New system could provide detailed images — even of soft tissue — from a lightweight, portable device.
The head of a Nuclear Regulatory Commission team investigating the radioactive phosphorus contamination of an MIT researcher has said he cannot exclude that the contamination may have been accidental, but "some of the things we would expect to see in an accidental spill were not there."
Dr. John Glenn, head of the Incident Investigation Team, said that the NRC Office of Investigations has initiated a separate investigation into "potential wrongdoing" to determine if there was "a deliberate contamination of food or drink ingested by the individual."
Dr. Glenn made the statements October 25 at a Nuclear Regulatory Commission "open exit meeting" as they prepared to leave MIT after their eight-day initial investigation on-site of the ingestion of phosphorus 32 (P-32) by a researcher at MIT.
P-32 is used as a tracer in genetic research; it has a half-life of 14 days. The MIT Radiation Protection Office determined that the man ingested up to 579 microcuries of P-32, which is 97 percent of the annual and one-time limit for a researcher using that substance. The limit is 600 microcuries, which translates into an effective dose equivalent of 5 rem. No medical effects are expected at the researcher's level of ingestion.
At the close of the meeting, Dr. Glenn took questions from two reporters who attended. A Washington Post reporter asked Dr. Glenn, "Have you been able to exclude any possibilities?"
Dr. Glenn replied, " Well, we cannot exclude, but I think if you listened to the facts as I related to them, the things we would expect to see in an accidental spill, we did not see. We did not see laboratory contamination. We did not see contamination in the home. We did not see contamination in other individuals. So some of the things we would expect to see in an accidental spill were not there."
The reporter then asked, "Is there any reason to think that this was a self-inflicted poisoning?" Dr. Glenn responded, "That's why our Office of Investigations is looking at this, to find out what the cause is. We have not come to any conclusions about the cause."
Dr. Glenn was asked whether the man, an experienced researcher who knows how to handle P-32, suffered "any medical consequences." Dr. Glenn said, "The individual did report symptoms. I will note that at the dose levels that we're talking about, 579 microcuries-which, really, in terms of dose to an individual would translate into approximately 4.8, 4.9 rem of effective dose equivalent-that's the amount of dose that a worker is permitted to receive within one year. We wouldn't expect to see medical consequences at that level of exposure. At the 5 rem level, we would not expect to see what are called deterministic effects, where you would actually be able to observe physical symptoms."
Dr. Glenn said that, based in part on contamination found on clothing the man said he wore on August 14, it is believed the contamination occurred that day, after he had worked with P-32 and after he performed the customary Geiger counter survey of himself. It was not discovered until August 19, when the man next worked with phosphorus and, upon surveying himself, found he was contaminated. When the radioactivity was first measured in his body on August 19, it was below 200 microcuries. By the 50th day, it was below 9 microcuries.
A WBUR reporter asked, "Did the researcher report having the symptoms before he found out that he had been contaminated?"
"Not that I am aware," said Dr. Glenn, who declined to describe the symptoms of the man because he said it might violate confidentiality of medical information. He said he understood that the man was not working in the laboratory at this point. (A person who receives the annual limit of radioactive intake is barred from working with radioactivity for the rest of that year.)
Regarding access to radioactive materials, Dr. Glenn mentioned there had been a lapse in MIT security, but he said that MIT had taken additional action to ensure security after NRC investigators found a laboratory's outside door was locked but had been propped open by a chair on October 22. He said, "The team observed and was told in its interviews that during off hours, certain areas in which radioactive material is stored or used can be entered without a key and without being challenged.
"We were also told that MIT's policy was to require that such buildings be locked in off hours and that radioactive material use areas are to be locked except when authorized individuals are in attendance. The team's principal contacts at MIT were informed of these observations on October 23, and these contacts informed the team on October 24 of additional actions being taken to ensure the security of radioactive materials against unauthorized removal. The NRC's Region 1 office will monitor and review the adequacy of these corrective actions," Dr. Glenn said.
He said the Incident Investigation Team (IIT) for this case was formed on October 17 and arrived at MIT the same day. He said the IIT process is used only once or twice a year. "The decision to form an IIT was based on MIT's notification to our Region 1 office on October 16 about an internal exposure to P-32 which occurred last August. Although this reported intake of P-32 would not result in an exposure in excess of NRC limits, the reported whole-body dose was close to the annual limit, and the circumstances of the exposure included the possibility that the individual was deliberately exposed. Further, ingestion of such a large quantity of P-32 is rare; and this was the second such event in a few months."
The first incident, he said, occurred at the National Institutes of Health in June. There, a pregnant woman reported she was exposed June 30 to more than 600 microcuries after some P-32 allegedly was put on her food. The annual radiation dose to a fetus is 1/10th the annual limit for a radiation worker. Subsequently, on July 14, a water cooler at NIH was found to be contaminated with P-32 and more than two dozen people were exposed.
In response to a question about the IIT coming to MIT, Dr. Glenn said, "It was felt that we needed to take a broader look. One thing that is different is that the Incident Investigation Team is to take a look not only at the incident and the institution at which the incident occurred, but also to take a look at the NRC's regulatory framework and to see whether it's adequate."
Dr. Glenn said "the purposes of the team are to establish what happened, to identify probable causes and to document our findings and conclusions and issue a report in about 45 days."
Dr. Glenn expressed his appreciation to MIT for its cooperation and responsiveness in making facilities, equipment and personnel available to the NRC.
Professor J. David Litster, vice president and dean of research, commented, "I do believe that it is in all of our interests to understand as fully as we can what happened and to take whatever steps are necessary to make it unlikely that such an event can recur. As you know, we have already begun to reexamine our procedures and policies, and see if there are ways in which they could be improved. We look forward to hearing the conclusions of your report."
A version of this article appeared in MIT Tech Talk on November 1, 1995.