update length_neutron values.

[rowlesmr]

From #1

As far as I can tell, the values in 2004 ITC Table 4.4.4.1 are the bound coherent scattering lengths in fm from:

Neutron scattering lengths and cross sections
Varley F. Sears
Pages 26-37 |
https://doi.org/10.1080/10448639208218770
Neutron News
Volume 3, 1992 - Issue 3

I don't have access to a newer ITC
.

I've put the look up on _atom_type.element_symbol & _atom_type.mass_number. Neither of those appear in ATOM_TYPE_SCAT, so I don't know how to reference those in an enumeration in _atom_type_scat.length_neutron without adding linked data names

[rowlesmr]

I've put the look up on _atom_type.element_symbol & _atom_type.mass_number. Neither of those appear in ATOM_TYPE_SCAT, so I don't know how to reference those in an enumeration in _atom_type_scat.length_neutron without adding linked data names

i can update core to have those linked data items and have the enumeration default added to _atom_scat.length_neutron

[rowlesmr]

I've added SU values to all lengths in a single commit. That can be reverted if you think that goes too far

[vaitkus]

Thank you for the work.

I don't have access to a newer ITC

I believe someone from COMCIFS should have access to the latest version. We should ask to borrow it for tabulation purposes. I hope that the values will not differ too much. Could you email me a full list on tables you need?

I've put the look up on _atom_type.element_symbol & _atom_type.mass_number. Neither of those appear in ATOM_TYPE_SCAT, so I don't know how to reference those in an enumeration in _atom_type_scat.length_neutron without adding linked data names

I think that can _atom_type.element_symbol and _atom_type.mass_number can be added a s keys directly without requiring linked data names. ATOM_TYPE_SCAT is a child category of the ATOM_TYPE category, both of which are looped, and can thus be considered a single category (i.e. in the CIF they can appear in the same or separate loops with the implication that they should generally be treated as the same category).