San José State University |
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applet-magic.comThayer WatkinsSilicon Valley & Tornado Alley USA |
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The Quantization of the Magnetic Momentsand Angular Momenta of Even-Even Nuclides |
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The magnetic moment of a nucleus is due to the spinning of its charges. One part comes from the net sum of the intrinsic spins of its nucleons. The other part is due to the rotation of the positively charged protons in the nuclear structure.

However nucleons form spin pairs with other nucleons of the same type but opposite spin. Therefore for an even p, even n nucleus there should be zero magnetic moment due to the intrinsic spins of its nucleons.

The magnetic moment of a nucleus μ due to the rotation of its charges is proportional to ωr²Q, where ω is the rotation rate of the nucleus, Q is its total charge and r is an average radius of the charges' orbits. The angular momentum L of a nucleus is equal to ωr²M, where M is the total mass of the nucleus. The average radii could be different but they would be correlated. Thus the magnetic moment of a nucleus could be computed by dividing its angular momentum by its mass and multiplying by it charge; i.e.,

where α is a constant of proportionality. Angular momentum may be quantized. This would make μ directly proportional to Q and inversely proportional to M. But Q and M can be expected to be approximately proportional to each other. That means that if L is quantized then μ is quantized. This means means that μ should approximately be a constant independent of the scale of the nucleus.

There would be a variation in μ with the neutron number n or proton number p because of their effects on the ratio (Q/M). The charge of a nucleus is proportional to its proton number. Its mass is roughly proportional to the sum its proton number and its neutron number; more precisely to (p+gn) where g is the ratio of the mass of a neutron to the mass of a proton.

The quantization of angular momentum can be tested by inverting the above formula to get angular momentum as a function of magnetic moment and the mass/charge ratio; i.e.,

L = βμ(p+gn)/p = βμ(1 + gn/p)

The relationship between (1 + gn/p) and p for the even-even nuclides is shown below:

The quantity μ(1 + gn/p) was computed for the 221 even-even nuclides and a frquency distribution tabulated. Here is that frequency distribution.

Angular momentum appears to be quantized. One peak dominates the distribution. There are secondary peaks but not necessarily at values which are multiples of the location of the principal peak.

Since the magnetic moment of a nuclide is given by

and (Q/M) as a function of p has the form

the plot of magnetic moment versus proton number would be expected to look like this

Here is the actual plot of the data

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