# ACE Cross Sections – pyne.ace¶

This module is for reading ACE-format cross sections. ACE stands for “A Compact ENDF” format and originated from work on MCNP. It is used in a number of other Monte Carlo particle transport codes.

ACE-format cross sections are typically generated from ENDF files through a cross section processing program like NJOY. The ENDF data consists of tabulated thermal data, ENDF/B resonance parameters, distribution parameters in the unresolved resonance region, and tabulated data in the fast region. After the ENDF data has been reconstructed and Doppler-broadened, the ACER module generates ACE-format cross sections.

All functionality may be found in the ace package:

from pyne import ace


The information below represents the complete specification of the classes in the ace module. For examples of usage, please refer to the User’s Guide entry for ACE Cross Sections.

## Library Class¶

class pyne.ace.Library(filename)

A Library objects represents an ACE-formatted file which may contain multiple tables with data.

Parameters
filenamestr

Path of the ACE library file to load.

Attributes
binarybool

Identifies Whether the library is in binary format or not

tablesdict

Dictionary whose keys are the names of the ACE tables and whose values are the instances of subclasses of AceTable (e.g. NeutronTable)

verbosebool

Determines whether output is printed to the stdout when reading a Library

find_table(name)

Returns a cross-section table with a given name.

Parameters
namestr

Name of the cross-section table, e.g. 92235.70c

read(table_names=None)

Read through and parse the ACE-format library.

Parameters
table_namesNone, str, or iterable, optional

Tables from the file to read in. If None, reads in all of the tables. If str, reads in only the single table of a matching name.

class pyne.ace.AceTable(name, awr, temp)

Abstract superclass of all other classes for cross section tables.

class pyne.ace.NeutronTable(name, awr, temp)

A NeutronTable object contains continuous-energy neutron interaction data read from an ACE-formatted Type I table. These objects are not normally instantiated by the user but rather created when reading data using a Library object and stored within the tables attribute of a Library object.

Parameters
namestr

ZAID identifier of the table, e.g. ‘92235.70c’.

awrfloat

Atomic mass ratio of the target nuclide.

tempfloat

Temperature of the target nuclide in eV.

Attributes
awrfloat

Atomic mass ratio of the target nuclide.

energylist of floats

The energy values (MeV) at which reaction cross-sections are tabulated.

namestr

ZAID identifier of the table, e.g. 92235.70c.

nu_p_energylist of floats

Energies in MeV at which the number of prompt neutrons emitted per fission is tabulated.

nu_p_typestr

Indicates how number of prompt neutrons emitted per fission is stored. Can be either “polynomial” or “tabular”.

nu_p_valuelist of floats

The number of prompt neutrons emitted per fission, if data is stored in “tabular” form, or the polynomial coefficients for the “polynomial” form.

nu_t_energylist of floats

Energies in MeV at which the total number of neutrons emitted per fission is tabulated.

nu_t_typestr

Indicates how total number of neutrons emitted per fission is stored. Can be either “polynomial” or “tabular”.

nu_t_valuelist of floats

The total number of neutrons emitted per fission, if data is stored in “tabular” form, or the polynomial coefficients for the “polynomial” form.

reactionslist of Reactions

A list of Reaction instances containing the cross sections, secondary angle and energy distributions, and other associated data for each reaction for this nuclide.

sigma_alist of floats

The microscopic absorption cross section for each value on the energy grid.

sigma_tlist of floats

The microscopic total cross section for each value on the energy grid.

tempfloat

Temperature of the target nuclide in eV.

class pyne.ace.SabTable(name, awr, temp)

A SabTable object contains thermal scattering data as represented by an S(alpha, beta) table.

Parameters
namestr

ZAID identifier of the table, e.g. lwtr.10t.

awrfloat

Atomic mass ratio of the target nuclide.

tempfloat

Temperature of the target nuclide in eV.

Attributes
awrfloat

Atomic mass ratio of the target nuclide.

elastic_e_inlist of floats

Incoming energies in MeV for which the elastic cross section is tabulated.

elastic_Plist of floats

Elastic scattering cross section for data derived in the incoherent approximation, or Bragg edge parameters for data derived in the coherent approximation.

elastic_typestr

Describes the behavior of the elastic cross section, i.e. whether it was derived in the incoherent or coherent approximation.

inelastic_e_inlist of floats

Incoming energies in MeV for which the inelastic cross section is tabulated.

inelastic_sigmalist of floats

Inelastic scattering cross section in barns at each energy.

namestr

ZAID identifier of the table, e.g. 92235.70c.

tempfloat

Temperature of the target nuclide in eV.

class pyne.ace.Reaction(MT, table=None)

A Reaction object represents a single reaction channel for a nuclide with an associated cross section and, if present, a secondary angle and energy distribution. These objects are stored within the reactions attribute on subclasses of AceTable, e.g. NeutronTable.

Parameters
MTint

The ENDF MT number for this reaction. On occasion, MCNP uses MT numbers that don’t correspond exactly to the ENDF specification.

tableAceTable

The ACE table which contains this reaction. This is useful if data on the parent nuclide is needed (for instance, the energy grid at which cross sections are tabulated)

Attributes
ang_energy_inlist of floats

Incoming energies in MeV at which angular distributions are tabulated.

ang_energy_coslist of floats

Scattering cosines corresponding to each point of the angular distribution functions.

ang_energy_pdflist of floats

Probability distribution function for angular distribution.

ang_energy_cdflist of floats

Cumulative distribution function for angular distribution.

e_dist_energylist of floats

Incoming energies in MeV at which energy distributions are tabulated.

e_dist_lawint

ACE law used for secondary energy distribution.

IEint

The index on the energy grid corresponding to the threshold of this reaction.

MTint

The ENDF MT number for this reaction. On occasion, MCNP uses MT numbers that don’t correspond exactly to the ENDF specification.

Qfloat

The Q-value of this reaction in MeV.

sigmalist of floats

Microscopic cross section for this reaction at each point on the energy grid above the threshold value.

TYint

An integer whose absolute value is the number of neutrons emitted in this reaction. If negative, it indicates that scattering should be performed in the center-of-mass system. If positive, scattering should be preformed in the laboratory system.

threshold()

Return energy threshold for this reaction.