Update I/O format for thermal neutron scattering

docs/source/io_formats/nuclear_data.rst

@@ -215,11 +215,9 @@ Thermal Neutron Scattering Data
 **/<thermal name>/**
 
 :Attributes: - **atomic_weight_ratio** (*double*) -- Mass in units of neutron masses
-             - **nuclides** (*char[][]*) -- Names of nuclides for which the thermal
-               scattering data applies to
-             - **secondary_mode** (*char[]*) -- Indicates how the inelastic
-               outgoing angle-energy distributions are represented ('equal',
-               'skewed', or 'continuous').
+             - **energy_max** (*double*) -- Maximum energy in [eV]
+             - **nuclides** (*char[][]*) -- Names of nuclides for which the
+               thermal scattering data applies to
 
 **/<thermal name>/kTs/**
 
@@ -237,11 +235,13 @@ temperature-dependent data set.  For example, the data set corresponding to
 temperature-dependent data set.  For example, the data set corresponding to
 300 Kelvin would be located at `300K`.
 
-:Datasets: - **xs** (:ref:`tabulated <1d_tabulated>`) -- Thermal inelastic
+:Datasets:
+           - **xs** (:ref:`function <1d_functions>`) -- Thermal elastic
              scattering cross section for temperature TTT (in Kelvin)
-           - **mu_out** (*double[][]*) -- Distribution of outgoing energies
-             and angles for coherent elastic scattering for temperature TTT
-             (in Kelvin)
+
+:Groups:
+         - **distribution** -- Format for angle-energy distributions are
+           detailed in :ref:`angle_energy`.
 
 **/<thermal name>/inelastic/<TTT>K/**
 
@@ -249,18 +249,13 @@ temperature-dependent data set.  For example, the data set corresponding to
 temperature-dependent data set.  For example, the data set corresponding to
 300 Kelvin would be located at `300K`.
 
-:Datasets: - **xs** (:ref:`tabulated <1d_tabulated>`) -- Thermal inelastic
+:Datasets:
+           - **xs** (:ref:`function <1d_functions>`) -- Thermal inelastic
              scattering cross section for temperature TTT (in Kelvin)
-           - **energy_out** (*double[][]*) -- Distribution of outgoing
-             energies for each incoming energy for temperature TTT (in Kelvin).
-             Only present if secondary mode is not continuous.
-           - **mu_out** (*double[][][]*) -- Distribution of scattering cosines
-             for each pair of incoming and outgoing energies. for temperature
-             TTT (in Kelvin).  Only present if secondary mode is not continuous.
 
-If the secondary mode is continuous, the outgoing energy-angle distribution is
-given as a :ref:`correlated angle-energy distribution
-<correlated_angle_energy>`.
+:Groups:
+         - **distribution** -- Format for angle-energy distributions are
+           detailed in :ref:`angle_energy`.
 
 .. _product:
 
@@ -332,7 +327,17 @@ Coherent elastic scattering
 :Datatype: *double[2][]*
 :Description: The first row lists Bragg edges and the second row lists structure
               factor cumulative sums.
-:Attributes: - **type** (*char[]*) -- 'bragg'
+:Attributes: - **type** (*char[]*) -- 'CoherentElastic'
+
+Incoherent elastic scattering
+-----------------------------
+
+:Object type: Dataset
+:Datatype: *double[2]*
+:Description: The first value is the characteristic bound cross section in [b]
+              and the second value is the Debye-Waller integral in
+              [eV\ :math:`^{-1}`].
+:Attributes: - **type** (*char[]*) -- 'IncoherentElastic'
 
 .. _angle_energy:
 
@@ -434,6 +439,68 @@ N-Body Phase Space
                target nuclide in neutron masses
              - **q_value** (*double*) -- Q value for the reaction in eV
 
+Coherent Elastic
+----------------
+
+This angle-energy distribution is used specifically for coherent elastic thermal
+neutron scattering.
+
+:Object type: Group
+:Attributes: - **type** (*char[]*) -- "coherent_elastic"
+:Hard link: - **xs** -- Link to the coherent elastic scattering cross section
+
+Incoherent Elastic
+------------------
+
+This angle-energy distribution is used specifically for incoherent elastic
+thermal neutron scattering (derived from an ENDF file directly).
+
+:Object type: Group
+:Attributes: - **type** (*char[]*) -- "incoherent_elastic"
+:Datasets:
+           - **debye_waller** (*double*) -- Debye-Waller integral in
+             [eV\ :math:`^{-1}`]
+
+Incoherent Elastic (Discrete)
+-----------------------------
+
+This angle-energy distribution is used for discretized incoherent elastic
+thermal neutron scattering distributions that are present in ACE files.
+
+:Object type: Group
+:Attributes: - **type** (*char[]*) -- "incoherent_elastic_discrete"
+:Datasets:
+           - **mu_out** (*double[][]*) -- Equiprobable discrete outgoing
+             angles for each incident neutron energy tabulated
+
+Incoherent Inelastic
+--------------------
+
+This angle-energy distribution is used specifically for (continuous) incoherent
+inelastic thermal neutron scattering.
+
+:Object type: Group
+:Attributes: - **type** (*char[]*) -- "incoherent_inelastic"
+:Datasets: The datasets for this angle-energy distribution are the same as for
+           :ref:`correlated angle-energy distributions
+           <correlated_angle_energy>`.
+
+Incoherent Inelastic (Discrete)
+-------------------------------
+
+This angle-energy distribution is used specifically for incoherent inelastic
+thermal neutron scattering where the distributions have been discretized into
+equiprobable bins.
+
+:Object type: Group
+:Attributes: - **type** (*char[]*) -- "incoherent_inelastic_discrete"
+:Datasets: - **energy_out** (*double[][]*) -- Distribution of outgoing
+             energies for each incoming energy.
+           - **mu_out** (*double[][][]*) -- Distribution of scattering cosines
+             for each pair of incoming and outgoing energies.
+           - **skewed** (*int8_t*) -- Whether discrete angles are equi-probable
+             (0) or have a skewed distribution (1).
+
 .. _energy_distribution:
 
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