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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 fuses with a target nucleus, transmuting it to a heavier isotope, while the proton half is ejected. An example would be the nuclear transmutation of carbon-12 to carbon-13.

The process is considered important because the cross section for the interaction is enhanced over that expected from the Bohr model due to a polarization of the deuteron where the proton-end faces away from the incident nucleus and the neutron-end faces towards the incident nucleus during the most energetically favorable arrangement for the reaction.

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.

Mechanism

The Coulomb barrier sets the requisite energy which interacting atomic nuclei need to fuse. Since nuclei are always positively charged the electrostatic force is always repulsive. However, for neutrons, since they have no charge, there is no Coulomb barrier.

During the O-P process, the deuteron's positive charge is spatially polarized, as if at one end of a barbell, the proton end. As the deuteron approaches the target nucleus, it is repelled by the electrostatic field, converting kinetic energy to potential energy until, assuming the energy is not sufficient for it to surmount the barrier, the deuteron approaches to a minimum distance. Fusion proceeds when the unstable deuterated nucleus decays into daughter nuclei, normally a proton being one of the products.

As the neutron is drawn to the target nucleus, the binding force exerted by it pulls the proton closer than it would otherwise have approached on its own. If the neutron is captured, the proton is stripped from it and is ejected by the electrostatic field, and since it has half the mass of the deuteron, it can recoil with more than double the incident velocity, and may carry away more than the incident kinetic energy of the deuteron, leaving the transmuted nucleus in a state as if it had fused with a neutron of negative kinetic energy.

References

1. ^ Friendlander, 2008, p. 68-69
2. 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.
3. Blatt, 1991, pp. 508-509
4. 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. {{cite book}}: Check |isbn= value: invalid character (help)
• Gerhart Friedlander (1949). Introduction to Radiochemistry. John Wiley And Sons. ISBN 1443723096, 9781443723091. {{cite book}}: Check |isbn= value: invalid character (help)
• M. Blatt, John (1991). Theoretical Nuclear Physics (illustrated ed.). Courier Dover Publications. pp. 505–516. ISBN 0486668274, 9780486668277. {{cite book}}: Check |isbn= value: invalid character (help); Unknown parameter |coauthor= ignored (|author= suggested) (help)

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