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restricted to those radicals which do not form
parts of radical pairs.
Depending upon the core atom that pos-
R sesses the unpaired electron, the radicals can be
described as carbon-, oxygen-, nitrogen-, metal-
centered radicals. If the unpaired electron occu-
pies an orbital having considerable s or more or
P,
radiant (energy) flux, P, ) ) ) Although flux less pure p character, the respective radicals are
P,
is generally used in the sense of the “rate of trans- termed σ-or π-radicals.
fer of fluid, particles or energy across a given sur- In the past, the term “radical” was used to des-
face,” the radiant energy flux has been adopted ignate a substituent group bound to a molecular
by IUPAC as equivalent to radiant power, P . entity, as opposed to “free radical,” which now-
(P = ) = dQ/dt, simplified expression: P = adays is simply called radical. The bound entities
) = Q/t when the radiant energy, Q, is constant may be called groups or substituents, but should
over the time considered). In photochemistry, ) no longer be called radicals.
is reserved for quantum yield.
radioactive The property of a nuclide of
radiant exposure, H H H The irradiance, E
undergoing spontaneous nuclear transformations
integrated over the time of irradiation ( Edt,
with the emission of radiation.
simplified expression H = Et when the irradi-
ance is constant over the time considered). For a
parallel and perpendicularity, incident beam not radioactive decay Nuclear decay in which
scattered or reflected by the target or its surround- particles or electromagnetic radiation are emit-
ings, fluence (H ) is an equivalent term. ted or the nucleus undergoes spontaneous fission
0
or electron capture.
radiant power, P, ) ) ) Same as radiant
P,
P,
(energy) flux, ). Power emitted, transferred, or radioactivity The property of certain
received as radiation. nuclides of showing radioactive decay.
radiation A term embracing electromag- radiochemistry That part of chemistry
netic waves as well as fast moving particles. In which deals with radioactive materials. It
radioanalytical chemistry the term usually refers includes the production of radionuclides and
to radiation emitted during a nuclear process their compounds by processing irradiated mate-
(radioactive decay, nuclear reaction, nuclear fis- rials or naturally occurring radioactive materials,
sion, accelerators). the application of chemical techniques to nuclear
studies, and the application of radioactivity to
radical (free radical) A molecular entity
the investigation of chemical, biochemical, or
·
such as CH , SnH ,Cl possessing an unpaired biomedical problems.
˙
3
3
electron. (In these formulae the dot, symboliz-
ing the unpaired electron, should be placed so
radioluminescence Luminiscence arising
as to indicate the atom of highest spin density, if
from excitation by high energy particles or
this is possible.) Paramagnetic metal ions are not
radiation.
normally regarded as radicals. However, in the
“isolobal analogy” the similarity between certain
paramagnetic metal ions and radicals becomes radionuclide A nuclide that is radioactive.
apparent.
At least in the context of physical organic radius of gyration, s s s A parameter charac-
chemistry, it seems desirable to cease using the terizing the size of a particle of any shape.
adjective “free” in the general name of this type For a rigid particle consisting of mass ele-
of chemical species and molecular entity, so that ments of mass m , each located at a distance r
i i
the term “free radical” may in the future be from the center of mass, the radius of gyration s,

c

© 2003 by CRC Press LLC
© 2003 by CRC Press LLC