Changes

*the strong force

*the strong force

The electric and magnetic forces were once considered to be separate, but they were unified so straightforwardly in the late 19^th century that they are no longer treated as separate.  The electromagnetic and weak forces were unified in the late 1960's, into the "electroweak force", but that connection is sufficiently esoteric that it has not supplanted the separate electromagnetic and weak forces.  There are "grand unified theories" unifying the last three of these forces, and the physics community continues to search for a "theory of everything" that brings gravity into the picture. For all practical purposes, the four forces listed above are generally considered the fundamental forces.

The electric and magnetic forces were once considered to be separate, but they were unified so straightforwardly in the late 19th century that they are no longer treated as separate.  The electromagnetic and weak forces were unified in the late 1960s, into the "electroweak force", but that connection is sufficiently esoteric that it has not supplanted the separate electromagnetic and weak forces.  There are "grand unified theories" unifying the last three of these forces, and the physics community continues to search for a "theory of everything" that brings gravity into the picture. For all practical purposes, the four forces listed above are generally considered the fundamental forces.

The first two of these forces are well known without specialized knowledge of nuclear physics, mostly because they operate at macroscopic distances.  The last two only operate at microscopic distances (about 10^-15 meters, or the diameter of a proton), so they are limited to subatomic particles.

The first two of these forces are well known without specialized knowledge of nuclear physics, mostly because they operate at macroscopic distances.  The last two only operate at microscopic distances (about 10⁻¹⁵ meters, or the diameter of a proton), so they are limited to subatomic particles.

*Q: Why are they called "forces"?  What is doing the pushing?

*Q: Why are they called "forces"?  What is doing the pushing?

When dealing with beta transformations, one needs to take note of various conservation laws.  (For alpha and gamma transformations, particles don't change, so these issues don't come up.)

When dealing with beta transformations, one needs to take note of various conservation laws.  (For alpha and gamma transformations, particles don't change, so these issues don't come up.)

*Charge - this is the electric charge.  So a neutron, with zero charge, can decay into a proton (+1), and electron (-1), and a neutrino (zero).

*Charge - this is the electric charge.  So a neutron, with zero charge, can decay into a proton (+1), and electron (-1), and a neutrino (zero).

*Baryon number - Baryons are "big" nucleons.  For our purposes, they are protons and neutrons.  They can't just go away.  Nor can the transform into their antiparticles.  (A proton and antiproton annihilating each other would satisfy this, since the baryon numbers are +1 and -1, but that transformation is beyond the scope of this article.)

*Baryon number - Baryons are "big" nucleons.  For our purposes, they are protons and neutrons.  They can't just go away.  Nor can they transform into their antiparticles.  (A proton and antiproton annihilating each other would satisfy this, since the baryon numbers are +1 and -1, but that transformation is beyond the scope of this article.)

*Lepton number.  The lepton numbers can be thought of as "electron-ness", "mu-ness", and "tau-ness".  Electrons and positrons have electron-ness of +1 and -1 respectively (and zero for the other two).  Here is where the neutrinos come into play.  An electron neutrino has an electron-ness of +1, while and anti-neutrino has -1.  That's why the neutron-to-proton-and-electron transformation needs to create the antineutrino to carry off the -1, compensating for the +1 of the electron.

*Lepton number.  The lepton numbers can be thought of as "electron-ness", "mu-ness", and "tau-ness".  Electrons and positrons have electron-ness of +1 and -1 respectively (and zero for the other two).  Here is where the neutrinos come into play.  An electron neutrino has an electron-ness of +1, while and anti-neutrino has -1.  That's why the neutron-to-proton-and-electron transformation needs to create the antineutrino to carry off the -1, compensating for the +1 of the electron.

==Given that something can happen, how often does it happen?==

==Given that something can happen, how often does it happen?==

The probability, per unit time, of a beta transformation happening, varies enormously, and determines the substance's half-life.  This probability is determined by how "close" the particles get to each other.  They must be extremely close—the weak force is weak, and only acts over a distance of about the size of a nucleon, or 10^-15 meter.  This distance is measured in terms of the size of the [[quantum mechanics|quantum mechanical wave function]].  It can actually be quite large (compared with the size of a nucleon) in electron capture, because electrons typically have a rather dispersed wave function.

The probability, per unit time, of a beta transformation happening, varies enormously, and determines the substance's half-life.  This probability is determined by how "close" the particles get to each other.  They must be extremely close—the weak force is weak, and only acts over a distance of about the size of a nucleon, or 10⁻¹⁵ meter.  This distance is measured in terms of the size of the [[quantum mechanics|quantum mechanical wave function]].  It can actually be quite large (compared with the size of a nucleon) in electron capture, because electrons typically have a rather dispersed wave function.

*Q: How about neutron decay?  How can the closeness of approach be theorized for a single particle?

*Q: How about neutron decay?  How can the closeness of approach be theorized for a single particle?

*A: In such cases it is necessary to consider the more esoteric theory involving quarks, that this article is ignoring for the most part.  In the diagram above, two quarks collided within the neutron, initiating the decay.  One can think of larger particles like neutron as having quarks rattling around inside, ready to collide.

*A: In such cases it is necessary to consider the more esoteric theory involving quarks, that this article is ignoring for the most part.  In the diagram above, two quarks collided within the neutron, initiating the decay.  One can think of larger particles like neutrons as having quarks rattling around inside, ready to collide.

==Half-life==

==Half-life==

Now consider the hypothetical beta-plus decay of Argon-37 to Chlorine-37.  This Argon atom has 18 protons and 19 neutrons, and a nuclear mass of 36.9569019 amu.  The Chlorine atom has 17 protons and 20 neutrons, and a nuclear mass of 36.9565767 amu.  The beta-plus particle (positron) ejected by the nucleus weighs .00054858 amu.  There would be an overall mass ''increase'' of .00022343 amu.  This decay cannot happen.

Now consider the hypothetical beta-plus decay of Argon-37 to Chlorine-37.  This Argon atom has 18 protons and 19 neutrons, and a nuclear mass of 36.9569019 amu.  The Chlorine atom has 17 protons and 20 neutrons, and a nuclear mass of 36.9565767 amu.  The beta-plus particle (positron) ejected by the nucleus weighs .00054858 amu.  There would be an overall mass ''increase'' of .00022343 amu.  This decay cannot happen.

But suppose that, instead of releasing an electron and positron, the excess electron from the atom's electron cloud simply went down into the nucleus.  The nuclear transformation would be:

But suppose that, instead of releasing a positron, the excess electron from the atom's electron cloud simply went down into the nucleus.  The nuclear transformation would be:

:<math>\begin{align}

:<math>\begin{align}

p + \beta^- &\to n + \nu_e

p + \beta^- &\to n + \nu_e

\end{align}</math>

\end{align}</math>

This would release .0008737 amu of mass.  It is an electron capture event.  This decay occurs with a half-life of 35 days.

This would release .0008737 amu of mass.  It is an electron capture event.  This decay occurs with a half-life of 35 days.

*Q: If neutrons weigh more than protons, why does a beta-plus event that turns a neutron into a proton ''increase'' the mass, and hence the energy?

*Q: If neutrons weigh more than protons, why does a beta-minus event that turns a neutron into a proton sometimes ''increase'' the mass, and hence the energy?

*A: There is a contribution to the nuclear mass from the electric repulsion force of the protons.  Adding a proton increases that repulsion.  This, by the way, is why elements other than the very lightest have more neutrons than protons.

*A: There is a contribution to the nuclear mass from the electric repulsion force of the protons.  Adding a proton increases that repulsion.  This, by the way, is why elements other than the very lightest have more neutrons than protons.

==The curious case of Beryllium-7==

==The curious case of Beryllium-7==

==References==

==References==