2. Nuclear Data File Format¶

2.1. Incident Neutron Data¶

/

Attributes:	version (int[2]) – Major and minor version of the data

/<nuclide name>/

Attributes:	Z (int) – Atomic number A (int) – Mass number. For a natural element, A=0 is given. metastable (int) – Metastable state (0=ground, 1=first excited, etc.) atomic_weight_ratio (double) – Mass in units of neutron masses n_reaction (int) – Number of reactions
Datasets:	energy (double[]) – Energy points at which cross sections are tabulated

/<nuclide name>/kTs/

<TTT>K is the temperature in Kelvin, rounded to the nearest integer, of the temperature-dependent data set. For example, the data set corresponding to 300 Kelvin would be located at 300K.

Datasets:	<TTT>K (double) – kT values (in eV) for each temperature TTT (in Kelvin)

/<nuclide name>/reactions/reaction_<mt>/

Attributes:	mt (int) – ENDF MT reaction number label (char[]) – Name of the reaction Q_value (double) – Q value in eV center_of_mass (int) – Whether the reference frame for scattering is center-of-mass (1) or laboratory (0) n_product (int) – Number of reaction products

/<nuclide name>/reactions/reaction_<mt>/<TTT>K/

<TTT>K is the temperature in Kelvin, rounded to the nearest integer, of the temperature-dependent data set. For example, the data set corresponding to 300 Kelvin would be located at 300K.

Datasets:

xs (double[]) – Cross section values tabulated against the nuclide energy grid for temperature TTT (in Kelvin)
Attributes:
threshold_idx (int) – Index on the energy grid that the reaction threshold corresponds to for temperature TTT (in Kelvin)

/<nuclide name>/reactions/reaction_<mt>/product_<j>/

Reaction product data is described in Reaction Products.

/<nuclide name>/urr/<TTT>K/

<TTT>K is the temperature in Kelvin, rounded to the nearest integer, of the temperature-dependent data set. For example, the data set corresponding to 300 Kelvin would be located at 300K.

Attributes:	interpolation (int) – interpolation scheme inelastic (int) – flag indicating inelastic scattering other_absorb (int) – flag indicating other absorption factors (int) – flag indicating whether tables are absolute or multipliers
Datasets:	energy (double[]) – Energy at which probability tables exist table (double[][][]) – Probability tables

/<nuclide name>/total_nu/

This special product is used to define the total number of neutrons produced from fission. It is formatted as a reaction product, described in Reaction Products.

/<nuclide name>/fission_energy_release/

Datasets:

fragments (polynomial) – Energy released in the form of fragments as a function of incident neutron energy.
prompt_neutrons (polynomial or tabulated) – Energy released in the form of prompt neutrons as a function of incident neutron energy.
delayed_neutrons (polynomial) – Energy released in the form of delayed neutrons as a function of incident neutron energy.
prompt_photons (polynomial) – Energy released in the form of prompt photons as a function of incident neutron energy.
delayed_photons (polynomial) – Energy released in the form of delayed photons as a function of incident neutron energy.
betas (polynomial) – Energy released in the form of betas as a function of incident neutron energy.
neutrinos (polynomial) – Energy released in the form of neutrinos as a function of incident neutron energy.
q_prompt (polynomial or tabulated) – The prompt fission Q-value (fragments + prompt neutrons + prompt photons - incident energy)
q_recoverable (polynomial or tabulated) – The recoverable fission Q-value (Q_prompt + delayed neutrons + delayed photons + betas)

2.2. Thermal Neutron Scattering Data¶

/

Attributes:	version (int[2]) – Major and minor version of the 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’).

/<thermal name>/kTs/

<TTT>K is the temperature in Kelvin, rounded to the nearest integer, of the temperature-dependent data set. For example, the data set corresponding to 300 Kelvin would be located at 300K.

Datasets:	<TTT>K (double) – kT values (in eV) for each temperature TTT (in Kelvin)

/<thermal name>/elastic/<TTT>K/

<TTT>K is the temperature in Kelvin, rounded to the nearest integer, of the temperature-dependent data set. For example, the data set corresponding to 300 Kelvin would be located at 300K.

Datasets:	xs (tabulated) – Thermal inelastic 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)

/<thermal name>/inelastic/<TTT>K/

<TTT>K is the temperature in Kelvin, rounded to the nearest integer, of the temperature-dependent data set. For example, the data set corresponding to 300 Kelvin would be located at 300K.

Datasets:

xs (tabulated) – 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 correlated angle-energy distribution.

2.3. Reaction Products¶

Object type:

Group

Attributes:

particle (char[]) – Type of particle
emission_mode (char[]) – Emission mode (prompt, delayed, total)
decay_rate (double) – Rate of decay in inverse seconds
n_distribution (int) – Number of angle/energy distributions

Datasets:

yield (function) – Energy-dependent yield of the product.

Groups:

distribution_<k> – Formats for angle-energy distributions are detailed in Angle-Energy Distributions. When multiple angle-energy distributions occur, one dataset also may appear for each distribution:
Datasets:
applicability (function) – Probability of selecting this distribution as a function of incident energy

2.4. One-dimensional Functions¶

2.4.1. Scalar¶

Object type:	Dataset
Datatype:	double
Attributes:	type (char[]) – ‘constant’

2.4.2. Tabulated¶

Object type:	Dataset
Datatype:	double[2][]
Description:	x-values are listed first followed by corresponding y-values
Attributes:	type (char[]) – ‘Tabulated1D’ breakpoints (int[]) – Region breakpoints interpolation (int[]) – Region interpolation codes

2.4.3. Polynomial¶

Object type:	Dataset
Datatype:	double[]
Description:	Polynomial coefficients listed in order of increasing power
Attributes:	type (char[]) – ‘Polynomial’

2.4.4. Coherent elastic scattering¶

Object type:	Dataset
Datatype:	double[2][]
Description:	The first row lists Bragg edges and the second row lists structure factor cumulative sums.
Attributes:	type (char[]) – ‘bragg’

2.5. Angle-Energy Distributions¶

2.5.1. Uncorrelated Angle-Energy¶

Object type:

Group

Attributes:

type (char[]) – ‘uncorrelated’

Datasets:

angle/energy (double[]) – energies at which angle distributions exist
angle/mu (double[3][]) – tabulated angular distributions for each energy. The first row gives \(\mu\) values, the second row gives the probability density, and the third row gives the cumulative distribution.
Attributes:
offsets (int[]) – indices indicating where each angular distribution starts

interpolation (int[]) – interpolation code for each angular distribution

Groups:

energy/ (energy distribution)

2.5.2. Correlated Angle-Energy¶

Object type:

Group

Attributes:

type (char[]) – ‘correlated’

Datasets:

energy (double[]) – Incoming energies at which distributions exist
Attributes:
interpolation (double[2][]) – Breakpoints and interpolation codes for incoming energy regions

energy_out (double[5][]) – Distribution of outgoing energies corresponding to each incoming energy. The distributions are flattened into a single array; the start of a given distribution can be determined using the offsets attribute. The first row gives outgoing energies, the second row gives the probability density, the third row gives the cumulative distribution, the fourth row gives interpolation codes for angular distributions, and the fifth row gives offsets for angular distributions.

Attributes:	offsets (double[]) – Offset for each distribution interpolation (int[]) – Interpolation code for each distribution n_discrete_lines (int[]) – Number of discrete lines in each distribution

mu (double[3][]) – Distribution of angular cosines corresponding to each pair of incoming and outgoing energies. The distributions are flattened into a single array; the start of a given distribution can be determined using offsets in the fifth row of the energy_out dataset. The first row gives angular cosines, the second row gives the probability density, and the third row gives the cumulative distribution.

2.5.3. Kalbach-Mann¶

Object type:

Group

Attributes:

type (char[]) – ‘kalbach-mann’

Datasets:

energy (double[]) – Incoming energies at which distributions exist
Attributes:
interpolation (double[2][]) – Breakpoints and interpolation codes for incoming energy regions

distribution (double[5][]) – Distribution of outgoing energies and angles corresponding to each incoming energy. The distributions are flattened into a single array; the start of a given distribution can be determined using the offsets attribute. The first row gives outgoing energies, the second row gives the probability density, the third row gives the cumulative distribution, the fourth row gives Kalbach-Mann precompound factors, and the fifth row gives Kalbach-Mann angular distribution slopes.

Attributes:	offsets (double[]) – Offset for each distribution interpolation (int[]) – Interpolation code for each distribution n_discrete_lines (int[]) – Number of discrete lines in each distribution

2.5.4. N-Body Phase Space¶

Object type:	Group
Attributes:	type (char[]) – ‘nbody’ total_mass (double) – Total mass of product particles n_particles (int) – Number of product particles atomic_weight_ratio (double) – Atomic weight ratio of the target nuclide in neutron masses q_value (double) – Q value for the reaction in eV

2.6. Energy Distributions¶

2.6.1. Maxwell¶

Object type:	Group
Attributes:	type (char[]) – ‘maxwell’ u (double) – Restriction energy in eV
Datasets:	theta (tabulated) – Maxwellian temperature as a function of energy

2.6.2. Evaporation¶

Object type:	Group
Attributes:	type (char[]) – ‘evaporation’ u (double) – Restriction energy in eV
Datasets:	theta (tabulated) – Evaporation temperature as a function of energy

2.6.3. Watt Fission Spectrum¶

Object type:	Group
Attributes:	type (char[]) – ‘watt’ u (double) – Restriction energy in eV
Datasets:	a (tabulated) – Watt parameter \(a\) as a function of incident energy b (tabulated) – Watt parameter \(b\) as a function of incident energy

2.6.4. Madland-Nix¶

Object type:	Group
Attributes:	type (char[]) – ‘watt’ efl (double) – Average energy of light fragment in eV efh (double) – Average energy of heavy fragment in eV

2.6.5. Discrete Photon¶

Object type:	Group
Attributes:	type (char[]) – ‘discrete_photon’ primary_flag (int) – Whether photon is a primary energy (double) – Photon energy in eV atomic_weight_ratio (double) – Atomic weight ratio of target nuclide in neutron masses

2.6.6. Level Inelastic¶

Object type:	Group
Attributes:	type (char[]) – ‘level’ threshold (double) – Energy threshold in the laboratory system in eV mass_ratio (double) – \((A/(A + 1))^2\)

2.6.7. Continuous Tabular¶

Object type:

Group

Attributes:

type (char[]) – ‘continuous’

Datasets:

energy (double[]) – Incoming energies at which distributions exist
Attributes:
interpolation (double[2][]) – Breakpoints and interpolation codes for incoming energy regions

distribution (double[3][]) – Distribution of outgoing energies corresponding to each incoming energy. The distributions are flattened into a single array; the start of a given distribution can be determined using the offsets attribute. The first row gives outgoing energies, the second row gives the probability density, and the third row gives the cumulative distribution.

Attributes:	offsets (double[]) – Offset for each distribution interpolation (int[]) – Interpolation code for each distribution n_discrete_lines (int[]) – Number of discrete lines in each distribution