Lesson 5 Transmutation, Nuclear Fission and Nuclear Fusion

Nuclear Transmutation

is the result from the bombardment of nuclei by neutrons, protons, or other nuclei.

Natural Transmutation

by stellar nucleosynthesis in the past created most of the heavier chemical elements in the known existing universe, and continues to take place to this day, creating the vast majority of the most common elements in the universe, including He, O and C.

Natural Transmutation occurs

certain radioactive elements present in nature spontaneously decay by a process that causes transmutation, such as alpha or beta decay.

Artificial transmutation

when stable nuclei is bombarded with a particle and forced to become unstable and result in transmutation.
-It may occur in machinery that has enough energy to cause changes in the nuclear structure of the elements. Such machines include particle accelerators.

Particle accelerators

made it possible to synthesize the socalled transuranium elements (elements with atomic numbers greater than 92). It uses electric and magnetic fields to increase the kinetic energy of charged species so that a reaction will occur.

Neptunim

was first prepared in 1940

Edwin Mattison McMillan and Philip Hauge Abelson

working at the University of California at Berkeley, exposed uranium oxide to neutrons from cyclotron target, Since then, 23 other transuranium elements have been synthesized. All isotopes of these elements are radioactive.

Nuclear fission

is the process in which a heavy nucleus (mass number > 200) divides to form smaller nuclei of intermediate mass and one or more neutrons.
-atoms are split apart, which releases energy
-a neutron collides with a uranium atom and splits it, releasing a large amount of energy in the form of heat and radiation.
-This process releases a large amount of energy because the heavy nucleus is less stable than its products.

Uranium-235

The first nuclear fission reaction to be studied was______ bombarded with slow neutrons, whose speed is comparable to that of air molecules at room temperature.

Nuclear chain reaction

is a self-sustaining sequence of nuclear fission reactions. The neutrons generated during the initial stages of fission can induce fission in other uranium235 nuclei, which in turn produce more neutrons, and so on. In less than a second, the reaction can become uncontrollable, liberating a tremendous amount of heat to the surroundings.

Nuclear Reactor

number of fissionable nuclei available is carefully controlled to prevent a “runaway” chain reaction.

Atomic Bomb

a very rapid growth in the number of fissions is sought.

Uranium 235 and Plutonium 239

Fission weapons are normally made with materials having high concentrations of the fissile isotopes :

Nuclear Fusion

the combining of small nuclei into larger ones, is largely exempt from the waste disposal problem.
- occurs constantly in the sun.

Nuclear fusion advantages

The fuels are cheap and almost inexhaustible and the process produces little radioactive waste.