Speaking to members of the Indian Science Writers Association here yesterday, Iyengar said that big figures quoted for creating a nuclear deterrent have no basis.

Justifying last week's underground tests as a necessity, Iyengar said there was nothing ethically wrong in India keeping nuclear bombs ready for its own defence. He said countries which want India to sign the test ban treaty are still engaged in research on weapons deadlier than atomic bombs. He corrected the impression that the Bhabha Atomic Research Centre (BARC) in Mumbai, the flagship of DAE, had been giving more importance to weapons research at the cost of producing nuclear electricity.

While BARC has some 6,000 scientists, ``not even two per cent were involved in this activity,'' Iyengar saidadding that work on bomb design was a continuing activity at BARC since 1971. ``It was not a story of stops and gaps.''

The only gap was during the Emergency (1975-76) and after that. But with the shifting of Raja Ramanna, then director of BARC, to the Defence Ministry, the project was renewed with vigour.

Giving details of the 1974 test at Pokhran, Iyengar said the device was ready in 1973 and used five to seven kg of plutonium. The device took about two years to assemble and it took about five months time to dig a hole for carrying out the underground test. He said this was because the 100-metre deep, seven-metre wide hole was dug like digging a village well -- with a pulley, rope pick-axe and spades.