Helium-5

Properties and data of the isotope ⁵He.

Contents

Helium-5 is an isotope of the element helium, which consists of two protons and three neutrons in the nucleus. Unlike other isotopes of helium that occur in the atmosphere through natural processes, helium-5 is very rare and is usually only produced through the influence of cosmic rays that originate in outer space. ⁵He is radioactive and has a half-life of approximately 7.6 × 10^-22 seconds, which means it exists for a very short time. Helium-5 is of interest in nuclear physics and astrophysics because it could shed light on the origin and structure of the universe.

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

General data

Name of the isotope:Helium-5; He-5Symbol:⁵He or 52HeMass number A:5 (= number of nucleons)Atomic number Z:2 (= number of protons)Neutrons N:3Isotopic mass:5.012057(21) u (atomic weight of Helium-5)Nuclide mass:5.0109598 u (calculated nuclear mass without electrons)Mass excess:11.23102 MeVMass defect:0.029587812 u (per nucleus)Nuclear binding energy:27.56086935 MeV (per nucleus)
5.51217387 MeV (average binding energy per nucleon)Separation energy:
S_P = 20.68(10) MeV (first proton)Half-life:7.61833 × 10^-22 sDecay constant λ:9.098413701689 × 10⁺²⁰ s^-1Specific activity α:1.095838578271 × 10⁺⁴⁴ Bq g^-1
2.961725887219 × 10⁺³³ Ci g^-1Spin and parity:
(nuclear angular momentum)3/2-Isobaric spin: 1/2Mirror nucleus:Lithium-5Year of discovery:1937

Radioactive Decay

Half-life T_½ = 7.61833 × 10^-22 s respectively 7.61833 × 10^-22 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
n ?	⁴He		0.290(71) MeV

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 3) and isobaric (same nucleon number A = 5) with Helium-5. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.