San José State University
Thayer Watkins
Silicon Valley
& Tornado Alley

The Significance of the Nonexistence of
Neutron and Proton Spin Pairs Outside of Nuclei


When a neutron and proton come together to form a deuteron a gamma ray of 2.225 million electron volts of energy(MeV) is emitted. If deuterons are irradiated with gamma ray photons of at least 2.225 MeV energy some of those deuterons are broken apart into neutrons and protons. A deuteron is a spin pair of a neutron and a proton and its constituent neutron and proton are also held together by what is usually called the nuclear strong force. This is not a good name for the force because it is not as strong as the forces associated with spin pair formation. A better name would be nucleonic force; i.e., the force between nucleons. In this material it will be called the nuclear strong force.

Two neutrons also form a spin pair but only within a nucleus. Likewise two protons also form a spin pair but only within a nucleus. We know no such spin pairs are formed outside of nuclei because there is no gamma rays emitted with energies comparable to the 2.225 MeV photons emitted in the formation of deuterons.

The conventional view is that neuterons and protons are attracted to each other equally through the strong force. Werner Heisenberg after the neutron was discovered in the 1930's asserted that perhaps the neutron and the proton were the same particle but differing only in that the electrostatic charge was turned on in the case of the proton. This made it plausible that a neutron and proton would behave identically with respect to the nuclear strong force. Heisenberg's speculation proved to be untrue, but the perception of the neutron and proton being the same with respect to the nuclear strong force.

The neutron is electrically neutral but it has a charge distribution. There is positive electrical charge in the interior of the neutron which is counter balanced by a negative charge toward the surface. The proton's charge distribution is all positive.

Two protons coming close together have positive charge confronting positive charge. There would be repulsion. Likewise two neutrons coming close together would involve negative charge confronting negative charge and hence there would be repulsion. On the other hand, a neutron coming close to a proton would have negative charge confronting positive charge and there would be an attraction. This is a plausible explanation of why neutron-proton pairs are formed and neutron-neutron or proton-proton pairs are not formed. However the problem with this argument is that it would equally apply in the interior of a nucleus.

The Forces Between Like and Unlike Nucleons

Elsewhere it is demonstrated that the binding energy data for nuclei implies that like nucleons repel each other and unlike nucleons are attracted to each other.

Below is depicted the energy level of pairs of nucleons as a function of their separation distance.


The spin pair formation is depicted as a potential well effective only up to a limited distance, say s0. It does not matter that the magnitude of the effect of the spin pair formation is many times larger than the force which is an inverse function of distance. The repelling force prevents the like nucleons from getting close enough to where the spin pair formation is possible. On the other hand, if a spin pair of like nucleons were formed the repelling force would drive the separation out to s0 where disturbances could break up the pair. In contrast for unlike nucleons the attracting force propels the nucleons together to where the spin pair formation is possible. There is no tendency to drive the separation distance out to the limit for the spin pair formation. Thus spin pairs of unlike nucleons form and spin pairs of like nucleons do not.

The spin pairs of like nucleons that exist in nuclei are there as a result of the conditions that existed at the time of the Big Bang. The high densities and high pressures that existed at the time forced the creation of nuclei that could not be created otherwise. Spin pairs of like nucleons within nuclei are prevented from coming apart by being part of the nuclear structure.

HOME PAGE OF applet-magic