Nuclear Physics (1986) / Chapter Skim
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4 Nuclei Under Extreme Conditions
4 Nuclei Under Extreme Conditions
Pages 87-106
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From page 87... ...
Increasingly, nuclear projectiles with heavier and heavier masses accelerated from medium to relativistic energies are being used in collisions with other nuclei to raise nuclear matter to high temperatures and densities, to create new elements and exotic isotopes, and to produce highly excited and deformed nuclear systems. Some projectile fragments that are formed in relativistic nuclear collisions appear to exhibit totally unexpected behavior not explained by current theory.
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From page 88... ...
Although tantalizing glimpses of extremely energetic heavy nuclei were caught in cosmic-ray experiments, these events were rare and uncontrollable. In 1974, however, the Bevalac accelerator at the Lawrence Berkeley Laboratory became capable of accelerating nuclei as heavy as iron to energies as high as 2.1 GeV per nucleon.
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From page 89... ...
collision of two heavy nuclei at relativistic energy, a nuclear fireball is created in which hundreds of individual nucleonnucleon collisions occur very rapidly before the produced particles are blasted outward in all directions. (This fireball is so infinitesimal that, if it exploded in one's eye, it would only appear as a pinpoint flash of light.)
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From page 90... ...
By contrast, the more nearly uniform angular distribution for the heavier niobium system indicated a much closer approach to equilibrium. This demonstrates the need for using the heaviest possible projectiles and targets in relativistic nuclear collisions.
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From page 91... ...
,~ ''/ 1 , ~ .. 1 ~ i' FIGURE 4.3 The participant-spectator model of relativistic nuclear collisions.
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From page 92... ...
The results of these correlations indicate source sizes 2 to 4 fermis in radius, which are typical of most atomic nuclei and hence plausible. Theoretical calculations using an intranuclear cascade model in which the nuclei are treated as collections of independently interacting particles for central argon-on-argon collisions at energies of 1 to 2 GeV per nucleon yield mean nuclear densities of about 4 times normal, or about 10~5 grams per cubic centimeter.
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From page 93... ...
· It could provide a testing ground for the growing list of theoretical ideas such as the existence of extraordinary forms of nuclear matter called density isomers and pion condensates" that have been among the foremost stimuli for experimental work in relativistic nuclear collisions in the past decade. · It would be progress toward the determination of such global nuclear properties as viscosity and thermal conductivity, which are important indicators of otherwise hidden aspects of the internucleon force.
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From page 94... ...
was the bombardment of radioactive targets heavier than uranium with nuclear projectiles as heavy as neon, to produce compound nuclei. Since heavy-ion accelerators are required for this research, the efforts have been concentrated at the Lawrence Berkeley Laboratory, the Joint Institute for Nuclear Research (JINR)
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From page 95... ...
This sequence of events is compatible only with a decay series starting with the nuclide 266109 and proceeding via two successive alpha emissions and one beta capture to the nuclide 258104, which then undergoes spontaneous fission. If corroborated, this event will represent the first identification of a new element through the characteristics of a single atom.
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From page 96... ...
Even under optimal conditions, however, the resulting compound nucleus contains substantial internal excitation (tens of MeV) and angular momentum, which must be quickly dissipated by the emission of light particles (mostly neutrons)
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From page 97... ...
The other 2400 are radioactive ones that, for the most part, have been artificially produced in particle accelerators or nuclear reactors; about 30 to 40 new ones are discovered each year. Studies of these unstable nuclides provide a wealth of valuable information about exotic nuclear decay modes, about the behavior of the nuclear ground state (mass, shape, and angular momentum)
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From page 98... ...
Within the past decade, however, as developing techniques have permitted the observation of predicted nuclides at or near the edge of stability, decay modes have been observed that involve the emission of more than one particle after the beta decay namely, beta-delayed two-neutron, three-neutron, and two-proton emission. Consider two representatives of these exotic nuclei, each of which lies at a limit of stability for the element in question.
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From page 99... ...
Since these studies require the detection of neutrons, which is difficult because they are neutral, the parent lithium nuclide is first separated and identified by an ingenious technique developed at the Laboratory for Nuclear and Mass Spectroscopy at Orsay, France. In this technique, the target for the accelerator beam also acts as a preferential collector of product alkali metal nuclei, which in turnowing to their particular surface-ionization properties-act as the ion source for an attached mass spectrometer.
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From page 101... ...
Among the most significant developments in the study of nuclei far from stability has been the increasing use of atomic-beam and laser techniques, which provide extremely accurate determinations of such quantities as the nuclear spin and the magnetic moment. The sensitivity of these methods permits measurements to be made on very small quantities of relatively short-lived isotopes, and long sequences of
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From page 102... ...
in Geneva, have made great progress possible. Nuclei with Extremely High Spin Nuclear reactions between heavy nuclear projectiles and heavyelement targets often produce compound nuclei that are spinning extremely fast, i.e., they have high angular momentum.
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From page 103... ...
Stephens, Lawrence Berkeley Laboratory.) The sudden internal rearrangement of the nucleus could be called a nucleusquake.
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From page 104... ...
Nonetheless, the similarity between these two phenomena from opposite ends of the cosmic scale provides a striking example of the universality of physical laws and of their power to extend our intellectual grasp of events far beyond ordinary experience.
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From page 105... ...
II Impacts of Nuclear Physics
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