# 3. Nuclear Data File Formats¶

## 3.1. Incident Neutron Data¶

/

Attributes
• filetype (char[]) – String indicating the type of file

• 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[]) – Energies in [eV] 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

• redundant (int) – Whether reaction is redundant

/<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 (function) – Energy released in the form of fragments as a function of incident neutron energy.

• prompt_neutrons (function) – Energy released in the form of prompt neutrons as a function of incident neutron energy.

• delayed_neutrons (function) – Energy released in the form of delayed neutrons as a function of incident neutron energy.

• prompt_photons (function) – Energy released in the form of prompt photons as a function of incident neutron energy.

• delayed_photons (function) – Energy released in the form of delayed photons as a function of incident neutron energy.

• betas (function) – Energy released in the form of betas as a function of incident neutron energy.

• neutrinos (function) – Energy released in the form of neutrinos as a function of incident neutron energy.

• q_prompt (function) – The prompt fission Q-value (fragments + prompt neutrons + prompt photons - incident energy)

• q_recoverable (function) – The recoverable fission Q-value (Q_prompt + delayed neutrons + delayed photons + betas)

## 3.2. Incident Photon Data¶

/

Attributes
• filetype (char[]) – String indicating the type of file

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

/<element>/

Attributes
• Z (int) – Atomic number

Datasets
• energy (double[]) – Energies in [eV] at which cross sections are tabulated

/<element>/bremsstrahlung/

Attributes
• I (double) – Mean excitation energy in [eV]

Datasets
• electron_energy (double[]) – Incident electron energy in [eV]

• photon_energy (double[]) – Outgoing photon energy as fraction of incident electron energy

• dcs (double[][]) – Bremsstrahlung differential cross section at each incident energy in [mb/eV]

• ionization_energy (double[]) – Ionization potential of each subshell in [eV]

• num_electrons (int[]) – Number of electrons per subshell, with conduction electrons indicated by a negative value

/<element>/coherent/

Datasets
• xs (double[]) – Coherent scattering cross section in [b]

• integrated_scattering_factor (tabulated) – Integrated coherent scattering form factor

• anomalous_real (tabulated) – Real part of the anomalous scattering factor

• anomalous_imag (tabulated) – Imaginary part of the anomalous scattering factor

/<element>/compton_profiles/

Datasets
• binding_energy (double[]) – Binding energy for each subshell in [eV]

• num_electrons (double[]) – Number of electrons in each subshell

• pz (double[]) – Projection of the electron momentum on the scattering vector in units of $$me^2 / \hbar$$ where $$m$$ is the electron rest mass and $$e$$ is the electron charge

• J (double[][]) – Compton profile for each subshell in units of $$\hbar / (me^2)$$

/<element>/heating/

Datasets
• xs (double[]) – Total heating cross section in [b-eV]

/<element>/incoherent/

Datasets
• xs (double[]) – Incoherent scattering cross section in [b]

• scattering_factor (tabulated) –

/<element>/pair_production_electron/

Datasets
• xs (double[]) – Pair production (electron field) cross section in [b]

/<element>/pair_production_nuclear/

Datasets
• xs (double[]) – Pair production (nuclear field) cross section in [b]

/<element>/photoelectric/

Datasets
• xs (double[]) – Total photoionization cross section in [b]

/<element>/subshells/

Attributes
• designators (char[][]) – Designator for each shell, e.g. ‘M2’

/<element>/subshells/<designator>/

Attributes
• binding_energy (double) – Binding energy of the subshell in [eV]

• num_electrons (double) – Number of electrons in the subshell

Datasets
• transitions (double[][]) – Atomic relaxation data

• xs (double[]) – Photoionization cross section for subshell in [b] tabulated against the main energy grid

Attributes
• threshold_idx (int) – Index on the energy grid of the reaction threshold

## 3.3. 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

• energy_max (double) – Maximum energy in [eV]

• nuclides (char[][]) – Names of nuclides for which the thermal scattering data applies to

/<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 (function) – Thermal elastic scattering cross section for temperature TTT (in Kelvin)

Groups

/<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 (function) – Thermal inelastic scattering cross section for temperature TTT (in Kelvin)

Groups

## 3.4. 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

## 3.5. One-dimensional Functions¶

### 3.5.1. Scalar¶

Object type

Dataset

Datatype

double

Attributes
• type (char[]) – ‘constant’

### 3.5.2. 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

### 3.5.3. Polynomial¶

Object type

Dataset

Datatype

double[]

Description

Polynomial coefficients listed in order of increasing power

Attributes
• type (char[]) – ‘Polynomial’

### 3.5.4. 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[]) – ‘CoherentElastic’

### 3.5.5. 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$$^{-1}$$].

Attributes
• type (char[]) – ‘IncoherentElastic’

### 3.5.6. Sum of functions¶

Object type

Group

Attributes
• type (char[]) – “Sum”

• n (int) – Number of functions

Datasets
• *func_<i> (function) – Dataset for the i-th function (indexing starts at 1)

## 3.6. Angle-Energy Distributions¶

### 3.6.1. 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

### 3.6.2. 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.

### 3.6.3. 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

### 3.6.4. 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

### 3.6.5. Coherent Elastic¶

This angle-energy distribution is used specifically for coherent elastic thermal neutron scattering.

Object type

Group

Attributes
• type (char[]) – “coherent_elastic”

• xs – Link to the coherent elastic scattering cross section

### 3.6.6. 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$$^{-1}$$]

### 3.6.7. 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

### 3.6.8. 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 correlated angle-energy distributions.

### 3.6.9. 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).

### 3.6.10. Mixed Elastic¶

This angle-energy distribution is used when an evaluation specifies both coherent and incoherent elastic thermal neutron scattering.

Object type

Group

Attributes
• type (char[]) – “mixed_elastic”

Groups

## 3.7. Energy Distributions¶

### 3.7.1. Maxwell¶

Object type

Group

Attributes
• type (char[]) – ‘maxwell’

• u (double) – Restriction energy in eV

Datasets
• theta (tabulated) – Maxwellian temperature as a function of energy

### 3.7.2. Evaporation¶

Object type

Group

Attributes
• type (char[]) – ‘evaporation’

• u (double) – Restriction energy in eV

Datasets
• theta (tabulated) – Evaporation temperature as a function of energy

### 3.7.3. 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

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

### 3.7.5. 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

### 3.7.6. Level Inelastic¶

Object type

Group

Attributes
• type (char[]) – ‘level’

• threshold (double) – Energy threshold in the laboratory system in eV

• mass_ratio (double) – $$(A/(A + 1))^2$$

### 3.7.7. 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