Deconvolution of the Photon Strength
Function
Richard B. Firestone
There is ongoing interest in comparing photonuclear PSF data with reaction PSF
data measured at the Oslo cyclotron and elsewhere. Significant differences in these
measurements occur due to large variations in the spin distributions and level
densities populated by each reaction. It is important to recognize that the PSF is
different from the nuclear structure GSF which is based on reduced matrix elements
defined as B(σ L) values. This is because the PSF is defined as the product of LDF
and GSF functions. In addition, photonuclear reactions excite higher levels from the
ground state while reactions populate γ -rays that deexcite these higher levels. The
GSF depends on the γ -ray direction due to differences in the population of magnetic
substates in the initial and final states. Thus a γ -ray populating an excited state may
have a different strength than the same energy γ -ray deexciting that state.
Photonuclear reactions measure the cross section for predominantly E1 excitation
of levels above the neutron separation energy, S n . These transitions populate only a
narrow range of excited state spins, J XS , with respect to the ground state spin, J GS ,
where J XS = J GS , J GS ±1, and a single parity, π XS = −π GS . For even–even nuclei
only J π
XS = 1 − states are populated. In order to extract the photonuclear GSF a J π
dependent LDF is required. Conversely, Oslo charged particle reactions populate
levels below the neutron separation energy, S n , that deexcite by γ -rays of all
multipolarities. These data are analyzed by the Oslo method [1] which determines
both an absolute LDF and a relative PSF. Attempts to renormalize the Oslo PSF
data for comparison with the photonuclear PSF and other PSF data is problematic
because the level densities and spin distributions populated in these experiments
vary widely.
R. B. Firestone ()
Nuclear Engineering Department, University of California, Berkeley, CA, USA
e-mail: rbfirestone@lbl.gov
© This is a U.S. government work and not under copyright protection
in the U.S.; foreign copyright protection may apply 2021
J. Escher et al. (eds.), Compound-Nuclear Reactions, Springer Proceedings in
Physics 254, https://doi.org/10.1007/978-3-030-58082-7_21
179
Function
Richard B. Firestone
There is ongoing interest in comparing photonuclear PSF data with reaction PSF
data measured at the Oslo cyclotron and elsewhere. Significant differences in these
measurements occur due to large variations in the spin distributions and level
densities populated by each reaction. It is important to recognize that the PSF is
different from the nuclear structure GSF which is based on reduced matrix elements
defined as B(σ L) values. This is because the PSF is defined as the product of LDF
and GSF functions. In addition, photonuclear reactions excite higher levels from the
ground state while reactions populate γ -rays that deexcite these higher levels. The
GSF depends on the γ -ray direction due to differences in the population of magnetic
substates in the initial and final states. Thus a γ -ray populating an excited state may
have a different strength than the same energy γ -ray deexciting that state.
Photonuclear reactions measure the cross section for predominantly E1 excitation
of levels above the neutron separation energy, S n . These transitions populate only a
narrow range of excited state spins, J XS , with respect to the ground state spin, J GS ,
where J XS = J GS , J GS ±1, and a single parity, π XS = −π GS . For even–even nuclei
only J π
XS = 1 − states are populated. In order to extract the photonuclear GSF a J π
dependent LDF is required. Conversely, Oslo charged particle reactions populate
levels below the neutron separation energy, S n , that deexcite by γ -rays of all
multipolarities. These data are analyzed by the Oslo method [1] which determines
both an absolute LDF and a relative PSF. Attempts to renormalize the Oslo PSF
data for comparison with the photonuclear PSF and other PSF data is problematic
because the level densities and spin distributions populated in these experiments
vary widely.
R. B. Firestone ()
Nuclear Engineering Department, University of California, Berkeley, CA, USA
e-mail: rbfirestone@lbl.gov
© This is a U.S. government work and not under copyright protection
in the U.S.; foreign copyright protection may apply 2021
J. Escher et al. (eds.), Compound-Nuclear Reactions, Springer Proceedings in
Physics 254, https://doi.org/10.1007/978-3-030-58082-7_21
179