Thread: decay

why do heavy elements undergo radioactive decay?
under what conditions do lighter elements become unstable?

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You answered your first question with your second: their nuclei are unstable. Of course, it might take a particular atom a million years before it fissions, but nature is very patient.

A nucleus is either stable or unstable when it forms. A stable atom cannot change by itself. The unstable isotopes of the lighter elements are created by certain powerful external processes. For example, carbon-14 is formed in the upper atmosphere by the bombardment of nitrogen-14 by cosmic rays.

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Does this have to do with the negative binding energy of the nucleus? I'm admittedly unlearned in this area, but from what I've been exposed to I believe that once the number of (therefore the weight of) protons / neutrons starts to exceed the binding energy (as in heaver elements), or the particle falls into a lower energy state, the nucleus starts to shed particles. Lighter molecules usually aren't radioactive because they weigh much less than the binding energy, so their protons and neutrons stay tightly bound to the nucleus.

Please correct me if I'm way off center =)

Originally Posted by parag1973

why do heavy elements undergo radioactive decay?
under what conditions do lighter elements become unstable?

Large atoms in the earths atmosphere under the natural radiation present are not stable. That is why the real scientists stopped at element 86 and called the higher elements radio active isotopes. Because they were not able to purify them on earth. And no one will on earth, so close to the sun.

Just like the atomic clocks are effected by different velocity/radiation, large atoms are effected by the velocity of ambient radiation being slowed by the sun. It would require so much shielding, and such a cold environment that it probably would not be practical on earth.

Carbon 14 has large radio active atoms contaminating the carbon. Carbon seems to be an excellent substance to form radio active elements, in the presence of large radio active elements (radio active isotopes) and high heat. Through fusion.

I believe it used to be called carbon fusion chaining. It is amazing how fast it works. And how little source materials you need. I created one, one day, it is not pretty.

The graphite nuclear pile that Einstein built was an irresponsible device, that could have jeopardized the entire earth. It had no purpose. It was already totally understood.

Sincerely,


William McCormick

Atoms with an equal number of protons and neutrons in their nucleus are typically very stable. An overabundance of neutrons reduces the cohesion of the atom, so it can dissolve into smaller parts. Or neutrons can spontaneously decay into a proton, an electron and an antineutrino (beta decay), because the energy level of a neutron is higher than that of a proton. A neutron is also heavier for that reason. A large number of protons increases the repelling force because of a large number of positive electric charges. This makes an atom also unstable.

Lighter elements can be "activated" by irradiation with neutrons.

For those not reading the Physics threads: William McCormick's posts do not reflect the commonly accepted physical theories. So, caution is strongly advised here.