Helium-9

Properties and data of the isotope ⁹He.

Contents

Helium-9 is a radioisotope of the chemical element helium, which, in addition to the element-specific 2 protons, has 7 neutrons in the atomic nucleus, resulting in the mass number 9. The very short-lived, unstable and therefore radioactive nuclide, which can only be produced artificially, has no practical significance; the study of ⁹He serves exclusively academic purposes.

See also: List of individual Helium isotopes (and general data sources).

General data

Name of the isotope:Helium-9; He-9Symbol:⁹He or 92HeMass number A:9 (= number of nucleons)Atomic number Z:2 (= number of protons)Neutrons N:7Nucleon pairing (Z - N):even - oddNuclear ratio (N/Z ratio):3.5 (= neutron-proton ratio)Neutron excess (N-Z):5Isotopic mass:9.04395(5) u (atomic weight of Helium-9)Nuclide mass:9.0428528 u (calculated nuclear mass without electrons)Mass excess:40.93916 MeVMass defect:0.032354476 u (per nucleus)Nuclear binding energy:30.13800027 MeV (per nucleus)
3.3486667 MeV (average binding energy per nucleon)Half-life:7.03231 zsDecay constant λ:9.856607296321 × 10⁺¹⁹ s^-1Specific activity α:6.595319726614 × 10⁺⁴² Bq g^-1
1.782518845030 × 10⁺³² Ci g^-1Spin and parity:
(nuclear angular momentum)1/2+Isobaric spin: 5/2Year of discovery:1986

Radioactive Decay

Half-life T_½ = 7.03231 zs respectively 7.03231 × 10^-21 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
n	⁸He	100 %	14.816(60) MeV

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 7) and isobaric (same nucleon number A = 9) with Helium-9. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 7	Isobar A = 9
2	⁹He	⁹He
3	¹⁰Li	⁹Li
4	¹¹Be	⁹Be
5	¹²B	⁹B
6	¹³C	⁹C
7	¹⁴N	⁹N
8	¹⁵O
9	¹⁶F
10	¹⁷Ne
11	¹⁸Na
12	¹⁹Mg
13	²⁰Al

External data and identifiers

Adopted Levels, Gammas:NuDat 9He

Literature and References

[1] - Kamal K. Seth et al.:
Exotic Nucleus Helium-9 and its Excited States.
In: Physical Review Letters, 58, 1930, (1987), DOI 10.1103/PhysRevLett.58.1930.