Constraining Level Densities Using
Spectral Data
G. P. A. Nobre, D. A. Brown, and M. W. Herman
1 Introduction
As the nuclear excitation energy grows, due to the exponential increase of the
number of levels, one must deal with the level densities (LD) rather than with
individual levels. Several phenomenological models exist to describe the general
behavior of (LD), such as the Gilbert-Cameron (GC) [1] and others, which assume
simplified functional forms of the LD and are constrained by the often limited
availability of experimental data. It is known that there are only a few ways to
experimentally constrain LD, such as through the D 0 (LD at neutron separation
energy of the compound nucleus) or the matching at the excitation energy region
transitioning from discrete levels to LD.
More fundamental and predictive LD models like the microscopic Hartree-FockBogoliubov (HFB) [2] incorporated to the RIPL-3 parameter library [3] provide
more global and consistent LD, based on the intrinsic structure properties of nuclei
and observed distribution of discrete levels. This brings reliability to the LD in the
whole range of excitation energy, not only near the discrete-level cut-off or at D 0 .
Additionally, the HFB model provides more realistic spin and parity distributions
which emerge naturally from the model, while a phenomenological model such
as GC simplistically assumes equal distributions for parities and a Gaussian-like
distribution for spins.
G. P. A. Nobre () · D. A. Brown
National Nuclear Data Center, Brookhaven National Laboratory, Upton, NY, USA
e-mail: gnobre@bnl.gov
M. W. Herman
National Nuclear Data Center, Brookhaven National Laboratory, Upton, NY, USA
Los Alamos National Laboratory, Los Alamos, NM, USA
© 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_15
133
Spectral Data
G. P. A. Nobre, D. A. Brown, and M. W. Herman
1 Introduction
As the nuclear excitation energy grows, due to the exponential increase of the
number of levels, one must deal with the level densities (LD) rather than with
individual levels. Several phenomenological models exist to describe the general
behavior of (LD), such as the Gilbert-Cameron (GC) [1] and others, which assume
simplified functional forms of the LD and are constrained by the often limited
availability of experimental data. It is known that there are only a few ways to
experimentally constrain LD, such as through the D 0 (LD at neutron separation
energy of the compound nucleus) or the matching at the excitation energy region
transitioning from discrete levels to LD.
More fundamental and predictive LD models like the microscopic Hartree-FockBogoliubov (HFB) [2] incorporated to the RIPL-3 parameter library [3] provide
more global and consistent LD, based on the intrinsic structure properties of nuclei
and observed distribution of discrete levels. This brings reliability to the LD in the
whole range of excitation energy, not only near the discrete-level cut-off or at D 0 .
Additionally, the HFB model provides more realistic spin and parity distributions
which emerge naturally from the model, while a phenomenological model such
as GC simplistically assumes equal distributions for parities and a Gaussian-like
distribution for spins.
G. P. A. Nobre () · D. A. Brown
National Nuclear Data Center, Brookhaven National Laboratory, Upton, NY, USA
e-mail: gnobre@bnl.gov
M. W. Herman
National Nuclear Data Center, Brookhaven National Laboratory, Upton, NY, USA
Los Alamos National Laboratory, Los Alamos, NM, USA
© 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_15
133