MIT Police and the MIT Radiation Protection Office are investigating how a tiny drop of radioactive phosphorus was ingested by a postdoctoral fellow doing research in an MIT laboratory.
The Radiation Protection Office has concluded, after 50 days of monitoring, that the incident exposed the researcher to an intake of about 579 microcuries of radioactive material. That amount is within the permissible one-time and annual limit of 600 microcuries of phosphorus-32 for a person working with radiation. The researcher regularly works with phosphorus-32 as a tracer in research.
Investigators have thus far been unable to determine whether the radioactive material intake was accidental or deliberate.
The Radiation Protection Office, working with the researcher, has determined that the incident probably occurred Monday, Aug. 14. It was not discovered until Saturday, Aug. 19, when the man next worked with radioactive materials. At that time, he routinely used a Geiger counter to check for contamination after handling the materials.
The researcher called the MIT emergency number and the radiation protection officer on call came in that Saturday evening and began the assessment of his intake. The researcher was examined by the Medical Department and then released, though he subsequently was seen by the Medical Department and by Environmental Medical Services a number of times. No health effects were noted.
Because phosphorus-32 has a short half life of two weeks and is gradually excreted from the body, enough time has passed since the incident that the amount of radioactive material in his body is now down to about nine microcuries.
The intake appears to be an isolated incident as no one else in the laboratory has been found to have measurable contamination. The Radiation Protection Office took control of radioactive substances in the laboratory for a period of nine days in August in order to inventory the materials and account for their use. The laboratory has continued daily operation and the investigation is continuing.
A microcurie is a unit of radioactivity; it is the amount of a radioactive chemical element which provides 37,000 disintegrations per second. It is one millionth of a curie. A rem (Roentgen Equivalent in Man) is the quantity of ionizing radiation whose biological effect is equal to that produced by one roentgen of x-rays.
A dose of 600 microcuries of phosphorus-32 results in a whole-body dose of five rem, which is both the one-time and the annual permissible limit of exposure for a worker who uses radiation.
Twenty-five rem is the permissible limit for a planned special exposure, such as for an astronaut in space.
A version of this article appeared in MIT Tech Talk on October 18, 1995.