Helium-8

Properties and data of the isotope ⁸He.

Content

General Data

Radioactive Decay

Parent Nuclides

Isotones und Isobares

General data

Name of the isotope:Helium-8; He-8Symbol:⁸He or 82HeMass number A:8 (= number of nucleons)Atomic number Z:2 (= number of protons)Neutrons N:6Isotopic mass:8.03393439(10) u (atomic weight of Helium-8)Nuclide mass:8.0328372 u (calculated nuclear mass without electrons)Mass excess:31.60968 MeVMass defect:0.033705169999999 u (per nucleus)Nuclear binding energy:31.39616362 MeV (per nucleus)
3.92452045 MeV (average binding energy per nucleon)Separation energy:S_N = 2.535(8) MeV (first neutron)
S_P = 24.81(100) MeV (first proton)Half-life:119.1(12) msDecay constant λ:6.1937912658381 s^-1Specific activity α:4.662485432490 × 10⁺²³ Bq g^-1
12601311979704 Ci g^-1Spin and parity:
(nuclear angular momentum)0+Isobaric spin: 2Charge radius:1.9239(306) femtometer fmMirror nucleus:Carbon-8Year of discovery:1965

Radioactive Decay

Half-life T_½ = 119.1(12) ms respectively 1.1191 × 10^-1 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β^-	⁸Li	84 %	10.66388(10) MeV
β^-, n	⁷Li	16 %	8.63126(9) MeV

Parent Nuclides

Direct parent isotopes are: ⁹He, ¹⁰He.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 6) and isobaric (same nucleon number A = 8) with Helium-8. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.