Oppenheimer–Phillips process defeats Coulomb barrier
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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.[1]
History
Explanation of this effect was published by J. Robert Oppenheimer and
Melba Phillips in 1935, considering experiments with the Berkeley
cyclotron showing that some elements became radioactive under deuteron
bombardment.[2]
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 distribution, 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:
2D + AX -> 1H + A+1X
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.[1][3][4]
References
^ a b Friendlander, 2008, p. 68-69
^ Oppenheimer, 1995, page 192 cf. Note on the transmutation function
for deuterons, J. Robert Oppenheimer and Melba Phillips, Phys. Rev.
48, September 15, 1935, 500-502, received July 1, 1935.
^ Blatt, 1991, pp. 508-509
^ Blatt, 1991, pp. 508-509
J. Robert Oppenheimer (1995). Alice Kimball Smith, Charles Weiner. ed.
Robert Oppenheimer: Letters and Recollections (reimpressed,
illustrated ed.). Stanford University Press. ISBN 0804726205,
9780804726207. http://books.google.com/books?id=jwH4X5htJaYC&pg=PA192&lpg=PA192&dq=Oppenheimer%E2%80%93Phillips+process.
Gerhart Friedlander (1949). Introduction to Radiochemistry. John Wiley
And Sons. ISBN 1443723096, 9781443723091.
M. Blatt, John; Victor F. Weisskopf (1991). Theoretical Nuclear
Physics (illustrated ed.). Courier Dover Publications. pp. 505–516.
ISBN 0486668274, 9780486668277.
http://books.google.com/books?id=R3BzWYQqNGsC&pg=PA505&dq=Oppenheimer%E2%80%93Phillips+process&as_brr=3&hl=es.
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%E2%80%93Phillips_process"