What is Radiation?
The emission of energy in the form of waves or particles
is considered radiation. Radiation waves are described by
their wavelength and frequency. These wavelengths and frequencies
span the entire electromagnetic spectrum. Some areas of the
electromagnetic spectrum are X-rays, gamma rays, ultraviolet
rays, visible rays, and infrared rays. To be continued…
What is Radioactive Decay?
Radioactive decay occurs when an unstable nucleus rearranges
its structure to achieve stability and emits particles or photons
in the process. Not all of these particles or photons come
from the nucleus. Some may originate in or between electron
shells as the electrons themselves are ejected from an atom
or as they drop into lower energy levels to fill the gaps left
by ejected or absorbed elections.
Because radioactive decay is a random process, we can say
only that there is a probability it will occur within a specified
interval. For a population of atoms of the same element and
mass number, this probability is called the decay constant,
lambda (λ). λ is equal
to the natural logarithm of 2 divided by the half-life.
Radioactive atoms decay in accordance with the
relationship:
N = Noe-λ * t where N=
number of atoms at time t, Noº=number of atoms at start (time t = 0), and e = base
of natural logarithms.
The decay constant λ is specific for the particular
radionuclide and has units of time-1: λ
= ln2 / T 1/2 where T 1/2 is
the half-life of the radionuclide.
The decay equation can also be used to describe the activity
(A) at any time (t) following the initial activity (Ao)
by the following relationship:
A = Aoe-λ * t
Revised: May 4, 2009 SF