Refuting the doubts raised recently over the success of the May 1998 Pokhran-II tests, Anil Kakodkar, Chairman of the Atomic Energy Commission (AEC) and R. Chidambaram, AEC Chairman in 1998 and now Principal Scientific Adviser to the Union government, said on Thursday that the controversy was “unnecessary” and the doubts had “no scientific basis.”

In defence of the accuracy of the tests, Mr. Chidambaram made an elaborate power point presentation to the press and members of the scientific community. He sought to clear doubts about the test yield raised by scientists K. Santhanam, Project Leader, Pokhran-II, and P.K. Iyengar, a former AEC Chairman.

Santhanam’s contention

Mr. Santhanam had spoken about the differences in the yield estimates of the Defence Research and Development Organisation (DRDO) and the Bhabha Atomic Research Centre (BARC).

He had contended, “The fission bomb yield from DRDO’s seismic instrumentation was 25 kiloton (kt).”( The Hindu, September 17, 2009: “Pokhran-II thermonuclear test, a failure”).

In his response, Mr. Chidambaram clarified, “The BARC estimate of the yield for the fission device is 15 kiloton [not 25 kiloton] and for the thermonuclear device 45 kiloton. One of the methods used for the estimation of the device yield was close-in acceleration measurement, for which both DRDO and BARC had set up instrumentation. It soon became apparent that after discussion among the two groups of specialists that the DRDO data had anomalies and had to be rejected and that the BARC data, which had the expected waveforms, would be accepted.”

Dr. Kakodkar added there were different methods to find out the yields’ seismic measurement, instrumentation, radiochemical, actual simulation of ground motion, among others.

“These are all different disciplines; there are different groups which do it. BARC is a large institution and assessment is done by different expert groups.”

On crater’s diameter

To Mr. Santhanam’s yardstick of the diameter of the crater, Mr. Chidambaram said: “The fission device was emplaced in rhyolite medium whereas the fusion device was emplaced in the pink granite medium. The medium for the Pokhran-I test was shale and sandstone. The geology in the Pokhran region is inhomogeneous. The propagation of the shock wave is affected by every interface. 3-D simulation calculations of the rock mechanical effects, done by BARC scientists, after considering all these factors accounted for the observed effects in the thermonuclear test.” He said he failed to understand what scaling laws Mr. Santhanam had used.

On the question of finding trace-levels of radioisotopes in Apsara, a pure fission reactor, Mr. Chidambaram stated, “The tail of the fission neutron spectrum extends to beyond the excitation energy of these reactions. But the fusion neutrons are of 14 MeV. That is why isotopes like Mn-54 and Na-22 are found in significant [not trace] quantities in the rock samples from the thermonuclear device site rock samples.”

“If one sees the gamma-ray spectrum of a typical rock sample of the thermonuclear test site, published in refereed journals by BARC scientists, sharp peaks for these radioisotopes are seen, not just bumps in the background! In the Mn-54/Ce-144 ratios from the samples of the two test sites, reproduced by R. Ramachandran in his Frontline article of 25th September 2009, this ratio for the thermonuclear test samples is seen as a high multiple of the ratio for the fission test samples.”

Poser to P.K. Iyengar

Mr. Chidambaram pointed out, that Dr. Iyengar, in his contention made in 2000, had not disputed the yield of the thermonuclear test. However, he said: “We do not understand, how, without knowledge of the design and, therefore without knowledge of the fusion-fission break-up and the quantity of thermonuclear material in the device and its isotopic composition, he [Dr. Iyengar] has tried to calculate the efficiency of fusion burn.”

“No need for more nuclear tests”

R. Chidambaram, Principal Scientific Adviser to the Union government, said on Thursday that no nuclear weapon state ever revealed the thermonuclear design as that information would be proliferation-sensitive.

He and Chairman of the Atomic Energy Commission Anil Kakodkar stressed that India was the only country to release so much information on the Pokhran II tests through scientific media. They said the tests had gone through peer review and been discussed in international scientific journals.

Reiterating that there was no need for more nuclear tests, Dr. Kakodkar said: “We want to re-emphasise that the 1998 tests were fully successful and had achieved in toto their scientific objectives and the capability to build fission and thermonuclear weapons with yields up to 200 kt.”

While the U.S. had conducted several tests, they stopped after 1991, Mr. Chidambaram said. With the increase in scientific knowledge and advancements in computer technology, “there is no need for so many tests.” Also, the charge of being hasty, applied to Pokhran II “is unfounded.” The team was waiting since 1974 (Pokhran-I), Mr. Chidambaram argued.

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