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!
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