Isotopes of helium

From Wikipedia, the free encyclopedia

You have new messages (last change).

Helium (He)
Standard atomic mass: 4.002602(2) u

The isotopes of helium include two naturally occurring isotopes and six unstable exotic helium isotopes.

1 Natural helium isotopes
- 1.1 Helium-3
- 1.2 Helium-4
2 Exotic helium isotopes
3 Table
- 3.1 Notes
4 References
5 See also
6 External links

[edit] Natural helium isotopes

[edit] Helium-3

For more details on this topic, see Helium-3.

[edit] Helium-4

For more details on this topic, see Helium-4.

[edit] Exotic helium isotopes

A subset of exotic light nuclei, the exotic helium isotopes have larger atomic masses than helium's natural isotopes. Although all exotic helium isotopes decay with a half-life of less than one second, researchers have eagerly created exotic light isotopes through particle accelerator collisions to create unusual atomic nuclei for elements such as helium, lithium, and nitrogen. The bizarre nuclear structures of such isotopes may offer insight into the isolated properties of neutrons.

The most widely-studied exotic helium isotope, for example, is helium-8. This isotope is thought to consist of a normal helium-4 nucleus surrounded by four neutrons dubbed a "halo" (⁶He also has a halo of neutrons). Halo nuclei have become an area of intense research. Isotopes up to helium-10, with two protons and eight neutrons, have been confirmed. By comparison, the most common He-4 isotope has only two neutrons.

[edit] Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
nuclide symbol	notes
³He	2	1	3.0160293191(26)	STABLE	1/2+	0.00000134(3)	4.6×10^-10-0.000041
⁴He	2	2	4.00260325415(6)	STABLE	0+	0.99999866(3)	0.999959-1
⁵He	2	3	5.01222(5)	700(30)E-24 s [0.60(2) MeV]	3/2-
⁵He	Highly unstable, decays to ⁴He.
⁶He	2	4	6.0188891(8)	806.7(15) ms	0+
⁶He	Produced from ⁷He or ¹¹Li, decomposes to ⁶Li through beta decay (beta-minus).
⁷He	2	5	7.028021(18)	2.9(5)E-21 s [159(28) keV]	(3/2)-
⁷He	Highly unstable, decays to ⁶He.
⁸He	2	6	8.033922(7)	119.0(15) ms	0+
⁸He	Produced from ⁹He, decomposes to ⁷Li through beta decay then emits a delayed neutron.
⁹He	2	7	9.04395(3)	7(4)E-21 s [100(60) keV]	1/2(-#)
⁹He	Highly unstable, decays to ⁸He.
¹⁰He	2	8	10.05240(8)	2.7(18)E-21 s [0.17(11) MeV]	0+
¹⁰He	Highly unstable, decays to ⁹He.

[edit] Notes

The isotopic composition refers to that in air.
The precision of the isotope abundances and atomic mass is limited through variations. The given ranges should be applicable to any normal terrestrial material.
Geologically exceptional samples are known in which the isotopic composition lies outside the reported range. The uncertainty in the atomic mass may exceed the stated value for such specimens.
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.

[edit] References

Isotope masses from Ame2003 Atomic Mass Evaluation by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in Nuclear Physics A729 (2003).
Isotopic compositions and standard atomic masses from Atomic weights of the elements. Review 2000 (IUPAC Technical Report). Pure Appl. Chem. Vol. 75, No. 6, pp. 683-800, (2003) and Atomic Weights Revised (2005).
Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.
- Audi, Bersillon, Blachot, Wapstra. The Nubase2003 evaluation of nuclear and decay properties, Nuc. Phys. A 729, pp. 3-128 (2003).
- National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the NuDat 2.1 database (retrieved Sept. 2005).
- David R. Lide (ed.), Norman E. Holden in CRC Handbook of Chemistry and Physics, 85th Edition, online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.