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Nuclear Physics is the branch of physics that deals with the properties and structure of matter on the hadronic level. In this article we review briefly the history of this field, which has a major role in the development of our understanding of nature. We then proceed to give an outline of a current perspective of the field and of some of the issues that are now on its frontiers.
The concepts of temperature and equilibrium are not well defined in systems of particles with time-varying external forces. An example is a radio frequency ion trap, with the ions laser cooled into an ordered solid, characteristic of sub-mK temperatures, whereas the kinetic energies associated with the fast coherent motion in the trap are up to 7 orders of magnitude higher. Simulations with 1,000 ions reach equilibrium between the degrees of freedom when only aperiodic displacements (secular motion) are considered. The coupling of the periodic driven motion associated with the confinement to the nonperiodic random motion of the ions is very small at low temperatures and increases quadratically with temperature.
Excitation curves at 0° and 90° were studied for neutrons and γ rays produced in bombardment of thin targets of Be9, B10, B11, C13, and O18 by α particles with energies of from 1.8 to 5.3 Mev. Resonances were observed in the Be9(α, n)C12 reaction at bombarding energies of 1.9, 2.3, 2.6, 3.98, 4.4, and 5.0 Mev. The C13(α, n)O16 reaction showed resonances at 2.09, 2.25, 2.42, 2.605, 2.69, 2.775, 2.825, 3.09, 3.33, 3.42, 3.67, 3.73, 4.125, 4.42, 4.50, 4.63, 4.75, and 5.05 Mev. The B10(α, n)N13 excitation curve has resonances at 2.16, 2.25, 2.90, 4.53, 4.85, and 5.36 Mev, while the γ-ray yield from the B10(α, pγ)C13 reaction showed all these as well as resonances at 3.6 and 3.95 Mev. The B11(α, n)C13 reaction has resonances at bombarding energies of 2.06, 2.60, 2.93, 2.97, 3.23, 3.54, 3.72, 3.92, 4.25, 4.34, and 5.00 Mev. The O18(α, n)Ne21...
Comment: 15 pages, 13 figures, 4 tables, submitted to Phys. Rev. C, typos corrected
The simple structures formed by charged particles confined in a harmonic potential have been investigated and the configurations of minimum potential energy were identified. For fewer than 12 particles these form polyhedrons centered on the origin. For structures with 13-22 particles one sits in the middle, for 23-26 particles two are in the interior, etc., until a third shell starts forming at 60. When the isotropy of the trap is changed, distortions and discrete phase changes are seen. These structures should correspond to ones formed in ion traps at very low temperatures
The branching ratio for the electron-capture decay of 7Be to the 478 keV state in 7Li has been measured. 7Be nuclei recoiling near zero degrees from the 1H(7Li, 7Be)n reaction were counted by and implanted into a Si detector placed in the focal plane of an Enge split-pole spectrograph. After determining the total number of implanted 7Be nuclei from the pulse height spectrum, the absolute number of 478 keV γ rays was measured with a Ge(Li) detector. The resulting branching ratio of 10.61±0.23% agrees well with previous measurements.
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