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-------------------- 2594 - ATOM - what happens inside atoms?
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- Those protons and neutrons cluster together, bound by what's called the strong force. And the numbers of protons and neutrons determine whether the atom is iron or oxygen or xenon, and whether it's radioactive or stable.
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- No one knows how those protons and neutrons (together known as nucleons) behave inside an atom. Outside an atom, protons and neutrons have definite sizes and shapes. Each of them is made up of three smaller particles called quarks, and the interactions between those quarks are so intense that no external force should be able to deform them, not even the powerful forces between particles in a nucleus.
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- But for decades, researchers have known that the theory is in some way wrong. Experiments have shown that, inside a nucleus, protons and neutrons appear much larger than they should be. Physicists have developed two competing theories that try to explain that weird mismatch.
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- Since at least the 1940s, physicists have known that nucleons move in tight little orbitals within the nucleus. The nucleons, confined in their movements, have very little energy. They are restrained by the “strong force“.
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- In 1983, physicists at the European Organization for Nuclear Research (CERN) noticed something strange: Beams of electrons bounced off iron in a way that was very different from how they bounced off free protons. That was unexpected; if the protons inside hydrogen were the same size as the protons inside iron, the electrons should have bounced off in much the same way.
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- Over time, scientists came to believe it was a size issue. For some reason, protons and neutrons inside heavy nuclei act as if they are much larger than when they are outside the nuclei. Researchers call this phenomenon the EMC effect, after the European Muon Collaboration, the group that accidentally discovered it. It violates existing theories of nuclear physics.
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- While quarks, the subatomic particles that make up nucleons, strongly interact within a given proton or neutron, quarks in different protons and neutrons can't interact much with each other. The strong force inside a nucleon is so strong it eclipses the strong force holding nucleons to other nucleons.
And as long as nucleons stay in their orbitals, that's the case. However, recent experiments have shown that at any given time, about 20% of the nucleons in a nucleus are in fact outside their orbitals. Instead, they're paired off with other nucleons, interacting in "short range correlations.
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- Under those circumstances, the interactions between the nucleons are much higher-energy than usual. That's because the quarks poke through the walls of their individual nucleons and start to directly interact, and those quark-quark interactions are much more powerful than nucleon-nucleon interactions.
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- These interactions break down the walls separating quarks inside individual protons or neutrons. The quarks making up one proton and the quarks making up another proton start to occupy the same space. This causes the protons (or neutrons, as the case may be) to stretch and blur. They grow a lot, albeit for very short periods of time. That skews the average size of the entire cohort in the nucleus producing the EMC effect.
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- QCD stands for quantum chromodynamics, the system of rules that govern the behavior of quarks. The problem is that the complete QCD equations describing all the quarks in a nucleus are too difficult to solve. Modern supercomputers are about 100 years away from being fast enough for the task. And even if supercomputers were fast enough today, the equations haven't advanced to the point where you could plug them into a computer.
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- The fields operate at such tiny distances that they're of negligible magnitude outside the nucleus, but they're powerful inside of it. These force fields, which he calls "mean fields" actually deform the internal structure of protons, neutrons and pions (a type of strong force-carrying particle). Just like if you take an atom and you put it inside a strong magnetic field, you will change the internal structure of that atom.
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- Mean-field theorists think that possible short-range correlations likely explain some portion of the EMC effect. The results of experiments in the next few years could resolve the question. An experiment underway at Jefferson National Accelerator Facility in Virginia that will move nucleons closer together, bit by bit, and allow researchers to watch them change.
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- This "polarized EMC experiment" would break up the effect based on the spin (a quantum trait) of the protons involved. It might reveal unseen details of the effect that could aid calculations.
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- Other Reviews to help you learn about atoms:
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- 2377 - ATOM - defining the atom All the other elements in the periodic table above hydrogen and helium were created in the nuclear fusion of the stars The first stars formed with only hydrogen and helium. When they burned all their fuel and exploded as supernova they splattered the surrounding space with all the atoms in the higher level elements.
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- 2452 - ATOMS -Michael Discovers Atoms. - My grandson, Michael, was looking at pond water under his microscope. He could see small plants and animals moving around in the water. But, he also saw all the little pieces of dust jiggling, almost vibrating, in a zigzag manner. He asked me what causes everything to move like that?
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- 2333 - Rainbows can tell us what the Universe is made of. Introduction to the science of spectroscopy.
- 2318 - Brownian motion from atoms you can not see.
- 2315 - About how atoms were first discovered.
- 2307 - How small is the atom?
- 2255 - History of the atom.
- 2256 - Atom’s stability and uncertainty?
- 983 - How an atom works? All the math formulas.
- 985 - Measuring how an atom works?
- 924 - Rutherford’s atom. How the atom was discovered in 1911.
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- January 23, 2020 2594
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