Isotopes of americium
| Actinides | Half-life | Fission products | ||||||
|---|---|---|---|---|---|---|---|---|
| 244Cm | 241Pu f | 250Cf | 243Cmf | 10–30 y | 137Cs | 90Sr | 85Kr | |
| 232U f | 238Pu | f is for fissile |
69–90 y | 151Sm nc➔ | ||||
| 4n | 249Cf f | 242Amf | 141–351 | No fission product has half-life 102 to 2×105 years |
||||
| 241Am | 251Cf f | 431–898 | ||||||
| 240Pu | 229Th | 246Cm | 243Am | 5–7 ky | ||||
| 4n | 245Cmf | 250Cm | 239Pu f | 8–24 ky | ||||
| 233U f | 230Th | 231Pa | 32–160 | |||||
| 4n+1 | 234U | 4n+3 | 211–290 | 99Tc | 126Sn | 79Se | ||
| 248Cm | 242Pu | 340–373 | Long-lived fission products | |||||
| 237Np | 4n+2 | 1–2 My | 93Zr | 135Cs nc➔ | ||||
| 236U | 4n+1 | 247Cmf | 6–23 My | 107Pd | 129I | |||
| 244Pu | 80 My | >7% | >5% | >1% | >.1% | |||
| 232Th | 238U | 235U f | 0.7–12 Gy | fission product yield | ||||
Americium (Am) is an artificial element, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 241Am in 1944.
Trace quantities are found in nature from neutron capture by uranium atoms.[1]
19 radioisotopes of americium have been characterized, with the most stable being 243Am with a half-life of 7,370 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).
Contents |
[edit] Some notable isotopes
[edit] Americium-241
Americium-241 is the most prevalent isotope of americium in nuclear waste.[2] It is the americium isotope used in an americium smoke detector based an ionization chamber. It is a potential fuel for long-lifetime radioisotope thermoelectric generators.
| Parameter | Value |
|---|---|
| Atomic mass | 241.056823 u |
| Mass excess | 52930 keV |
| Beta decay energy | -767 keV |
| Spin | 5/2- |
| Half-life | 432.2 years |
| Spontaneous fissions | 1200 per kg/s |
| Decay heat | 114 watts/kg |
Possible parent nuclides: beta from 241Pu, electron capture from 241Cm, alpha from 245Bk.
Americium-241 decays by alpha emission, with a by-product of gamma rays. Its presence in plutonium is determined by the original concentration of plutonium-241 and the sample age. Because of the low penetration of alpha radiation, Americium-241 only poses a health risk when ingested or inhaled. Older samples of plutonium containing plutonium-241 contain a buildup of 241Am. A chemical removal of americium from reworked plutonium, e.g. during reworking of plutonium pits, may be required.
[edit] Americium-242m
Fission percentage is 100 minus shown percentages.
Total rate of transmutation varies greatly by nuclide.
245Cm–248Cm are long-lived with negligible decay.
| Probability | Decay mode | Decay energy | Decay product |
|---|---|---|---|
| 99.54% | isomeric transition | 0.05 MeV | 242Am |
| 0.46% | alpha decay | 5.64 MeV | 238Np |
| (1.5±0.6)×10−10[4] | spontaneous fission | ~200 MeV | fission products |
Americium-242m has a mass of 242.0595492 g/mol. It is one of the rare cases, like 180mTa, where a higher-energy nuclear isomer is more stable than the lower-energy one, Americium-242.[5]
242mAm is fissile (because it has an odd number of neutrons) and has a low critical mass, comparable to that of 239Pu.[6] It has a very high cross section for fission, and if in a nuclear reactor is destroyed relatively quickly. Another report claims that 242mAm has a much lower critical mass, can sustain a chain reaction even as a thin film, and could be used for a novel type of nuclear rocket.[7]
| Probability | Decay mode | Decay energy | Decay product |
|---|---|---|---|
| 82.70% | beta decay | 0.665 MeV | 242Cm |
| 17.30% | electron capture | 0.751 MeV | 242Pu |
[edit] Americium-243
Americium-243 has a mass of 243.06138 g/mol and a half-life of 7,370 years, the longest lasting of all americium isotopes. It is formed in the nuclear fuel cycle by neutron capture on plutonium-242 followed by beta decay.[8] Production increases exponentially with increasing burnup as a total of 5 neutron captures on 238U are required.
It decays by either emitting an alpha particle (with a decay energy of 5.27MeV)[8] to become 239Np, which then quickly decays to 239Pu, or infrequently, by spontaneous fission.[9]
243Am is a hazardous substance, because it can cause cancer. 239Np, which is formed from 243Am, emits dangerous gamma rays, making 243Am the most dangerous isotope of Americium.[2]
[edit] Table
| nuclide symbol |
Z(p) | N(n) | isotopic mass (u) |
half-life | decay mode(s)[10][n 1] |
daughter isotope(s) |
nuclear spin |
|---|---|---|---|---|---|---|---|
| excitation energy | |||||||
| 231Am | 95 | 136 | 231.04556(32)# | 30# s | β+ | 231Pu | |
| α (rare) | 227Np | ||||||
| 232Am | 95 | 137 | 232.04659(32)# | 79(2) s | β+ (98%) | 232Pu | |
| α (2%) | 228Np | ||||||
| β+, SF (.069%) | (various) | ||||||
| 233Am | 95 | 138 | 233.04635(11)# | 3.2(8) min | β+ | 233Pu | |
| α | 229Np | ||||||
| 234Am | 95 | 139 | 234.04781(22)# | 2.32(8) min | β+ (99.95%) | 234Pu | |
| α (.04%) | 230Np | ||||||
| β+, SF (.0066%) | (various) | ||||||
| 235Am | 95 | 140 | 235.04795(13)# | 9.9(5) min | β+ | 235Pu | 5/2-# |
| α (rare) | 231Np | ||||||
| 236Am | 95 | 141 | 236.04958(11)# | 3.6(1) min | β+ | 236Pu | |
| α | 232Np | ||||||
| 237Am | 95 | 142 | 237.05000(6)# | 73.0(10) min | β+ (99.97%) | 237Pu | 5/2(-) |
| α (.025%) | 233Np | ||||||
| 238Am | 95 | 143 | 238.05198(5) | 98(2) min | β+ | 238Pu | 1+ |
| α (10−4%) | 234Np | ||||||
| 238mAm | 2500(200)# keV | 35(10) µs | |||||
| 239Am | 95 | 144 | 239.0530245(26) | 11.9(1) h | EC (99.99%) | 239Pu | (5/2)- |
| α (.01%) | 235Np | ||||||
| 239mAm | 2500(200) keV | 163(12) ns | (7/2+) | ||||
| 240Am | 95 | 145 | 240.055300(15) | 50.8(3) h | β+ | 240Pu | (3-) |
| α (1.9×10−4%) | 236Np | ||||||
| 241Am[n 2] | 95 | 146 | 241.0568291(20) | 432.2(7) a | α | 237Np | 5/2- |
| CD (7.4×10−10%) | 207Tl, 34Si | ||||||
| SF (4.3×10−10%) | (various) | ||||||
| 241mAm | 2200(100) keV | 1.2(3) µs | |||||
| 242Am | 95 | 147 | 242.0595492(20) | 16.02(2) h | β- (82.7%) | 242Cm | 1- |
| EC (17.3%) | 242Pu | ||||||
| 242m1Am | 48.60(5) keV | 141(2) a | IT (99.54%) | 242Am | 5- | ||
| α (.46%) | 238Np | ||||||
| SF (1.5×10−8%) | (various) | ||||||
| 242m2Am | 2200(80) keV | 14.0(10) ms | (2+,3-) | ||||
| 243Am[n 2] | 95 | 148 | 243.0613811(25) | 7,370(40) a | α | 239Np | 5/2- |
| SF (3.7×10−9%) | (various) | ||||||
| 244Am | 95 | 149 | 244.0642848(22) | 10.1(1) h | β- | 244Cm | (6-)# |
| 244mAm | 86.1(10) keV | 26(1) min | β- (99.96%) | 244Cm | 1+ | ||
| EC (.0361%) | 244Pu | ||||||
| 245Am | 95 | 150 | 245.066452(4) | 2.05(1) h | β- | 245Cm | (5/2)+ |
| 246Am | 95 | 151 | 246.069775(20) | 39(3) min | β- | 246Cm | (7-) |
| 246m1Am | 30(10) keV | 25.0(2) min | β- (99.99%) | 246Cm | 2(-) | ||
| IT (.01%) | 246Am | ||||||
| 246m2Am | ~2000 keV | 73(10) µs | |||||
| 247Am | 95 | 152 | 247.07209(11)# | 23.0(13) min | β- | 247Cm | (5/2)# |
| 248Am | 95 | 153 | 248.07575(22)# | 3# min | β- | 248Cm | |
| 249Am | 95 | 154 | 249.07848(32)# | 1# min | β- | 249Cm | |
- ^ Abbreviations:
CD: Cluster decay
EC: Electron capture
IT: Isomeric transition
SF: Spontaneous fission - ^ a b Most common isotopes
[edit] 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.
[edit] See also
 |
Book: Americium |
| Wikipedia books are collections of articles that can be downloaded or ordered in print. | |
[edit] References
- ^ Emsley, John (2011). Nature's Building Blocks: An A-Z Guide to the Elements (New ed.). New York, NY: Oxford University Press. ISBN 978-0-19-960563-7.
- ^ a b "Americium". Argonne National Laboratory, EVS. Retrieved 25 December 2009.
- ^ Sasahara, Akihiro; Matsumura, Tetsuo; Nicolaou, Giorgos; Papaioannou, Dimitri (April 2004). "Neutron and Gamma Ray Source Evaluation of LWR High Burn-up UO2 and MOX Spent Fuels". Journal of NUCLEAR SCIENCE and TECHNOLOGY 41 (4): 448–456. doi:10.3327/jnst.41.448. http://www.jstage.jst.go.jp/article/jnst/41/4/448/_pdf.
- ^ Phys. Rev. 155 (1967): J. T. Caldwell, S. C. Fultz, C. D. Bowman, and R. W. Hoff - Spontaneous Fission Half-Life of 242mAm (halflife (9.5±3.5)×1011
- ^ 95-Am-242
- ^ http://typhoon.jaea.go.jp/icnc2003/Proceeding/paper/6.5_022.pdf
- ^ Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two Weeks
- ^ a b "Americium-243". Oak Ridge National Laboratory. Retrieved 25 December 2009.
- ^ "Isotopes of the Element Americium". Jefferson Lab Science Education. Retrieved 25 December 2009.
- ^ http://www.nucleonica.net/unc.aspx
- Isotope masses from:
- G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties". Nuclear Physics A 729: 3–128. Bibcode 2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001. http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf.
- Isotopic compositions and standard atomic masses from:
- J. R. de Laeter, J. K. Böhlke, P. De Bièvre, H. Hidaka, H. S. Peiser, K. J. R. Rosman and P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry 75 (6): 683–800. doi:10.1351/pac200375060683. http://www.iupac.org/publications/pac/75/6/0683/pdf/.
- M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry 78 (11): 2051–2066. doi:10.1351/pac200678112051. http://iupac.org/publications/pac/78/11/2051/pdf/. Lay summary.
- Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
- G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties". Nuclear Physics A 729: 3–128. Bibcode 2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001. http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf.
- National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. http://www.nndc.bnl.gov/nudat2/. Retrieved September 2005.
- N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide. CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0849304859.
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