Oppenheimer-Phillips process
Encyclopedia
The Oppenheimer–Phillips process or strip reaction is a type of deuteron-induced nuclear reaction
. In this process the neutron
half of an energetic deuteron (a stable isotope
of hydrogen
with one proton
and one neutron) fuses with a target nucleus
, transmuting the target to a heavier isotope while ejecting a proton. An example is the nuclear transmutation
of carbon-12
to carbon-13
.
The process allows a nuclear interaction to take place at lower energies than would be expected from a simple calculation of the Coulomb barrier
between a deuteron and a target nucleus. This is because as the deuteron approaches the positively charged target nucleus, it experiences a charge polarization where the "proton-end" faces away from the target and the "neutron-end" faces towards the target. The fusion proceeds when the binding energy of the neutron and the target nucleus exceeds the binding energy of the deuteron and a proton is then repelled from the new heavier nucleus.
in 1935, considering experiments with the Berkeley cyclotron
showing that some elements became radioactive under deuteron bombardment.
, nominally, the "proton end". As the deuteron approaches the target nucleus, the positive charge is repelled by the electrostatic field until, assuming the incident energy is not sufficient for it to surmount the barrier, the "proton end" approaches to a minimum distance having climbed the Coulomb barrier as far as it can. If the "neutron end" is close enough for the strong nuclear force, which only operates over very short distances, to exceed the repulsive electrostatic force on the "proton end", fusion of a neutron with the target nucleus may begin. The reaction proceeds as follows:
In the O-P process, as the neutron fuses to the target nucleus, the deuteron binding force pulls the "proton end" closer than a naked proton could otherwise have approached on its own, increasing the potential energy
of the positive charge. As a neutron is captured, a proton is stripped from the complex and is ejected. The proton at this point is able to carry away more than the incident kinetic energy of the deuteron since it has approached the target nucleus more closely than what is possible for an isolated proton with the same incident energy. In such instances, the transmuted nucleus is left in an energy state as if it had fused with a neutron of negative kinetic energy
. There is an upper bound of how much energy the proton can be ejected with, set by the ground state
of the daughter nucleus.
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...
. In this process the 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...
half of an energetic deuteron (a stable isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
with one 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....
and one neutron) fuses with a target nucleus
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...
, transmuting the target to a heavier isotope while ejecting a proton. An example is the nuclear transmutation
Nuclear transmutation
Nuclear transmutation is the conversion of one chemical element or isotope into another. In other words, atoms of one element can be changed into atoms of other element by 'transmutation'...
of carbon-12
Carbon-12
Carbon-12 is the more abundant of the two stable isotopes of the element carbon, accounting for 98.89% of carbon; it contains 6 protons, 6 neutrons, and 6 electrons....
to carbon-13
Carbon-13
Carbon-13 is a natural, stable isotope of carbon and one of the environmental isotopes. It makes up about 1.1% of all natural carbon on Earth.- Detection by mass spectrometry :...
.
The process allows a nuclear interaction to take place at lower energies than would be expected from a simple calculation of the Coulomb barrier
Coulomb barrier
The Coulomb barrier, named after Coulomb's law, which is named after physicist Charles-Augustin de Coulomb , is the energy barrier due to electrostatic interaction that two nuclei need to overcome so they can get close enough to undergo a nuclear reaction...
between a deuteron and a target nucleus. This is because as the deuteron approaches the positively charged target nucleus, it experiences a charge polarization where the "proton-end" faces away from the target and the "neutron-end" faces towards the target. The fusion proceeds when the binding energy of the neutron and the target nucleus exceeds the binding energy of the deuteron and a proton is then repelled from the new heavier nucleus.
History
Explanation of this effect was published by J. Robert Oppenheimer and Melba PhillipsMelba Phillips
Melba Newell Phillips was an American physicist and science educator. She completed her doctoral studies under J. Robert Oppenheimer and was also known for refusing to testify before a U.S. Senate Judiciary Committee's subcommittee on internal security, her actions leading to her dismissal by...
in 1935, considering experiments with the Berkeley cyclotron
Cyclotron
In technology, a cyclotron is a type of particle accelerator. In physics, the cyclotron frequency or gyrofrequency is the frequency of a charged particle moving perpendicularly to the direction of a uniform magnetic field, i.e. a magnetic field of constant magnitude and direction...
showing that some elements became radioactive under deuteron bombardment.
Mechanism
During the O-P process, the deuteron's positive charge is spatially polarized, and collects preferentially at one end of the deuteron's density distributionProbability amplitude
In quantum mechanics, a probability amplitude is a complex number whose modulus squared represents a probability or probability density.For example, if the probability amplitude of a quantum state is \alpha, the probability of measuring that state is |\alpha|^2...
, nominally, the "proton end". As the deuteron approaches the target nucleus, the positive charge is repelled by the electrostatic field until, assuming the incident energy is not sufficient for it to surmount the barrier, the "proton end" approaches to a minimum distance having climbed the Coulomb barrier as far as it can. If the "neutron end" is close enough for the strong nuclear force, which only operates over very short distances, to exceed the repulsive electrostatic force on the "proton end", fusion of a neutron with the target nucleus may begin. The reaction proceeds as follows:
| → |
In the O-P process, as the neutron fuses to the target nucleus, the deuteron binding force pulls the "proton end" closer than a naked proton could otherwise have approached on its own, increasing the potential energy
Potential energy
In physics, potential energy is the energy stored in a body or in a system due to its position in a force field or due to its configuration. The SI unit of measure for energy and work is the Joule...
of the positive charge. As a neutron is captured, a proton is stripped from the complex and is ejected. The proton at this point is able to carry away more than the incident kinetic energy of the deuteron since it has approached the target nucleus more closely than what is possible for an isolated proton with the same incident energy. In such instances, the transmuted nucleus is left in an energy state as if it had fused with a neutron of negative kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
. There is an upper bound of how much energy the proton can be ejected with, set by the ground state
Ground state
The ground state of a quantum mechanical system is its lowest-energy state; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state...
of the daughter nucleus.