Volume 8, Number 2
Apr 1984

Gamma

A search for information on gamma radiation in two encyclopedias has yielded the following information:

Definition

1) High-energy photons of wavelength shorter than 0.1 nm emitted from atomic nuclei during radioactive decay. Usually their emission follows the ejection of an electron (beta ray) from the nucleus. The most penetrating of the radioactive emissions, gamma rays find use in engineering quality control--as a source for exposing radiographs--and in radiation therapy. (Phaidon Concise Encyclopedia of Science and Technology, 1978)

2) Penetrating electromagnetic radiation of the same nature as an X-ray though usually of somewhat shorter wavelength, emitted spontaneously by some radioactive substances. (Encyclopedia Britannica, 1982)

Classically, radiant energy [electromagnetic radiation] is regarded as a wave motion.... At the beginning of the 20th century Planck proposed that certain properties of radiant energy were best explained by regarding it as transporting energy in discrete amounts called quanta. Einstein later proposed the name photon for the electromagnetic quantum. The energy of each photon is proportional to the frequency of the associated radiation. (Phaidon)

Sources

People constantly receive electromagnetic radiation in mixed form from a variety of sources. The most frequently mentioned kinds of radiation are alpha, beta, gamma and X-radiation. Beta radiation is a stream of beta particles (electrons or positrons) but gamma radiation is not associated with any atomic particle; the photon is only an energy packet. Anything can emit gamma rays whenever there is enough energy, according to an informant at the Columbia University Physics Library.

Cosmic radiation, radioactive isotopes in the soil, fallout from nuclear explosions, fallout from burning coal that contains radium, and medical radiation for diagnosis and treatment are the main sources of everyday radiation. Cosmic rays include a great variety of radiation, including genres radiation; isotopes in the ground may result in radioactive water, emitted gas and building materials; nuclear fallout includes alpha, beta and gamma radiation, of which gamma radiation is the shortest-lived; and medical radiation is usually with X-rays, but may be done with gamma radiation. Particle accelerators and cobalt 60 are the chief sources of gamma radiation for research and treatment.

Sterilization Use

In its article on Infectious Diseases, p. 54, the Encyclopedia Britannica says, "Many articles perish or deteriorate if [sterilized with moist or dry heat]; leather, rubber, or some plastics, for example. These may be treated with formaldehyde in special cabinets, an old but fairly efficient method, or exposed to gamma radiation, which may be the method of the future--it is already being increasingly used for surgical instruments and materials, especially for disposable plastic syringes, catheters and dressing utensils. It can also be used for sterilizing meat carcasses and canned foods. Ethylene oxide may also be used for sterilizing without heat, but its use requires special apparatus and skilled technique, for it is a toxic gas."

This paragraph is misleading, because gamma radiation also requires special apparatus (shielding and monitoring equipment, at the very least) and skilled technique (i.e., expensive training). For this reason, it is not suitable as an in-house process, but should be sent out to specialists.

For More Information

The American National Standards Institute has about 10 standards dealing with radioactivity in general and gamma radiation and X-radiation in particular.

The Bureau of Radiological Health, in the Food and Drug Administration, regulates irradiation of food and may be a good general source of information, especially on relevant laws and regulations. The Nuclear Regulatory Commission may also be of help.

This August there will be two papers on this topic. The first will be given jointly by Nancy McCall and Dr. Walter J. Chappas, the nuclear engineer who consulted on the Johns Hopkins medical archives project. This will be at the 6th International Biodeterioration Symposium in Washington, DC, August 5-10, at George Washington University. The section on libraries and archives will be chaired by Alan Calmes. For more information write Dr. Charles E. O'Rear, Biodeterioration Symposium Registrar, Dept. of Forensic Science, George Washington University, Washington, DC 20052.

Nancy McCall will also present a paper at the Society of American Archivists' meeting in Washington, DC, August 30-September 3. Write SAA, 600 5. Federal, Suite 504, Chicago, IL 60605 (312/922-0140) for registration and program material.

The Encyclopedia Britannica has a lot of information on safety, biological effects, other applications, and so on.

A long article in the Spring 1982 issue of the Journal of the American Institute for Conservation has a short section on irradiation disinfestation: "Eradication of Insects from Wool Textiles," by Barbara M. Reagan. It has seven references on this topic, four of which are by 5. 0. Nelson and appear in the Journal of Economic Entomology, Bulletin of the Entomological Society of America, and Transactions of the American Society of Agricultural Engineers.