Volume 8, Number 2
Apr 1984

Gamma Radiation

In the November 1983 issue of the SAA Newsletter, the Alan Mason Chesney Medical Archives of the Johns Hopkins Medical Institutions reports the use of gamma radiation as an exterminant for mold and insect infestation. The pilot project conducted by the Medical Archives indicates that:

1) Gamma radiation is a highly effective exterminant for mold and insect infestation--295 record storage boxes of valuable historic papers with extensive mold and insect infestation were exposed to 0.45 megarads of gamma radiation (cobalt) for approximately 45 minutes. Microbiological tests made prior to irradiation indicated extensive and varied types of mold and bacteria, the most prevalent being Aspergillus niger. Ten cultures made from a broad sampling of the irradiated materials produced only one minor and incidental strain of Penicillium sp. (commonly found on the cleanest of kitchen tables). The microbiologist who took the cultures suggests that this one very small amount of fungal flora was introduced at the time the materials were unpacked, since the other samples were essentially sterile.

2) Gamma radiation is an inexpensive and logistically simple process--The cost of having the infested materials treated with gamma radiation at a commercial radiation plant was $1.00 per cubic foot. Gamma radiation is in addition cost effective in that it eliminates the costly two-step process (ethylene oxide followed by thymol) that was recommended to us for treatment of these materials. Gamma radiation as a volume sterilant is also more effective than EtO or thymol, which are surface sterilants.

3) Gamma radiation in low and carefully regulated dosage will not damage paper and ink composition--Preliminary tests using a linear accelerator helped to establish dosage level and exposure time so that the extermination process would be effective and yet not damage paper and ink composition.

4) The gamma radiation process does not leave any hazardous residues (chemical or radioactive) on the treated papers--Gamma radiation does not activate substances and therefore does not leave any residual radiation.

The pilot gamma radiation project was supported by an emergency grant from the National Endowment for the Humanities. Archivists with questions about this process may contact Nancy McCall, Chesney Medical Archives, 35 Turner Auditorium, 720 Rutland Ave., Baltimore, MD 21205 (301/ 955-3043).