This package provides a periodic table of the elements with support for mass, density and xray/neutron scattering information.
Neutron scattering calculations use values collected by the Atomic Institute of the Austrian Universities as they appear in the neutron data booklet, with support for some energy dependent scattering in rare earth elements given by Lynn and Seeger (1990). Xray scattering calculations use a combination of empirical and theoretical values from the LBL Center for Xray Optics.
Tabulated values differ from those given in other sources such as the International Tables for Crystallography, Volume C, and so computed cross sections may give different results from other packages.
Neutron activation calculations are based on Shleien (1998), with isotopes important to health physics. They do not perform a full activation analysis, but instead give a gross estimate of the amount of activation expected for a sample in the beam.
Install using:
pip install periodictable
There are several web interfaces to this package:
 NIST Center for Neutron Research (NCNR)
 ForschungsNeutronenquelle Heinz MaierLeibnitz (FRM II)
 SLD Calulator
Documentation is available online.
Source links:
 Incoherent scattering computed for contrast matched mixture in D2O_sld(), differs from the value that would be computed for a compound with the same isotope proportions and density computed in neutron_sld(). This may change in a future release.
 Incoherent scattering calculations for energydependent rare earth elements is underestimated. The calculation requires bound incoherent scattering length (b_i) but only the bound coherent scattering length (b_c) is included.
Modified:
 Move to IAEA AME2020 for isotope mass
 Move to IUPAC CIAAW 2021 for atomic weight and isotopic abundance
 Li6:Li7 mass ratio changed from 12.2 to 19.6 (delta = 2.7%)
 Isotope percentage changed by 0.1 to 0.5 for B, Zn, Ge, Se, Mo, Er, Yb, Pt, Hg
 Atomic weight changed by 0.04% for Zn, 0.02% for S and 0.01% for Li, Ge, Se, Mo
 Neutron b_c changed for Zn70 from 6.9 to 6.0 (fixes a typo in the original table)
 Fix typos in uncertainties in the neutron table (Zr90, Te124, Ba138, Sm147)
Modified:
 Calculate decay time correctly in the presence of significant longlived activation.
 Calculate b mode activation correctly for Eu[151] => Gd[152]
New:
 Add energy dependence for rare earths (Lynn and Seeger, 1990).
Modified:
 Use complex b_c when computing the coherent cross section, leading to correct values of sigma_c and sigma_i for materials with large absorption. With this change the tabulated values for B[10] are now shown to be selfconsistent within a few percent.
Breaking changes:
 Neutron scattering factors are returned with one value for each wavelength even for energy independent elements. Previous versions returned a scalar if the returned value was identical for each wavelength.
Breaking changes:
 Fix calculation of contrast match points for biomolecules. The old formula used the density of H2O for the D2O sld calculation.
 Modify biomolecule support to use H[1] rather than T for labile hydrogen. This will result in less error when the labile formula is used in lieu of the natural formula or the contrastmatched formula, and make it more obvious from glancing at the formula that labile hydrogen is present.
 Modify fasta.Molecule attributes, dropping Hmass and Hsld. Hnatural has been moved to natural_formula. The formula with labile hydrogen is stored in labile_formula, as well as formula as before.
New:
 Add replace() method to formula to allow isotope substitution.
 Add nsf.D2O_match() and nsf.D2O_sld() functions.
Modified:
 Neutron wavelength now defaults to 1.798 A when wavelength and energy are both None in neutron_sld() and neutron_scattering() rather than throwing an assertion error.
 table can be passed to neutron sld calculators as the source of isotope information when parsing the chemical formula.
 Switch unit test framework from nose to pytest.
 Update docs.
Modified:
 Carbon density changed from 2.1 to 2.2 to match CXRO, CRC and RSC. The NIST Xray attenuation tables use 2.26; the Handbook of Mineralogy has 2.092.23. The Neutron Data Booklet gave the value as 1.92.3, and 2.1 was chosen from this range. The remaining density will continue to use values from the Neutron Data Booklet, which cites CRC as the primary source.
 Updated references.
Modified:
 fasta uses natural abundance of H for biomolecule when computing the D2O contrast match rather than the biomolecule with pure H[1].
 remove halflife units from column header in activation table since each row gives its own units.
New:
 mixture by mass and volume, e.g., 5 g NaCl // 50 mL H2O@1
 multilayer materials, e.g., 5 um Si // 3 nm Cr // 8 nm Au
 add support for bio molecules with labile hydrogens
 update list of possible oxidation states to include rare states
Modified:
 fixed computation of incoherent cross section so it is consistent with coherent cross section and total cross section
Modified:
 default density is now the isotopic density rather than the natural density
 support python 3.3
Modified:
 fix activation calculation to ignore fast neutrons in thermal environment
 add emission spectra for remaining elements above neon
Modified:
 Update requirements to pyparsing<2.0.0 (we don't support python 3 yet)
New:
 formula parser supports density spec and mix by weight/mix by volume
Modified:
 py2exe/py2app wrapping now includes missing activation.dat
 skipping bad 1.3.7 build which didn't include all changes
New:
 add activation decay time to neutron activation calculator
Modified:
 Change neutron scattering calculations for incoherent cross section to be the linear combination of the incoherent cross sections of the individual atoms rather than total cross section minus the coherent cross section. Penetration depth of the unscattered beam still uses the total cross section plus the absorption cross section.
New:
 formulas now report charge and mass_fraction
 formula parser accepts ions as Yy{#+} or Yy[#]{#+} for isotopes
 support neutron activation calculations
 support xray refraction index and mirror reflectivity
Modified:
 update Xray scattering tables for Zr
 adjust ion mass for number of electrons
 ions now display as Yy{#+} rather than Yy^{#+}
 fix formula.natural_density
 fix formula.hill so C,H come first
 fix element.interatomic_distance
 formula(value=...) > formula(compound=...)
New:
 mix_by_weight and mix_by_volume formula constructors
 use natural density to set density for isotope specific formulas
 add neutron_scattering function which returns xs, sld and penetration depth
Modified:
 need wavelength= or energy= for xray/neutron sld
 improved docs and testing
New:
 support pickle: id(H) == id(loads(dumps(H)))
 support ions, with magnetic form factors and xray f0 scattering factor
 support py2exe wrappers
 allow density to be calculated from structure (bcc, fcc, hcp, cubic, diamond)
 estimate molecular volume
 support private tables with some values replaced by application
Modified:
 rename package periodictable
 rename table to periodictable.elements
 neutron sld returns real and imaginary coherent and incoherent instead of coherent, absorption and incoherent
 bug fix: sld for H[2] was wrong when queried before sld for H.
 remove CrysFML ionic radius definitions
Modified:
 Restructure package, separating tests into different directory

When defining table extensions, you should now do:
from elements.core import periodic_table, Element, Isotope
rather than:
from elements import periodic_table from elements.elements import Element, Isotope