Английская Википедия:Isotopes of americium
Шаблон:Short description Шаблон:Infobox americium isotopes Americium (95Am) is an artificial element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no known stable isotopes. The first isotope to be synthesized was 241Am in 1944. The artificial element decays by ejecting alpha particles. Americium has an atomic number of 95 (the number of protons in the nucleus of the americium atom). Despite Шаблон:Chem being an order of magnitude longer lived than Шаблон:Chem, the former is harder to obtain than the latter as more of it is present in spent nuclear fuel.
Nineteen radioisotopes of americium—223Am, 229Am, 230Am, and those ranging from 232Am to 247Am—have been characterized, with the most stable being 243Am with a half-life of 7,370 years, and 241Am with a half-life of 432.2 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 242m1Am (t1/2 = 141 years). This isomer is unusual in that its half life is far longer than that of the ground state of the same isotope.
List of isotopes
Шаблон:Isotopes table |- | 223Am | style="text-align:right" | 95 | style="text-align:right" | 128 | 223.04584(32)# | 10(9) ms | α | 219Np | 9/2–# |- | 229Am | style="text-align:right" | 95 | style="text-align:right" | 134 | 229.04528(11) | 1.8(15) s | α | 225Np | 5/2–# |- | rowspan=2 | 230Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 135 | rowspan=2 | 230.04603(15)# | rowspan=2 | 40(9) s | β+ (<70%) | 230Pu | rowspan=2 | 1–# |- | β+SF (>30%) | (various) |- | rowspan=3 | 232Am | rowspan=3 style="text-align:right" | 95 | rowspan=3 style="text-align:right" | 137 | rowspan=3 | 232.04661(32)# | rowspan=3 | 1.31(4) min | β+ (97%) | 232Pu | rowspan=3 | 1–# |- | α (3%) | 228Np |- | β+SF (0.069%) | (various) |- | rowspan=2 | 233Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 138 | rowspan=2 | 233.04647(12)# | rowspan=2 | 3.2(8) min | β+ (95.5%) | 233Pu | rowspan=2 | 5/2–# |- | α (4.5%) | 229Np |- | rowspan=3 | 234Am | rowspan=3 style="text-align:right" | 95 | rowspan=3 style="text-align:right" | 139 | rowspan=3 | 234.04773(17)# | rowspan=3 | 2.32(8) min | β+ (99.95%) | 234Pu | rowspan=3 | 0–# |- | α (0.039%) | 230Np |- | β+, SF (0.0066%) | (various) |- | rowspan=2 | 235Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 140 | rowspan=2 | 235.047906(57) | rowspan=2 | 10.3(6) m | β+ (99.60%) | 235Pu | rowspan=2 | 5/2−# |- | α (0.40%) | 231Np |- | rowspan=2 | 236Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 141 | rowspan=2 | 236.04943(13)# | rowspan=2 | 3.6(1) m | β+ | 236Pu | rowspan=2 | 5− |- | α (4×10−3%) | 232Np |- | rowspan=2 | 236mAm | rowspan=2 colspan=3 | 50(50)# keV | rowspan=2 | 2.9(2) m | β+ | 236Pu | rowspan=2 | (1−) |- | α ? | 232Np |- | rowspan=2 | 237Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 142 | rowspan=2 | 237.049995(64)# | rowspan=2 | 73.6(8) min | β+ (99.975%) | 237Pu | rowspan=2 | 5/2− |- | α (.025%) | 233Np |- | rowspan=2 | 238Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 143 | rowspan=2 | 238.051983(63) | rowspan=2 | 98(3) m | β+ | 238Pu | rowspan=2 | 1+ |- | α (1.0×10−4%) | 234Np |- | rowspan=2 style="text-indent:1em" | 238mAm | rowspan=2 colspan="3" style="text-indent:2em" | 2500(200)# keV | rowspan=2 | 35(18) μs | SF | (various) | rowspan=2 | |- | IT ? | 238Am |- | rowspan=2 | 239Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 144 | rowspan=2 | 239.0530227(21) | rowspan=2 | 11.9(1) h | EC (99.99%) | 239Pu | rowspan=2 | 5/2− |- | α (0.01%) | 235Np |- | rowspan=2 style="text-indent:1em" | 239mAm | rowspan=2 colspan="3" style="text-indent:2em" | 2500(200) keV | rowspan=2 | 163(12) ns | SF | (various) | rowspan=2 | (7/2+) |- | IT ? | 239Am |- | rowspan=2 | 240Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 145 | rowspan=2 | 240.055298(15) | rowspan=2 | 50.8(3) h | β+ | 240Pu | rowspan=2 | (3−) |- | α (1.9×10−4%) | 236Np |- | rowspan=2 style="text-indent:1em" | 240mAm | rowspan=2 colspan="3" style="text-indent:2em" | 3000(200) keV | rowspan=2 | 940(40) μs | SF | (various) | rowspan=2 | |- | IT ? | 240Am |- | rowspan=2 | 241Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 146 | rowspan=2 | 241.0568273(12) | rowspan=2 | 432.6(6) y | α | 237Np | rowspan=2 | 5/2− |- | SF (3.6×10−10%) | (various) |- | style="text-indent:1em" | 241mAm | colspan="3" style="text-indent:2em" | 2200(200) keV | 1.2(3) μs | SF | (various) | |- | rowspan=2 | 242Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 147 | rowspan=2 | 242.0595474(12) | rowspan=2 | 16.02(2) h | β− (82.7%) | 242Cm | rowspan=2 | 1− |- | EC (17.3%) | 242Pu |- | rowspan=3 style="text-indent:1em" | 242m1Am | rowspan=3 colspan="3" style="text-indent:2em" | 48.60(5) keV | rowspan=3 | 141(2) y | IT (99.54%) | 242Am | rowspan=3 | 5− |- | α (.46%) | 238Np |- | SF ? | (various) |- | rowspan=2 style="text-indent:1em" | 242m2Am | rowspan=2 colspan="3" style="text-indent:2em" | 2200(80) keV | rowspan=2 | 14.0(10) ms | SF | (various) | rowspan=2 | (2+, 3−) |- | IT ? | 242Am |- | rowspan=2 | 243Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 148 | rowspan=2 | 243.0613799(15) | rowspan=2 | 7,350(9) y | α | 239Np | rowspan=2 | 5/2− |- | SF (3.7×10−9%) | (various) |- | rowspan=2 style="text-indent:1em" | 243mAm | rowspan=2 colspan="3" style="text-indent:2em" | 2300(200) keV | rowspan=2 | 5.5(5) μs | SF | (various) | rowspan=2 | |- | IT ? | 243Am |- | 244Am | style="text-align:right" | 95 | style="text-align:right" | 149 | 244.0642829(16) | 10.01(3) h | β− | 244Cm | (6−) |- | rowspan=2 style="text-indent:1em" | 244m1Am | rowspan=2 colspan="3" style="text-indent:2em" | 89.3(16) keV | rowspan=2 | 26.13(43) min | β− (99.96%) | 244Cm | rowspan=2 | 1+ |- | EC (0.0364%) | 244Pu |- | rowspan=2 style="text-indent:1em" | 244m2Am | rowspan=2 colspan="3" style="text-indent:2em" | 2000(200)# | rowspan=2 | 900(150) μs | SF | (various) | rowspan=2 | |- | IT ? | 244Am |- | rowspan=2 style="text-indent:1em" | 244m3Am | rowspan=2 colspan="3" style="text-indent:2em" | 2200(200)# | rowspan=2 | ~6.5 μs | SF | (various) | rowspan=2 | |- | IT ? | 244Am |- | 245Am | style="text-align:right" | 95 | style="text-align:right" | 150 | 245.0664528(20) | 2.05(1) h | β− | 245Cm | 5/2+ |- | rowspan=2 style="text-indent:1em" | 245mAm | rowspan=2 colspan="3" style="text-indent:2em" | 2400(400)# | rowspan=2 | 640(60) ns | SF | (various) | rowspan=2 | |- | IT ? | 245Am |- | 246Am | style="text-align:right" | 95 | style="text-align:right" | 151 | 246.069774(19)# | 39(3) min | β− | 246Cm | (7−) |- | rowspan=2 style="text-indent:1em" | 246m1Am | rowspan=2 colspan="3" style="text-indent:2em" | 30(10)# keV | rowspan=2 | 25.0(2) min | β− | 246Cm | rowspan=2 | 2(−) |- | IT ? | 246Am |- | rowspan=2 style="text-indent:1em" | 246m2Am | rowspan=2 colspan="3" style="text-indent:2em" | 2000(800)# keV | rowspan=2 | 73(10) μs | SF | (various) | rowspan=2 | |- | IT ? | 246Am |- | 247Am | style="text-align:right" | 95 | style="text-align:right" | 152 | 247.07209(11)# | 23.0(13) min | β− | 247Cm | 5/2# Шаблон:Isotopes table/footer
Actinides vs fission products
Шаблон:Actinidesvsfissionproducts
Notable isotopes
Americium-241
Americium-241 is the most prevalent isotope of americium in nuclear waste.[1] It is the isotope used in an americium smoke detector based on an ionization chamber. It is a potential fuel for long-lifetime radioisotope thermoelectric generators.
| Parameter | Value |
|---|---|
| Atomic mass | 241.056829 u |
| Mass excess | 52930 keV |
| Beta decay energy | −767 keV |
| Spin | 5/2− |
| Half-life | 432.6 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.
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) × 10−10Шаблон:Tsp[3] | spontaneous fission | ~200 MeV | fission products |
Americium-242m has a mass of 242.0595492 g/mol. It is one of the rare cases, like 108mAg, 166mHo, 180mTa, 186mRe, 192mIr, 210mBi, 212mPo and others, where a higher-energy nuclear isomer is more stable than the ground state, americium-242.[4]
242mAm is fissile and has a low critical mass, comparable to that of 239Pu.[5] It has a very high cross section for fission, and is quickly destroyed if it is produced in a nuclear reactor. Work has been done investigating if this isotope could be used for a novel type of nuclear rocket.[6][7]
| Probability | Decay mode | Decay energy | Decay product |
|---|---|---|---|
| 82.70% | beta decay | 0.665 MeV | 242Cm |
| 17.30% | electron capture | 0.751 MeV | 242Pu |
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 [[uranium-238|Шаблон:SupU]] are required. If MOX-fuel is used, particularly MOX-fuel high in Шаблон:Chem and Шаблон:Chem, more americium overall and more Шаблон:Chem will be produced.
It decays by either emitting an alpha particle (with a decay energy of 5.27 MeV)[8] to become Шаблон:SupNp, which then quickly decays to [[plutonium-239|Шаблон:SupPu]], or rarely, by spontaneous fission.[9]
As for the other americium isotopes, and more generally for all alpha emitters, Шаблон:SupAm is carcinogenic in case of internal contamination after being inhaled or ingested. Шаблон:SupAm also presents a risk of external irradiation associated with the gamma ray emitted by its short-lived decay product [[neptunium-239|Шаблон:SupNp]]. The external irradiation risk for the other two americium isotopes (Шаблон:SupAm and Шаблон:SupAm) is less than 10% of that for americium-243.[1]
References
Sources
- Isotope masses from:
- Half-life, spin, and isomer data selected from the following sources.
- Шаблон:NNDC
- IAEA - Nuclear Data Section. Live Chart of Nuclides. Vienna International Centre.
- Шаблон:CRC85
Шаблон:Navbox element isotopes
- ↑ 1,0 1,1 "Americium" Шаблон:Webarchive. Argonne National Laboratory, EVS. Retrieved 25 December 2009.
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite journal (halflife (9.5±3.5)×1011 years)
- ↑ 95-Am-242 Шаблон:Webarchive
- ↑ Шаблон:Cite web
- ↑ Шаблон:Cite press release
- ↑ Шаблон:Cite journal
- ↑ 8,0 8,1 "Americium-243" Шаблон:Webarchive. Oak Ridge National Laboratory. Retrieved 25 December 2009.
- ↑ "Isotopes of the Element Americium". Jefferson Lab Science Education. Retrieved 25 December 2009.
