Creation of Nuclei
From Mbscientific_wiki
Creation of Atoms
Through a big bang event all of the permutations of possibilities of particles are formed. Of these, the stable proton-neutron-electron combinations go on to form atoms. Protons and electrons, having a positive and a negative charge attract one another in a one-to-one manner. For each proton in a nucleus, typically one neutron acts as a buffer, otherwise protons, by the virtue of having the same positive charge would repel each other. So the process of atom creation adds one electron, one proton and at least one neutron to the atom until the periodic table of elements is complete. Atoms have isotopes, that is the same number of electrons and protons but more neutrons.
The process for creation of atoms takes shape in two manners. First is the creation of nuclei and second is the formation of the electron orbitals.
Creation of Atomic Nuclei in Stellar Cores as well as Supernova and Hyper-Nova Events
Protons and neutrons, subjected to the strong nuclear forces, fuse together to create nuclei. The simplest element's nucleus, hydrogen, having a single proton (2 up and one down quarks), is formed in the cooling process of a big bang event. Once gravity takes hold, dense hydrogen clouds form proto-galaxies. Eventually, gravity collapses portions of the clouds into denser and denser balls until the gravitational squeeze forms a star and starts fusion reactions. In proton-proton fusion reaction, hydrogen nuclei are fused together at about 700000-1 million Kelvin (MK), forming helium nuclei in a 3 step cascade (isotopes are noted in parenthesis):
1- deuterium isotope formation: 2 protons ==> (proton/neutron) + positron + neutrino
2- light helium isotope formation from deuterium isotope: (proton/neutron) + proton ==> (proton/proton/neutron)
3- helium nuclei formation: 2(proton/proton/neutron) ==> (proton/proton/neutron/neutron)+ 2 protons.
Once enough helium nuclei are formed, the helium fusion cascade starts at about 100MK. It is a 3 step cascade as well (P= Proton, N= Neutron), called triple-alpha (helium nucleus) process:
1- helium to beryllium fusion: 2 P2N2 ==> P4N4
2- beryllium fuses to helium producing carbon:
P4N4 + P2N2 ==> P6N6
3- sometimes carbon fuses to helium producing oxygen:
P6N6+ P2N2 ==> P8N8
At about 600+ MK, carbon fusion proceeds. One reaction, demonstrated in a 4-step cyclical cascade, is called the carbon cycle:
1- carbon isotope formation: P6N6 + P ==> P6N7 + positron + neutrino
2- the isotope fuses with proton to form nitrogen: P6N7+ P ==> P7N7
3- nitrogen isotope step: P7N7 + P ==> P7N8 + positron + neutrino
4- completing carbon cycle P7N8 + P ==> P6N6 + P2N2 , expelling helium and rejoining the cycle
Stars that achieve fusion beyond carbon are much more massive than the sun and run at much higher temperatures. The list below summarizes some known fusion cascades:
Hydrogen - Helium - 1 Million K
Helium - Carbon (Oxygen) - 100 Million K
Carbon - Neon - 600 Million K
Neon - Oxygen - 1 Billion K
Oxygen - Silicon- 1.5 Billion K
Silicon - Iron - 3 Billion K
Larger nuclei require yet more temperature/pressures to be produced. That is achieved in super-nova explosions. In fact super-nova explosions recycle stars. That is the supernova clouds form stellar nurseries, which in turn condense the elements, including heavy elements, back into new stars. Much stronger, hyper-nova explosions, obliterate entire portions of galaxies, thereby creating all of the heavy elements and recycling them back into the newly modified galaxy.
Courses
Courses from Massachusetts Institute of Technology (MIT) OpenCourseWare:
http://ocw.mit.edu/OcwWeb/Physics/8-701Spring2004/CourseHome/ - MIT - 8.701 Introduction to Nuclear and Particle Physics
http://ocw.mit.edu/OcwWeb/Nuclear-Engineering/22-101Fall-2006/CourseHome/ - MIT - 22.101 Applied Nuclear Physics
http://ocw.mit.edu/OcwWeb/Nuclear-Engineering/22-012Spring-2006/CourseHome/ - MIT - 22.012 / 22.S27 Seminar: Fusion and Plasma Physics
http://ocw.mit.edu/OcwWeb/Nuclear-Engineering/22-615Spring-2007/CourseHome/ - MIT - 22.615 MHD Theory of Fusion Systems
links
http://www.astro.ubc.ca/~scharein/a311/Sim/fusion/Fusion.html - nice animation of hydrogen==>helium fusion pathway
http://library.thinkquest.org/17940/texts/ppcno_cycles/ppcno_cycles.html - Another animation page of H==>He, and C, N, O Cycle
http://en.wikipedia.org/wiki/Nuclear_fusion - wikipedia fusion page\
http://www.visionlearning.com/library/flash_viewer.php?oid=2747 - terestial fusion reactor animation: Concept simulation reenacts the fusion of deuterium and tritium inside of a tokamak reactor.
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