- 3571 - PARTICLE ACCELERATORS - smashing atoms to see inside? A $942,000,000 particle accelerator in Michigan is officially inaugurating on May 2, 2022. Its experiments will chart unexplored regions of the landscape of exotic atomic nuclei and shed light on how stars and supernova explosions create most of the elements in the Universe.
---- 3571- PARTICLE ACCELERATORS - smashing atoms to see inside?
- The power of this facility, FRIB, could produce rare isotopes orders of magnitude faster than is possible with the NSCL and similar accelerators worldwide. The vanishing neutrinos could upend fundamental physics.
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- All FRIB experiments will start in the facility’s basement. Atoms of a specific element, typically uranium, will be ionized and sent into a 450-meter-long accelerator that bends like a paper clip to fit inside the 150-meter-long hall.
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- At the end of the pipe, the beam of ions will hit a graphite wheel that spins continuously to avoid overheating any particular spot. Most of the nuclei will pass through the graphite, but a fraction will collide with its carbon nuclei. This causes the uranium nuclei to break up into smaller combinations of protons and neutrons, each a nucleus of a different element and isotope.
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- This beam of assorted nuclei will then be directed up to a ‘fragment separator’ at ground level. The separator consists of a series of magnets that deflect each nucleus towards the right, each at an angle that depends on its mass and charge. By fine-tuning this process, the FRIB operators will be able to produce a beam consisting entirely of one isotope for each particular experiment.
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- The desired isotope can then be routed through a maze of beam pipes to one of many experimental halls. In the case of the rarest isotopes, production rates could be as low as “one nucleus a week“.
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- A unique feature of FRIB is that it has a second accelerator that can take the rare isotopes and smash them against a fixed target, to mimic the high-energy collisions that happen inside stars or supernovae.
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- Each uranium ion will also travel faster to the graphite target, carrying an energy of 200 mega-electronvolts, compared with the 140 MeV carried by ions in the NSCL. FRIB’s higher energy is in the ideal range for producing a vast number of different isotopes, including hundreds that have never been synthesized before.
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- The forces that hold atomic nuclei together are the result of the “strong force” , one the four fundamental forces of nature, and the same force that binds three quarks together to make a neutron or a proton. But nuclei are complex objects with many moving parts, and it is impossible to predict their structures and properties.
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- Acientists will study isotopes that have ‘magic’ numbers of protons and neutrons — 2, 8, 20, 28 or 50 — that make the structure of the nucleus especially stable because they form complete energy levels (known as shells).
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- Magic isotopes are particularly important because they provide the cleanest tests for the theoretical models. For many years scientists have studied tin isotopes with progressively fewer neutrons, edging towards tin-100, which has magic numbers of both neutrons and protons.
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- The Big Bang produced essentially only hydrogen and helium; the other chemical elements in the table up to iron and nickel formed mostly through nuclear fusion inside stars.
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- Heavier elements cannot form by fusion. They were forged by other means, typically through radioactive β-decay. This happens when a nucleus gains so many neutrons that it becomes unstable, and one or more of its neutrons turns into a proton, creating an element with a higher atomic number.
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- This can happen when nuclei are bombarded with neutrons in brief but cataclysmic events, such as a supernova or the merger of two neutron stars. One of FRIB’s main strengths will be to explore the neutron-rich isotopes that are made during these supernovae events.
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- The facility will help to answer the fundamental question of “how many neutrons can one add to a nucleus, and how does it change the interactions inside the nucleus?”.
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- A “Facility for Antiproton and Ion Research” (FAIR), an atom smasher that is under construction in Darmstadt, Germany, is scheduled to be completed in 2027 (although the freezing of Russia’s participation following the invasion of Ukraine could bring some delays).
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- FAIR will produce antimatter as well as matter, and will be able to store nuclei for longer periods of time. The smaller you go the bigger it gets!
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May 6, 2022 PARTICLE ACCELERATORS - smashing atoms to see inside? 3567
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