Isotopes of aluminium

Aluminium (Al) has 22 known isotopes from ²¹Al to ⁴²Al and 4 known isomers. Only ²⁷Al (stable isotope) and ²⁶Al (radioactive isotope, t_1/2 = 7.2 × 10⁵ y) occur naturally, however ²⁷Al has a natural abundance of 99.9+ %. Other than ²⁶Al, all radioisotopes have half-lives under 7 minutes, most under a second. Relative atomic mass is 26.9815386(8). ²⁶Al is produced from argon in the atmosphere by spallation caused by cosmic-ray protons. Aluminium isotopes have found practical application in dating marine sediments, manganese nodules, glacial ice, quartz in rock exposures, and meteorites. The ratio of ²⁶Al to ¹⁰Be has been used to study the role of sediment transport, deposition, and storage, as well as burial times, and erosion, on 10⁵ to 10⁶ year time scales.

Cosmogenic Aluminium-26 was first applied in studies of the Moon and meteorites. Meteorite fragments, after departure from their parent bodies, are exposed to intense cosmic-ray bombardment during their travel through space, causing substantial ²⁶Al production. After falling to Earth, atmospheric shielding protects the meteorite fragments from further ²⁶Al production, and its decay can then be used to determine the meteorite's terrestrial age. Meteorite research has also shown that ²⁶Al was relatively abundant at the time of formation of our planetary system. Most meteoriticists believe that the energy released by the decay of ²⁶Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.^[1]

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)[2][n 1]	daughter isotope(s)[n 2]	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
	excitation energy
^19Al	13	6	19.0218#	<35 ns	p	^18Mg
^20Al	13	7	20.0194#	<35 ns	p	^19Mg
^21Al	13	8	21.02804(32)#	<35 ns	p	^20Mg	1/2+#
^22Al	13	9	22.01952(10)#	59(3) ms	β^+ (96.7%)	^22Mg	(3)+
					β^+, 2p (2.5%)	^20Ne
					β^+, p (0.8%)	^21Na
^23Al	13	10	23.007267(20)	470(30) ms	β^+ (92%)	^23Mg	5/2+#
					β^+, p (8%)	^22Na
^23mAl				~0.35 s			#79
^24Al	13	11	23.9999389(30)	2.053(4) s	β^+ (99.95%)	^24Mg	4+
					β^+, α (.0349%)	^20Ne
					β^+, p (.0159%)	^23Na
^24mAl	425.8(1) keV			131.3(25) ms	IT (82%)	^24Al	1+
					β^+ (18%)	^24Mg
					β^+, α	^20Ne
^25Al	13	12	24.9904281(5)	7.183(12) s	β^+	^25Mg	5/2+
^26Al[n 3]	13	13	25.98689169(6)	7.17(24)×10^5 years	β^+	^26Mg	5+	Trace[n 4]
^26mAl	228.305(13) keV			6.3452(19) s	β^+	^26Mg	0+
^27Al	13	14	26.98153863(12)	Stable			5/2+	1.0000
^28Al	13	15	27.98191031(14)	2.2414(12) min	β^−	^28Si	3+
^29Al	13	16	28.9804450(13)	6.56(6) min	β^−	^29Si	5/2+
^30Al	13	17	29.982960(15)	3.60(6) s	β^−	^30Si	3+
^31Al	13	18	30.983947(22)	644(25) ms	β^− (98.4%)	^31Si	(3/2,5/2)+
					β^−, n (1.6%)	^30Si
^32Al	13	19	31.98812(9)	31.7(8) ms	β^− (99.3%)	^32Si	1+
					β^−, n (.7%)	^31Si
^32mAl	955.7(4) keV			200(20) ns			(4+)
^33Al	13	20	32.99084(8)	41.7(2) ms	β^− (91.5%)	^33Si	(5/2+)#
					β^−, n (8.5%)	^32Si
^34Al	13	21	33.99685(12)	56.3(5) ms	β^− (87.5%)	^34Si	4−#
					β^−, n (12.5%)	^33Si
^35Al	13	22	34.99986(19)	38.6(4) ms	β^− (74%)	^35Si	5/2+#
					β^−, n (26%)	^34Si
^36Al	13	23	36.00621(23)	90(40) ms	β^− (69%)	^36Si
					β^−, n (31%)	^35Si
^37Al	13	24	37.01068(36)	10.7(13) ms	β^−	^37Si	3/2+
^38Al	13	25	38.01723(78)	7.6(6) ms	β^−	^38Si
^39Al	13	26	39.02297(158)	7.6(16) ms	β^−	^39Si	3/2+#
^40Al	13	27	40.03145(75)#	10# ms [>260 ns]
^41Al	13	28	41.03833(86)#	2# ms [>260 ns]			3/2+#
^42Al	13	29	42.04689(97)#	1 ms

1. Abbreviations:
   IT: Isomeric transition
2. Bold for stable isotopes
3. Used in radiodating events early in the Solar System's history and meteorites
4. cosmogenic

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

References

• Isotope masses from:
  • G. Audi; A. H. Wapstra; C. Thibault; J. Blachot; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
• 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; 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.
  • 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. Lay summary.
  • G. Audi; A. H. Wapstra; C. Thibault; J. Blachot; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
  • National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005. Check date values in: |access-date= (help)
  • 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 978-0-8493-0485-9.

1. R. T. Dodd. Thunderstones and Shooting Stars. pp. 89–90. ISBN 0-674-89137-6.
2. "Universal Nuclide Chart". Nucleonica. Retrieved 2012-08-15. (registration required (help)).

External links

• Aluminum isotopes data from The Berkeley Laboratory Isotopes Project's