A day after the origin of Cobalt-60 was traced to Delhi University's chemistry department, the varsity authorities today said it was a 'miscalculation' that the material had outlived its radioactive time, following which it was auctioned.

Vice-Chancellor Prof Deepak Pental also said the university takes "moral responsibility and was very "apologetic" for what happened and the damages caused.

Exposure to the radioactive material has led to the death of a scrap shop worker in west Delhi. A few others, including the shop owner, are undergoing treatment after they were exposed to the same material earlier this month.

"If there is a mistake, the mistake is that it was not realised that the source (the radioactive material) may be much stronger than what people (of the department) were thinking. Because they are not the people who bought the source," he told reporters.

The Cobalt-60 was imported by Prof V K Sharma in 1968 from Canada with the permission of BARC. The material was last used in 1985. The material was lying in a room for 25 years and the chemistry department wanted to sell it off.

"It was calculated that it had outlived its radioactive time... because it comes to half in every five years," Pental explained.

He said he spoke to the Department of Atomic Energy this morning on the issue. This body has already set up a committee for further investigation.

Pental said the varsity has set up a separate three-member committee under S C Pancholi, a retired professor and a nuclear scientist, to investigate the issue. The other members are Dr N C Goomer and Dr Dwarkanath.

"Our university has a very strong desire that it should be investigated. We must learn from this incident so that these things do not occur," he said.

Pental said he has written to all departments in the university to take all precautions, adding the varsity will ask its employees to contribute towards compensation for the victims of the mishap.

To a question, he said, hopefully, the students have not been exposed to the radioactive material.

Eleven sources of radiation were detected in the Mayapuri scrap market where Cobalt-60 was recovered this month. It is a radioactive isotope of cobalt, which is a hard, lustrous, grey metal and is used in cancer therapy machines and other medical equipment.