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Mobile virtual network operators (MVNOs) in the United States lease wireless telephone and data service from the four major cellular carriers in the country—AT&T Mobility, Boost Mobile, T-Mobile US, and Verizon—and offer various levels of free and/or paid talk, text and data services to their customers.
The top five wireless providers operate nationwide wireless networks which cover most of the population in the United States, while smaller carriers provide native network coverage across selected regions of the United States while supplementing nationwide coverage through roaming agreements with other carriers.
Helium-4 makes up about one quarter of the ordinary matter in the universe by mass, with almost all of the rest being hydrogen. While nuclear fusion in stars also produces helium-4, most of the helium-4 in the Sun and in the universe is thought to have been produced during the Big Bang, known as "primordial helium". However, primordial helium-4 ...
These commonly bind together into an atomic nucleus, e.g. a helium-4 nucleus is composed of two protons and two neutrons. Most hadrons do not live long enough to bind into nucleus-like composites; those that do (other than the proton and neutron) form exotic nuclei. Overlap between Bosons, Hadrons, and Fermions
Illustration of a proton–proton chain, from hydrogen forming deuterium, helium-3, and regular helium-4. Nuclear transmutation is the conversion of one chemical element or an isotope into another chemical element. [1] Nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus of an atom is changed.
Helium 3 is rare on Earth, primarily produced by the radioactive decay of tritium, but it does reside in abundance in the lunar regolith, deposited by billions of years of solar wind.
An exception to this general trend is the helium-4 nucleus, whose binding energy is higher than that of lithium, the next heavier element. This is because protons and neutrons are fermions, which according to the Pauli exclusion principle cannot exist in the same nucleus in exactly the same state. Each proton or neutron's energy state in a ...
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