Isotopes of americium
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Americium (Am) has no stable isotopes. A standard atomic mass cannot be given.
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 (t½ 141 years). The isotopes of americium range in atomic weight from 231.046 u (231Am) to 249.078 u (249Am).
Table
| nuclide symbol |
Z(p) | N(n) | isotopic mass (u) |
half-life | nuclear spin |
|---|---|---|---|---|---|
| excitation energy | |||||
| 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) y | 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.