The Pokhran story started in 1964, when the International Atomic Energy Agency (IAEA) highlighted the industrial and engineering applications of PNE. Then, against the background of several nuclear explosions being carried out by the (now erstwhile) U.S.S.R., China and U.S.A., Dr. Raja Ramanna, during 1967, asked Dr. Chidambaram (present chairman, AEC) to take up the work of designing a nuclear explosive.

Thereafter, between 1967 and 69, both Chidambaram and I made trips to the USA to witness and study the phenomenology of PNE projects for gas stimulation. By 1972, when the then Prime Minister, Indira Gandhi, gave a green signal to our department to carry out an underground nuclear explosion, Ramanna asked me to indicate potentia sites in India.

Out of the five-odd sites indicated, Pokhran was approved by Dr. Sethna and Ramanna. The site was located in a protected area under the control of military authorities. At that time, the friendship between Ramanna and Dr. Nag Chowdhary, the scientific adviser to the defence minister, proved extremely beneficial for the project's success.

During 1973, test drilling started for obtaining core samples. These revealed geological and other parameters we would encounter at and around the location of the shaft. Shaft-sinking operations were also completed by the end of April 1974.

The plutonium implosion device was placed at a depth of 107 metres in a chamber at the end of an L-shaped shaft. The total weight of the device was about a tonne and a half, while the plutonium was only a few kilograms.

Shales were used to surround the shaft, overlain by a thick column of sandstones and a gravel bed upto the surface. The chamber containing the device was effectively sealed with concrete blocks and sandbags. The shaft was also securely packed with sandbags, rock-waste and loose sand. The device had already been connected to the firing circuit and was being watched continuously, by TV cameras located in the chamber.

On May 18, 1974, the countdown started at 08.00 hours and the nuclear device was fired from a remote-control switch about five kilometres away from Ground Zero (point of the implosion device) at 08.05 hrs.

Within a few microseconds, we saw a rounded sand dome, about 170 metres in diameter and 35 metres in height, rising in the midst of an extensive desert. Almost simultaneously, we felt a severe tremor, like an earthquake.

The sand dome sank within a few seconds into a crater, about 90 metres in diameter and 15 metres deep. The tremor of magnitude five on the Richter scale, equivalent to an explosive energy of 15 KT (15,000 tons of TNT) was recorded at BARC's Gauribidnur Seismic Station as well as places like Sweden, Norway, Scotland, Canada, USA and Australia.

The news was announced at 1 p.m. the same day. India had joined the nuclear club.

There was jubilation amongst the 50-odd scientists and army personnel present there. All of us signed a register. Radiation monitoring instruments, special surveillance teams and a helicopter surveillance crew reported no abnormal radioactivity after the explosion. Also, large samples of soil, air, water, vegetation and dust gathered did not indicate any abnormal radioactivity.

We visited the crater about two hours after the explosion without recording any abnormal radioactivity on the way from the watch tower. The explosion was thus totally contained from the point of any radioactive fall-out.All this stress and tension was interspersed with light-hearted moments too. This helped us keep our cool. I remember just when the first blow of the pick-axe was about to be delivered at the site of the shaft, someone murmured about having a puja and breaking a coconut. Ramanna, on hearing it, reacted, ``No breaking of coconuts or puja. All of us are scientists here.''

(Writer is former director A.M. Directorate of Exploration and Research Department of Atomic Energy)