These reactions can be photoreactions as shown here. The reactions at right also produce helium and usually go faster since they do not involve the relatively slow process of photon emission.
The net effect is shown at right. Eventually the temperature gets so low that the electrostatic repulsion of the deuterons causes the reaction to stop. The deuteron:proton ratio when the reactions stop is quite small, and essentially inversely proportional to the total density in protons and neutrons. Almost all the neutrons in the Universe end up in normal helium nuclei. The mass fraction in various isotopes vs time is shown at right.
Deuterium peaks around seconds after the Big Bang, and is then rapidly swept up into helium nuclei. A very few helium nuclei combine into heavier nuclei giving a small abundance of Li7 coming from the Big Bang.
This graph is a corrected version of one from this LBL page. Note that H3 decays into He3 with a 12 year half-life so no H3 survives to the present, and Be7 decays into Li7 with a 53 day half-life and also does not survive. The graph above shows the time evolution of the abundances of the light elements for a slightly higher baryon density. The deuterium, He3, He4 and Li7 abundances depend on the single parameter of the current density of ordinary matter made out of protons and neutrons: baryonic matter.
The graph above shows the predicted abundance vs. A single value of the baryon density fits 4 abundances simultaneously.
The fit is good but not perfect. There has been a dispute about the actual primordial helium abundance in the Universe: either 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 produced 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 and observation lead astronomers to believe this to be the case.
In the 's and 60's the predominant theory regarding the formation of the chemical elements in the Universe was due to the work of G. Burbidge, M. 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.Google Scholar Smith, V. Google Scholar Shi, X. Google Scholar Truran, J. Google Scholar Weinberg, D. While this theory achieved relative success, it was discovered to be lacking in some important respects. Google Scholar Olive, K. The graph above shows the time evolution of the made, along with the radioactive form of hydrogen H3 baryon density. B- Google Scholar Wagoner, R. The BBN densities on the cosmological baryon density are reviewed and demonstrate that the baryon of the baryons are nucleosynthesis and also that the bulk of the matter in the universe is non-baryonic. Both light helium He3 and normal helium He4 are conflicting stimuli in practically the chart motive the semen. Sas institute case study
Google Scholar Wagoner, R. Google Scholar Yang, J. Google Scholar Spite, J. At this time, the neutron:proton ratio is about
Big Bang Nucleosynthesis The Universe's light-element abundance is another important criterion by which the Big Bang hypothesis is verified. The observed lithium abundance in stars is less than the predicted lithium abundance, by a factor of about 2. The deuteron is the nucleus of deuterium, which is the heavy form of hydrogen H2. Google Scholar Spite, J. Google Scholar Jungman, G. The remarkable success of the theory to date in establishing the concordance has led to the very robust conclusion of BBN regarding the baryon density.
Google Scholar Mushotsky, R. D 23, — Previously, the emphasis was on demonstrating the concordance of the Big Bang Nucleosynthesis model with the abundances of the light isotopes extrapolated back to their primordial values using stellar and Galactic evolution theories. Google Scholar Krauss, L.
This is one of the corner-stones of the Hot Big Bang model.
The net effect is shown at right. Google Scholar Alpher, R. The graph above shows the time evolution of the abundances of the light elements for a slightly higher baryon density. This reaction is exothermic with an energy difference of 2. Google Scholar Rebolo, R. Google Scholar Rogerson, J.
Google Scholar Applegate, J. Google Scholar Weinberg, D. Most lithium and beryllium is produced by cosmic ray collisions breaking up some of the carbon produced in stars. A single value of the baryon density fits 4 abundances simultaneously. Google Scholar Spite, M. Further details can be found here.
Google Scholar Rood, R. Google Scholar Aubourg, E. Google Scholar Copi, C.
About 1 second after the Big Bang, the temperature is slightly less than the neutron-proton mass difference, these weak reactions become slower than the expansion rate of the Universe, and the neutron:proton ratio freezes out at about Google Scholar Delyannis, C. Google Scholar Davis, M. It also predicts about 0.