Ternary fission
Encyclopedia
Ternary fission is a comparatively rare (0.2 to 0.4% of events) type of nuclear fission
in which three charged products are produced rather than two. As in other nuclear fission processes, other uncharged particles such as multiple neutron
s and gamma ray
s are produced in ternary fission.
Ternary fission may happen during neutron-induced fission or in spontaneous fission
(the type of radioactive decay). About 25% more ternary fission happens in spontaneous fission compared to the same fissioning system formed after thermal neutron capture, illustrating that these processes remain physically slightly different, even after the absorption of the neutron, possibly because of the extra energy present in the nuclear reaction
system of thermal neutron-induced fission.
In anywhere from 2 to 4 fissions per 1000 in a nuclear reactor, the alternative ternary fission process produces three positively charged fragments (plus neutrons, which are not charged and not counted in this reckoning). The smallest of the charged products may range from so small a charge and mass as a single proton
(Z=1), up to as large a fragment as the nucleus of argon
(Z=18).
Although particles as large as argon nuclei may be produced as the smaller (third) charged product in the usual ternary fusion, the most common small fragments from ternary fission are helium-4 nuclei, which make up about 90% of the small fragment products. This high incidence is related to the stability (high binding energy) of the alpha particle
, which makes more energy available to the reaction. The second-most common particles produced in ternary fission are tritons (the nuclei of tritium
), which make up 7% of the total small fragments, and the third-most are helium-6 nuclei (which decay in about 0.8 seconds to lithium-6). Protons and larger nuclei are in the small fraction (< 2%) which make up the remainder of the small charged products. The two larger charged particles from ternary fission, particularly when alphas are produced, are quite similar in size distribution to those produced in binary fission.
, they are accordingly called "long range alphas" (referring to their longer range in air or other media).
The other two larger fragments carry away, in their kinetic energies, the remainder of the fission kinetic energy (typically totalling ~ 170 MeV in heavy element fission) that does not appear as the 10 to 20 MeV kinetic energy carried away by the third smaller product. Thus, the larger fragments in ternary fission are each less energetic, by a typical 5 to 10 MeV, than they are seen to be in binary fission.
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
in which three charged products are produced rather than two. As in other nuclear fission processes, other uncharged particles such as multiple neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s and gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s are produced in ternary fission.
Ternary fission may happen during neutron-induced fission or in spontaneous fission
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...
(the type of radioactive decay). About 25% more ternary fission happens in spontaneous fission compared to the same fissioning system formed after thermal neutron capture, illustrating that these processes remain physically slightly different, even after the absorption of the neutron, possibly because of the extra energy present in the nuclear reaction
Nuclear reaction
In nuclear physics and nuclear chemistry, a nuclear reaction is semantically considered to be the process in which two nuclei, or else a nucleus of an atom and a subatomic particle from outside the atom, collide to produce products different from the initial particles...
system of thermal neutron-induced fission.
Products
The most common nuclear fission process is "binary fission." It produces two charged asymmetrical fission products with maximally probable charged product at 95±15 and 135±15 u atomic mass. However, in this conventional fission of large nuclei, the binary process happens merely because it is the most energetically probable.In anywhere from 2 to 4 fissions per 1000 in a nuclear reactor, the alternative ternary fission process produces three positively charged fragments (plus neutrons, which are not charged and not counted in this reckoning). The smallest of the charged products may range from so small a charge and mass as a single proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
(Z=1), up to as large a fragment as the nucleus of argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
(Z=18).
Although particles as large as argon nuclei may be produced as the smaller (third) charged product in the usual ternary fusion, the most common small fragments from ternary fission are helium-4 nuclei, which make up about 90% of the small fragment products. This high incidence is related to the stability (high binding energy) of the alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...
, which makes more energy available to the reaction. The second-most common particles produced in ternary fission are tritons (the nuclei of tritium
Tritium
Tritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...
), which make up 7% of the total small fragments, and the third-most are helium-6 nuclei (which decay in about 0.8 seconds to lithium-6). Protons and larger nuclei are in the small fraction (< 2%) which make up the remainder of the small charged products. The two larger charged particles from ternary fission, particularly when alphas are produced, are quite similar in size distribution to those produced in binary fission.
Product energies
The energy of the third much-smaller product usually ranges between 10 and 20 MeV. In keeping with their origin, alpha particles produced by ternary fission typically have mean energies of about ~ 16 MeV (energies this great are never seen in alpha decay). Since these typically have significantly more energy than the ~ 5 MeV alpha particles from alpha decayAlpha decay
Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less...
, they are accordingly called "long range alphas" (referring to their longer range in air or other media).
The other two larger fragments carry away, in their kinetic energies, the remainder of the fission kinetic energy (typically totalling ~ 170 MeV in heavy element fission) that does not appear as the 10 to 20 MeV kinetic energy carried away by the third smaller product. Thus, the larger fragments in ternary fission are each less energetic, by a typical 5 to 10 MeV, than they are seen to be in binary fission.