120454940
Quantum calculation of the barrier and internal wave contributions to light- and heavy-ion elastic scattering
We propose a new technique allowing the decomposition of the light- and heavy-ion elastic scattering amplitude into its barrier and internal wave components as defined by Brink and Takigawa. The method requires only minimum programming as it makes use of the reflection coefficients generated by any optical model code. Also, it can be applied to a wide range of potentials including folding model and model-independent potentials. The use and physical interest of the method are illustrated by applying it to a few representative examples ranging from ..cap alpha.. to heavy-ion scattering.
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
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.
42706318
Alpha-cluster spectroscopy in 40Ca and in the sd-shell closure region.
The low-energy {sup 36}Ar({alpha},{alpha}) elastic scattering data of Gaul {ital et} {ital al}. are analyzed within the frame of the optical model, using energy-independent Woods-Saxon squared or model-independent geometries for the real part of the potential. The optical-model scattering amplitude is decomposed into its barrier and internal wave components to understand the rapid and complicated evolution of the angular distributions with incident energy. The properties of the low-energy bound and quasibound states supported by this potential are compared with those of the states of the deformed 4p-4h rotational band in {sup 40}Ca, built on the {ital J}{sup {pi}}=0{sup +}, {ital E}{sub {ital x}}=3.35 MeV state. The possibility of extending this local potential model approach to neighboring nuclei near the {ital sd}-shell closure is discussed. A negative-parity band of states with appreciable {alpha}-cluster character, starting around the {alpha}-particle threshold, is expected to be systematically present in this mass region.
42989902
Potential description of the positive- and negative-energy properties of the alpha + 40Ca system and alpha -cluster structure of 44Ti.
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.
121467224
PARITY NONCONSERVATION IN NUCLEI
BS>The influence of the known weak interactions on the parity of nuclear states is discussed. Derivation of a parity nonconserving interaction rests on the assumption of a current-current hypothesis for the weak interactions. Consequently, observation of parity impurity effects would be an important confirmation of this hypothesis. A simple approximate method of treating the nuclear parity impurity is developed and applied in an effort to find experimental situations favorable to observation of effects due to such impurity. Parity-forbidden alpha decay from excited states of light nuclei and certain electromagnetic transitions in the heavy nuclei appear to be promising. Special attention was paid to the internal conversion electrons from the 123kev transition nn Lu/sup 173/ whose polarization is estimated to be about 0.4%. An effect on polarized neutrons analogous to optical rotation is also discussed. (auth)
120405009
NEUTRAL WEAK INTERACTION CURRENTS