Nuclear Fusion Reactions
and the formation of 'heavy elements'
At the extremely high
temperatures in the 'heart' of stars the atomic nuclei have such enormous speeds
and kinetic energies that on collision they can fuse together.
The extremely high energy is
needed to overcome the natural and massive repulsion of the two positive
The process by
which a heavier atomic nucleus is made from two smaller atomic nuclei is called fusion
and these changes also release enormous amounts of energy.
The smallest atom is hydrogen, this is converted to helium and gradually all the
other elements up to uranium must have been formed in stars like the Sun.
Attempts are being made by
nuclear scientists and engineers to build prototype nuclear fusion reactors
BUT the task of maintaining nuclear fusion is proving extremely difficult.
You have to maintain an extremely high temperature and confine and control
the plasma of hydrogen atoms. So far, fusion has only been created for a
fraction of a second?
Examples of fusion nuclear equations
(get the balancing?) ....
(initially a heavier isotope of hydrogen is formed and a positron)
(the most abundant helium isotope found today)
helium nuclei fuse to form lithium,
then from carbon to oxygen etc.
and lots of alternative fusions like
gradually building up elements with increasing atomic and mass numbers, and
finally the massive isotope of uranium, the biggest 'naturally' occurring
(a), (b) and
(f) are believed to be the main initial energy releasing fusion nuclear reactions in the Sun,
they happen quite nicely at 15000000oC!
On 'Earth' super-heavy' elements
are being made in nuclear reactors by bombarding elements like uranium (atomic
number 92) with lighter particles (described below).
The production of Trans-Uranium Elements
Heavy atomic nuclei tend
to be naturally unstable and for example, many long lived isotopes of uranium
(U92) finally decay via a series of relatively short-lived radioisotopes to
produce stable isotopes of lead (82Pb).
No element higher than
uranium (92U) is found in nature except for traces of neptunium (93Np)
and plutonium (94Pu) isotopes. These are found in uranium ores
but are produced by neutron-uranium collisions rather than from the Earth's
origin. The neutrons come
from the spontaneous fission of the unstable
uranium isotope 235U and
gives rise to heavy element 'synthesis' sequence.
Even heavier or
'trans-uranium' elements can be made by
bombarding a heavy atomic nucleus with a smaller ionised atom particle, in an ion
However many of the
heaviest are only produced in minute quantities as little as a few
hundred atoms in accelerator collisions.
In an accelerator the two
atoms are ionised and accelerated in powerful electromagnetic fields to very high speeds eg close to speed
of light, but in opposite directions and are then allowed to collide. The high kinetic
energies are needed to overcome the repulsion of the two positive
See examples 1. to 3. below.
The heavier elements are also
made by neutron bombardment in a nuclear reactor.
So, from these two methods, a
whole series of man-made or 'artificial' elements from atomic number
93 to 112 have been synthesised.
Where they are formed in nuclear
reactors from neutron collision (e.g. plutonium), they can be chemically separated in quantities ranging
from micrograms to kg in order study their physical and chemical properties.
Note again, the balancing of nuclear equations e.g.
formation of einsteinium from uranium and nitrogen nuclei
formation of californium from uranium and carbon
formation of lawrencium from californium and boron nuclei
formation of americium from plutonium and neutrons
multiple choice QUIZZES and WORKSHEETS
word-fills on radioactivity
puzzle on radioactivity
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