HELIUM gas (He)

(above) helium image: HELIUM GAS: picture showing He atoms. This image is 600 x 600 pixels; the original image is 4096 x 4096 pixels.

HELIUM: is the second element (in the periodic table and in terms of creation and in terms of abundance ...) and exists as an atomic gas under all but the most extreme conditions. It liquifies at one degree above absolute zero and becomes gaseous at few degrees more. It was named after the Sun (Latin: Helios) owing to its discovery in solar emission spectra. The helium nucleus consists of two protons and two neutrons and so is the same as an alpha particle. In the helium atom the two protons are balanced by two electrons. These electrons occupy the first shell and make the element very unreactive (it is a noble gas). Helium was synthesised in the early universe by the collision of protons (= hydrogen nuclei). This promordial generation ceased as the early universe cooled. Indeed, no other elements were created because of dispersion and cooling of the primordial particles in the early stages after the big bang. It had to wait for the creation of stars before nuclear synthesis could start again. Inside stars, the immense temperatures and pressures forced particles together (nuclear fusion) and the generation of helium from hydrogen started again. Other elements were formed by nuclear synthesis although these remain in trace amounts compared to hydrogen and helium.

PRIMORDIAL GENERATION OF HELIUM: soon after the big bang deuterium (or heavy hydrogen whose nuclei consist of one proton and one neutron) was formed by the collision of protons and neutrons. Later, as temeratures dropped the more stable helium could form from collisions of deuterium, hydrogen and neutrons in various combinations.

STELLAR GENERATION OF HELIUM: proton proton fusion in stars creates neutrons. This happens when a couple of protons collide and end up as a proton-neutron pair (the positive charge of one of the protons is emitted as a positron). This proton-neutron couple can then combine with another proton to form a proton-proton-neutron group (or ³He). This intermediate species, an isotope of helium (Helium-3) can then fuse with a similar group to generate 4H, along with the emission or protons and so the process continues. Positrons are anti-particles of electrons. When these complementary particles meet they cancel each other out and release high energy photons. This energy release is what powers the sun.