Problem of Level Densities
119
of discrete levels and the neutron binding energy. However, such an approach still
needs experimental support. Theoretical studies based on Monte-Carlo Shell model
calculations [27] support decreasing of the spin cutoff parameter at low energies in
the region of iron isotopes.
It has been shown in Ref. [28] that the anisotropy of the angular distribution
of outgoing particles in compound nuclear reactions is determined by the orbital
momentums of incoming and outgoing particles and by the spin distribution of
the levels populated in residual nucleus. It creates possibility of studying the
spin cutoff parameter experimentally from studying particle angular distributions
from compound nuclear reactions. There are few experimental studies available in
literature [18, 29, 30]. In some of them there are indications of deviations of the
spin cutoff parameter from the form of the Eq. 2. However, there are no established
conclusions achieved so far, which suggests that more experiments are needed.
There is an experimental technique to study the level density for specific spin
states and parities using high resolution (p, p ) experiments [31]. Level density is
extracted from fluctuations of high resolution spectra of outgoing protons. Such
a technique with combination of other techniques, for example, with particle
evaporation spectra would allow us to study the spin cutoff parameter as well.
Further experimental studies of the spin cutoff parameter are considered to be
extremely important for constraining level density models.
4 Possible Projects on Constraining Level Density Models
It appears that widely used level density models based only on data from neutron
resonances reached the limit of their accuracy. It suggests that the best strategy to
constrain model uncertainties is to conduct analysis of experimental information
delivered by all experimental techniques and methods including, but not limited
to, neutron resonances, the Oslo and particle evaporation methods, inelastic proton
scattering. This type of analysis has not been performed so far and all level density
models used in modern reaction codes continue using parameterizations based on
neutron resonances only. The following possible projects to address this problem
appear to be important
• Study of systematics deviations of the level density excitation energy dependence
from the constant temperature model using experimental data obtained with Oslo
and particle evaporation techniques. It would help constraining the excitation
energy dependence of model functions, including problem of distinguishing
between FGM and GCM.
• Study of level densities with the analysis of particle evaporation spectra from
compound nuclear reactions. It would be possible to obtain absolute values
of level densities. By comparing the absolute values with data from neutron
resonance spacings, the spin distribution and the spin cutoff parameter can be
estimated.
119
of discrete levels and the neutron binding energy. However, such an approach still
needs experimental support. Theoretical studies based on Monte-Carlo Shell model
calculations [27] support decreasing of the spin cutoff parameter at low energies in
the region of iron isotopes.
It has been shown in Ref. [28] that the anisotropy of the angular distribution
of outgoing particles in compound nuclear reactions is determined by the orbital
momentums of incoming and outgoing particles and by the spin distribution of
the levels populated in residual nucleus. It creates possibility of studying the
spin cutoff parameter experimentally from studying particle angular distributions
from compound nuclear reactions. There are few experimental studies available in
literature [18, 29, 30]. In some of them there are indications of deviations of the
spin cutoff parameter from the form of the Eq. 2. However, there are no established
conclusions achieved so far, which suggests that more experiments are needed.
There is an experimental technique to study the level density for specific spin
states and parities using high resolution (p, p ) experiments [31]. Level density is
extracted from fluctuations of high resolution spectra of outgoing protons. Such
a technique with combination of other techniques, for example, with particle
evaporation spectra would allow us to study the spin cutoff parameter as well.
Further experimental studies of the spin cutoff parameter are considered to be
extremely important for constraining level density models.
4 Possible Projects on Constraining Level Density Models
It appears that widely used level density models based only on data from neutron
resonances reached the limit of their accuracy. It suggests that the best strategy to
constrain model uncertainties is to conduct analysis of experimental information
delivered by all experimental techniques and methods including, but not limited
to, neutron resonances, the Oslo and particle evaporation methods, inelastic proton
scattering. This type of analysis has not been performed so far and all level density
models used in modern reaction codes continue using parameterizations based on
neutron resonances only. The following possible projects to address this problem
appear to be important
• Study of systematics deviations of the level density excitation energy dependence
from the constant temperature model using experimental data obtained with Oslo
and particle evaporation techniques. It would help constraining the excitation
energy dependence of model functions, including problem of distinguishing
between FGM and GCM.
• Study of level densities with the analysis of particle evaporation spectra from
compound nuclear reactions. It would be possible to obtain absolute values
of level densities. By comparing the absolute values with data from neutron
resonance spacings, the spin distribution and the spin cutoff parameter can be
estimated.