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Isotopes of americium

Americium (Am) has no stable isotopes. A standard atomic mass cannot be given.

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19 radioisotopes of americium have been characterized, with the most stable being ²⁴³Am with a half-life of 7370 years, and ²⁴¹Am with a half-life of 432.7 years. All of the remaining radioactive isotopes have half-lives that are less than 51 hours, and the majority of these have half-lives that are less than 100 minutes. This element also has 8 meta states, with the most stable being ^242mAm (t_½ 141 years). The isotopes of americium range in atomic weight from 231.046 u (²³¹Am) to 249.078 u (²⁴⁹Am).

Americium has also been called eka-europium and, erroneously, eka-iridium.

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	nuclear spin
nuclide symbol	excitation energy			half-life	nuclear spin
²³¹Am	95	136	231.04556(32)#	30# s
²³²Am	95	137	232.04659(32)#	79(2) s
²³³Am	95	138	233.04635(11)#	3.2(8) min
²³⁴Am	95	139	234.04781(22)#	2.32(8) min
²³⁵Am	95	140	235.04795(13)#	9.9(5) min	5/2-#
²³⁶Am	95	141	236.04958(11)#	3.6(1) min
²³⁷Am	95	142	237.05000(6)#	73.0(10) min	5/2(-)
²³⁸Am	95	143	238.05198(5)	98(2) min	1+
^238mAm	2500(200)# keV			35(10) µs
²³⁹Am	95	144	239.0530245(26)	11.9(1) h	(5/2)-
^239mAm	2500(200) keV			163(12) ns	(7/2+)
²⁴⁰Am	95	145	240.055300(15)	50.8(3) h	(3-)
²⁴¹Am	95	146	241.0568291(20)	432.2(7) a	5/2-
^241mAm	2200(100) keV			1.2(3) µs
²⁴²Am	95	147	242.0595492(20)	16.02(2) h	1-
^242m1Am	48.60(5) keV			141(2) a	5-
^242m2Am	2200(80) keV			14.0(10) ms	(2+,3-)
²⁴³Am	95	148	243.0613811(25)	7.37(4)E+3 a	5/2-
²⁴⁴Am	95	149	244.0642848(22)	10.1(1) h	(6-)#
^244mAm	86.1(10) keV			26(1) min	1+
²⁴⁵Am	95	150	245.066452(4)	2.05(1) h	(5/2)+
²⁴⁶Am	95	151	246.069775(20)	39(3) min	(7-)
^246m1Am	30(10) keV			25.0(2) min	2(-)
^246m2Am	~2000 keV			73(10) µs
²⁴⁷Am	95	152	247.07209(11)#	23.0(13) min	(5/2)#
²⁴⁸Am	95	153	248.07575(22)#	3# min
²⁴⁹Am	95	154	249.07848(32)#	1# min

Notes

Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses - ( ).
Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.

References

Isotope masses from Ame2003 Atomic Mass Evaluation by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in Nuclear Physics A729 (2003).
Isotopic compositions and standard atomic masses from Atomic weights of the elements. Review 2000 (IUPAC Technical Report). Pure Appl. Chem. Vol. 75, No. 6, pp. 683-800, (2003) and Atomic Weights Revised (2005).
Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.
- Audi, Bersillon, Blachot, Wapstra. The Nubase2003 evaluation of nuclear and decay properties, Nuc. Phys. A 729, pp. 3-128 (2003).
- National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the NuDat 2.1 database (retrieved Sept. 2005).
- David R. Lide (ed.), Norman E. Holden in CRC Handbook of Chemistry and Physics, 85th Edition, online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.