How is nuclear fission different from radioactive decay?

Answer 1

The basic difference is that in radioactive decay, an unstable isotope spontaneously undergoes a nuclear change. In nuclear fission, a fissionable isotope absorbs a neutron, becomes unstable, and then fissions by breaking into a couple of pieces and releasing one or more neutrons plus some energy. Nuclear fission is usually thought of as intentionally caused.

Note: It is possible for a fissionable isotope to spontaneously fission without capturing a neutron. This is not the usual mode of "breakdown" of the isotope, but it is possible in a small number of cases.

Links to the relevant Wikipedia articles are provided.

Answer 2

Some atomic nuclei are naturally unstable, and they will spontaneously "change" in various ways according to the type of nucleus is being inspected. The possibilities for decay include beta decay, alpha decay, and spontaneous fission. The two former ones see the nucleus kick out a particle and change its composition. In the latter, the nucleus just "splits" approximately in two, releasing neutrons. Separate questions here already speak to these processes, and they are linked below.

Answer 3

Radioactive decay happens to the unstable atom nuclei in its efforts striving to reach stability. The nucleus of any element atom should have specific neutron/proton ratio to be a stable nucleus. Also, the absolute number of protons should not exceed certain limit.

For a nucleus with neutron/proton different than the stability ratio, radioactive decay occurs to reach the stability ratio. For a nucleus with the absolute number of protons exceeding a certain limit, the nucleus may reach stability by radioactive decay and/or fission of the nucleus into two or more smaller nuclei with emission of one or more neutrons (as the spontaneous fission of one of the plutonium isotopes) and gamma electromagnetic radiation.

For more details:

For a nucleus with neutron/proton is higher than the stability ratio, two types of radioactive decay may occur to decrease the ratio in the nucleus in order to reach stability:

• radioactive beta decay: in which a neutron transforms into proton plus electron where the proton remains in the nucleus and the electron is emitted from the nucleus as beta radiation

• radioactive neutron decay: in which a neutron is emitted from the nucleus as neutron radiation (this transformation is relatively rare. Example of this transformation is the unstable Krypton-87)

For a nucleus with neutron/proton is lower than the stability ratio, two types of radioactive decay may occur to increase the ratio in the nucleus in order to reach stability:

• radioactive proton decay: in which a proton in the nucleus transforms into neutron plus positron where the neutron remains in the nucleus and the positron is emitted from the nucleus as positive beta radiation

• proton attraction of one electron from the nearest orbit to the nucleus to form neutron that remains in the nucleus.

For an unstable nucleus with number of protons exceeding the stability limit, the nucleus may reach stability with one or more of the above four nuclear transformations or by:

• fission of the nucleus into two or more smaller nuclei with emission of one or more neutrons (as the spontaneous fission of one of the plutonium isotopes).

Answer 4

There are a number of different types of radioactive decay, and nuclear fission is one of them. Others include alpha decay and beta decay.