# 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

**/<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/**

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

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

- Datasets
**xs**(function) – Thermal elastic scattering cross section for temperature TTT (in Kelvin)

- Groups
**distribution**– Format for angle-energy distributions are detailed in Angle-Energy Distributions.

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

- Datasets
**xs**(function) – Thermal inelastic scattering cross section for temperature TTT (in Kelvin)

- Groups
**distribution**– Format for angle-energy distributions are detailed in Angle-Energy Distributions.

## 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¶

### 3.6.3. 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”

- Hard link
**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
**coherent**– Distribution for coherent elastic scattering. The format is given in Angle-Energy Distributions.**incoherent**– Distribution for incoherent elastic scattering. The format is given in Angle-Energy Distributions.

## 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¶

### 3.7.4. 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

### 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