On March 9 this year, a section of the US media reported that the New York State Department of Environmental Conservation (DEC), state Department of Health and US Environmental Protection Agency
found a lucite tube, about 9 inches long and 1 inch around, that contained a cavity with a small amount of low-level radioactive material, below the townhouse of a medical physicist who resides at 7 Tupelo Drive, apartment F.
The Government agencies visited the home after receiving an anonymous call about a possible radioactive device being buried and cemented into the basement floor of the apartment.
Workers measured a radiation level of approximately 20 microrem per hour, or .02 millirem per hr at the floor. A normal chest X-ray is equal to 10 millirems.
A DEC official assured the public that the source does not pose an immediate threat to public health. The report did not mention the name of the radioactive material. US EPA assisted safe disposal of the source
In India calibration sources are used in radiotherapy departments in our hospitals. One such source is Sr-90 (Half life about 30 Y). I remember that about 30 such sources were imported by the erstwhile Directorate of Radiation Protection(DRP) . They were in the form of silver foils (4cmx4cm) on which about 30 mCi Sr-90 was deposited. These sources can deliver very high beta dose for a long time.
The foil remains folded in the form of a tube. The entire assembly had a brass cover. These sources were used as standards to be kept in radiotherapy centres along with a secondary standard dosimeter.
The source assembly was such that the pencil like chamber of the dosimeter can be inserted in to it in fixed geometry to get a reference dose. Prior to using the dosimeter to measure gamma dose from Co-60 units, the source was used to check the overall performance of the dosimeter
These sources were supplied by DRP to radiotherapy centres who had the dosimeter. Over the years, these dosimeters develop snag and will no longer will be in use, leaving the Sr-90 source without any use.Though appropriate instructions were given when the source was delivered, the compliance with the instructions may not be satisfactory in course of time. There is at least one instance in which a calibration source was found missing from a premier hospital in India.
Similarly Sr-90 sources are also available in some hospitals as opthalmic appicators to treat eye lesions. These tend to remain unused.
I have brought the possibility of such sources and calibration sources becoming “orphans” to the notice of AERB. The general policy of AERB is to withdraw all unused sources and dispose them of safely. Bhabha Atomic Research Centre (BARC) and the Indira Gandhi Centre for Atomic Research (IGCAR) which have the expertise in collecting and disposing of radiation sources help the institutions.
The medical physicists/ radiological safety officers employed in the radiotherapy departments must advise the hospital administration to dispose of all unwanted sources safely under intimation to AERB. They must include calibration sources also in the source inventory and include them in the annual report to AERB after verifying their presence.