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Line 39: + + + + + + + + + + + − Antiparticles.+ + + + + − Backwards.+ + + − Conservation laws (lepton number, baryon number, charge)+ − Anything possible if energy is released.+
Preliminaries done. Now I can explain electron capture and the peculiarities of Beryllium-7.
*A: The term "force", applied to the gravitational and electromagnetic forces, is obviously reasonable. Also, the strong force could sort of be thought of as a force, making nucleons stick together. It takes a certain amount of mechanical pressure to pull nucleons out of a nucleus. But the weak "force" is hard to visualize as a force. Nevertheless, all four of these interactions are called "forces" for historical consistency.
*A: The term "force", applied to the gravitational and electromagnetic forces, is obviously reasonable. Also, the strong force could sort of be thought of as a force, making nucleons stick together. It takes a certain amount of mechanical pressure to pull nucleons out of a nucleus. But the weak "force" is hard to visualize as a force. Nevertheless, all four of these interactions are called "forces" for historical consistency.
== The common transformations==
The weak force acts on just abut every particle that exists—baryons (protons and neutrons), hadrons (various other things made of quarks), leptons (electrons, neutrinos, etc.), bosons, and so on. For example, the interaction shown in the above right corner shows weak interactions involving up and down quarks, a "weak vector boson", an electron, and an antineutrino. For all but extremely esoteric analysis of fundamental particle physics, hardly any of that matters. What's important is that a neutron turned into ("decayed into") a proton, and electron and an antineutrino. The various quarks, and the vector boson underwent beta transformations, but, in a simpler sense, we can just say that the neutron underwent a beta transformation. The interaction shown in the figure is the first of these:
The weak force acts on just abut every particle that exists—baryons (protons and neutrons), hadrons (various other things made of quarks), leptons (electrons, neutrinos, etc.), bosons, and so on. For example, the interaction shown in the above right corner shows weak interactions involving up and down quarks, a "weak vector boson", an electron, and an antineutrino. For all but extremely esoteric analysis of fundamental particle physics, hardly any of that matters. What's important is that a neutron turned into ("decayed into") a proton, and electron and an antineutrino. The various quarks, and the vector boson underwent beta transformations, but, in a simpler sense, we can just say that the neutron underwent a beta transformation. The interaction shown in the figure is the first of these:
:<math>\begin{align}
:<math>\begin{align}
The "e" subscript on the neutrino is still used, to distinguish electron-type neutrinos from muon-type and tau-type.
The "e" subscript on the neutrino is still used, to distinguish electron-type neutrinos from muon-type and tau-type.
== The reverse transformations ==
All physical processes are supposedly reversible in time, so that, for example, if an alpha particle is thrown at a <sup>222</sup>Rn<sub>86</sub> nucleus with just the right energy, it could undergo "reverse alpha decay", producing a <sup>226</sup>Ra<sub>88</sub> nucleus. Or an antineutrino could combine with and electron and a proton with just the right energy to produce a neutron:
:<math>\begin{align}
p + \beta^- + \bar\nu_e &\to n
\end{align}</math>
But this is a [[statistical impossibility]]—it would require that the particles be in exactly the right place and with exactly the right energy. It is in the same category as heat flowing uphill—a violation of the [[Second Law of Thermodynamics]].
==Antiparticles==
These transformations work on antiparticles also. Note that the electron ("beta-minus particle") and positron ("beta-plus particle") are antiparticles. So, in principle, we could have:
:<math>\begin{align}
\bar{n} &\to \bar{p} + \beta^+ + \nu_e
\end{align}</math>
==Conservation laws==
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).
*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.)
*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.
==What can happen==
With these preliminaries out of the way, the general rule can be stated:
:Any beta transformation will happen, with some probability, if the conservation laws are satisfied and the masses of the results add up to less than the masses of the original particle(s).
The mass of the neutron is 1.008664916 amu, that of the proton is 1.007276467 amu, and that of the electron is .000548579909070 amu. (The pass of the antineutrino is negligible.) The lost mass is .00083986909093, which is carried off in the kinetic energy of the result particles, in accordance with [[E=mc²]].
The reverse transformation, turning a proton into a neutron, positron, and neutrino, has a negative energy budget, so it does not occur.
==References==
==References==