Sticking by a claim

Published : Jun 06, 1998 00:00 IST

SOME nuclear scientists abroad and in India have questioned the claim of the Department of Atomic Energy (DAE) that one of the five nuclear devices tested at Pokhran on May 11 and 13 was a thermonuclear device or a "hydrogen bomb". The sceptics argue that the yield of thermonuclear devices strongly tends to be of the order of megatons. (One megaton is equivalent to 1,000 kilotons, or one million tons; a nuclear device with a yield of one megaton releases energy equivalent to the explosion of one million tons of trinitrotoluene.) The yield from the Indian test on May 11 was claimed to be only 45 kilotons. Therefore, the sceptics argue, the device could not be categorised as a true hydrogen bomb. In their opinion, the device tested was almost certainly a boosted fission device.

In a hydrogen bomb, the fission process generates heat up to millions of degrees Celsius, which triggers a fusion process similar to the creation of the sun. When the hydrogen gets fused, massive quantities of energy are released, generating shock waves and heat waves that can annihilate everything over a vast area.

Scientists at the DAE, however, assert that a thermonuclear device was indeed tested at Pokhran. They stand by Atomic Energy Commission Chairman and DAE Secretary Dr. R. Chidambaram's official explanation that the yield of the thermonuclear device was intentionally kept down to 45 kilotons to avoid seismic damage to villages near the test site.

According to DAE scientists, there are methods to keep the yield of thermonuclear devices in the order of kilotons. One scientist contended that it can be done by "not allowing the energy to concentrate... There are means to diffuse and disseminate the energy, depending on the medium of propagation - whether it is rock or sand." He added that it is comparatively easy to reduce the yield; the difficulty lies only in increasing the yield. "In this case, the yield was skilfully kept low so as not to affect the nearby villages."

This scientist asserted that technical data from the tests also indicated that it was a thermonuclear device. There were other "signatures" that confirmed this; among these were "shock wave patterns", which "tallied with computer simulations." The scientist explained that the three simultaneous tests of a fission device, a low-yield device and the thermonuclear device on May 11 had probably "confused" international seismic stations, which interpreted the tremors as "an earthquake at a depth of 50 metres on the Indo-Pakistan border."

The nuclear scientist said that the expression of scepticism about the DAE's claim was part of an "exercise by Western scientists to keep needling us so that we will come out with the details."

Another DAE scientist said that the yield was "deliberately restricted" to 45 kilotons because the shaft of the fission device that was also tested simultaneously was only 1 km away. He added that the "tremendous technological development" in the last 25 years had made it possible to lower the yield.

Yet another scientist said that there were three possibilities. The first was that the yield was "intentionally" brought down to 45 kilotons with an improved design, "which is an achievement". The second was that the fission device in the two-stage device exploded but the fusion device did not. The third was that it was not a thermonuclear device at all, and that both the scientists and the Union Government were "bluffing". The scientist, however, added that the sceptics who were raising questions about the authenticity of the DAE's claim had no access to "authentic information" and were resorting to "guesswork". He further pointed to the difficulty of estimating the yield from an underground nuclear device, as distinct from an atmospheric test: in the case of an underground explosion, the radioactivity was contained in the earth. "In an underground test, unless one goes to the site and drills, one cannot conclude what material (fuel) was used."

A former Chairman of the AEC analysed it thus: it was a fact that 33 kilotons out of the 45 kiloton yield came from the fusion part of the device and the remaining 12 kiloton yield emanated from the fission part, which triggered the fusion. All atomic weapons with the United States were fission weapons, which used a bit of tritium to boost the energy and to reduce the amount of plutonium used. They were, therefore, called boosted fission devices. "But this (thermonuclear device) does not come under that category (of a boosted fission device). Perhaps, they have not used tritium gas at all. The amount of tritium that you put in is very small and it, therefore, cannot explain the yield of 33 kilotons from the fusion part. Therefore, Dr. Chidambaram's statement that it is a device with two separate parts - a fission part and a fusion part - is true. The device therefore falls under the category of a fusion weapon."

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