# Known issues

- 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 energy-dependent 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.

- For very high fluences, e.g., more than 1E16 n/cm2, the activation equations give erroneous results because of the precision limitations. If there is doubt simply do the calculation at a lower flux and proportion the result. This will not work for the cascade reactions, i.e., two neutron additions.

- Post-exposure decay for b reaction daughter nuclides do not include activity from the decaying parent nuclide.

# Change history

## 2026-02-27 R2.1.0

Modified:

- Use NUBASE2020 for half-life values in activation. The following change by 20% or more: 32Si, 38Clm, 41Ca, 79Se, 97Tc, 108Ag, 121Snm, 126Sn, 135Cs, 157Tb, 177Lum

- Update b_c bp bm and incoherent attributes for 13C

- Update b_c for Li 6Li 7Li 141Pr Nd 142-146,148,150Nd 144,147-150,152,154Sm 153Eu 174Yb

- Update nuclear_spin for 77Se 177Hf 182W

- Generate html table of scattering lengths and cross sections

- Add comparison tables checking b_c and σ_i against b+ and b-

- Add type hinting to many of the functions

## 2024-12-19 R2.0.2

Modified:

- Revert bound coherent scattering length updates for C-12, O-16, Sn-119, Pb-207 from R2.0.0 and instead update nat-C, nat-O, nat-Sn, and nat-Pb.

## 2024-12-06 R2.0.1

- Documentation tweaks

## 2024-12-03 R2.0.0

Modified:

- Move to IAEA AME2020 for isotope mass

- Move to IUPAC CIAAW 2021 for atomic mass and isotopic abundance

- Move old mass/abundance tables into periodictable.mass_2001

- Li-6:Li-7 mass ratio changed from 12.2 to 19.6 (delta = 2.7%)

- Isotope abundance 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

- Fix typos in uncertainties in the neutron table (Zr-90, Te-124, Ba-138, Sm-147)

- Use correct activation for Pb-208 which was entered as barns rather than mbarns

- Use Aug 2023 update to X-ray scattering factors (Pt, Cr, Nb, Y, Er)

- Update physical constants to CODATA 2022. Values have changed by as much as 1e-7 (relative) in Avogadro number, Planck constant, J/eV, electron radius, electron mass, neutron mass and atomic mass constant.

- Updated bound coherent scattering length for H-1, H-2, He-4, C-12†, O-16†, O-17, O-18, Sn-119†, Sm-154, Eu-153, Ir-191, Ir-193, Pb-207†, Bi-209

- Neutron b_c changed for Zn-70 from 6.9 to 6.0 (fixes a typo in the table)

- Updated total cross section for He, Kr, Xe

- Use log-log interpolation for X-ray f’’

† Some scattering length updates were reverted in R2.0.2. They should have been updates to the element in natural abundance rather than the isotope.

Breaking changes:

- Remove Z=0 (bare neutron) from the PeriodicTable iterator.

- Replace constants.plancks_constant (eV s) with constants.planck_constant (J/Hz).

## 2024-07-08 R1.7.1

Updated:

- Support numpy 2.x, which removed the alias np.NaN

## 2024-03-22 R1.7.0

New:

- Use wt% and vol% for mixtures. The non-standard %wt and %vol are still supported, but may be removed in a future version if they cause ambiguity in the parser.

- Support mixtures containing FASTA components such as dna:CGCTAATC

- Support unicode subscripts in chemical formula input.

Modified:

- Fasta calculations for formula, density and sld have changed. DNA/RNA now use Buckin (1989) for unit volumes. DNA/RNA no longer include sodium ions from tables in Perkins (1988). Sequences now include H+ and OH- terminators.

- Use correct halflife for Tm-171, Ho-163 and W-188 activation products.

- Fix decay time estimation routine.

- Tested on Python 3.8 and above. Support for python 2.7 dropped.

- Remove eval() from codebase.

## 2022-05-18 R1.6.1

Modified:

- Calculate decay time correctly in the presence of significant long-lived activation.

- Calculate b mode activation correctly for Eu[151] => Gd[152]

## 2021-04-21 R1.6.0

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 self-consistent 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.

## 2020-11-04 R1.5.3

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 contrast-matched 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.

## 2019-11-19 R1.5.2

Modified:

- Carbon density changed from 2.1 to 2.2 to match CXRO, CRC and RSC. The NIST X-ray attenuation tables use 2.26; the Handbook of Mineralogy has 2.09-2.23. The Neutron Data Booklet gave the value as 1.9-2.3, 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.

## 2019-09-09 R1.5.1

Modified:

- fasta uses natural abundance of H for biomolecule when computing the D2O contrast match rather than the biomolecule with pure H[1].

- remove half-life units from column header in activation table since each row gives its own units.

## 2017-05-11 R1.5.0

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

## 2014-02-04 R1.4.1

Modified:

- default density is now the isotopic density rather than the natural density

## 2013-12-20 v1.4.0

- support python 3.3

## 2013-10-25 R1.3.10

Modified:

- fix activation calculation to ignore fast neutrons in thermal environment

- add emission spectra for remaining elements above neon

## 2013-04-23 R1.3.9

Modified:

- Update requirements to pyparsing<2.0.0 (we don’t support python 3 yet)

## 2013-04-08 R1.3.8

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

## 2013-03-05 R1.3.6

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.

## 2013-02-26 R1.3.5

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 X-ray 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=…)

## 2010-12-05 R1.3

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

## 2010-04-28 R1.2

New:

- support pickle: id(H) == id(loads(dumps(H)))

- support ions, with magnetic form factors and x-ray 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

## 2009-01-20 R1.1

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