5) Features of fission reactions with charged particles
In nuclear physics and nuclear chemistry, nuclear fission is either a nuclear reaction or a radioactive decay process in which the nucleus of a particle splits into smaller parts (lighter nuclei). The fission process often produces free neutrons and photons (in the form of gamma rays), and releases a very large amount of energy even by the energetic standards of radioactive decay.
Nuclear fission produces energy for nuclear power and drives the explosion of nuclear weapons. Both uses are possible because certain substances called nuclear fuels undergo fission when struck by fission neutrons, and in turn emit neutrons when they break apart. This makes possible a self-sustaining nuclear chain reaction that releases energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon.
Fission
is a form of nuclear
transmutation because
the resulting fragments are not the same element as
the original atom. The two nuclei produced are most often of
comparable but slightly different sizes, typically with a mass ratio
of products of about 3 to 2, for common fissile isotopes. Most
fissions are binary fissions (producing two charged fragments), but
occasionally (2 to 4 times per 1000 events), three positively
charged fragments are produced, in a ternary
fission.
The smallest of these fragments in ternary processes ranges in size
from a proton to an argon nucleus.
14) Types of nuclear reactions. When the target nuclei are bombarded by particles, there are some general types of interactions.
Elastic Scattering. When no energy is transferred between the target nucleus and the incident particle, the process is known as 208Pb elastic scattering
208Pb (n, n) 208Pb, Q = 0.
Inelastic Scattering. When energy is transferred, the process is called inelastic scattering
40Ca (a, a') 40mCa,
where a and a' have different kinetic energies.
In cases when the incident particle is a complicated nuclide, it may also be left in excited state, 208Pb (12C, 12mC) 208mPb This process is called mutual excitation.
Capture Reactions. Both charged and neutral particles can be captured by nuclei. For example,
197Au (p, g) 198Hg. 238U (n, g) 239U.Neutron capture reactions are used to produce many radioactive nuclides.
Rearrangement Reactions. The absorption of a particle accompanied by the emission of one or more particles is called a rearrangement reaction. 197Au (p, d) 196mAu, 4He (a, p) 7Li, 27Al (a, n) 30P, 54Fe (a, d) 58Co, 54Fe (a, 2 n) 56Ni, 54Fe (32S, 28Si) 58Ni. Various rearrangement reactions change the number of neutrons and the number of protons of the target nuclide. Fission Reactions. Typical and well-known neutron-induced fission reactions are: 235U (n, 3 n) fission products 239Pu (n, 3 n) fission product. These reactions release energy. The released neutrons induce further reactions, causing contineous chain reactions.Fusion Reactions. The fusion reaction of deuterium and tritium is particularly interesting because of its potential of providing energy for the future. T (d, n) He
23) Nuclear reactor as a source of neutrino. A neutrino is an electrically neutral, weakly interacting elementary subatomic particle with half-integer spin. The is denoted by the Greek letter ν (nu). All evidence suggests that neutrinos have mass but that their mass is tiny even by the standards of subatomic particles. Their mass has never been measured accurately. Nuclear reactors are the major source of human-generated neutrinos. Antineutrinos are made in the beta-decay of neutron-rich daughter fragments in the fission process. Generally, the four main isotopes contributing to the antineutrino flux are 235U, 238U, 239Pu and 241Pu. The average nuclear fission releases about 200 MeV of energy, of which roughly 4.5% (or about 9 MeV) is radiated away as antineutrinos. For a typical nuclear reactor with a thermal power of 4,000 MW, meaning that the core produces this much heat, and an electrical power generation of 1,300 MW, the total power production from fissioning atoms is actually 4,185 MW, of which 185 MW is radiated away as antineutrino radiation and never appears in the engineering. This is to say, 185 MW of fission energy is lost from this reactor and does not appear as heat available to run turbines, since the antineutrinos penetrate all building materials essentially without any trace, and disappear. The antineutrino energy spectrum depends on the degree to which the fuel is burned (plutonium-239 fission antineutrinos on average have slightly more energy than those from uranium-235 fission), but in general, the detectable antineutrinos from fission have a peak energy between about 3.5 and 4 MeV, with a maximum energy of about 10 MeV. There is no established experimental method to measure the flux of low energy antineutrinos. Only antineutrinos with an energy above threshold of 1.8 MeV can be uniquely identified. An estimated 3% of all antineutrinos from a nuclear reactor carry an energy above this threshold. Thus, an average nuclear power plant may generate over 1020 antineutrinos per second above this threshold, but also a much larger number (97%/3% = ~30 times this number) below the energy threshold, which cannot be seen with present detector technology.