NIST: Isotopic Compositions of the Elements

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

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).

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	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).