May 17, 2009
What is ionizing radiation ?
What are the types and sources of ionizing
1: European Space Agency
Atoms and molecules (such as those making up the cells in your body)
exist normally in the neutral or uncharged state, the number of positive
protons in the nucleus balancing the number of negative orbiting electrons
outside the nucleus. If an electron is lost (due to being struck by an
energetic particle) the resulting atom/molecule is called an ion and its
properties are greatly changed. The particles that can cause this type of
event are called Ionizing Radiation Not only does the ion now appear
from a distance as a charged particle, the missing electron causes profound
changes in the way the molecule bonds or interacts with other molecules.
For this reason, radiations which lack sufficient energy to ionize common
molecules (referred to as non-ionizing radiation ) are of much less concern
than those higher energy particles which can easily ionize and break
chemical bonds. A typical high energy particle of radiation found
in the space environment is ionized itself and as it passes through
material such as human tissue it disrupts the electronic clouds of
the constituent molecules and leaves a path of ionization in its
wake. These particles are either singly charged protons or more
highly charged nucleii called "HZE" particles. (Z is the symbol for
nuclear charge and the disruption caused is proportional to Z squared.
Thus a particle with High Z and High Energy is called HZE. )
2: Questions & Answers About Irradiation, a technology for protecting our food supply, Minn. Dept. of Health.
The radiation used for product and food irradiation is known as
ionizing radiation. Radiation is all around us, part of what is
known as the electromagnetic spectrum. This spectrum includes radio
waves, heat in the form of infrared radiation, microwaves and even
the light that allows us to see the world around us. Ultraviolet rays,
x-rays and even gamma radiation are all a part of this
Radio waves have very long wavelengths, low frequency and hence,
low energy. Microwaves have higher energy, and x-rays and gamma rays
have the highest.
When an atom, the fundamental building block of all matter,
is irradiated by higher wavelength forms of energy, the atom is
changed by knocking an electron from it. The atom then becomes
an ion. This ion is not radioactive, but is different from the
If a very high energy wave - like that from a uranium or plutonium
source - hits an atom, enough energy is transferred to actually split
that atom, causing the it to become radioactive.
The sources of radiation allowed for food and product sterilization -
cobalt-60, cesium-137, accelerated electrons, and X-rays - cannot make
food radioactive because no atoms are split. But there is no question
that the irradiation process changes the atoms of the product being
All organisms are made up of atoms and molecules. The same irradiation
that knocks electrons out of atoms also fatally damages the cells of
organisms. That is how insects and bacteria are killed by irradiation.
A low dose of radiation inhibits the sprouting of potatoes,
delays the ripening of some fruits and vegetables, kills
insects in fruits and stored grains, and kills some parasites
in products of animal origin. Higher doses of radiation kills
pathogenic microbes responsible for foodborne illnesses.
3: E-BEAM Services, Inc.
Packaging Materials Issues
in Irradiation Processing of Foods
At this time, the most common commercial sources of ionizing radiation
are 60Co and 137Cs for gamma irradiation, and electron accelerators
for e-beam irradiation. When the electron beam generated by an
accelerator is directed at a target consisting of a high-atomic-number
metal, such as tungsten or gold, X-rays with a broad spectrum of energies
are produced. The amount of energy absorbed, also known as the dose,
is measured in units of kiloGrays (kGy), where 1 kGy is equal to
1,000 Joules per kilogram, or MegaRads (MR or Mrad), where 1 MR
is equal to 1,000,000 ergs per gram. With respect to food processing,
irradiation applications can be categorized by dose level effects
as follows: (1) low dose (up to 1 kGy): sprout inhibition of tubers,
ripening delay of fruits, insect de-infestation; (2) medium dose
(ca. 1-10 kGy): reduction of pathogenic and spoilage bacteria and
parasites; and (3) high dose (over 10 kGy): complete sterility.
Maximum doses approved for poultry and meat cold pasteurization
are 3 kGy and 7 kGy respectively. Foods currently irradiated to
high doses (e.g., 44 kGy min.) include those for use by astronauts during
space flight, and for consumption by hospital patients with severely
compromised immune systems.
While the ionizing radiation provided by e-beams is in the form
of electrons, in the case of X-rays and gamma rays, it is provided
by photons. The latter have no mass and are thus able to penetrate
deeper into materials. Electrons, on the other hand, have a small
mass, and are characterized by more limited penetration.
4: DOE Openness: Human Radiation Experiments:
Roadmap to the Project ACHRE Report
As its name implies, radioactivity is the act of emitting radiation
spontaneously. This is done by an atomic nucleus that, for some reason,
is unstable; it "wants" to give up some energy in order to shift to
a more stable configuration. During the first half of the twentieth
century, much of modern physics was devoted to exploring why this
happens, with the result that nuclear decay was fairly well
understood by 1960. Too many neutrons in a nucleus lead it to
emit a negative beta particle, which changes one of the neutrons
into a proton. Too many protons in a nucleus lead it to emit a
positron (positively charged electron), changing a proton into a
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