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How can you cause fission to common molecular structures or is it only possible with plutonium?
Question Date: 2015-11-26
Answer 1:

An excellent question!

The answer is a quite a bit complicated and is part of an entire area of study known as nuclear engineering.

The short answer is it is possible for other substances other than plutonium to undergo fission. Other elements (or compounds containing these elements) such as technetium (Tc), polonium (Po), and even carbon (C) also can undergo fission. The question is how long does it take (i.e., what is its half-life ) and is it energetically favorable to do so.

You probably know that all of matter is composed of atoms, and at the center of the atoms is the nucleus, composed of protons and neutrons. What is interesting is that if you sum the number of protons and neutrons using the mass of individual protons, electrons, and neutrons, it is not the same mass listed on the periodic table.

For example in atomic mass units (u), carbon-12 has 6 protons (m_proton = 1.007276 u), 6 electrons (m_electron = 0.00054858 u) and 6 neutrons (m_neutron = 1.008664 u) but the mass of a carbon atom is 12.000 u. That's a difference of 0.098931 u! Where did that mass go? Answer: It went into the binding energy needed to hold all those protons and neutrons together.

This is possible due to the mass-energy equivalence that Einstein famously showed (E = mc2). This binding energy is important for determining the stability of a substance to fission.

Fission can occur as either natural radioactive decay or in a nuclear reaction (e.g., in a nuclear power plant), and is basically when a large nucleus splits into multiple smaller nuclei and releases energy. Fission tends to occur in heavier elements because those heavier elements can achieve a greater binding energy per nucleon (nucleon = proton or neutron) by splitting into smaller nuclei.

The classic diagram for this is the binding energy . Iron (Fe) turns out to be the most stable (i.e., highest binding energy), and so many fission reactions will involve a decay to iron or elements of similar binding energies.

A very common form of fission is the radioactive decay of carbon-14 (an isotope of carbon-12). This is known as radiocarbon dating and its most well-known use is in archeology for determining the age of organic materials. The basic idea is that there is a certain proportion of all organic matter that contains carbon-14. The rate at which radioactive decay occurs is measured by the half-life (around 5730 years), which is a fixed property of the material. Knowing the half-life and how much carbon-14 you have left, you can estimate the how old something is.

How do you know if something will undergo fission? This is actually a difficult question to answer and is something people are still uncertain today! Nuclear scientists have thought of various schemes to try and predict, but we don't have a complete understanding or way of predicting. For example, there is a model called the semi-empirical mass formula that attempts to predict how stable a nucleus of a certain number of protons and neutrons is. It is based on parameters like if the protons are arranged to be really close together and how big the nucleus is. However, there are these magic numbers (quite literally the name) of protons and neutrons that are stable when predicted to be not, and at the moment, we don't have a good explanation why.

Hope this helps!

Answer 2:

There are other isotopes apart from plutonium (in particular, uranium-235) that are capable of fission, but most atomic nuclei simply aren't capable of it. Molecular structures cannot fission in any case; it's a nuclear phenomenon.

Answer 3:

Fission is the process of an atom (note: not a molecule, but just a single atom) splitting into smaller parts. It's a nuclear reaction, meaning that the process splits the nucleus of the atom into lighter nuclei.

Only some atoms are capable of undergoing fission. Mostly these atoms are isotopes in the actinide series on the periodic table (atomic number 89-103). An isotope is an atom with a different number of neutrons than protons. As you mentioned, a few of the plutonium isotopes are fissile (capable of undergoing fission) including 239 and 241. Other important and useful fissile isotopes are uranium 235 and 233. These plutonium and uranium isotopes are the ones used for nuclear fuels for electricity production.

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