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May 17, 2009

What is ionizing radiation ?
What are the types and sources of ionizing radiation ?

4 References
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 
electromagnetic spectrum. 
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 
original atom. 
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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