Mention source of elements database in docstring

doc/reference/material.rst

@@ -18,7 +18,9 @@
 .. autoattribute:: exspy.material.elements
  :annotation:
 
-Database of element properties. The following properties are included:
+Database of element properties.
+
+The following properties are included:
 
 .. code::
 
@@ -32,32 +34,50 @@ Database of element properties. The following properties are included:
  └── Physical_properties
  └── density_gcm3
 
-Examples:
+The X-ray lines energies are taken from Chantler et al. [1]_.
 
-.. code::
+The line weight, more precisely the approximate line weight for K,L M
+shells are taken from Electron Probe Quantitation (EPQ) library [2]_.
+
+The field ``threshold`` and ``edge`` are taken from Gatan EELS atlas
+https://eels.info/atlas, as retrieved in June 2020.
+
+Examples
+
+>>> exspy.material.elements.Fe.General_properties
+├── Z = 26
+├── atomic_weight = 55.845
+└── name = iron
+>>> exspy.material.elements.Fe.Physical_properties
+└── density (g/cm^3) = 7.874
+>>> exspy.material.elements.Fe.Atomic_properties.Xray_lines
+├── Ka
+│ ├── energy (keV) = 6.404
+│ └── weight = 1.0
+├── Kb
+│ ├── energy (keV) = 7.0568
+│ └── weight = 0.1272
+├── La
+│ ├── energy (keV) = 0.705
+│ └── weight = 1.0
+├── Lb3
+│ ├── energy (keV) = 0.792
+│ └── weight = 0.02448
+├── Ll
+│ ├── energy (keV) = 0.615
+│ └── weight = 0.3086
+└── Ln
+ ├── energy (keV) = 0.62799
+ └── weight = 0.12525
+
+
+References
+
+.. [1] Chantler, C.T., Olsen, K., Dragoset, R.A., Kishore, A.R.,
+ Kotochigova, S.A., and Zucker, D.S. (2005), X-Ray Form Factor,
+ Attenuation and Scattering Tables (version 2.1).
+ https://dx.doi.org/10.18434/T4HS32
 
- >>> exspy.material.elements.Fe.General_properties
- ├── Z = 26
- ├── atomic_weight = 55.845
- └── name = iron
- >>> exspy.material.elements.Fe.Physical_properties
- └── density (g/cm^3) = 7.874
- >>> exspy.material.elements.Fe.Atomic_properties.Xray_lines
- ├── Ka
- │ ├── energy (keV) = 6.404
- │ └── weight = 1.0
- ├── Kb
- │ ├── energy (keV) = 7.0568
- │ └── weight = 0.1272
- ├── La
- │ ├── energy (keV) = 0.705
- │ └── weight = 1.0
- ├── Lb3
- │ ├── energy (keV) = 0.792
- │ └── weight = 0.02448
- ├── Ll
- │ ├── energy (keV) = 0.615
- │ └── weight = 0.3086
- └── Ln
- ├── energy (keV) = 0.62799
- └── weight = 0.12525
+.. [2] Ritchie, N. EPQ is the Electron Probe Quantification library
+ - the basis for DTSA-II.
+ https://github.com/usnistgov/EPQ

exspy/_misc/elements.py

@@ -4996,6 +4996,14 @@
  └── Physical_properties
  └── density_gcm3
 
+The X-ray lines energies are taken from Chantler et al. [1]_.
+
+The line weight, more precisely the approximate line weight for K,L M
+shells are taken from Electron Probe Quantitation (EPQ) library [2]_.
+
+The field ``threshold`` and ``edge`` are taken from Gatan EELS atlas
+https://eels.info/atlas, as retrieved in June 2020.
+
 Examples
 --------
 >>> exspy.material.elements.Fe.General_properties
@@ -5023,6 +5031,18 @@
 └── Ln
  ├── energy (keV) = 0.62799
  └── weight = 0.12525
+
+ 
+References
+----------
+.. [1] Chantler, C.T., Olsen, K., Dragoset, R.A., Kishore, A.R.,
+ Kotochigova, S.A., and Zucker, D.S. (2005), X-Ray Form Factor,
+ Attenuation and Scattering Tables (version 2.1).
+ https://dx.doi.org/10.18434/T4HS32
+
+.. [2] Ritchie, N. EPQ is the Electron Probe Quantification library
+ - the basis for DTSA-II.
+ https://github.com/usnistgov/EPQ
 """
 
 # read dictionary of atomic numbers from eXSpy, and add the elements that