Materials are the primary container for radionuclides. They map nuclides to mass weights, though they contain methods for converting to/from atom fractions as well. In many ways they take inspiration from numpy arrays and python dictionaries. Materials have two main attributes which define them.
By keeping the mass and the composition separate, operations that only affect one attribute may be performed independent of the other. Additionally, most of the functionality is implemented in a C++ class by the same name, so this interface is very fast and light-weight. Materials may be initialized in a number of different ways. For example, initializing from dictionaries of compositions are shown below.
In [1]:
from pyne.material import Material
In [2]:
leu = Material({'U238': 0.96, 'U235': 0.04}, 42)
leu
Out[2]:
In [3]:
nucvec = {10010: 1.0, 80160: 1.0, 691690: 1.0, 922350: 1.0,
922380: 1.0, 942390: 1.0, 942410: 1.0, 952420: 1.0,
962440: 1.0}
mat = Material(nucvec)
print mat
Materials may also be initialized from plain text or HDF5 files (see Material.from_text() and
Material.from_hdf5()). Once you have a Material instance, you can always obtain the unnormalized
mass vector through Material.mult_by_mass(). Normalization routines to normalize the mass
Material.normalize() or the composition Material.norm_comp() are also available.
In [4]:
leu.mult_by_mass()
Out[4]:
In [5]:
mat.normalize()
mat.mult_by_mass()
Out[5]:
In [6]:
mat.mass
Out[6]:
In [7]:
other_mat = mat * 2
other_mat
Out[7]:
In [8]:
other_mat.mass
Out[8]:
In [9]:
weird_mat = leu + mat * 18
print weird_mat
In [10]:
other_mat.mass = 10
other_mat.comp = {10020: 3, 922350: 15.0}
print other_mat
Of course when you do this you have to be careful because the composition and mass may now be out of sync. This may always be fixed with normalization.
In [11]:
other_mat.norm_comp()
print other_mat
Additionally (and very powerfully!), you may index into either the material or the composition to get, set, or remove sub-materials. Generally speaking, the composition you may only index into by integer-key and only to retrieve the normalized value. Indexing into the material allows the full range of operations and returns the unnormalized mass weight. Moreover, indexing into the material may be performed with integer-keys, string-keys, slices, or sequences of nuclides.
In [12]:
leu.comp[922350000]
Out[12]:
In [13]:
leu['U235']
Out[13]:
In [14]:
weird_mat['U':'Am']
Out[14]:
In [15]:
other_mat[:920000000] = 42.0
print other_mat
In [16]:
del mat[962440, 'TM169', 'Zr90', 80160]
mat[:]
Out[16]:
Other methods also exist for obtaining commonly used sub-materials, such as gathering the Uranium or Plutonium vector.
In [17]:
leu.molecular_weight()
Out[17]:
Note that by default, materials are assumed to have one atom per molecule. This is a poor assumption for more complex materials. For example, take water. Without specifying the number of atoms per molecule, the molecular weight calculation will be off by a factor of 3. This can be remedied by passing the correct number to the method. If there is no other valid number of molecules stored on the material, this will set the appropriate attribute on the class.
In [18]:
h2o = Material({10010: 0.11191487328808077, 80160: 0.8880851267119192})
h2o.molecular_weight()
Out[18]:
In [19]:
h2o.molecular_weight(3.0)
h2o.atoms_per_mol
Out[19]:
It is often also useful to be able to convert the current mass-weighted material to
an atom fraction mapping. This can be easily done via the Material.to_atom_frac()
method. Continuing with the water example, if the number of atoms per molecule is
properly set then the atom fraction return is normalized to this amount. Alternatively,
if the atoms per molecule are set to its default state on the class, then a truly
fractional number of atoms is returned.
In [20]:
h2o.to_atom_frac()
Out[20]:
In [21]:
h2o.atoms_per_mol = -1.0
h2o.to_atom_frac()
Out[21]:
Additionally, you may wish to convert the an existing set of atom fractions to a
new material stream. This can be done with the Material.from_atom_frac() method,
which will clear out the current contents of the material's composition and replace
it with the mass-weighted values. Note that when you initialize a material from atom
fractions, the sum of all of the atom fractions will be stored as the atoms per molecule
on this class. Additionally, if a mass is not already set on the material, the molecular
weight will be used.
In [22]:
h2o_atoms = {10010: 2.0, 'O16': 1.0}
h2o = Material()
h2o.from_atom_frac(h2o_atoms)
print h2o.comp
print h2o.atoms_per_mol
print h2o.mass
print h2o.molecular_weight()
Moreover, other materials may also be used to specify a new material from atom fractions. This is a typical case for reactors where the fuel vector is convolved inside of another chemical form. Below is an example of obtaining the Uranium-Oxide material from Oxygen and low-enriched uranium.
In [23]:
uox = Material()
uox.from_atom_frac({leu: 1.0, 'O16': 2.0})
print uox
NOTE: Materials may be used as keys in a dictionary because they are hashable.
Materials also have an attrs attribute which allows users to store arbitrary
custom information about the material. This can include things like units, comments,
provenance information, or anything else the user desires. This is implemented as an
in-memory JSON object attached to the C++ class. Therefore, what may be stored in
the attrs is subject to the same restrictions as JSON itself. The top-level
of the attrs should be a dictionary, though this is not explicitly enforced.
In [24]:
leu = Material({922350: 0.05, 922380: 0.95}, 15, attrs={'units': 'kg'})
leu
Out[24]:
In [25]:
print leu
In [26]:
leu.attrs
Out[26]:
In [27]:
a = leu.attrs
a['comments'] = ['Anthony made this material.']
leu.attrs['comments'].append('And then Katy made it better!')
a['id'] = 42
leu.attrs
Out[27]:
In [28]:
leu.attr = {'units': 'solar mass'}
leu.attr
Out[28]:
In [29]:
a
Out[29]:
In [30]:
leu.attr['units'] = 'not solar masses'
leu.attr['units']
Out[30]:
As you can see from the above, the attrs interface provides a view into the underlying
JSON object. This can be manipulated directly or by renaming it to another variable.
Additionally, attrs can be replaced with a new object of the appropriate type.
Doing so invalidates any previous views into this container.