The Atomic Energy Regulatory Board (AERB) has identified and accounted for all the cobalt-60 radioactive sources originally present in the gamma cell irradiator of the Chemistry Department of Delhi University.
Stating this in a pres release here on Wednesday, the AERB said that the sources would continue to remain in the safe custody of the Department of Atomic Energy (DAE).
It would be recalled that the irradiator, supplied by the Atomic Energy of Canada Ltd. (AECL) in 1968, had been in disuse since 1985 and was auctioned away to scrap dealers on February 26. This had found its way to the metal scrap market of Mayapuri in West Delhi. Without realising that there was a radioactive source in the scrap, two Mayapuri shops where the scrap had finally landed dismantled the equipment and cut open the irradiator into several pieces. This resulted in the people directly involved in the operation and handling the pieces to high doses of radiation. This caused severe radiation poisoning of seven people engaged in the scrap metal business one of whom has since died. The other six continue to battle for life – one at Apollo Hospitals and the rest at the All India Institute of Medical Sciences (AIIMS), New Delhi.
Following a complete survey of the market, officials of the AERB and the National Disaster Management Authority (NDMA) stated that they located 11 radioactive sources in all — eight from one shop, two from another and one from an individual who was in its possession. Given the badly mangled state of the irradiator and its pieces, it was not clear then whether the 11 sources were all separate sources or were pieces of a single source. These radioactive materials were moved from Mayapuri in mid-April to the Narora Atomic Power Station (NAPS) in U. P.
Detailed inspections of the materials recovered were carried out by the AERB officials at NAPS on May 3 and 4 following which the statement was issued. The statement clarifies that all the pieces originated from this single Delhi University gamma irradiator's Co-60 source. This also makes it clear that reports appearing in the media about ‘missing radioactive pencils' and the ‘source trail leading to Rewari (in Haryana)' were incorrect.
According to S. K. Malhotra of the DAE, the reconstruction was made possible by the details of the original device that was supplied to the university in 1968, which the AERB managed to obtain from the AECL. Apparently the AECL responded to the query with great efficiency and supplied the details of the sale 42 years ago within a couple of hours. Mr. Malhotra also confirmed the initial activity of the source was over 3,000 curies (Ci). After 42 years, or 8 half-life periods of Co-60, the activity would have dropped by a factor of 2 to the power of 8, or 256, only. (One curie stands for 37 billion radioactive decays/sec.)
According to the details provided by the AECL, the source chamber had provision for 54 pencils of Co-60 of which only 16 were occupied at the time of supply based on the requirements specified by the user. Each cylindrical pencil is made of 7 ‘slugs' or pieces of Co-60, each measuring about 2.5 cm x 0.6 cm stacked together and all the pencils constitute a unit that can be placed around any material to be irradiated with gamma rays. The AERB claimed that they were able to account for all the 112 slugs of the 16-pencil Co-60 source unit.
Probe demanded
In a related development, the Delhi University teachers' Association (DUTA) has demanded an impartial enquiry by the President of India, who is the Visitor of the university, into the callous disposal of the Co-60 source to scrap dealers. In particular, the DUTA has called for a enquiry into the constitution by the vice-chancellor of the committee that authorised its disposal and into the inexplicable silence on the part of the university authorities for as long as 20 days when the Delhi police and the AERB were groping in darkness to hunt down the origin of the radioactive material. “In this context, the speedy work by the Delhi Police in tracking down the origin to the Chemistry Department of Delhi University needs to be commended, it said.
