Nuklida · stabil · alami
Helium-4 (⁴He)
Helium-4 (⁴He) adalah isotop stabil helium dengan 2 proton dan 2 neutron (nomor massa 4). Kelimpahan alaminya 0.999 998(2).
Data nuklida
- Unsur
- Helium (He, Z = 2)
- Nomor massa (A)
- 4
- Proton (Z)
- 2
- Neutron (N)
- 2
- Massa atom
- 4.00260325413 ± 0.00000000016 u
- Waktu paruh
- Stabil
- Mode peluruhan
- Tidak meluruh
- Kelimpahan alami
- 0.999 998(2)
- Tahun penemuan
- 1908
- Sumber data
- IAEA Atomic Mass Data Center (NUBASE) and IUPAC CIAAW, via PubChem
Kegunaan isotop helium
- 3He is a product of the radioactive decay of 3H (half-life of 12.31 years). The relative variations in the amount ratio n(3He)/n(3H) can be interpreted in terms of elapsed time. This has been especially useful in aquatic systems, including oceans, lakes, and aquifers, that received large inputs of 3H from precipitation following thermonuclear bomb test periods. 3H- 3He dating provides the elapsed time since a water mass became isolated from the atmosphere in the time range from the mid-1950s to the present. Such studies are important for establishing the sustainability of groundwater resources in shallow aquifers,. 4He is a product of radioactive decay in the uranium and thorium decay series. As a result, 4He concentration is used to estimate the relative ages of minerals and groundwater. In closed systems (systems that do not exchange matter with their surroundings), relative variations in the amount ratio n(4He)/n(U) can be interpreted in terms of elapsed time, although other processes can alter the distribution of helium, which is highly mobile in terrestrial environments,. 4He concentrations commonly increase along groundwater flow paths through a cumulative release from aquifer materials. This rate of accumulation is used to estimate the time since the groundwater was recharged at the surface. The 4He accumulation method of groundwater dating is typically used in deeper aquifers, where groundwater is relatively old and the 3H- 3He method cannot be used because of the relatively short half-life of 12.31 years for 3H.