Halo Nuclei and Strong Force Range Limits
The effective absolute limit of the range of the strong force is represented by halo nuclei such as lithium-11 or boron-14, in which dineutrons, or other collections of neutrons, orbit at distances of about ten fermis (roughly similar to the 8 fermi radius of the nucleus of uranium-238). These nuclei are not maximally dense. Halo nuclei form at the extreme edges of the chart of the nuclides—the neutron drip line and proton drip line—and are all unstable with short half-lives, measured in milliseconds; for example, lithium-11 has a half-life of less than 8.6 milliseconds.
Halos in effect represent an excited state with nucleons in an outer quantum shell which has unfilled energy levels "below" it (both in terms of radius and energy). The halo may be made of either neutrons or protons . Nuclei which have a single neutron halo include 11Be and 19C. A two-neutron halo is exhibited by 6He, 11Li, 17B, 19B and 22C. Two-neutron halo nuclei break into three fragments, never two, and are called Borromean because of this behavior (referring to a system of three interlocked rings in which breaking any ring frees both of the others). 8He and 14Be both exhibit a four-neutron halo. Nuclei which have a proton halo include 8B and 26P. A two-proton halo is exhibited by 17Ne and 27S. Proton halos are expected to be more rare and unstable than the neutron examples, because of the repulsive electromagnetic forces of the excess proton(s).
Read more about this topic: Atomic Nucleus
Famous quotes containing the words halo, strong, force, range and/or limits:
“There is a touch of divinity even in brutes, and a special halo about a horse, that should forever exempt him from indignities.”
—Herman Melville (1819–1891)
“Strong currents drag many stones and bushes along with them, strong intellects many dense and muddled minds.”
—Friedrich Nietzsche (1844–1900)
“Making social comment is an artificial place for an artist to start from. If an artist is touched by some social condition, what the artist creates will reflect that, but you can’t force it.”
—Bella Lewitzky (b. 1916)
“Jane Addams, founder of Hull House, once asked, “How shall we respond to the dreams of youth?” It is a dazzling and elegant question, a question that demands an answer—a range of answers, really, spiraling outward in widening circles.”
—William Ayers, U.S. author. To Teach: The Journey of a Teacher, ch. 7 (1993)
“Predatory capitalism created a complex industrial system and an advanced technology; it permitted a considerable extension of democratic practice and fostered certain liberal values, but within limits that are now being pressed and must be overcome. It is not a fit system for the mid- twentieth century.”
—Noam Chomsky (b. 1928)