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. 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:

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=mc²]]) 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 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.

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.

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]].

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=mc²]].

==Beta Decay==

==Beta Decay==

==Antiquated notions==

==Antiquated notions==

In the early decades of the 20^th century, when it was a newly discovered phenomenon, there was much confusion about it, leading to some strange hypotheses.  No less an intellectual than [[H. G. Wells]] wrote strange things about it.  In his 1909 novel ''Tono-Bungay'', the narrator muses:

In the early decades of the 20th century, when it was a newly discovered phenomenon, there was much confusion about it, leading to some strange hypotheses.  No less an intellectual than [[H. G. Wells]] wrote strange things about it.  In his 1909 novel ''Tono-Bungay'', the narrator muses:

:To my mind radio-activity is a real disease of matter. Moreover, it is a contagious disease. It spreads. You bring those debased and crumbling atoms near others and those too presently catch the trick of swinging themselves out of coherent existence. It is in matter exactly what the decay of our old culture is in society, a loss of traditions and distinctions and assured reactions. ...I am haunted by a grotesque fancy of the ultimate eating away and dry-rotting and dispersal of all our world. So that while man still struggles and dreams his very substance will change and crumble from beneath him. I mention this here as a queer persistent fancy. Suppose, indeed, that is to be the end of our planet; no splendid climax and finale, no towering accumulation of achievements, but just—atomic decay!<ref>Wells, H. G. (1909) [http://www.gutenberg.org/files/718/718-h/718-h.htm Tono-Bungay], online Project Gutenberg text; search for text string "real disease"</ref>

:To my mind radio-activity is a real disease of matter. Moreover, it is a contagious disease. It spreads. You bring those debased and crumbling atoms near others and those too presently catch the trick of swinging themselves out of coherent existence. It is in matter exactly what the decay of our old culture is in society, a loss of traditions and distinctions and assured reactions. ...I am haunted by a grotesque fancy of the ultimate eating away and dry-rotting and dispersal of all our world. So that while man still struggles and dreams his very substance will change and crumble from beneath him. I mention this here as a queer persistent fancy. Suppose, indeed, that is to be the end of our planet; no splendid climax and finale, no towering accumulation of achievements, but just—atomic decay!<ref>Wells, H. G. (1909) [http://www.gutenberg.org/files/718/718-h/718-h.htm Tono-Bungay], online Project Gutenberg text; search for text string "real disease"</ref>