35383178
Molecular interpretation of the oscillations of the fusion excitation function for the alpha +40Ca system.
The oscillations observed in the experimental ..cap alpha..+ /sup 40/Ca fusion excitation function between E/sub ..cap alpha../ -- 10 and 27 MeV are described within the frame of the optical model. Use is made of an existing optical potential giving a precise description of the elastic scattering data for E/sub ..cap alpha../>24 MeV on a broad angular range, which is extrapolated to lower incident energies. A correct description of elastic scattering experimental excitation functions between E/sub ..cap alpha../ -- 12 and 18 MeV, as well as of the fusion excitation function, is achieved by using different imaginary geometries for both processes. The oscillations appearing in the calculated fusion excitation function are due to maxima in the even-l transmission coefficients, for l ranging from 6 to 12; these maxima correspond to shape resonances in the underlying potential, which are associated with states belonging to an excited positive parity band with N -- 14 in the ..cap alpha..+ /sup 40/Ca system. The same potential predicts an N -- 12 positive parity band of states whose energies are in good agreement with the /sup 44/Ti experimental ground state band. It is shown that the correct reproduction of the spacing between the fusion oscillationsmore » achieved here results from the use of a deep real potential, which automatically yields a decoupling between positive and negative parity bands.« less
119969931
Optical-model Description of Alpha+o-16 Elastic-scattering and Alpha-cluster Structure in Ne-20
O16(,) elastic scattering angular distributions have been measured for incident energies 39.3, 49.5, and 69.5 MeV. These data, and previous measurements at 32.2, 104, and 146 MeV, have been subjected to a global optical model analysis. The deduced global potential has two energy-dependent parameters which are found to vary smoothly with energy and it is uniquely determined by the data. Backward angular distributions measured between 40 and 54 MeV are also presented and shown to be nicely reproduced by the model. The sensitivity of the cross sections to the various regions of the real potential has been investigated as a function of energy using the notch test technique. The low energy behavior of the differential cross sections can be understood in terms of the semiclassical decomposition of Brink and Takigawa. A natural extrapolation of the global potential below 30 MeV is shown to reproduce the wide bump observed in the experimental excitation functions around 20 MeV. This bump is shown to be due to an l=8 shape resonance and is interpreted as the J=8+ member of the K=04+ rotational band of Ne20, in contradiction with the current attribution. Other bound and quasibound states supported by the potential are discussed in the light of orthogonality condition model-type arguments and shown to be consistent with the well-known K=01+ and 0- bands, and with the first three states of the K=04+ band of Ne20. NUCLEAR REACTIONS O16(,), measured (), E=39.3, 49.5, 69.5 MeV; global optical model analysis, E=32-146 MeV; semiclassical decomposition of the scattering amplitude; investigation of the compatibility of the potential description with existing low energy data and comparison with cluster models. © 1983 The American Physical Society.
123154942
Elastic and inelastic scattering of alpha particles from Ca-40, Ca-44 over a broad range of energies and angles
Angular distributions for alpha -particle elastic scattering by /sup 40,44/Ca and excitation of the 3.73 MeV 3/sup -/ collective state of /sup 40/Ca were measured for incident energies ranging from 40 to 62 MeV. An extensive optical model analysis of these elastic scattering cross sections and other available data, using squared Woods-Saxon form factors, results in potentials with fixed geometry for both real and imaginary parts and depths with smooth energy behavior over a broad incident energy range. These results are discussed in the frame of the semi-classical approximation developed by Brink and Takigawa (1977). The sensitiveness of the calculated elastic scattering cross sections to the real part of the potentials as a function of the projectile-target distance has been investigated by means of a notch test. Distorted-wave Born-approximation calculations for the excitation of the 3.73 MeV 3/sup -/ state of /sup 40/Ca are presented.
123108693
Connection of Kukulin's nucleon-nucleon deep potential with realistic repulsive core interactions
The on-shell equivalence of the deep quantum-chromodynamically motivated realistic nucleon-nucleon interaction recently proposed by Kukulin et al. with more conventional repulsive-core forces is investigated by eliminating its unphysical deeply bound states, while preserving its scattering properties and the binding energy of the deuteron. The resulting interaction, which is built both in the singlet and triplet channels, displays ar−2 singular repulsive core followed by a shallow attraction of intermediate range, in good semiquantitative agreement with existing realistic nucleon-nucleon interactions.
123123854
Evidence for alpha-particle clustering in the Ti44 nucleus
The ..cap alpha..-particle cluster structure of /sup 44/Ti, which is of considerable interest for investigation of the persistence of ..cap alpha.. clustering in the region of the sd-shell closure, is studied within the frame of a local-potential approach. It is shown that the model leads to specific predictions if continuity with existing unique ..cap alpha..+ /sup 40/Ca optical potentials is insisted upon; in particular, the existence of an as yet experimentally unknown ..cap alpha..-cluster negative-parity band, starting just above the ..cap alpha..+ /sup 40/Ca threshold, is strongly suggested.
42989902
Potential description of the positive- and negative-energy properties of the alpha + 40Ca system and alpha -cluster structure of 44Ti.
37852212
Quark matter or new particles?
It has been argued that compression of nuclear matter to somewhat higher densities may lead to the formation of stable quark matter. A plausible alternative, which leads to radically new astrophysical scenarios, is that the stability of quark matter simply represents the stability of new particles compounded of quarks. A specific example is the SU(3)-symmetric version of the ..cap alpha.. particle, composed of spin-zero pairs of each of the baryon octet (an ''octet'' particle).