INTERNATIONAL UNION OF PURE 
AND APPLIED CHEMISTRY

INORGANIC CHEMISTRY DIVISION 
COMMISSION ON ATOMIC WEIGHTS AND ISOTOPIC ABUNDANCES*

SUBCOMMITTEE FOR ISOTOPIC ABUNDANCE MEASUREMENTS**

ISOTOPIC COMPOSITIONS OF 
THE ELEMENTS 1997

Prepared for publication by
K.J.R. ROSMAN1 AND P.D.P. TAYLOR2

1Department of Applied Physics, Curtin University of Technology, GPO Box U1987, Perth 6001, Australia. 
2Institute for Reference Materials and Measurements, European Commission-JRC, B-2440 Geel, Belgium.

* Membership of the Commission for the period 1996–1997 was as follows:

L. Schultz (FRG, Chairman); R. D. Vocke, Jr.(USA, Secretary); J. K. Böhlke (USA, Associate); H. J. Dietze (FRG, Associate); T. Ding (China, Associate), M. Ebihara (Japan, Titular); J. W. Gramlich (USA, Associate); A. N. Halliday (USA, Associate), H. R. Krouse (Canada, Titular); H.K Kluge (FRG, Associate); R. D. Loss (Australia, Titular); G. I. Ramendik (Russia, Titular); D. E. Richardson (USA, Associate); M. Stiévenard (France, Associate); P. D. P. Taylor (Belgium, Titular); J. R. de Laeter (Australia, National Representative); P. De Bièvre (Belgium, National Representative); Y. Xiao (China, National Representative); M. Shima (Japan, National Representative); A. Pires de Matos (Portugal, National Representative); N. N. Greenwood (UK, National Representative); H. S. Peiser (USA, National Representative). 

** Membership of the Subcommittee for Isotopic Abundance Measurements 1991-1997: P. D. P. Taylor (Belgium, Chairman 1995-97); R. D. Loss (Australia, Secretary 1995-97); Members: P.De Bièvre (Belgium), J. Césario (France), J. R. de Laeter (Australia), H. J. Dietze (FRG), M. Ebihara (Japan), J. W. Gramlich (USA), A. N. Halliday (USA,), N. E. Holden (USA), K. G. Heumann (FRG), H.K Kluge (FRG), T. J. Murphy (USA), H. S. Peiser (USA), D. E. Richardson (USA), D. J. Rokop (USA), E. R. Roth (France), K. J. R. Rosman (Australia), M. Shima (Japan ), R. D. Vocke (USA).

ISOTOPIC COMPOSITIONS OF THE ELEMENTS 1997

Abstract- The  Commission’s Subcommittee for the Isotopic Composition of the Elements (SIAM) has carried out its biennial review of isotopic compositions, as determined by mass spectrometry and other relevant methods.  This involves a  critical evaluation of the published literature, element by element, and forms the basis of the Table of Isotopic Compositions of the Elements as Determined by Mass Spectrometry presented here.  New guidelines have been used to arrive at the uncertainties on the isotopic abundances and there are numerous changes to the Table since it was last published in 1991. Atomic Weights calculated from this table are consistent with Ar(E) values listed in the Table of Standard Atomic Weights 1997. 

INTRODUCTION

Previous compilations of “The isotopic compositions of the elements” were published in 1983 (ref. 1), 1984 (ref. 2) and 1991 (ref. 3) for the purpose of yielding atomic weights consistent with the Commission's “Table of Standard Atomic Weights ” [4, 5, 6]. 

During the past six years the Commission, through its Subcommittee for Isotopic Abundance Measurements (SIAM), has continued to assemble and evaluate new data which has led to improvements to the tabulated isotopic composition of a number of elements. In 1993, the statistical guidelines for assigning uncertainties to the representative abundances were revised and extended by the Commission's Working Party on Statistical Evaluation of Isotopic Abundances (members: K. J. R. Rosman (Chairman), P. De Bièvre and J. W. Gramlich).  All the data presented in the Table were reassessed according to these guidelines.

The present table was assembled for publication following the meeting of SIAM held at Kloster Seeon (Germany), just prior to the 39th IUPAC General Assembly held at Geneva (Switzerland) in 1997 and is presented here as a companion paper to the Atomic Weights of the Elements 1997.

REFERENCES

1. N.E. Holden, R.L. Martin and I.L. Barnes,  Pure Appl. Chem., 55, 1119-1136 (1983).  
2. N.E. Holden, R.L. Martin and I.L. Barnes,  Pure Appl. Chem., 56, 675-694 (1984).
3. IUPAC Commission on Atomic Weights and Isotopic Abundances, Pure Appl. Chem. 63, 991-1002 (1991).
4. IUPAC Commission on Atomic Weights and Isotopic Abundances, Pure Appl. Chem. 55, 1101-1118 (1983).
5. IUPAC Commission on Atomic Weights and Isotopic Abundances, Pure Appl. Chem. 56, 653-674 (1984).
6. IUPAC Commission on Atomic Weights and Isotopic Abundances,  Pure Appl. Chem. 63, 975-990 (1991).

THE TABLE OF ISOTOPIC COMPOSITIONS OF THE ELEMENTS AS DETERMINED BY MASS SPECTROMETRY

The Subcommittee for Isotopic Abundance Measurements (SIAM) has examined the literature available to it through July l997 and has evaluated these data to produce a table of recommended isotopic abundances for the elements. The table is intended to include values for normal terrestrial samples and does not include values published for meteoritic or other extra-terrestrial materials. 

The column contents are as follows:

Column l: 	The elements are tabulated in ascending order of their atomic numbers.

Column 2: 	The symbols for the elements are listed using the abbreviations recommended by IUPAC.

Column 3: 	The mass number for each isotope is listed.

Column 4: 	Range of natural variations.
Given are the highest and lowest abundances published for each isotope from measurements which have been accepted by the Subcommittee.  No data are given in this Column unless a range has been reliably established. The limits given do not include certain exceptional samples, these are noted with a "g" in Column 5.

Column 5: 	Annotations 
The letters appended in this Column have the following significance:

g	geologically exceptional specimens are known in which the element has an isotopic composition outside the reported range. (refers to column 4)

m	modified isotopic compositions may be  found  in commercially available material because it has been subjected to an undisclosed or inadvertent isotopic fractionation. Substantial deviations from the isotopic compositions given can occur. (refers to column 9)

r	range in isotopic composition existing in normal terrestrial material limits the precision of the isotopic abundances. (refers to column 9)

Column 6: 	The best measurement from a single terrestrial source. 
The values are reproduced from the original literature. The uncertainties on the last digits are given in parenthesis as reported in the original publication. As they are not reported in any uniform manner in the literature, SIAM indicates this as follows: ls, 2s, 3s indicates l, 2, or 3 standard deviations, P indicates some other error as defined by the author, and se indicates standard error (standard deviation of the mean).  Where data are published as isotopic ratios, they, including their uncertainties, are converted to abundances using orthodox procedures.

"C" is appended when calibrated mixtures have been used to correct the mass spectrometer for bias, giving an "absolute" result within the errors stated in the original publication.  

"F" is appended when calibrated mixtures have been used to correct for isotopic fractionation but the measurement fails to fulfil all of the requirements of a C measurement. 

"L" is appended when the linearity of the mass spectrometer has been established for the relevant abundance ratios by using synthetic mixtures of isotopes or certified materials produced by an appropriate Standards laboratory. 

"N" is appended when none of the above requirements are met.  

The user is cautioned that: 
a) Since the data are reproduced from the literature, the sum of the isotopic abundances may not equal l00 percent.  
b) When a range of compositions has been established, the samples used for the best measurement may come from any part of the range. 
c) An uncalibrated "Best Measurement" is not necessarily free of systematic errors.
              
Column 7: 	The reference shown is that from which the data shown in column 6 were taken (Appendix A).

Column 8: 	Reference materials or samples with normal terrestrial isotopic values which are known to be available are listed.  An asterisk indicates the reference material used for the best measurement.  When additional reference materials are available, the distributors are listed in lieu of specific reference materials (Appendix B). 

Column 9: 	Representative Isotopic Composition.
In this column are listed the values which, in the opinion of SIAM, represent the isotopic composition of the chemicals and/or materials most commonly encountered in the laboratory. They may not, therefore, correspond to the most abundant natural material. For example, in the case of hydrogen, the deuterium abundance quoted corresponds to that in fresh water in temperate climates rather than to ocean water.  The uncertainties listed in parenthesis cover the range of probable variations of the materials as well as experimental errors. The number of significant figures is chosen to be consistent with the uncertainties, which in turn are derived by applying the statistical guidelines SIAM uses for assigning uncertainties to published isotope abundance measurements.  An Atomic Weight calculated from these abundances will be consistent with Ar(E) values listed in the Table of Standard Atomic Weights 1997.

Warning 
1) Values in column 9 should be used to determine the average properties of material of unspecified natural terrestrial origin, though no actual sample having the exact composition listed may be available. 

2) When precise work is to be undertaken, such as assessment of individual properties, samples with more precisely known isotopic abundances (such as those listed in column 8) should be obtained or suitable measurements should be made. 

TABLE 1. Isotopic compositions of the elements as determined by mass spectrometry

						Best			 
				Range of		Measurement		Available	Representaive
				Natural		from a Single		Reference	Isotopic
	Atomic		Mass	Variations	Annot-	Terrestrial Source	Reference	Materialsa	Composition
	Number	 Symbol	Number	(Atom %)	ations	(Atom %)	(App. A)	(App. B)	(Atom %)
	1	2	3	4	5	6	7	  8	9

	1	H	1	99.9816 - 99.9975	m,r	99.984426 (5) 2s C	70HAG1	VSMOW*	99.9885 (70)
			2	0.0184 - 0.0025 		0.015574 (5)		CEA	0.0115 (70) b 
								IAEA	(in water)
								NIST

	2	He	3	4.6x10-8-0.0041	g,r	0.0001343(13) 1s C	88SAN1	Air*	 0.000137 (3)
			4	100 - 99.9959		99.9998657 (13)			99.999863 (3)
									(in air)

 	3	Li	6	7.21 - 7.71	m,r	7.589 (24)   2s C	97QI1	IRMM-016*	[7.59(4)]c
			7	92.79 - 92.29		92.411 (24)		IAEA	[92.41(4)]
								IRMM
								NIST

	4	Be	9			100	63LEI1		100

	5	B	10	18.927 - 20.337	m,r	19.82 (2)   2s C	69BIE1	IRMM-011*	19.9 (7)
			11	81.073- 79.663		80.18 (2)		NIST	80.1 (7)

	6	C	12	98.85 - 99.02	r	98.8922 (28) P C	90CHA1	NBS19*	98.93 (8)
			13	1.15 - 0.98		1.1078 (28)		IAEA	1.07 (8)
								NIST	

	7	N	14	99.890 -99.652	r	99.6337 (4)  P  C	58JUN1	Air*	99.632 (7) d
			15	0.411 - 0.348		 0.3663 (4)		IAEA	0.368 (7)
								NIST

	8	O	16	99.7384 -99.7756	r	99.7628 (5)  1s N	76BAEl	VSMOW*	99.757 (16)
			17	0.0399 - 0.0367		 0.0372 (4) e	88LI1	IAEA	0.038 (1)
			18	0.2217 - 0.1877		 0.20004 (5)		NIST	0.205 (14)

	9	F	19			100	20AST1		100

	10	Ne	20	90.514  - 88.47	g,m	90.4838 (90)  1s C	84BOT1	Air*	90.48 (3)
			21	1.71   -  0.266	r	 0.2696 (5)			 0.27 (1)
			22	9.96   -  9.20		 9.2465 (90)			 9.25 (3)
									(in air)

	11	Na	23			100	56WHI1		100

	12	Mg	24			78.992 (25)  2s C	66CAT1	NIST-SRM980*	78.99 (4)
			25			10.003 (9)			10.00 (1)
			26			11.005 (19)			11.01 (3)

	13	Al	27			100	56WHI1		100

						Best			 
				Range of		Measurement		Available	Representaive 
				Natural		from a Single		Reference	Isotopic
	Atomic		Mass	Variations	Annot-	Terrestrial Source	Reference	Materialsa	Composition
	Number	 Symbol	Number	(Atom %)	ations	(Atom %)	(App. A)	(App. B)	(Atom %)
	1	2	3	4	5	6	7	  8	9

	14	Si	28	92.21 - 92.25	r	92.22968 (44) 2s C	97GON1	IAEA	92.2297 (7) 
			29	4.69 - 4.67		 4.68316 (32)		IRMM	 4.6832 (5) 
			30	3.10 - 3.08		 3.08716 (48)		NIST	 3.0872 (5)

	15	P	31			100	63LEI1		100

	16	S	32	94.537 - 95.261	r	95.018 (4) P C	50MAC1	CEA	94.93 (31)
			33	0.787 - 0.731		 0.750 (7)		IAEA	 0.76 (2)
			34	4.655 - 3.993		 4.215 (4)		NIST	 4.29 (28)
			36	0.021 -0.015		0.017 (2)			 0.02 (1)

	17	Cl	35	75.64 - 75.86	m	75.771 (45)  2s C	62SHI1	NIST-SRM975*	75.78 (4)
			37	24.36 - 24.14		24.229 (45)			24.22 (4)

	18	Ar	36		g	 0.3365 (6)  P C	50NIE1	Air*	 0.3365 (30)
			38			 0.0632 (1)			 0.0632 (5)
			40			99.6003 (6)			99.6003 (30)
									(in air)

	19	K	39			93.25811 (292) 2s C	75GAR1	NIST-SRM985*	93.2581 (44)
			40			 0.011672 (41)			 0.0117 (1)
			41			 6.73022 (292)			 6.7302 (44)

	20	Ca	40	96.982  -  96.880	g,r	96.941 (6)  2s N	72MOO1	NIST-SRM915*	96.941 (156) h
			42	0.656  -  0.640		 0.647 (3)			 0.647 (23)
			43	0.146  -  0.131		 0.135 (2)			 0.135 (10)
			44	2.130  -  2.057		 2.086 (4)			 2.086 (110)
			46	0.0046  -  0.0031		 0.004 (1)			 0.004 (3)
			48	0.200  -  0.179		 0.187 (1)			 0.187 (21)

	2l	Sc	45			100	50LEL1		100

	22	Ti	46			 8.249 (21)  2s C	93SHI1		 8.25 (3)
			47			 7.437 (14)			 7.44 (2)
			48			73.720 (22)			73.72 (3)
			49			 5.409 (10)			 5.41 (2)
			50			 5.185 (13)			 5.18 (2)

	23	V	50	0.2502 - 0.2487	g	 0.2497 (6)  1s F	66FLE1		 0.250 (4)
			51	99.7513 - 99.7498		99.7503 (6)			99.750 (4)

	24	Cr	50			 4.3452 (85) 2s C	66SHI1	NIST-SRM979*	 4.345 (13)
			52			83.7895 (117)			83.789 (18)
			53			 9.5006 (110)			 9.501 (17)
			54			 2.3647 (48)			 2.365 (7)

						Best			 
				Range of		Measurement		Available	Representaive 
				Natural		from a Single		Reference	Isotopic
	Atomic		Mass	Variations	Annot-	Terrestrial Source	Reference	Materialsa	Composition
	Number	 Symbol	Number	(Atom %)	ations	(Atom %)	(App. A)	(App. B)	(Atom %)
	1	2	3	4	5	6	7	  8	9

	25	Mn	55			100	63LEI1		100

	26	Fe	54			 5.845(23)  2s C	92TAY1	IRMM-014*	5.845 (35)
			56			91.754(24)			91.754 (36)
			57			 2.1191(65)			2.119 (10)
			58			 0.2819(27)			0.282 (4)

	27	Co	59			100	63LEI1		100

	28	Ni	58			68.0769 (59) 2s C	89GRA1		68.0769 (89)
			60			26.2231 (51)			26.2231 (77)
			61			 1.1399 (4)			 1.1399 (6)
			62			 3.6345 (11)			 3.6345 (17)
			64			 0.9256 (6)			 0.9256 (9)

	29	Cu	63	69.24  -  68.98	r	69.174 (20)  2s C	64SHI1	NIST-SRM976*	69.17 (3)
			65	31.02  -  30.76		30.826 (20)			30.83 (3)

	30	Zn	64			48.63 (20)  2s F	72ROS1		48.63 (60)
			66			27.90 (9)			27.90 (27)
			67			 4.10 (4)			 4.10 (13)
			68			18.75 (17)			18.75 (51)
			70			 0.62 (1)			0.62 (3)

	31	Ga	69		m	60.1079 (62) 2s C	86MAC1	NIST-SRM994*	60.108 (9)
			71			39.8921 (62)			39.892 (9)

	32	Ge	70			21.234 (31) 1s L	86GRE1		20.84 (87)k
			72			27.662 (29)			27.54 (34)
			73			 7.717 (5)			 7.73 (5)
			74			35.943 (25)			36.28 (73)
			76			 7.444 (14)			 7.61 (38)

	33	As	75			100		63LEI1		100

	34	Se	74		r	 0.889 (3)  1s N	89WAC1		0.89 (4)
			76			 9.366 (18)			 9.37 (29)
			77			 7.635 (10)			 7.63 (16)
			78			23.772 (20)			23.77 (28)
			80			49.607 (17)			49.61 (41)
			82			 8.731 (10)			 8.73 (22)

	35	Br	79			50.686 (26)  2s C	64CAT1   	NIST-SRM977*	50.69 (7)
			81			49.314 (26)			49.31 (7) 

	36	Kr	78		g,m	 0.35351 (7)  2s N	94VAL1		 0.35 (1)
			80			 2.28086(29)			 2.28 (6)
			82			11.58304 (76)			11.58 (14)
			83			11.49533 (35)			11.49 (6)
			84			56.98890 (62)			57.00 (4)
			86			17.29835(26)			17.30 (22)
									(in air)

						Best			 
				Range of		Measurement		Available	Representaive 
				Natural		from a Single		Reference	Isotopic
	Atomic		Mass	Variations	Annot-	Terrestrial Source	Reference	Materialsa	Composition
	Number	 Symbol	Number	(Atom %)	ations	(Atom %)	(App. A)	(App. B)	(Atom %)
	1	2	3	4	5	6	7	  8	9

	37	Rb	85		g	72.1654 (132) 2s C	69CAT1	NIST-SRM984	72.17 (2)
			87			27.8346 (132)			27.83 (2)

	38	Sr	84	0.58 - 0.55	g,r	 0.5574 (16) 2s C	82MOO1	NIST-SRM 987*	 0.56 (1)
			86	9.99 - 9.75		 9.8566 (34)		NIST	 9.86 (1)
			87	7.14 - 6.94		 7.0015 (26)			 7.00 (1) h
			88	82.75 - 82.29		82.5845 (66)			82.58 (1)

	39	Y	89			100	57COL1		100

	40	Zr	90		g	51.452 (9)   2s N	83NOM1		51.45 (40)
			91			11.223 (12)			11.22 (5)
			92			17.146 (7)			17.15 (8)
			94			17.380 (12)			17.38 (28)
			96			2.799 (5)			 2.80 (9)

	41	Nb	93			100	56WHI1		100

	42	Mo	92		g	14.8362 (148) 2s N	74MOO1		14.84 (35)
			94			 9.2466 (92)			 9.25 (12)
			95			15.9201 (159)			15.92 (13)
			96			16.6756 (167)			16.68 (2)
			97			 9.5551 (96)			 9.55 (8)
			98			24.1329 (241)			24.13 (31)
			100			 9.6335 (96)			 9.63 (23)

	43	Tc					--	---	------

	44	Ru	96		g	 5.5420 (1)   1s N	97HUA1		 5.54 (14)
			98			 1.8688 (2)			 1.87 (3)
			99			12.7579 (6)			12.76 (14)
			100			12.5985 (4)			12.60 (7)
			101			17.0600 (10)			17.06 (2)
			102			31.5519 (11)			31.55 (14)
			104			18.6210 (11)			18.62 (27)

	45	Rh	103			100	63LEI1		100

	46	Pd	102		g,r	 1.020 (8) 2s C	78SHI1		 1.02 (1)
			104			11.14 (5)			11.14 (8)
			105			22.33 (5)			22.33 (8)
			106			27.33 (2)			27.33 (3)
			108			26.46 (6)			26.46 (9)
			110			11.72 (6)			11.72 (9)

	47	Ag	107		g	51.8392 (51) 2s C	82POW1	NIST-SRM978*	51.839 (8)
			109			48.1608 (51)			48.161 (8)

						Best			 
				Range of		Measurement		Available	Representaive 
				Natural		from a Single		Reference	Isotopic
	Atomic		Mass	Variations	Annot-	Terrestrial Source	Reference	Materialsa	Composition
	Number	 Symbol	Number	(Atom %)	ations	(Atom %)	(App. A)	(App. B)	(Atom %)
	1	2	3	4	5	6	7	  8	9

	48	Cd	106		g	 1.25 (2) 2s F	80ROS1		 1.25 (6)
			108			 0.89 (1)			 0.89 (3)
			110			12.49 (6)			12.49 (18)
			111			12.80 (4)			12.80 (12)
			112			24.13 (7)			24.13 (21)
			113			12.22 (4)			12.22 (12)
			114			28.73 (14)			28.73 (42)
			116			 7.49 (6)			 7.49 (18)

	49	In	113		g	 4.288 (5) 2s N	91CHA1		 4.29  (5)
			115			95.712 (5)			95.71 (5)

	50	Sn	112		g	 0.973 (3) 1s C	83DEV1		 0.97 (1)
			114			 0.659 (3) f 	84ROS1		 0.66 (1)
			115			 0.339 (3) f			 0.34 (1)
			116			14.536 (31)			14.54 (9)
			117			 7.676 (22)			 7.68 (7)
			118			24.223 (30)			24.22 (9)
			119			 8.585 (13)			 8.59 (4)
			120			32.593 (20)			32.58 (9)
			122			 4.629 (9)			 4.63 (3)
			l24			 5.789 (17)			 5.79 (5)

	51	Sb	121		g	57.213 (32) 2s C	93CHA1		57.21 (5) 
			123			42.787 (32)			42.79 (5)

	52	Te	120		g	0.096 (1)  2se N	78SMI1		 0.09 (1)k
			122			2.603 (1)			 2.55 (12)
			123			0.908 (1)			 0.89 (3)
			124			4.816 (2)			 4.74 (14)
			125			7.139 (2)			 7.07 (15)
			126			18.952 (4)			18.84 (25)
			128			31.687 (4)			31.74 (8)
			130			33.799 (3)			34.08 (62)

	53	I	127			100	49LEL1		100

	54	Xe	124		g,m	 0.08913(3) 2s N	94VAL1		 0.09 (1)
			126			 0.08880 (2)			 0.09 (1)
			128			 1.91732 (12)			 1.92 (3)
			129			26.43964 (17)			26.44 (24)
			130			 4.08271 (15)			 4.08 (2)
			131			21.17961 (19)			21.18 (3)
			132			26.89157 (11)			26.89 (6)
			134			10.44232 (17)			10.44 (10)
			136			 8.86890 (14)			8.87 (16)

	55	Cs	133			100	56WHI1		100

						Best			 
				Range of		Measurement		Available	Representaive 
				Natural		from a Single		Reference	Isotopic
	Atomic		Mass	Variations	Annot-	Terrestrial Source	Reference	Materialsa	Composition
	Number	 Symbol	Number	(Atom %)	ations	(Atom %)	(App. A)	(App. B)	(Atom %)
	1	2	3	4	5	6	7	  8	9

	56	Ba	130		g	 0.1058 (2)  3se F	69EUG1		 0.106 (1)
			132			 0.1012 (2)			 0.101 (1)
			134			 2.417 (3)			 2.417 (18)
			135			 6.592 (2)			 6.592 (12)
			136			 7.853 (4)			 7.854 (24)
			137			11.232 (4)			11.232 (24)
			138			71.699 (7)			71.698 (42)

	57	La	138		g	0.09017 (5) 2se N	87MAK1		 0.090 (1)
			139			99.90983 (5)			99.910 (1)

	58	Ce	136	0.186 -0.185	g	 0.186 (1)  2s C	95CHA1		0.185 (2)
			138	0.254 - 0 251		 0.251 (1)			0.251 (2)h
			140	88.449 - 88.446		88.449 (34)			88.450 (51)
			142	11.114 - 11.114		11.114 (34)			11.114 (51)

	59	Pr	141			100	57COL1		100

	60	Nd	142	27.30 - 26.80	g	27.16 (4)  2se N	81HOL1		27.2 (5)
			143	12.32 - 12.12		12.18 (2)			12.2 (2) h 
			144	23.97 - 23.795		23.83 (4)			23.8 (3)
			145	8.35 - 8.23		8.30 (2)		 	 8.3 (1)
			146	17.35 - 17.06		17.17 (3)			17.2 (3)
			148	5.78 - 5.66		 5.74 (1)			 5.7 (1)
			150	5.69 - 5.53		 5.62 (1)			 5.6 (2)

	6l	Pm				---			---

	62	Sm	144		g	 3.0734 (9) 2s F	97CHA1		 3.07 (7)
			147			14.9934 (18)			14.99 (18)
			148			11.2406 (15)			11.24 (10)
			149			13.8189 (18)			13.82 (7)
			150			 7.3796 (14)			 7.38 (1)
			152			26.7421 (66)			26.75 (16)
			154			22.7520 (68)			22.75 (29)

	63	Eu	151		g	47.810 (42) 2se C	94CHA1		47.81 (3)
			153			52.190 (42)			52.19 (3)

	64	Gd	152		g	 0.2029 (4) 2se N	70EUG1		 0.20 (1)
			154			 2.1809 (4)			 2.18 (3)
			155			14.7998 (17)			14.80 (12)
			156			20.4664 (6)			20.47 (9)
			157			15.6518 (9)			15.65 (2)
			158			24.8347 (16)			24.84 (7)
			160			21.8635 (7)			21.86 (19)

	65	Tb	159			100	57COL1		100

						Best			 
				Range of		Measurement		Available	Representaive 
				Natural		from a Single		Reference	Isotopic
	Atomic		Mass	Variations	Annot-	Terrestrial Source	Reference	Materialsa	Composition
	Number	 Symbol	Number	(Atom %)	ations	(Atom %)	(App. A)	(App. B)	(Atom %)
	1	2	3	4	5	6	7	  8	9

	66	Dy	156		g	 0.056 (1) 2se N	81HOL1		 0.06 (1)
			158			 0.096 (2)			 0.10 (1)
			160			 2.34  (2)			 2.34 (8)
			161			18.91  (5)			18.91 (24)
			162			25.51  (7)			25.51 (26)
			163			24.90  (7)			24.90 (16)
			164			28.19  (8)			28.18 (37)

	67	Ho	165			100	57COLl		100

	68	Er	162		g	 0.137 (1) 2se N	81HOL1		 0.14 (1)
			164			 1.609 (5)			 1.61 (3)
			166			33.61  (7)			33.61 (35)
			167			22.93  (5)			22.93 (17)
			168			26.79  (7)			26.78 (26)
			170			14.93  (5)			14.93 (27)

	69	Tm	169			100	57COL1		100

	70	Yb	168		g	 0.127 (2) 2se N	81HOL1		0.13 (1)
			170			 3.04  (2)			3.04 (15)
			171			14.28  (8)			14.28 (57)
			172			21.83  (l0)			21.83 (67)
			173			16.13  (7)			16.13 (27)
			174			31.83  (14)			31.83 (92)
			176			12.76  (5)			12.76 (41)

	71	Lu	175		g	97.416 (5) 2se N	83PAT1		97.41 (2)
			176			 2.584 (5)			 2.59 (2)

	72	Hf	174	0.1621 - 0.1619		0.1620 (9)  2se N	 83PAT1		0.16 (1)
			176	5.271 - 5.206		5.2604 (56)			5.26 (7) h
			177	18.606 - 18.593		18.5953 (12)			18.60 (9)
			178	27.297 - 27.278		27.2811 (22)			27.28 (7)
			179	13.630 - 13.619		13.6210 (9)			13.62 (2)
			180	35.100 - 35.076		35.0802 (26)			35.08 (16)

	73	Ta	180			 0.0123 (3) 1se N	56WHI1		 0.012 (2)
			181			99.9877 (3)			99.988 (2)

	74	W	180			 0.1198 (2)  1s N	91VÖL2		 0.12 (1)
			182			26.4985 (49)			26.50 (16)
			183			14.3136 (6)			14.31 (4)
			184			30.6422 (13)			30.64 (2)
			186			28.4259 (62)			28.43 (19)

	75	Re	185			37.398 (16)  2s C	73GRA1	NIST-SRM989*	37.40 (2)
			187			62.602 (16)			62.60 (2)

						Best			 
				Range of		Measurement		Available	Representaive 
				Natural		from a Single		Reference	Isotopic
	Atomic		Mass	Variations	Annot- 	Terrestrial Source	 Reference	Materialsa	Composition
	Number	 Symbol	Number	(Atom %)	ations	(Atom %)	(App. A)	(App. B)	(Atom %)
	1	2	3	4	5	6	7	  8	9

	76	Os	184		g,r	 0.0197 (5)  1s N	91VÖL1		 0.02 (1)
			186			 1.5859 (44)			 1.59 (3)
			187			 1.9644 (12)			 1.96 (2) h 
			188			13.2434 (19)			13.24 (8)
			189			16.1466 (16)			l6.l5 (5)
			190			26.2584 (14)			26.26 (2)
			192			40.7815 (22)			40.78 (19)

	77	Ir	191			37.272 (15)  1s N	93WAL1		37.3 (2)
			193			62.728 (15)			62.7 (2)

	78	Pt	190			0.013634 (68) 1s N	96TAY1		 0.014 (1)
			192			0.782659 (35)			 0.782 (7) 
			194			32.96700 (77)			32.967 (99)
			195			33.831557 (42)			33.832 (10)
			196			25.24166 (36)			25.242 (41)
			198			7.16349 (42)			 7.163 (55)

	79	Au	197			100	63LEI1		100

	80	Hg	196			 0.15344(19) 1s N	89ZAD1		 0.15 (1)
			198			 9.968  (13)			 9.97 (20)
			199			16.873  (17)			16.87 (22)
			200			23.096  (26)			23.10 (19)
			201			13.181  (13)			13.18 (9)
			202			29.863  (33)			29.86 (26)
			204			 6.865  (7)			 6.87 (15)

	81	Tl	203			29.524 (9) 2s C	80DUN1	NIST-SRM997*	29.524 (14)
			205			70.476 (9)			70.476 (14)

	82	Pb	204	1.65 - 1.04	g,r	1.4245 (12) 2s C	68CAT1	NIST-SRM98l*	1.4 (1)
			206	27.48 - 20.84		24.1447 (57)		NIST 	24.1 (1) h
			207	23.65 - 17.62		22.0827 (27)			22.1 (1) h
			208	56.21 - 51.28		52.3481 (86)			52.4 (1) h

	83	Bi	209			100	63LEI1			100

	84	Po				

	85	At		

	86	Rn 		

	87	Fr		

	88	Ra		

	89	Ac		

						Best			 
				Range of		Measurement		Available	Representaive
				Natural		from a Single		Reference	Isotopic
	Atomic		Mass	Variations	Annot-	Terrestrial Source	Reference	Materialsa	Composition
	Number	 Symbol	Number	(Atom %)	ations	(Atom %)	(App. A)	(App. B)	(Atom %)
	1	2	3	4	5	6	7	  8	9

	90	Th	232		g	100	36DEM1		100

	91	Pa	231			100	77BRO1		100

	92	U	234	0.0059 - 0.0050	g,m	 0.00548 (2) i 1s N	69SMI1	IRMM-184	[0.0055(2)]
			235	0.7202 - 0.7198	r	 0.7200 (1)	76COW1	CEA	[0.7200(51)]c,h
			238	99.2752 - 99.2739		99.2745 (10)		IRMM	[99.2745(106)] 
								NBL

*Reference material used for the best measurement.
a NIST materials were previously labelled NBS.  IRMM materials were previously labelled CBNM. 
b The range of  2H in tank hydrogen is 0.0032 to 0.0184 atom percent.
c Materials depleted in 6Li and 235U are commercial sources of laboratory shelf reagents. In the case of Li such samples are known to have 6Li abundances in the range 2.007-7.672 atom percent, with natural materials at the higher end of this range. 
d The Commission recommends that the value of 272 be employed for 14N/15N of N2 in air for the calculation of atom percent 15N 	from measured 15 N  values.
e The reference reported a calibrated 16O/18O ratio on VSMOW; 17O abundance was derived from 88LI1. 
f Due to 115In contamination and an error in the 114Sn abundance the 115Sn and 114Sn abundances reported by 83DEV1 were adjusted using data from 84ROS1.
g  Not used since g is used in column 5.
h Evaluated isotopic composition is for most but not all commercial samples. 
i  The 234U abundance is from 69SMI1, 235U and 238U are from 76COW1. 
k An electron multiplier was used for these measurements and the measured abundances were adjusted the using a square root of the masses.  

APPENDIX A:  REFERENCES FOR TABLE 1

20AST1	F. W. Aston, Phil. Mag. 40, 628-634 (1920). 
	The Mass Spectra of Chemical Elements.  

36DEM1	A. J. Dempster, Nature 136, 120 (1936).   
	Atomic Masses of Uranium and Thorium.       

49LEL1	W. T. Leland, Phys. Rev. 76, 992 (1949).
	On the Abundance of 129I, 118Te and 190Pt.  

50LEL1	W. T. Leland, Phys. Rev. 77, 634-640 (1950).
	The Isotopic Composition of Scandium, Gadolinium, and Dysprosium. 

50MAC1	J. MacNamara, and H. G. Thode, Phys. Rev. 78, 307-308 (1950).
	Comparison of the Isotopic Constitution of Terrestrial and Meteoritic Sulphur. 

50NIE1	A. O. Nier, Phys. Rev. 77, 789-793 (1950). 
	A Redetermination of the Relative Abundances of the Isotopes of Carbon, Nitrogen, Oxygen, Argon and Potassium.   

56WHI1	F. A. White, T. L. Collins, Jr., and F. M. Rourke, Phys. Rev. 101, 1786-1791 (1956). 
	Search for Possible Naturally Occurring Isotopes of Low Abundance. 

57COL1	T. L. Collins, Jr., F. M. Rourke, and F. A. White, Phys. Rev. 105, 196-197 (1957). 
	Mass Spectrometric Investigation of the Rare Earth Elements for the Existence of New Stable Isotopes. 

58JUN1	G. Junk, and H. J. Svec, Geochim. Cosmochim. Acta 14, 234-243 (1958).
	The Absolute Abundance of the Nitrogen Isotopes in the Atmosphere and Compressed Gas from Various Sources. 

62SHI1	W.R.Shields, T.J.Murphy, E.L.Garner, and V.H.Dibeler, J.Am. Chem. Soc. 84, 1519-1522 (1962).
	Absolute Isotopic Abundance Ratios and the Atomic Weight of Chlorine.

63LEI1	F. D. Leipziger, Appl. Spec. 17, 158-160 (1963).
	Some New Upper Limits of Isotopic Abundance by Mass Spectrometry. 

64CAT1	E. J. Catanzaro, T. J. Murphy, E. L. Garner, and W. R. Shields, J. Res. Nat. Bur., Stand. (U.S.),68A, 593-599 (1964). 
	Absolute Isotopic Abundance Ratio and the Atomic Weight of Bromine.  

64SHI1	W.R. Shields, T.J. Murphy, and E.L. Garner, J.Res. Nat. Bur. Stand. (U.S.), 68A, 589-592 (1964). 
	Absolute Isotopic Abundance Ratios and the Atomic Weight of a Reference Sample of Copper. 

66CAT1	E. J. Catanzaro, T. J. Murphy, E. L. Garner, and W. R. Shields, J. Res. Nat. Bur. Stand. (U.S.),70A, 453-458 (1966). 
	Absolute Isotopic Abundance Ratios and the Atomic Weight of Magnesium. 
66FLE1	G. D. Flesch,J. Capellen, and H. J. Svec, Adv. Mass Spectrom. III, 571-581, (1966), Leiden and Son, London.
	The Abundance of the Vanadium Isotopes from Sources of Geochemical Interest. 

66SHI1	W. R. Shields, T. J. Murphy, E. J. Catanzaro, and E. L. Garner, J. Res. Nat. Bur. Stand. (U.S.), 70A, 193-197 (1966). 
	Absolute Isotopic Abundance Ratios and the Atomic Weight of a Reference Sample of Chromium. 

68CAT1	E. J. Catanzaro, T. J. Murphy, W. R. Shields, and E. L. Garner, J. Res. Nat. Bur. Stand. (U.S.), 72A, 261-266 (1968). 
	Absolute Isotopic Abundance Ratios of Common, Equal-Atom, and Radiogenic Lead Isotopic Standards. 

69BIE1	P. J. De Bievre, and G. H. Debus, Int. J. Mass Spectrom. Ion Phys. 2, 15-23 (1969). 
	Absolute Isotope Ratio Determination of a Natural Boron Standard. 

69CAT1	E. J. Catanzaro, T. J. Murphy, E. L. Garner, and W. R. Shields, J. Res. Nat. Bur. Stand. (U.S.),73A, 511-516(1969). 
	Absolute Isotopic Abundance Ratios and the Atomic Weight of Terrestrial Rubidium. 

69EUG1	O. Eugster, F. Tera, and G. J. Wasserburg, J. Geophys. Res. 74, 3897-3908 (1969). 
	Isotopic Analyses of Barium in Meteorites and in Terrestrial Samples.

69SMI1	R. F. Smith, and J. M. Jackson, U. S. Atomic Energy Commission Report KY-581 (1969). 
	Variations in U-234 Concentration of Natural Uranium. 

70EUG1	O. Eugster, F. Tera, D. S. Burnett, and G. J. Wasserburg, J. Geophys. Res. 75, 2753-2768 (1970).
	Isotopic Composition of Gadolinium and Neutron-capture Effects in Some Meteorites. 

70HAG1	R. Hagemann, G. Nief, and E. Roth, Tellus 22, 712-715 (1970). 
	Absolute Isotopic Scale for Deuterium Analysis of Natural Waters, Absolute D/H Ratio for SMOW. 

72MOO1	L. J. Moore, and L. A. Machlan, Anal. Chem. 44, 2291-2296 (1972). 
	High Accuracy Determination of Calcium in Blood Serum by Isotope Dilution Mass Spectrometry. 

72ROS1	K. J. R. Rosman, Geochim. Cosmochim. Acta 36, 801-819  (1972). 
	A Survey of the Isotopic and Elemental Abundance of Zinc. 

73GRA1	J. W. Gramlich, T. J. Murphy, E. L. Garner, and W. R. Shields, J. Res. Nat. Bur. Stand. (U.S.), 77A, 691-698 (1973). 
	Absolute Isotopic Abundance Ratio and Atomic Weight of a Reference Sample of Rhenium. 

74MOO1	L. J. Moore, L. A. Machlan, W. R. Shields, and E. L. Garner, Anal. Chem. 46, 1082-1089 (1974). 
	Internal Normalization Techniques for High Accuracy Isotope Dilution Analyses : Application to Molybdenum and Nickel in Standard Reference Materials. 

75GAR1	E. L. Garner, T. J. Murphy, J. W. Gramlich, P. J. Paulsen, and I. L. Barnes, J. Res. Nat. Bur. Stand.(U.S.), 79A, 713-725 (1975). 
	Absolute Abundance Ratios and the Atomic Weight of a Reference Sample of Potassium.

76BAE1	P. Baertschi, Earth Planet. Sci. Lett., 31, 341-344 (1976). 
	Absolute  180 Content of Standard Mean Ocean Water. 

76COW1	G. A. Cowan, and H. H. Adler, Geochim. Cosmochim. Acta, 40, 1487-1490 (1976). 
	The Variability of the Natural Abundance of U-235. 

76DEV1	C. Devillers, T. Lecomte, M. Lucas, and R. Hagemann, Proc. 7th Int. Mass Spectrom. Conf. Florence, 553-564 (1976).
	Mass Spectrometric Investigations on Ruthenium Isotopic Abundances. 

77BRO1	D. Brown, Gmelin Handbuch der Anorg. Chem., 8th ed., Syst.51, Erg.-Bd. 1, 6, Springer (1977).
	Occurrence of Protactinium Isotopes in Nature and Synthesis of Weighable Amounts in Nuclear Reactions.

78SHI1	M. Shima, C. E. Rees, and H. G. Thode, Can. J. Phys., 56, 1333-1339 (1978). 
	The Isotopic Composition and Atomic Weight of Palladium.    

78SMI1	C.L. Smith, K.J.R. Rosman, and J.R.De Laeter, Int. J. Mass Spectrom. Ion Phys., 28, 7-17 (1978). 
	The Isotopic Composition of Tellurium. 

80DUN1	L. P. Dunstan, J. W. Gramlich, I. L. Barnes, and W. C. Purdy, J. Res. Nat. Bur. Stand. (U.S.), 85, 1-10 (1980).
	The Absolute Isotopic Abundance and the Atomic Weight of a Reference Sample of Thallium. 

80ROS1	K.J.R. Rosman, I.L. Barnes, L.J. Moore, and J.W. Gramlich, Geochemical J., 14, 269-277 (1980). 
	Isotope Composition of Cd, Ca, and Mg in the Brownfield Chrondrite. 

81HOL1	P. Holliger and C. Devillers, Earth Planet. Sci. Lett., 52, 76-84 (1981). 
	Contribution a l' etude de la temperature dans les reacteurs fossiles d' Oklo par la mesure du rapport isotopique du Lutetium. 

82MOO1	L.J.Moore, T.J.Murphy, I.L.Barnes, and P.J.Paulsen, J.Res. Nat. Bur. Stand. (U.S.),87,1-8 (1982). Absolute Isotopic Abundance Ratios and Atomic Weight of a Reference Sample of Strontium. 

82POW1	L. J. Powell, T. J. Murphy, and J. W. Gramlich, J. Res. Nat. Bur. Stand. (U.S.), 87, 9-19 (1982). 
	The Absolute Isotopic Abundance and Atomic Weight of a Reference Sample of Silver. 

83DEV1	C. Devillers, T. Lecomte, and R. Hagemann, Int.J. Mass Spectrom. Ion Phys. 50, 205-217 (1983). 
	Absolute Isotope Abundances of Tin. 

83NOM1	M. Nomura, K. Kogure, and M. Okamoto, Int. J. Mass Spectrom. Ion Phys., 50, 219-227 (1983). 
	Isotopic Abundance Ratios and Atomic Weight of Zirconium. 

83MIC1	E. Michiels, and P. De Bievre, Int. J. Mass Spectrom. Ion Phys., 49, 265-274 (1983). 
	Absolute Isotopic Composition and the Atomic Weight of a Natural Sample of Lithium. 

83PAT1	P. J. Patchett, Geochim. Cosmochim. Acta 47, 81-91 (1983). 
	Importance of the Lu-Hf Isotopic System in Studies of Planetary Chronology and Chemical Evolution.

84BOT1	D.J. Bottomley, J.D. Ross, and W.B. Clarke, Geochim. Cosmochim. Acta, 48, 1973-1985 (1984).
	Helium and Neon Isotope Geochemistry of some Ground Waters from the Canadian Precambrian Shield.

84ROS1	K.J.R.Rosman, R.D.Loss, and J.R. DeLaeter, Int.J.Mass Spectrom. Ion Proc.,56, 281-291 (1984).
	The Isotopic Composition of Tin.

86GRE1	M.D.Green, K.J.R.Rosman, and J.R.DeLaeter, Int. J. Mass Spectrom. Ion Proc., 68, 15-24 (1986).
	The Isotopic Composition of Germanium in Terrestrial Samples.

86MAC1	L.A. Machlan, J.W. Gramlich, L.J. Powell, and G.M. Lambert, J. Res. Nat. Bur. Stand. (U.S.), 91, 323-331 (1986).
	Absolute Isotopic Abundance Ratio and Atomic Weight of a Reference Sample of Gallium.

87MAK1	A. Makishima, H. Shimizu, and A. Masuda, Mass Spectroscopy, 35, 64-72 (1987).
	Precise Measurement of Cerium and Lanthanum Isotope Ratios.

88LI1	W. Li, D. Jin, and T.L. Chang, Kexue Tinboa, 33, 1610-1613 (1988).
	Measurement of the absolute abundance of oxygen-17 in V-SMOW. 

88SAN1 	Y. Sano, H. Wakita, and X. Sheng, Geochem. J., 22, 177-181 (1988).
	Atmospheric Helium Isotope Ratio.

89GRA1	J.W. Gramlich, L.A. Machlan, I.L. Barnes, and P.J. Paulsen, J. Res. Natl. Inst. Stand. Technol.(U.S.), 94, 347-356 (1989).
	The Absolute Abundance Ratios and Atomic Weight of a Reference Sample of Nickel.

89WAC1	M. Wachsmann, and K. G. Heumann, Adv. Mass Spectrom., 11B, 1828-1829 (1989).
	Selenium Isotope Ratio Meaurements with Negative Thermal Ionization Mass Spectrometry using a Silica Gel Technique.

89ZAD1	M.G. Zadnik, S. Specht, and F. Begemann, Int. J. Mass Spectrom. Ion Proc., 89, 103-110 (1989).
	Revised Isotopic Composition of Terrestrial Mercury.

90CHA1	T.L.Chang, and W. Li, Chin. Sci. Bull., 35 , 290-296 (1990).
	A Calibrated Measurement of the Atomic Weight of Carbon. 

91CHA1	T.L.Chang, Y.K. Xiao, Chin. Chem. Letters, 2, 407-410 (1991).
	The Atomic Weight of Indium.

91VOL1	J. Volkening, T. Walzyck, and K.G.. Heumann, Int. J. Mass Spectrom. Ion Proc.,105, 147-159 (1991).
	Osmium Isotope ratio Determinations by Negative Thermal Ionisation Mass Spectrometry.

91VOL2	J. Volkening, M. Koppe, and K. Heumann, Int.J.Mass. Spectrom. Ion Proc., 107, 147-159 (1991).
	Tungsten Isotope Ratio Measurements by Negative Thermal Ionisation Mass Spectrometry.

92TAY1	P.D.P. Taylor, R. Maeck, and P. De Bievre, Int. J. Mass Spectrom. Ion Proc., 121, 111-125 (1992).
	Determination of the Absolute Isotopic Composition and Atomic Weight of a Reference Sample of Natural Iron.

93CHA1	T.L.Chang, Q.Y.Qian, M.T.Zhao, and J.Wang, Int.J. Mass Spectrom. Ion Proc.,123, 77-82 (1993).
	The Isotopic Abundance of Antimony.

93SHI1	M. Shima, and N. Torigoye, Int. J. Mass Spectrom. Ion Proc., 123,  29-39 (1993).
	The Isotopic Composition and Atomic Weight of Titanium.

93WAL1	T. Walczyk, and K.G. Heumann,  Int. J. Mass Spectrom. Ion Proc., 123, 139-147 (1993).
	Iridium Isotope Ratio Measurements by Negative Thermal Ionisation Mass Spectrometry and Atomic Weight of Iridium.

94CHA1	T.L. Chang, Q-Y.  Qian, M-T. Zhao, and J. Wang, Int.J. Mass Spectrom. Ion Proc.,139, 95-102 (1994).
	The Absolute Isotopic Composition of Europium.

94BIE1	P. De Bievre, S. Valkiers, and H. S. Peiser, J. Res. Natl. Inst. Stand. Technol., 99, 201-202 (1994).
	New Values for the Silicon Reference Materials, Certified for Isotope Abundance Ratios.

94VAL1	S. Valkiers, F. Schaefer, and P. De Bièvre,  Separation Tech. (E.F. Vansant, Edit) 965-968 (1994).
	Near-absolute Gas (isotope) Mass Spectrometry: Isotope Abundance (and Atomic Weight) Determinations of Neon, Krypton, Xenon and Argon.

95CHA1	T. L. Chang, Q-Y. Qian, M-T Zhao, J. Wang, and Q-Y Lang, Int. J. Mass Spectrom. Ion Proc., 142, 125-131 (1995).
	The Absolute Isotopic Composition of Cerium.

96TAY1	P.D.P.Taylor, and P. De Bièvre, Proc. 2nd Nier Symp. on Isot. Mass Spectrom, AECL report (AECL-11342), 90-94 (1996). 
Unconventional Stable Isotope Mass Spectrometry of Pt, Fe and W via Gas Source Mass Spectrometry.

97CHA1	T.L. Chang, and G.S. Qiao, Chin. Chem. Letters, 8, 91-94 (1997).
	Determination of the Atomic Weight of Samarium.

97GON1	R. Gonfiantini, P. De Bièvre, S. Valkiers and P.D.P. Taylor, IEEE Trans. Instrum. and Meas., 46, 566-571 (1997).
	Measuring the Molar Mass of Silicon for a Better Avogadro Constant: Reduced Uncertainty.

97HUA1	M. Huang, and A. Masuda, Anal. Chem., 69, 1135-1139 (1997). 
	Measurement of the Atomic Weight of Ruthenium by Negative Ionization Mass Spectrometry.

97Q1	H.P. Qi, M. Berglund and P. De Bièvre, Int.J. Mass Spectrom. Ion Proc. (1998)
	Calibrated Measurement of the Isotopic Composition and Atomic Weight of the Natural Li Isotopic Reference material IRMM-016.

APPENDIX B:  SOURCES OF REFERENCE MATERIALS

IAEA
			Reference and intercomparison samples such as VSMOW, SLAP, GISP, LSVEC, NSVEC, NBS18 and NBS19 may be purchased from: 

		International Atomic Energy Agency 
		Section of Isotope Hydrology 
		P. O. Box 100 
		1400 Vienna, Austria 

NIST
		NIST Standard Reference Materials may be purchased through: 

		Standard Reference Material Program
		National Institute of Standards and Technology
		Gaithersburg, MD 20899 U.S.A.

IRMM
		Reference Materials may be obtained through: 

		Institute for Reference Measurements and Materials
		Commission of the European Communities-JRC 
		B-2440 Geel, Belgium 

CEA 
		CEA distributes stable isotopes through its daughter company: 

		EUROISA-TOP
		Parc des Algorithmes (Bat. Homère),
		F-91190 St Aubin,
		FRANCE

		For nuclear reference materials, see also:

		CETAMA
		CEA/DCC
		Centre d'Etudes Nucléaires de Fontenay aux Roses 
		BP 6
		F 92265 Fontenay aux Roses
		FRANCE

NBL 
		Standards may be obtained through:

		U.S. Department of Energy
		New Brunswick Laboratory
		9800 S. Cass Ave.
		Argonne IL 60439