armi.nucDirectory package¶

The nucDirectory module contains general nuclide information through the nuclideBases module, and information for nuclide module.

Element data - name, symbol, atomic number (Z).
Generic nuclide data - this includes mass, atomic number, natural abundance and various names and labels that are used in ARMI for the nuclide. It also includes decay and transmutation modes.
Nuclide specific cross section information.

Elements¶

Elements are simple objects containing minimal information about… elements! This information is loaded from a data file within ARMI; consequently modifying the data file will modify the list of elements in ARMI.

Elements are not used very often within armi, and are mainly used as a building block of the nuclide objects discussed below. If you need to grab an element for some reason there are three available dictionaries provided for rapid access.:

>>> from armi.nucDirectory import elements
>>> uranium = elements.byZ[92]
>>> uranium.name
'uranium'
>>> uranium.z
92

Likewise, elements can be retrieved by their name or symbol.:

>>> ironFromZ = elements.byZ[26]
>>> ironFromName = elements.byName['iron']
>>> ironFromSymbol = elements.bySymbol['FE']
>>> ironFromZ == ironFromName == ironFromSymbol
True

Warning

Note that byName and bySymbol are case specific; names are lower case and symbols are UPPER CASE.

The elements are truly the same Element object. The nucDirectory makes efficient use of the memory being used by elements and will only ever contain ~118 Elements.:

>>> id(ironFromZ) == id(ironFromName) == id(ironFromSymbol)
True

Nuclide Bases¶

The nucDirectory allows ARMI to get information about various nuclides, like U235 or FE56. Often times you need to look up cross section or densities for nuclides, or you might need the atomic weight or the natural isotopic distribution. The nucDirectory is here to help you with these common tasks.

The fundamental object of nuclide management in ARMI is the INuclide object. After construction, they contain some basic information, such as Z, A, and atomic weight (if known). Similar to Elements, the information is loaded from a series of data files within ARMI. The data is originally from [NIST]:

>>> from armi.nucDirectory import nuclideBases
>>> u235= nuclideBases.byName['U235']
>>> u235.z
92
>>> u235.weight
235.0439299
>>> u235.a
235

NIST: http://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl

Upon loading the armi.nucDirectory package, the nuclideBases.instances, will be filled with nuclide base objects. Nuclide bases do not do much, but they contain a lot of basic information about a nuclide, such as the atomic mass, atomic number (Z), the mass number (A), the natural abundance, and all of the decay and transmutation modes (well, ARMI’s decay and transmutation modes).

Nuclide names, labels and MC**2 IDs¶

Nuclides have names, labels and IDs.

INuclide.name: The nuclide name is what should be used within ARMI itself. This is a human readable name such as, U235 or FE. The names contain only capital letters and numbers, made up from the corresponding element symbol and mass number (A).
INuclide.label: The nuclide label is a unique 4 character name which identifies the nuclide from all others within MC**2 and DIF3D. The label must be 4 characters, because MC**2 and DIF3D only allow 6 character labels, two of which we reserver for the cross section ID. Labels are not necessarily human readable, but are generally the nuclide symbol followed by the last two digits of the mass number (A), so the nuclide for U235 has the label U235, but PU239 has the label PU39.
INuclide.mc2id: The mc2id is the MC**2 id used for MC**2 version 2. This should only be used when loading an ISOTXS file, or writing MC**2 input.
INuclide.mc3id(): The mc3id is the MC**2 id used for MC**2 version 3. This should only be used when loading an ISOTXS file, or writing MC**2 input.

For reference, there is a complete list of the nuclides along with the names, labels and IDs here.

Indices - rapid access¶

There are three main ways to retrieve a nuclide, which are provided for convenience depending on what information you have, or “know,” about a nuclide. For example, if you know a nuclide name, use the byName dictionary. There are also dictionaries available for retrieving by the label, byLabel, and by the MC**2 ID, byMccId (this works for both version 2 and version 3 IDs).

>>> from armi.nucDirectory import nuclideBases
>>> pu239 = nuclideBases.byName['PU239']
>>> pu239.z
94

Just like with elements, the item retrieved from the various dictionaries are the same object.

>>> tinFromName = nuclideBases.byName['SN112']
>>> tinFromLabel = nuclideBases.byLabel['SN112']
>>> tinFromMcc2Id = nuclideBases.byName['SN1125']
>>> tinFromMcc3Id = nuclideBases.byLabel['SN1127']
>>> tinFromName == tinFromLabel == tinFromMcc2Id == tinFromMcc3Id
True
>>> id(tinFromName) == id(tinFromLabel) == id(tinFromMcc2Id) == id(tinFromMcc3Id)
True

Warning

If you find yourself using a name or label within ARMI itself, it is probably not as efficient as it could be. Many older, but still existing, data structures within ARMI use nuclide names and labels for indexing certain information about the nuclide, such as number density. However, often times they will also need other information, such as the mass. Consequently, the index which contains the name or label is not fulfilling its intended purpose; in order to perform the operation, weight * numberDensity, you’ll still need the nuclide object!

Nuclides¶

Another closely related object is the armi.nucDirectory.nuclide.Nuclide. Nuclides are created when loading an ISOTXS file from MC**2. Nuclides contain the same information as INuclides, but also contain multi-group microscopic cross section data.