Download RADIOACTIVITY involves the emission of energy and particles from

Nuclear Chemistry
• Nuclear chemistry is the study of the properties and reactions of
atomic nuclei.
• Radioactivity- the spontaneous emission of radiation from a
nucleus.
• Every element in the periodic table has at least one radioactive
isotope, or radioisotope.
• Radioactivity is the result of atoms having unstable nuclei.
 Radiation is emitted when an unstable radioactive nucleus, or
radionuclide spontaneously changes into a more stable one.
 The stability of an atom’s nucleus depends on the number and
type of nuclear particles, called nucleons (nucleon is a general
term for both protons and neutrons).
Main Types of Radiation
Ionizing Radiation
• High energy radiation of all kinds is often grouped together under the name
IONIZING RADIATION. This include not only alpha particles, beta
particles and gamma rays, but also X-rays and cosmic rays. X-rays are like
gamma rays. They have no mass and consist of high energy electromagnetic
radiation, however, the energy of X-rays are less than that of gamma rays.
Cosmic rays are not rays, but a mixture of high energy particles that shower
the Earth from outer space. They consist primarily of protons, along with
some alpha and beta particles.
The interaction of any kind of ionizing radiation with a molecule knocks out an
electron, converting the atom or molecule into an extremely reactive ion (a
highly unstable radical). This reactive ion can react with other molecules nearby,
creating still other fragments that can in turn cause further reactions.
A small dose of ionizing radiation may not cause visible symptoms, but
can be dangerous if it strikes a cell nucleus and damages the genetic
machinery inside.
The resultant changes might lead to a genetic mutation, to cancer, or to
cell death.
The nuclei of rapidly dividing cells, such as those in bone marrow, the
lymph system, the lining of the intestinal tract, or an embryo, are the most
rapidly damaged.
It is because of the susceptibility of rapidly dividing cells to radiation
effects that ionizing radiation is able to selectively destroy cancer cells.
Half-Life
•
The rate of radioactive decay varies greatly from one
radioisotope to another. Some radioisotopes such as uranium235 decay slowly over billions of years, while others, such as
carbon-17, decay within thousandths of a second.
• Rates of nuclear decay are measured in units of half-life (t1/2),
defined as the amount of time required for one half of the
radioactive sample to decay.
Fraction of original sample remaining = (1/2)n
where n = the number of half-lives.