THE ROLE PLAYED BY GR IN NEUTRON-NUCLEUS SCATTERING

  • Virtual excitation of GR in neutron-nucleus seattering is studied for a particular type of unclei. (Nuclei with a hole in a neutron close shell such as 87Sr.) It is found that for such type of nuclei the contribution to inelastic scattering is important even when the incident neutron energy is arround 3 MeV in contrast to the case of close shell target nuclei as investigated by V. Geramb.For an incident neutron energy En~3MeV, besides the compound nucleus formation, the following two processes also contribute to the inelastic cross section:

    The intermediate states involving the virtual excitation of the GR's are treated phenomenologically as well as microscopically. In the former case they are taken to be simple resonances with definite widths. For resonable values of parameters Cλτ (or (ao)λτ), Γλτ and Δ, the contribution to the inelastic cross section due to GR's is about 10 mb. In the latter case, the GR's are taken to be a collection of 1p1h RPA phonons each with definite width. Here the coupling constant x between phonon and nucleons is taken to be 0.00337 MeV in accordance with the value given by A. Bohr, Again the contribution to the inelastic cross section is about 10 mb. One can therefore expect that this reaction mechanism is present in a variety of reactions besides (n, n') with sizable cross section. The energy of the incident partiele E at which the effect of the GR's is expected to be strongest depends on the structure of the target nucleus. For (n, n'). E~hωλτ-Sn where Sn is the neutron seperation energy of the target plus one neutron nuclei in the ground state and hωλτ is energy of GR with isospin τ and multipolarity λ.It is needed further to investigate to what extent the phenomenological treatment of the intermediate states by representing the GR as a single resonance phonon will be valid and what best values for the width should be taken.This has somthing to do with the nature of the GR's when treated as oscillations in the quantum fluid, the nuclear matter of finite extension.
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  • [1] Von Cieramb et al., Nucl. Phys., A199 (1973),545;Phys. Lett., 52B(1974), 138; Phys. Rev., C12 (1975),1697.[2] J.H. E. Mattaueh. W. Thiele and A.H. Wapatra, Nucl. Phys., 67(1965), 1[3] M.B.Lewia and F. E. Bertranda Nucl. Phys., A196(1972), 337.[4] T.K.Temperley, Nuclear Science and Eng., 32(1968), 195.[5] A.Bohr and B. R. Mottelson, Nuclear Structure, Vol. 2, chap. 6.[6] A. Lepretre and M. Sugawara, Nucl. Phys., A175(1971),809; A.Likar, Nucl. Phys., A298 (1978), 217.[7] J. Bromqvist and a. Wahlborn, Arkiv or Fysik, 16146,(1959),545, G. E. Brown and J. H.Gunn, P. Could, Nucl. Phys., 64(1963), 598.[8] D. R. Bess and R. A. Broglia. Phys. Rev., C3(1971), 2349.[9] H. F. Liu and G. E. Brown, Nucl. Phys., A265(1976), 385.[10] D. R. Res and R. A. Borensen, Advance in Nuclear Physics, Vol. 2.
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YANG LI-MING, ZHONG YU-SHU and ZHOU ZHI-NING. THE ROLE PLAYED BY GR IN NEUTRON-NUCLEUS SCATTERING[J]. Chinese Physics C, 1981, 5(2): 255-264.
YANG LI-MING, ZHONG YU-SHU and ZHOU ZHI-NING. THE ROLE PLAYED BY GR IN NEUTRON-NUCLEUS SCATTERING[J]. Chinese Physics C, 1981, 5(2): 255-264. shu
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Received: 1980-11-11
Revised: 1900-01-01
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THE ROLE PLAYED BY GR IN NEUTRON-NUCLEUS SCATTERING

Abstract: Virtual excitation of GR in neutron-nucleus seattering is studied for a particular type of unclei. (Nuclei with a hole in a neutron close shell such as 87Sr.) It is found that for such type of nuclei the contribution to inelastic scattering is important even when the incident neutron energy is arround 3 MeV in contrast to the case of close shell target nuclei as investigated by V. Geramb.For an incident neutron energy En~3MeV, besides the compound nucleus formation, the following two processes also contribute to the inelastic cross section:

The intermediate states involving the virtual excitation of the GR's are treated phenomenologically as well as microscopically. In the former case they are taken to be simple resonances with definite widths. For resonable values of parameters Cλτ (or (ao)λτ), Γλτ and Δ, the contribution to the inelastic cross section due to GR's is about 10 mb. In the latter case, the GR's are taken to be a collection of 1p1h RPA phonons each with definite width. Here the coupling constant x between phonon and nucleons is taken to be 0.00337 MeV in accordance with the value given by A. Bohr, Again the contribution to the inelastic cross section is about 10 mb. One can therefore expect that this reaction mechanism is present in a variety of reactions besides (n, n') with sizable cross section. The energy of the incident partiele E at which the effect of the GR's is expected to be strongest depends on the structure of the target nucleus. For (n, n'). E~hωλτ-Sn where Sn is the neutron seperation energy of the target plus one neutron nuclei in the ground state and hωλτ is energy of GR with isospin τ and multipolarity λ.It is needed further to investigate to what extent the phenomenological treatment of the intermediate states by representing the GR as a single resonance phonon will be valid and what best values for the width should be taken.This has somthing to do with the nature of the GR's when treated as oscillations in the quantum fluid, the nuclear matter of finite extension.

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