Isotopes of americium
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Americium(95Am) is anartificial element,and thus astandard atomic weightcannot be given. Like all artificial elements, it has no knownstable isotopes.The firstisotopeto be synthesized was241Am in 1944. The artificial element decays by ejectingAlpha particles.Americium has an atomic number of 95 (the number of protons in the nucleus of the americium atom). Despite243
Ambeing an order of magnitude longer lived than241
Am,the former is harder to obtain than the latter as more of it is present inspent nuclear fuel.
Eighteenradioisotopesof americium, ranging from229Am to247Am with the exception of231Am, have been characterized; another isotope,223Am, has also been reported but is unconfirmed. The most stable isotopes are243Am with ahalf-lifeof 7,370 years and241Am with a half-life of 432.2 years. All of the remainingradioactiveisotopes 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 8meta states,with the most stable being242m1Am (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
[edit]Nuclide [n 1] |
Z | N | Isotopic mass(Da) [n 2][n 3] |
Half-life[1] |
Decay mode[1] [n 4] |
Daughter isotope |
Spinand parity[1] [n 5][n 6] | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Excitation energy[n 6] | |||||||||||||||||||
223Am[n 7] | 95 | 128 | 223.04584(32)# | 10(9) ms | α | 219Np | 9/2–# | ||||||||||||
229Am | 95 | 134 | 229.04528(11) | 1.8(15) s | α | 225Np | 5/2–# | ||||||||||||
230Am | 95 | 135 | 230.04603(15)# | 40(9) s | β+(<70%) | 230Pu | 1–# | ||||||||||||
β+SF(>30%) | (various) | ||||||||||||||||||
232Am | 95 | 137 | 232.04661(32)# | 1.31(4) min | β+(97%) | 232Pu | 1–# | ||||||||||||
α (3%) | 228Np | ||||||||||||||||||
β+SF (0.069%) | (various) | ||||||||||||||||||
233Am | 95 | 138 | 233.04647(12)# | 3.2(8) min | β+(95.5%) | 233Pu | 5/2–# | ||||||||||||
α (4.5%) | 229Np | ||||||||||||||||||
234Am | 95 | 139 | 234.04773(17)# | 2.32(8) min | β+(99.95%) | 234Pu | 0–# | ||||||||||||
α (0.039%) | 230Np | ||||||||||||||||||
β+,SF (0.0066%) | (various) | ||||||||||||||||||
235Am | 95 | 140 | 235.047906(57) | 10.3(6) min | β+(99.60%) | 235Pu | 5/2−# | ||||||||||||
α (0.40%) | 231Np | ||||||||||||||||||
236Am | 95 | 141 | 236.04943(13)# | 3.6(1) min | β+ | 236Pu | 5− | ||||||||||||
α (4×10−3%) | 232Np | ||||||||||||||||||
236mAm | 50(50)# keV | 2.9(2) min | β+ | 236Pu | (1−) | ||||||||||||||
α? | 232Np | ||||||||||||||||||
237Am | 95 | 142 | 237.049995(64)# | 73.6(8) min | β+(99.975%) | 237Pu | 5/2− | ||||||||||||
α (.025%) | 233Np | ||||||||||||||||||
238Am | 95 | 143 | 238.051983(63) | 98(3) min | β+ | 238Pu | 1+ | ||||||||||||
α (1.0×10−4%) | 234Np | ||||||||||||||||||
238mAm | 2500(200)# keV | 35(18) μs | SF | (various) | |||||||||||||||
IT? | 238Am | ||||||||||||||||||
239Am | 95 | 144 | 239.0530227(21) | 11.9(1) h | EC(99.99%) | 239Pu | 5/2− | ||||||||||||
α (0.01%) | 235Np | ||||||||||||||||||
239mAm | 2500(200) keV | 163(12) ns | SF | (various) | (7/2+) | ||||||||||||||
IT? | 239Am | ||||||||||||||||||
240Am | 95 | 145 | 240.055298(15) | 50.8(3) h | β+ | 240Pu | (3−) | ||||||||||||
α (1.9×10−4%) | 236Np | ||||||||||||||||||
240mAm | 3000(200) keV | 940(40) μs | SF | (various) | |||||||||||||||
IT? | 240Am | ||||||||||||||||||
241Am | 95 | 146 | 241.0568273(12) | 432.6(6) y | α | 237Np | 5/2− | ||||||||||||
SF (3.6×10−10%) | (various) | ||||||||||||||||||
241mAm | 2200(200) keV | 1.2(3) μs | SF | (various) | |||||||||||||||
242Am | 95 | 147 | 242.0595474(12) | 16.02(2) h | β−(82.7%) | 242Cm | 1− | ||||||||||||
EC (17.3%) | 242Pu | ||||||||||||||||||
242m1Am | 48.60(5) keV | 141(2) y | IT(99.54%) | 242Am | 5− | ||||||||||||||
α (.46%) | 238Np | ||||||||||||||||||
SF? | (various) | ||||||||||||||||||
242m2Am | 2200(80) keV | 14.0(10) ms | SF | (various) | (2+, 3−) | ||||||||||||||
IT? | 242Am | ||||||||||||||||||
243Am | 95 | 148 | 243.0613799(15) | 7,350(9) y | α | 239Np | 5/2− | ||||||||||||
SF (3.7×10−9%) | (various) | ||||||||||||||||||
243mAm | 2300(200) keV | 5.5(5) μs | SF | (various) | |||||||||||||||
IT? | 243Am | ||||||||||||||||||
244Am | 95 | 149 | 244.0642829(16) | 10.01(3) h | β− | 244Cm | (6−) | ||||||||||||
244m1Am | 89.3(16) keV | 26.13(43) min | β−(99.96%) | 244Cm | 1+ | ||||||||||||||
EC (0.0364%) | 244Pu | ||||||||||||||||||
244m2Am | 2000(200)# | 900(150) μs | SF | (various) | |||||||||||||||
IT? | 244Am | ||||||||||||||||||
244m3Am | 2200(200)# | ~6.5 μs | SF | (various) | |||||||||||||||
IT? | 244Am | ||||||||||||||||||
245Am | 95 | 150 | 245.0664528(20) | 2.05(1) h | β− | 245Cm | 5/2+ | ||||||||||||
245mAm | 2400(400)# | 640(60) ns | SF | (various) | |||||||||||||||
IT? | 245Am | ||||||||||||||||||
246Am | 95 | 151 | 246.069774(19)# | 39(3) min | β− | 246Cm | (7−) | ||||||||||||
246m1Am | 30(10)# keV | 25.0(2) min | β− | 246Cm | 2(−) | ||||||||||||||
IT? | 246Am | ||||||||||||||||||
246m2Am | 2000(800)# keV | 73(10) μs | SF | (various) | |||||||||||||||
IT? | 246Am | ||||||||||||||||||
247Am | 95 | 152 | 247.07209(11)# | 23.0(13) min | β− | 247Cm | 5/2# | ||||||||||||
This table header & footer: |
- ^mAm – Excitednuclear isomer.
- ^( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
- ^# – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
- ^
Modes of decay:
CD: Cluster decay EC: Electron capture IT: Isomeric transition SF: Spontaneous fission - ^( ) spin value – Indicates spin with weak assignment arguments.
- ^ab# – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
- ^The discovery of this isotope is uncertain due to disagreements between theoretical predictions and reported experimental data.[2]
Actinides vs fission products
[edit]Actinides[3]bydecay chain | Half-life range (a) |
Fission productsof235Ubyyield[4] | ||||||
---|---|---|---|---|---|---|---|---|
4n | 4n+ 1 | 4n+ 2 | 4n+ 3 | 4.5–7% | 0.04–1.25% | <0.001% | ||
228Ra№ | 4–6 a | 155Euþ | ||||||
248Bk[5] | > 9 a | |||||||
244Cmƒ | 241Puƒ | 250Cf | 227Ac№ | 10–29 a | 90Sr | 85Kr | 113mCdþ | |
232Uƒ | 238Puƒ | 243Cmƒ | 29–97 a | 137Cs | 151Smþ | 121mSn | ||
249Cfƒ | 242mAmƒ | 141–351 a |
No fission products have ahalf-life | |||||
241Amƒ | 251Cfƒ[6] | 430–900 a | ||||||
226Ra№ | 247Bk | 1.3–1.6 ka | ||||||
240Pu | 229Th | 246Cmƒ | 243Amƒ | 4.7–7.4 ka | ||||
245Cmƒ | 250Cm | 8.3–8.5 ka | ||||||
239Puƒ | 24.1 ka | |||||||
230Th№ | 231Pa№ | 32–76 ka | ||||||
236Npƒ | 233Uƒ | 234U№ | 150–250 ka | 99Tc₡ | 126Sn | |||
248Cm | 242Pu | 327–375 ka | 79Se₡ | |||||
1.53 Ma | 93Zr | |||||||
237Npƒ | 2.1–6.5 Ma | 135Cs₡ | 107Pd | |||||
236U | 247Cmƒ | 15–24 Ma | 129I₡ | |||||
244Pu | 80 Ma |
... nor beyond 15.7 Ma[7] | ||||||
232Th№ | 238U№ | 235Uƒ№ | 0.7–14.1 Ga | |||||
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Notable isotopes
[edit]Americium-241
[edit]![](https://upload.wikimedia.org/wikipedia/commons/thumb/4/4f/Americium_button_hd.jpg/200px-Americium_button_hd.jpg)
Americium-241is the most prevalent isotope of americium in nuclear waste.[8]It is the isotope used in anamericium smoke detectorbased on anionization chamber.It is a potential fuel for long-lifetimeradioisotope thermoelectric generators.
Parameter | Value |
---|---|
Atomic mass | 241.056829u |
Mass excess | 52930keV |
Beta decayenergy | −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 from241Pu,electron capture from241Cm, Alpha from245Bk.
Americium-241 decays byAlpha emission,with a by-product ofgamma rays.Its presence inplutoniumis 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 of241Am. A chemical removal of americium from reworked plutonium (e.g. during reworking ofplutonium pits) may be required.
Americium-242m
[edit]![](https://upload.wikimedia.org/wikipedia/commons/thumb/c/cc/Sasahara.svg/375px-Sasahara.svg.png)
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 | 0.05MeV | 242Am |
0.46% | Alpha decay | 5.64 MeV | 238Np |
(1.5±0.6) × 10−10 [10] | spontaneous fission | ~200 MeV | fission products |
Americium-242mhas a mass of 242.0595492 g/mol. It is one of the rare cases, like108mAg,166mHo,180mTa,186mRe,192mIr,210mBi,212mPoand others, where a higher-energynuclear isomeris more stable than the ground state,americium-242.[11]
242mAm isfissileand has a lowcritical mass,comparable to that of239Pu.[12]It has a very highcross sectionfor 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 ofnuclear rocket.[13][14]
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
[edit]![](https://upload.wikimedia.org/wikipedia/commons/thumb/d/dc/Am243.png/130px-Am243.png)
Americium-243has a mass of 243.06138 g/mol and ahalf-lifeof 7,370 years, the longest lasting of all americium isotopes. It is formed in thenuclear fuel cyclebyneutron captureonplutonium-242followed bybeta decay.[15]Production increases exponentially with increasingburnupas a total of 5 neutron captures on238Uare required. IfMOX-fuelis used, particularly MOX-fuel high in241
Puand242
Pu,more americium overall and more243
Amwill be produced.
It decays by either emitting anAlpha particle(with a decay energy of 5.27 MeV)[15]to become239Np, which then quickly decays to239Pu,or rarely, byspontaneous fission.[16]
As for the other americium isotopes, and more generally for all Alpha emitters,243Am iscarcinogenicin case of internal contamination after being inhaled or ingested.243Am also presents a risk of external irradiation associated with the gamma ray emitted by its short-lived decay product239Np.The external irradiation risk for the other two americium isotopes (241Am and242mAm) is less than 10% of that for americium-243.[8]
References
[edit]- ^abcdKondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021)."The NUBASE2020 evaluation of nuclear properties"(PDF).Chinese Physics C.45(3): 030001.doi:10.1088/1674-1137/abddae.
- ^Sun, M. D.; et al. (2017)."New short-lived isotope223Np and the absence of the Z = 92 subshell closure near N = 126 ".Physics Letters B.771:303–308.Bibcode:2017PhLB..771..303S.doi:10.1016/j.physletb.2017.03.074.
- ^Plus radium (element 88). While actually a sub-actinide, it immediately precedes actinium (89) and follows a three-element gap of instability afterpolonium(84) where no nuclides have half-lives of at least four years (the longest-lived nuclide in the gap isradon-222with a half life of less than fourdays). Radium's longest lived isotope, at 1,600 years, thus merits the element's inclusion here.
- ^Specifically fromthermal neutronfission of uranium-235, e.g. in a typicalnuclear reactor.
- ^Milsted, J.; Friedman, A. M.; Stevens, C. M. (1965). "The Alpha half-life of berkelium-247; a new long-lived isomer of berkelium-248".Nuclear Physics.71(2): 299.Bibcode:1965NucPh..71..299M.doi:10.1016/0029-5582(65)90719-4.
"The isotopic analyses disclosed a species of mass 248 in constant abundance in three samples analysed over a period of about 10 months. This was ascribed to an isomer of Bk248with a half-life greater than 9 [years]. No growth of Cf248was detected, and a lower limit for the β−half-life can be set at about 104[years]. No Alpha activity attributable to the new isomer has been detected; the Alpha half-life is probably greater than 300 [years]. " - ^This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".
- ^Excluding those "classically stable"nuclides with half-lives significantly in excess of232Th; e.g., while113mCd has a half-life of only fourteen years, that of113Cd is eightquadrillionyears.
- ^ab"Americium"Archived2012-07-30 at theWayback Machine.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.
- ^J. T. Caldwell; S. C. Fultz; C. D. Bowman; R. W. Hoff (March 1967). "Spontaneous Fission Half-Life of Am242m".Physical Review.155(4): 1309–1313.Bibcode:1967PhRv..155.1309C.doi:10.1103/PhysRev.155.1309.(halflife (9.5±3.5)×1011years)
- ^95-Am-242Archived2011-07-19 at theWayback Machine
- ^"Critical Mass Calculations for241Am,242mAm and243Am "(PDF).Archived fromthe original(PDF)on July 22, 2011.RetrievedFebruary 3,2011.
- ^"Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two Weeks"(Press release). Ben-Gurion University Of The Negev. December 28, 2000.
- ^Ronen, Yigal; Shwageraus, E. (2000). "Ultra-thin 241mAm fuel elements in nuclear reactors".Nuclear Instruments and Methods in Physics Research A.455(2): 442–451.Bibcode:2000NIMPA.455..442R.doi:10.1016/s0168-9002(00)00506-4.
- ^ab"Americium-243"Archived2011-02-25 at theWayback Machine.Oak Ridge National Laboratory. Retrieved 25 December 2009.
- ^"Isotopes of the Element Americium".Jefferson Lab Science Education. Retrieved 25 December 2009.
Sources
[edit]- Isotope masses from:
- Half-life, spin, and isomer data selected from the following sources.
- National Nuclear Data Center."NuDat 2.x database".Brookhaven National Laboratory.
- IAEA - Nuclear Data Section.Live Chart of Nuclides.Vienna International Centre.
- Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.).CRC Handbook of Chemistry and Physics(85th ed.).Boca Raton, Florida:CRC Press.ISBN978-0-8493-0485-9.