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Version History

Example of how to reference this online database: (Replace year, month day with database access date.)
Coursey, J.S., Schwab, D.J., Tsai, J.J., and Dragoset, R.A. (2010), Atomic Weights and Isotopic Compositions (version 3.0). [Online] Available: [year, month day]. National Institute of Standards and Technology, Gaithersburg, MD.
Optional addition:
Originally published as M.E. Wieser and M. Berglund, Atomic Weights of the Elements 2007, Pure Appl. Chem. 81(11), 2131 (2009); J.K. Böhlke, J.R. de Laeter, P. De Bièvre, H. Hidaka, H.S. Peiser, K.J.R. Rosman, and P.D.P. Taylor, Isotopic Compositions of the Elements, 2001, J. Phys. Chem. Ref. Data 34(1), 57 (2005); and G. Audi, A.H. Wapstra, and C. Thibault, The 2003 Atomic Mass Evaluation, Nuclear Physics A 729(1), 337 (2003).
Citation Form:
Author/editor (Year), Title (edition). [Type of medium] Available: URL [Access date].

Version 3.0
July 2010
The relative atomic masses have been have been updated according to The 2003 Atomic Mass Evaluation located at mass.mas03round. The isotopic compositions have been updated according to Isotopic Compositions of the Elements, 2001 located at The atomic weights have been updated according to Atomic weights of the elements 2007 located at The option to list data in HTML format is now available for all isotopes and the HTML format has been modified to provide decimal alignment.
Version 2.4.1
February 2005
Entries for elements Hs (Z=108) and Uun (Z=110) were modified to correct discrepancies when displaying the most common isotopes. For each of these elements, there is no available relative atomic mass for the most stable isotope.
Version 2.4
July 2003
The atomic weights of Zn, Kr, Mo, and Dy have been updated, based on the Atomic Weights of the Elements 2001, with changes reported in Chem. Int. 23, 179 (2001). The most stable isotopes of Hs, Uun, and Uub have also been updated.
Version 2.3.1
August 2002
An error which listed all isotopes of element 108 (Hs) with the isotopes for element 17 (Cl) was corrected. In addition, elements 112, 114 and 116 were added to the data output for all isotopes.
Version 2.3
February 2002
An option was added to allow users to access relative atomic masses for either the most common isotopes or all isotopes. (See Version 2.0 below for data source.) The atomic weights of N, S, Cl, Ge, Xe, Er, and U have been updated.
T. B. Coplen,
"Atomic Weights of the Elements 1999," Pure Appl. Chem. 73(4), 667 (2001).
Version 2.2.1
August 2001
Element Z=118 (293Uuo) was removed from the database because of a retraction by the Lawrence Berkeley National Laboratory. Also, the most stable isotope for element Z=116 (Uuh) was changed from 289 (a decay product of 293Uuo) to 292. Finally, the isotope 14C (Z=6) was added.
Version 2.2
March 2001
Four elements were added to the database; atomic numbers 112, 114, 116, and 118. However, the only information available on each of these elements is the most stable isotope, obtained from The Berkeley Laboratory Isotopes Project. Furthermore, based on information from this site, the most stable isotope (and therefore the relative atomic mass) was changed for three other elements: Z=106: 266Sg replaces 263Sg; Z=108: 269Hs replaces 265Hs; and Z=110: 271Uun replaces 269Uun. Finally, a typographical correction was made to the isotopic abundance of 1H.
Version 2.1
June 2000
The IUPAC's biennial review of atomic weight determinations warranted no changes to the standard atomic weights from that published in Atomic Weights of the Elements 1995 other than a change to the footnote for Lithium. Also, linearized ASCII output was added to the database to increase accessibility and to facilitate copying and pasting.
R. D. Vocke, Jr.,
"Atomic Weights of the Elements 1997," Pure Appl. Chem. 71(8), 1593 (1999).
Version 2.0.1
February 2000
Clarifications were added to the "Column Descriptions."
Version 2.0
January 2000
The relative atomic masses of the isotopes were added. The masses are from the authors' data file mass_rmd.mas95round. Note: The official IUPAC names and symbols for elements 104 and higher were not finalized at the time this file was originally produced. The file remains unchanged so as not to cause confusion. The correct values are associated with the atomic number rather than the symbol.
G. Audi and A. H. Wapstra,
"The 1995 Update To The Atomic Mass Evaluation," Nucl. Phys. A 595(4), 409 (1995).
Version 1.0
September 1999
The online database includes data from the following publications:
T. B. Coplen,
"Atomic Weights of the Elements 1995," J. Phys. Chem. Ref. Data, 26(5), 1239 (1997).
Reprinted with permission from Pure Appl. Chem. 68, 2339 (1996).

K.J.R. Rosman and P.D.P. Taylor,
"Isotopic Compositions of the Elements 1997," J. Phys. Chem. Ref. Data, 27(6), 1275 (1998).
Reprinted with permission from Pure Appl. Chem. 70, 217 (1998).

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