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词条 Isotopes of americium
释义

  1. Actinides vs fission products

  2. Notable isotopes

      Americium-241   Americium-242m  Americium-243 

  3. List of isotopes

      Notes  

  4. See also

  5. References

  6. Sources

{{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).

Eighteen radioisotopes of americium from 229Am to 247Am (with the exception of 231Am) 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 242mAm (t1/2 = 141 years).

Actinides vs fission products

{{Actinidesvsfissionproducts}}{{clear}}

Notable isotopes

Americium-241

{{main|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 mass241.056829 u
Mass excess52930 keV
Beta decay energy-767 keV
Spin5/2−
Half-life432.6 years
Spontaneous fissions1200 per kg s
Decay heat114 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

242mAm decay modes (half-life: 141 years)
ProbabilityDecay modeDecay energyDecay product
99.54%isomeric transition0.05 MeV242Am
  0.46%alpha decay5.64 MeV238Np
(1.5±0.6) × 10−10{{tsp}}[3]spontaneous fission~200 MeVfission 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.[4]

242mAm is fissile (because it has an odd number of neutrons) and has a low critical mass, comparable to that of 239Pu.[5] 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.[6][7]

242Am decay modes (half-life: 16 hours)
ProbabilityDecay modeDecay energyDecay product
82.70%beta decay0.665 MeV 242Cm
17.30%electron capture0.751 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 238U are required.

It decays by either emitting an alpha particle (with a decay energy of 5.27 MeV)[8] to become 239Np, which then quickly decays to 239Pu, or infrequently, by spontaneous fission.[9]

243Am is carcinogenic. 239Np, the daughter of 243Am, emits dangerous gamma rays, making 243Am the most dangerous isotope of americium.[1]

List of isotopes

nuclide
symbol		 Z(p) N(n)  
isotopic mass (u)[10]
 		half-lifedecay
mode(s)[11][12]		daughter
isotope(s)		nuclear
spin and
parity
excitation energy
229Am[13]95134 229.04525(9) 1.8(1.5) s α 225Np
230Am[14]95135230.04609(14)#32(+22-9) s β+ (64.7%) 230Pu
β+, SF (35.3%) (various)
232Am95137232.04659(32)#79(2) s β+ (98%) 232Pu
α (2%) 228Np
β+, SF (.069%) (various)
233Am95138233.04635(11)#3.2(8) min β+ 233Pu
α 229Np
234Am95139234.04781(22)#2.32(8) min β+ (99.95%) 234Pu
α (.04%) 230Np
β+, SF (.0066%) (various)
235Am95140235.04795(13)#9.9(5) min β+ 235Pu5/2−#
α (rare) 231Np
236Am95141236.04958(11)#3.6(1) min β+ 236Pu
α 232Np
237Am95142237.05000(6)#73.0(10) min β+ (99.97%) 237Pu5/2(−)
α (.025%) 233Np
238Am95143238.05198(5)98(2) min β+ 238Pu1+
α (10−4%) 234Np
238mAm2500(200)# keV 35(10) µs
239Am95144239.0530245(26)11.9(1) h EC (99.99%) 239Pu(5/2)−
α (.01%) 235Np
239mAm2500(200) keV 163(12) ns (7/2+)
240Am95145240.055300(15)50.8(3) h β+ 240Pu(3−)
α (1.9×10−4%) 236Np
241Am[15]95146241.0568291(20)432.2(7) y α 237Np5/2−
CD (7.4×10−10%) 207Tl, 34Si
SF (4.3×10−10%) (various)
241mAm2200(100) keV 1.2(3) µs
242Am95147242.0595492(20)16.02(2) h β− (82.7%) 242Cm1−
EC (17.3%) 242Pu
242m1Am48.60(5) keV141(2) y IT (99.54%) 242Am5−
α (.46%) 238Np
SF (1.5×10−8%) (various)
242m2Am2200(80) keV 14.0(10) ms (2+,3−)
243Am[15]95148243.0613811(25)7,370(40) y α 239Np5/2−
SF (3.7×10−9%) (various)
244Am95149 244.0642848(22) 10.1(1) h β− 244Cm (6−)#
244mAm86.1(10) keV26(1) min β− (99.96%) 244Cm1+
EC (.0361%) 244Pu
245Am95150 245.066452(4) 2.05(1) h β− 245Cm (5/2)+
246Am95151 246.069775(20) 39(3) min β− 246Cm (7−)
246m1Am30(10) keV25.0(2) min β− (99.99%) 246Cm2(−)
IT (.01%) 246Am
246m2Am~2000 keV 73(10) µs
247Am95152 247.07209(11)# 23.0(13) min β− 247Cm (5/2)#
1. ^1 "Americium" {{webarchive|url=https://www.webcitation.org/69WMA7eTu?url=http://www.ead.anl.gov/pub/doc/Americium.pdf |date=2012-07-29 }}. Argonne National Laboratory, EVS. Retrieved 25 December 2009.
2. ^{{cite journal|url=http://www.jstage.jst.go.jp/article/jnst/41/4/448/_pdf |title=Neutron and Gamma Ray Source Evaluation of LWR High Burn-up UO2 and MOX Spent Fuels |journal=Journal of Nuclear Science and Technology |volume=41 |issue=4 |pages=448–456 |date=April 2004 |doi=10.3327/jnst.41.448 |last=Sasahara |first=Akihiro |last2=Matsumura |first2=Tetsuo |last3=Nicolaou |first3=Giorgos |last4=Papaioannou |first4=Dimitri }}{{dead link|date=November 2016 |bot=InternetArchiveBot |fix-attempted=yes }}
3. ^{{cite journal |journal=Physical Review |volume=155 |issue = 4|date=March 1967 |author=J. T. Caldwell |author2=S. C. Fultz |author3=C. D. Bowman |author4=R. W. Hoff |title=Spontaneous Fission Half-Life of Am242m242m |doi=10.1103/PhysRev.155.1309 |pages=1309–1313|bibcode=1967PhRv..155.1309C }} (halflife (9.5±3.5)×1011
4. ^95-Am-242 {{webarchive|url=https://web.archive.org/web/20110719060944/http://www.matpack.de/Info/Nuclear/Nuclids/A/Am242.html |date=2011-07-19 }}
5. ^{{cite web|url=http://typhoon.jaea.go.jp/icnc2003/Proceeding/paper/6.5_022.pdf |archive-url=https://web.archive.org/web/20110722105207/http://typhoon.jaea.go.jp/icnc2003/Proceeding/paper/6.5_022.pdf |dead-url=yes |archive-date=July 22, 2011 |accessdate=February 3, 2011 }}
6. ^{{cite press release |url=https://www.sciencedaily.com/releases/2001/01/010103073253.htm |title=Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two Weeks |date=December 28, 2000 |publisher=Ben-Gurion University Of The Negev}}
7. ^{{cite journal|last1=Ronen|first1=Yigal|last2=Shwageraus|first2=E.|title=Ultra-thin 241mAm fuel elements in nuclear reactors|journal=Nuclear Instruments and Methods in Physics Research A|date=2000|volume=455|issue=2|pages=442–451|doi=10.1016/s0168-9002(00)00506-4|bibcode=2000NIMPA.455..442R}}
8. ^1 "Americium-243" {{webarchive|url=https://web.archive.org/web/20110225120159/http://www.ornl.gov/sci/isotopes/r_am243.html |date=2011-02-25 }}. Oak Ridge National Laboratory. Retrieved 25 December 2009.
9. ^"Isotopes of the Element Americium". Jefferson Lab Science Education. Retrieved 25 December 2009.
10. ^{{NUBASE 2016 II}}
11. ^{{cite web |url=http://www.nucleonica.net/unc.aspx |title=Universal Nuclide Chart |publisher=nucleonica |registration=yes}}
12. ^Abbreviations:
CD: Cluster decay
EC: Electron capture
IT: Isomeric transition
SF: Spontaneous fission
13. ^"Observation of new neutron-deficient isotopes with Z ≥ 92in multinucleon transfer reactions" http://inspirehep.net/record/1383747/files/scoap3-fulltext.pdf
14. ^{{cite journal|last=Kaji|first=D.|last2=Morimoto|first2=K.|last3=Haba|first3=H.|last4=Ideguchi|first4=E.|last5=Koura|first5=H.|last6=Morita|first6=K.|date=2016|title=Decay Properties of New Isotopes 234Bk and 230Am, and Even–Even Nuclides 234Cm and 230Pu|url=https://www.researchgate.net/publication/291009584|format=PDF|journal=Journal of the Physical Society of Japan|volume=84|issue=15002|pages=015002|doi=10.7566/JPSJ.85.015002}}
15. ^1 Most common isotopes

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.

See also

{{Wikipedia books|Americium}}{{Clear}}

References

Sources

  • Isotope masses from:
    • {{NNDC}}
  • Isotopic compositions and standard atomic masses from:
    • {{CAWIA 2003}}
    • {{CIAAW 2005}}
  • Half-life, spin, and isomer data selected from the following sources.
    • {{NNDC}}
    • {{NNDC}}
    • {{CRC85|chapter=11}}
{{Navbox element isotopes}}

3 : Americium|Isotopes of americium|Lists of isotopes by element
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