Isotopes of americium: Difference between revisions

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Actinides and fission products by half-life v t e
Actinides^[1] by decay chain				Half-life range (a)	Fission products of ²³⁵U by yield^[2]
4n	4n + 1	4n + 2	4n + 3	Half-life range (a)	4.5–7%	0.04–1.25%	<0.001%
²²⁸Ra^№				4–6 a		¹⁵⁵Eu^þ
²⁴⁴Cm^ƒ	²⁴¹Pu^ƒ	²⁵⁰Cf	²²⁷Ac^№	10–29 a	⁹⁰Sr	⁸⁵Kr	^113mCd^þ
²³²U^ƒ		²³⁸Pu^ƒ	²⁴³Cm^ƒ	29–97 a	¹³⁷Cs	¹⁵¹Sm^þ	^121mSn
²⁴⁸Bk^[3]	²⁴⁹Cf^ƒ	^242mAm^ƒ		141–351 a	No fission products have a half-life in the range of 100 a–210 ka ...
	²⁴¹Am^ƒ		²⁵¹Cf^ƒ^[4]	430–900 a
		²²⁶Ra^№	²⁴⁷Bk	1.3–1.6 ka
²⁴⁰Pu	²²⁹Th	²⁴⁶Cm^ƒ	²⁴³Am^ƒ	4.7–7.4 ka
	²⁴⁵Cm^ƒ	²⁵⁰Cm		8.3–8.5 ka
			²³⁹Pu^ƒ	24.1 ka
		²³⁰Th^№	²³¹Pa^№	32–76 ka
²³⁶Np^ƒ	²³³U^ƒ	²³⁴U^№		150–250 ka	⁹⁹Tc^₡	¹²⁶Sn
²⁴⁸Cm		²⁴²Pu		327–375 ka		⁷⁹Se^₡
				1.53 Ma	⁹³Zr
	²³⁷Np^ƒ			2.1–6.5 Ma	¹³⁵Cs^₡	¹⁰⁷Pd
²³⁶U			²⁴⁷Cm^ƒ	15–24 Ma		¹²⁹I^₡
²⁴⁴Pu				80 Ma	... nor beyond 15.7 Ma^[5]
²³²Th^№		²³⁸U^№	²³⁵U^ƒ№	0.7–14.1 Ga	... nor beyond 15.7 Ma^[5]
₡, has thermal neutron capture cross section in the range of 8–50 barns ƒ, fissile №, primarily a naturally occurring radioactive material (NORM) þ, neutron poison (thermal neutron capture cross section greater than 3k barns)

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 (t_½ 141 years). The isotopes of americium range in atomic weight from 231.046 u (²³¹Am) to 249.078 u (²⁴⁹Am).

Some notable isotopes

Americium-241

Americium-241 is the most prevalent isotope of americium in nuclear waste.^[6] It is the americium isotope used in smoke detectors based on ionization chambers. 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 Pu-241, electron capture from Cm-241, alpha from Bk-245

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 Am-241. A chemical removal of americium from reworked plutonium, e.g. during reworking of plutonium pits, may be required.

Americium-242m

Transmutation ﬂow between ²³⁸Pu and ²⁴⁴Cm in LWR.^[7]
Fission percentage is 100 minus shown percentages.
Total rate of transmutation varies greatly by nuclide.
²⁴⁵Cm–²⁴⁸Cm are long-lived with negligible decay.

^242mAm decay modes (halflife: 141 years)
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^[8]	spontaneous fission	~200 MeV	fission products

Americium-242m is one of the isotopes of americium, with 95 protons and electrons and 147 neutrons and a mass of 242.0595492 g/mol. It is one of the rare cases, like tantalum-180m, where a higher-energy nuclear isomer is more stable than the lower-energy one, Americium-242.^[9]

^242mAm is fissile (because it has an odd number of neutrons) and has a low critical mass, comparable to that of plutonium-239.^[10] 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.^[11]

²⁴²Am decay modes (halflife: 16 hours)
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 is a radioactive isotope of americium having 95 electrons and protons and 148 neutrons and has a mass of 243.06138 g/mol.

It has a half-life of 7370 years, the longest lasting of all americium isotopes, however, it is still not found in nature. It is formed in the nuclear fuel cycle by neutron capture on plutonium-242 followed by beta decay. ^[12] Production increases exponentially with increasing burnup as a total of 5 neutron captures on uranium-238 are required.

It either decays by emitting an alpha particle (the decay energy is 5.27MeV)^[13] to turn into neptunium-239, which then quickly decays to plutonium-239, or infrequently, by spontaneous fission. ^[14]

Americium-243 is a hazardous substance, because it can cause cancer. Neptunium-239, which is formed from Americium-243, emits dangerous gamma rays, making Americium-243 the most dangerous isotope of Americium. ^[15]

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)^[16]^{[n 1]}	daughter isotope(s)	nuclear spin
nuclide symbol	excitation energy			half-life	decay mode(s)^[16]^{[n 1]}	daughter isotope(s)	nuclear spin
²³¹Am	95	136	231.04556(32)#	30# s	β⁺	²³¹Pu
²³¹Am	95	136	231.04556(32)#	30# s	α (rare)	²²⁷Np
²³²Am	95	137	232.04659(32)#	79(2) s	β⁺ (98%)	²³³Pu
					α (2%)	²²⁸Np
					β⁺, SF (.069%)	(various)
²³³Am	95	138	233.04635(11)#	3.2(8) min	β⁺	²³³Pu
²³³Am	95	138	233.04635(11)#	3.2(8) min	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-#
²³⁵Am	95	140	235.04795(13)#	9.9(5) min	α (rare)	²³¹Np	5/2-#
²³⁶Am	95	141	236.04958(11)#	3.6(1) min	β⁺	²³⁶Pu
²³⁶Am	95	141	236.04958(11)#	3.6(1) min	α	²³²Np
²³⁷Am	95	142	237.05000(6)#	73.0(10) min	β⁺ (99.97%)	²³⁷Pu	5/2(-)
²³⁷Am	95	142	237.05000(6)#	73.0(10) min	α (.025%)	²³³Np	5/2(-)
²³⁸Am	95	143	238.05198(5)	98(2) min	β⁺	²³⁸Pu	1+
²³⁸Am	95	143	238.05198(5)	98(2) min	α (1E-4%)	²³⁴Np	1+
^238mAm	2500(200)# keV			35(10) µs
²³⁹Am	95	144	239.0530245(26)	11.9(1) h	EC (99.99%)	(5/2)-
²³⁹Am	95	144	239.0530245(26)	11.9(1) h	α (.01%)	(5/2)-	²³⁵Np
^239mAm	2500(200) keV			163(12) ns			(7/2+)
²⁴⁰Am	95	145	240.055300(15)	50.8(3) h	β⁺	²⁴⁰Pu	(3-)
²⁴⁰Am	95	145	240.055300(15)	50.8(3) h	α (1.9E-4%)	²³⁶Np	(3-)
²⁴¹Am	style="text-align:right" \| 95	146	241.0568291(20)	432.2(7) a	α	²³⁷Np	5/2-
					SF (4.3E-10%)	(various)
					CD (7.4E-10%)	²⁰⁷Tl, ³⁴Si
^241mAm	2200(100) keV			1.2(3) µs
²⁴²Am	95	147	242.0595492(20)	16.02(2) h	β^- (82.7%)	²⁴²Cm	1-
²⁴²Am	95	147	242.0595492(20)	16.02(2) h	EC (17.3%)	²⁴²Pu	1-
^242m1Am	48.60(5) keV			141(2) a	IT (99.54%)	²⁴²Am	5-
					α (.46%)	²³⁸Np
					SF (1.5E-8%)	(various)
^242m2Am	2200(80) keV			14.0(10) ms			(2+,3-)
²⁴³Am	95	148	243.0613811(25)	7.37(4)E+3 a	α	²³⁹Np	5/2-
²⁴³Am	95	148	243.0613811(25)	7.37(4)E+3 a	SF (3.7E-9%)	(various)	5/2-
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+
^244mAm	86.1(10) keV			26(1) min	EC (.0361%)	²⁴⁴Pl	1+
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(-)
^246m1Am	30(10) keV			25.0(2) min	IT (.01%)	²⁴⁶Am	2(-)
^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

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

^ Plus radium (element 88). While actually a sub-actinide, it immediately precedes actinium (89) and follows a three-element gap of instability after polonium (84) where no nuclides have half-lives of at least four years (the longest-lived nuclide in the gap is radon-222 with a half life of less than four days). Radium's longest lived isotope, at 1,600 years, thus merits the element's inclusion here.
^ Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear 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 Bk²⁴⁸ with a half-life greater than 9 [years]. No growth of Cf²⁴⁸ was 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 of ²³²Th; e.g., while ^113mCd has a half-life of only fourteen years, that of ¹¹³Cd is eight quadrillion years.
^ "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.
^ 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
^ "Americium-243". Oak Ridge National Laboratory. Retrieved 25 December 2009.
^ "Americium-243". Oak Ridge National Laboratory. Retrieved 25 December 2009.
^ "Isotopes of the Element Americium". Jefferson Lab Science Education. Retrieved 25 December 2009.
^ "Americium". Argonne National Laboratory, EVS. 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" (PDF). Nuclear Physics A. 729: 3–128. doi:10.1016/j.nuclphysa.2003.11.001.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
- 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. {{cite journal}}: Unknown parameter |laysummary= ignored (help)
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" (PDF). Nuclear Physics A. 729: 3–128. doi:10.1016/j.nuclphysa.2003.11.001.{{cite journal}}: CS1 maint: multiple names: authors list (link)
- National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005. {{cite web}}: Check date values in: |accessdate= (help)
- N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide (ed.). CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0849304859. {{cite book}}: Unknown parameter |nopp= ignored (|no-pp= suggested) (help)

[17] Abbreviations:
CD: Cluster decay
EC: Electron capture
IT: Isomeric transition
SF: Spontaneous fission

[1] Plus radium (element 88). While actually a sub-actinide, it immediately precedes actinium (89) and follows a three-element gap of instability after polonium (84) where no nuclides have half-lives of at least four years (the longest-lived nuclide in the gap is radon-222 with a half life of less than four days). Radium's longest lived isotope, at 1,600 years, thus merits the element's inclusion here.

[2] Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.

[3] 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 Bk²⁴⁸ with a half-life greater than 9 [years]. No growth of Cf²⁴⁸ was 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]."

[4] This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".

[5] Excluding those "classically stable" nuclides with half-lives significantly in excess of ²³²Th; e.g., while ^113mCd has a half-life of only fourteen years, that of ¹¹³Cd is eight quadrillion years.

[anl-6] "Americium". Argonne National Laboratory, EVS. Retrieved 25 December 2009.

[7] 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.

[8] 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

[9] 95-Am-242

[10] ttp://typhoon.jaea.go.jp/icnc2003/Proceeding/paper/6.5_022.pdf

[11] Extremely Efficient Nuclear Fuel Could Take Man To Mars In Just Two Weeks

[12] "Americium-243". Oak Ridge National Laboratory. Retrieved 25 December 2009.

[13] "Americium-243". Oak Ridge National Laboratory. Retrieved 25 December 2009.

[14] "Isotopes of the Element Americium". Jefferson Lab Science Education. Retrieved 25 December 2009.

[15] "Americium". Argonne National Laboratory, EVS. Retrieved 25 December 2009.

[16] ttp://www.nucleonica.net/unc.aspx

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