Nucleon pair breaking in fission
Encyclopedia
Nucleon pair breaking in fission has been an important topic in nuclear physics
for decades.
The most measured quantities in research on nuclear fission
are the charge and mass fragments yields for uranium 235 and other transuranics. In this sense, experimental results on charge distribution for low energy fission of actinides present a preference to even Z fragment, which is called odd-even effect on charge yield.
The importance of these distributions is because they are the result of rearrangement of nucleons on the fission process due to the interplay between collective variables and individual particle levels; therefore they permit to understand several aspects of dynamics of fission process. The process from saddle (when nucleus begins its irreversible evolution to fragmentation) to scission point (when fragments are formed and nuclear interaction between fragments dispels), fissioning system shape changes but also promote nucleons to excited particle levels.
Because, for even Z (proton number) and even N (neutron number
) nuclei, there is a gap from ground state to first excited particle state -which is reached by nucleon pair breaking-, fragments with even Z is expected to have a higher probability to be produced than those with odd Z.
The preference even Z even N divisions is interpreted as the preservation of superfluidity during the descent from saddle to scission. The absence of odd-even effect means that process is rather viscous.
Contrary to observed for charge distributions no odd-even effect on fragments mass number
(A) is observed. This result is interpreted by the hypothesis that in fission process always there will be nucleon pair breaking, which may be proton pair o neutron pair breaking in low energy fission of uranium
234, uranium 236, and plutonium 240 studied by Modesto Montoya
.
Nuclear physics
Nuclear physics is the field of physics that studies the building blocks and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those...
for decades.
The most measured quantities in research on nuclear 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...
are the charge and mass fragments yields for uranium 235 and other transuranics. In this sense, experimental results on charge distribution for low energy fission of actinides present a preference to even Z fragment, which is called odd-even effect on charge yield.
The importance of these distributions is because they are the result of rearrangement of nucleons on the fission process due to the interplay between collective variables and individual particle levels; therefore they permit to understand several aspects of dynamics of fission process. The process from saddle (when nucleus begins its irreversible evolution to fragmentation) to scission point (when fragments are formed and nuclear interaction between fragments dispels), fissioning system shape changes but also promote nucleons to excited particle levels.
Because, for even Z (proton number) and even N (neutron number
Neutron number
The neutron number, symbol N, is the number of neutrons in a nuclide.Atomic number plus neutron number equals mass number: Z+N=A....
) nuclei, there is a gap from ground state to first excited particle state -which is reached by nucleon pair breaking-, fragments with even Z is expected to have a higher probability to be produced than those with odd Z.
The preference even Z even N divisions is interpreted as the preservation of superfluidity during the descent from saddle to scission. The absence of odd-even effect means that process is rather viscous.
Contrary to observed for charge distributions no odd-even effect on fragments mass number
Mass number
The mass number , also called atomic mass number or nucleon number, is the total number of protons and neutrons in an atomic nucleus. Because protons and neutrons both are baryons, the mass number A is identical with the baryon number B as of the nucleus as of the whole atom or ion...
(A) is observed. This result is interpreted by the hypothesis that in fission process always there will be nucleon pair breaking, which may be proton pair o neutron pair breaking in low energy fission of uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
234, uranium 236, and plutonium 240 studied by Modesto Montoya
Modesto Montoya
Modesto Montoya in Salpo Peru is a nuclear physicist at the Instituto Peruano de Energía Nuclear in Lima, Peru and member of the Peruvian National Academy of Sciences. He is past president of that institute, and past president of the Peruvian Physical Society.-Education:He holds a B.Sc., a Lic. a...
.