Changes

As stated above, an alpha particle is the nucleus of a Helium atom, i.e., two protons and two neutrons. This arrangement means the alpha particle has a charge of +2, and an atomic mass of 4, the symbol for which is <math>{{}_2^4}He^{+2}</math>.

As stated above, an alpha particle is the nucleus of a Helium atom, i.e., two protons and two neutrons. This arrangement means the alpha particle has a charge of +2, and an atomic mass of 4, the symbol for which is <math>{{}_2^4}He^{+2}</math>.

For example, the most common [[isotope]] of Uranium is Uranium-238. Since all Uranium atoms have 92 protons, the remaining mass is composed of neutrons (238 - 92 = 146 neutrons). The neutron/proton ration is therefore 146 / 92 = 1.59. The initial step in Uranium-238 decaying (eventually) into Lead-206 is an alpha decay:

For example, the most common [[isotope]] of Uranium is Uranium-238. The [[mass number]]<ref>The mass number is the (integer) number of nucleons. It is very close to the [[atomic mass]] of the isotope measured in amu, because the masses of protons and neutrons are very close, and the deviations (due to [[E%3Dmc²]] are small. So the terms are often used nearly interchangeably.</ref>, 238, is the sum of the number of protons and the number of neutrons. Since all Uranium atoms have 92 protons, there are 146 neutrons. The initial step in Uranium-238 decaying (eventually) into Lead-206 is an alpha decay:

<center><math>{{}_{92}^{238}}U </math> &rarr; <math>{{}_2^4}He + {{}_{90}^{234}}Th</math></center>

<center><math>{{}_{92}^{238}}U </math> &rarr; <math>{{}_2^4}He + {{}_{90}^{234}}Th</math></center>

Note that the particle count is conserved, meaning on the left there are 92 protons, and on the right there are 2 + 90 = 92 protons as well. Likewise, the atomic masses are balanced, since on the left the total is 238, and on the right the total is 4 + 234 = 238.

Note that the proton count (92) is conserved, as is are the mass numbers (238). So the neutron count (146) is also balanced. No particles are created or destroyed.

However, from just this equation, it is difficult to understand how energy is balanced, too. Because this is a naturally occurring decay, we expect that the energy contained within the alpha particle and the Thorium atom will be <b>less than</b> the energy contained within the Uranium atom (because of the law of Entropy). So, where is that extra energy? We find the "missing" energy in the kinetic energies of the daughter products. This means that the alpha particle may be ejected from the original atom with significant speed (since kinetic energy is the energy of motion). The energy released by this decay is 4.3 MeV.

This decay releases about 4.3 MeV of kinetic energy, in the form of the motion of the alpha particle. In chemical terms we would say that this decay is an exothermic reaction. The energy comes from the potential nuclear energy of the Uranium atom&mdash;the Uranium atom has a higher potential energy (by 4.3 Mev) than the sum of the potential energies of the Thorium and Helium atoms. A careful accounting of the atomic masses (remember, atomic mass is only approximately equal to mass number) will show that mass was lost, in accordance with [[E%3Dmc²]].

==Beta Decay==

==Beta Decay==