Nucleosynthesis reactions

Timeline[ edit ] Periodic table showing the cosmogenic origin of each element. Elements from carbon up to sulfur may be made in small stars by the alpha process. Elements beyond iron are made in large stars with slow neutron capture s-processfollowed by expulsion to space in gas ejections see planetary nebulae. Elements heavier than iron may be made in neutron star mergers or supernovae after the r-processinvolving a dense burst of neutrons and rapid capture by the element.

Nucleosynthesis reactions

It is now known that the elements observed in the Universe were created in either of two ways. Light elements namely deuterium, helium, and lithium were Nucleosynthesis reactions in the first few minutes of the Big Bang, while elements heavier than helium are thought to have their origins in the interiors of stars which formed much later in the history of the Universe.

Both theory Nucleosynthesis reactions observation lead astronomers to believe this to be the case. Burbidge, Fowler, and Hoyle. The BBFH theory, as it came to be known, postulated that all the elements were produced either in stellar interiors or during supernova explosions.

While this theory achieved relative success, it was discovered to be lacking in some important respects. To begin with, it was estimated that only a small amount of matter found in the Universe should consist of helium if stellar nuclear reactions were its only source of production.

A similar enigma exists for the deuterium. According to stellar theory, deuterium cannot be produced in stellar interiors; actually, deuterium is destroyed inside of stars. Hence, the BBFH hypothesis could not by itself adequately explain the observed abundances of helium and deuterium in the Universe.

Thanks to the pioneering efforts of George Gamow and his collaborators, there now exists a satisfactory theory as to the production of light elements in the early Universe.

In the very early Universe the temperature was so great that all matter was fully ionized and dissociated. At this temperature, nucleosynthesis, or the production of light elements, could take place. In a short time interval, protons and neutrons collided to produce deuterium one proton bound to one neutron.

Most of the deuterium then collided with other protons and neutrons to produce helium and a small amount of tritium one proton and two neutrons.

Lithium 7 could also arise form the coalescence of one tritium and two deuterium nuclei. It also predicts about 0. The important point is that the prediction depends critically on the density of baryons ie neutrons and protons at the time of nucleosynthesis. Furthermore, one value of this baryon density can explain all the abundances at once.

In terms of the present day critical density of matter, the required density of baryons is a few percent the exact value depends on the assumed value of the Hubble constant. This relatively low value means that not all of the dark matter can be baryonic, ie we are forced to consider more exotic particle candidates.

This is one of the corner-stones of the Hot Big Bang model. Further support comes from the consistency of the other light element abundances for one particular baryon density and an independent measurement of the baryon density from the anisotropies in the cosmic microwave background radiation.

It seems like we really understand the physical processes which went on in the first few minutes of the evolution of the Universe! Further details can be found here.Since any reaction branch that completes this must turn 2 protons in 2 neutrons, two neutrinos are also emitted, which carry energy away from the reaction site.

Nucleosynthesis reactions

It is these neutrinos that directly confirm the occurrence of nuclear reactions in the. 33 rows · big bang nucleosynthesis By the first millisecond, the universe had cooled to a few trillion . By the time the universe was three minutes old the process had basically stopped and the relative abundances of the elements was fixed at ratios that didn't change for a very long time: 75% hydrogen, 25% helium, with trace amounts of deuterium (hydrogen-2), helium-3, and lithium Big Bang nucleosynthesis produced no elements heavier than lithium.

Big Bang Nucleosynthesis Gamow, Alpher and Herman proposed the hot Big Bang as a means to produce all of the elements. However, the lack of stable nuclei with atomic weights of 5 or 8 limited the Big Bang to producing hydrogen and helium.

According to the Big Bang theory, the early universe was hot enough to allow the nucleosynthesis of hydrogen, helium, and small amounts of lithium and beryllium.

Nucleosynthesis reactions

Deuterium, a common isotope of hydrogen, was also important as a reactant in many of the reactions required to form helium. The calculation of stellar nucleosynthesis requires the simultaneous Reactions involving 2H, Li, Be, and B go extremely quickly, as these nuclei are relatively brittle.

Li, for example, can be destroyed by cosmic-ray spallation on .

Nucleosynthesis – The Physics Hypertextbook