cooled so much fusion reactions stop. Mostly only hydrogen and helium are created.
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- Nuclear synthesis is when the first fusion created the first elements. When it first began the protons outnumbered the neutrons 7 to 1. The neutron is slightly heavier than the proton. In 10 minutes on average a neutron will decay into a proton, and electron and an anti-neutrino.
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- When fusion first occurred protons collided with neutrons and formed the nucleus of deuterium, H2. Deuterium is a proton and a neutron which is a stable isotope of hydrogen.
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- Deuterium nuclei formed 100 seconds after the Big Bang. This in turn lead to fusion reactions of nuclei with 2 protons and 2 neutrons which is the helium nuclei, He4. Further nuclear fusion created tritium, H3, and He3, or light helium. Fusion reactions in nuclear synthesis also created small amounts of lithium, Li3, and beryllium, Be4. At this point the Universe had expanded and cooled to where fusion reactions stopped.
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- None of the beryllium or tritium from nuclear synthesis survives till today. Beryllium 7 is not stable and the nucleus decays into Lithium 7 with a half-life of 53 days. Tritium decays to helium3 with a half-life of 12 years. The helium, He4, is stable and survived to represent 24% of all the elements. Hydrogen being 74% and all the other 114 elements are only 2%.
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----------------------------- Here is step by step how this nuclear synthesis occurred in the first 3 minutes:
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- A neutron collided with a deuterium nuclei, De2, releasing energy as radiation and forming tritium nuclei, H3.
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- A proton, hydrogen nuclei H1, collides with a tritium nuclei, H3, releasing energy and forming helium nuclei, He4.
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- A deuterium nuclei, De2, and a hydrogen nuclei collide releasing energy and form helium nuclei, He3.
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- A neutron and helium, He3, collide and create helium nuclei, He4, releasing more energy.
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- Helium nuclei, He4, collide with a tritium nuclei, H3, releasing energy and forming lithium nuclei, Li7
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- All this happened in the first 3 minutes when the Universe was dense enough and hot enough to have fusion reactions. After that it was too cool to sustain fusion. No more elements were created.
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- We have to wait 100 million years to when the first stars formed and later exploded as supernovae.
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- An atomic nucleus is tiny. 100,000,000,000 of atomic nuclei stacked on top of each other are the thickness of a piece of paper. (print first if you have a visualization problem). An electron is about 2,000 times smaller than a nucleus.
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- Energy is always seeking its lowest energy state. It so happens that the element that is in its lowest energy state is nickel. First iron, then nickel. So, why isn’t the Universe simply one nickel element? Why do we still have 116 different elements roaming about?
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- Only a few elements were produced in the Big Bang. More elements were produced later in the cores of stars. Still more elements were produced in star explosions, supernovae.
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------------------------- Here is the story of the creation of those 116 elements.
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- The Big Bang expanded too fast and cooled too fast to produce many elements. Really only 2 elements, hydrogen and helium. Lithium and Beryllium were also produced but rarely and under unusual circumstances. Basically, in round numbers, the Universe was 75% hydrogen and 25% helium until the first stars were formed.
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- Stars release energy by fusing hydrogen and helium into heavier elements. Forming a carbon atom, for example, involves the collision of two atoms beryllium 8 and helium 4. If the combined energy of their collision exactly equals the energy of a heavier element then they transform into that new element.
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- If the energy of motion, the kinetic energy of the collision, is too much the nuclei have to reduce energy by also emitting another particle in order to fuse. If the total energy of the collision is too little the atomic nuclei simply bounce off each other.
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- At about 100,000,000 Kelvin beryllium 8 and helium 4 nuclei have the right energy to collide and fuse into a carbon atom. Beryllium 8 decays in 10^-16 seconds, therefore, trillions of atoms must be involved in the collisions for much carbon to be produced.
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- Stars create all the elements heavier than helium up to the element nickel. Since nickel is the lowest energy element nuclear fusion stops there. Elements heavier than nickel must be formed by something other than star formation. Once nickel is formed nuclear fusion stops and the star explodes in a supernova and spreads its elements into interstellar space.
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- To get the heavier than nickel elements neutrons are involved. Since neutrons are neutral they can be captured by an atomic nucleus. Then, through radioactive decay the neutron turns into a proton, plus an electron, plus an anti-neutrino. This process adds a proton to the nucleus and creates a heavier element.
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- A catch here is that free neutrons , by themselves, decay in about 10 minutes. So, atomic nuclei do not have much time to capture a neutron in their nucleus. Fortunately, star formation emit’s a stream of neutrons and any nuclei in their path is a likely capture. This is a slow process of element production but over a billion years it accounts for about 50% of the heavier metals up to lead.
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- What about elements heavier than lead? Well, we need a whole lot of neutrons, in a very dense environment, and a very high temperature. Neutron Stars are certainly likely candidates for heavy element production. Supernovae explosions that create a Neutron Star at the core are the likely source for heavier than lead production.
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- Stars come in all sizes. With diameters the size of Earth’s orbit around the Sun to the size of a small island in the Pacific. All stats exist in a balancing act between their collapse due to gravity and the push of their own fusion radiation.
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- Small stars live a long time producing helium through hydrogen fusion. When the hydrogen runs out the helium fusion begins but it requires a much higher temperature. So the star expands in to a Red Giant. A star of 10 Solar Mass will swell to a 1,000 times greater size. This is how small stars die but only after billions of years.
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- Big stars burn their fuel much faster due to their immense gravity. They produce all the elements up to nickel in only 10’s of millions of years. Once nickel is produced fusion stops and the star explodes as a supernova.
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- Eventually all stars die. From ashes to ashes, from dust to dust, Everything formed from the first generation of stars will eventually cool and go dark. And, that Gomer, is the end of the story.
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May 16, 2022 ELEMENTS - Created in the 1st 3 Minutes? 1153 1154 3580
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--------------------- --- Tuesday, May 17, 2022 ---------------------------
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