After a long lull, doubts have once again been expressed about the efficacy of the Indian 1998 nuclear tests. In this context, many issues have been raised: How big a deterrent should India have? Should India sign the Comprehensive Test Ban Treaty? While many of these questions do have some relevance for Indian strategic planning, they have been linked to the success of the 1998 tests and, in particular, whether the yield of the 1998 tests were in conformity with the planned yields.
There is no confusion about the design/planned yield of the 1998 thermonuclear test: it was 45 kiloton. This has not been disputed by anybody. According to the Department of Atomic Energy (DAE), the estimated yield of the test was in rough agreement with the design yield subject to the usual errors associated with such estimates. It must be stated at the outset that there is no unanimity among the Indian critics of the DAE about the yield of the tests.
P.K. Iyengar, former DAE chairman, and the only nuclear scientist among those critical of the 1998 test, does not question the DAE estimates and is on record saying, “If one goes by the numbers for the total nuclear yield put out by the Department of Atomic Energy, which I see no reason to dispute, the yield of the thermonuclear device detonated on May 11, 1998 was around 40 kilotons.”
The DAE estimates are, however, contested by some Indian non-scientists and non-nuclear scientists. Till very recently, they had relied solely on the estimates of some foreign scientists for their contention. These estimates had been contested by DAE scientists and Indian scientific journals had carried an extensive debate on the issue with both the foreign and DAE scientists presenting their case. However, none of the Indian critics of the DAE ever presented any scientific argument in support of their case.
There are a number of ways of estimating nuclear test yields. Some on-site, some off-site; some off-site estimates that require data on the geology of the test site, and some that do not. The on-site methods are a) radiochemical analysis; b) close-in ground motion; c) hydrodynamic-CORRTEX. The off-site methods are seismic estimates using a) surface wave characteristics; independent of test-site geology data; b) body wave characteristics requiring some on-site geological data and c) using Lg wave characteristics requiring some on-site geological data.
Each of the above methods has its own estimate error. In terms of accuracy, the radiochemical analysis offers the best estimates. This was the method used by the United States estimating the yield of their nuclear devices. The Hydrodynamic (CORRTEX) and ground-in motion estimates rank second in their accuracy. While negotiating on the test methodology before ratification of the Threshold Test Ban Treaty, the US had insisted on the CORRTEX system for measuring the yield of an explosion, while the Soviets had favoured seismic monitoring. Seismic methods are the least reliable, especially when only one of the seismic methods is used.
The DAE had used all of the above methods in their estimates of the yields. The foreign experts who had disagreed with the DAE had employed only one method: the seismic method using body wave, which is the most unreliable of all of the above methods.
As mentioned earlier, till very recently the Indian critics of the DAE had based their criticism solely on the estimates of foreign scientists. Only very recently, former Defence Research and Development Organisation (DRDO) scientist K. Santhanam revealed that there was a disagreement between the DAE and the DRDO on the yield of the 1998 test based on one method used by both parties, namely the close-in ground motion characteristics of the test. The DRDO seemed to have used only this method for estimating the 1998 yields.
As in all experiments, the success of the effort depends much on the instruments used and the calibration of these instruments. While Santhanam is on record as stating that the DRDO’s calibrations “were acknowledged to [have met international standards] by the BARC [Bhabha Atomic Research Centre]”, it’s a matter of record that much before the tests, the DAE had strongly questioned both the sensitivity of the DRDO instruments and their calibration and these had not been agreed to by the DAE. So, it’s not surprising to find the DAE and DRDO estimates not matching each other.
However, notwithstanding the fact that the DAE had used all six methods of estimation of nuclear yields, and that the DRDO had used only one method and that too under circumstances that were questioned by the DAE before the tests, it should be possible to resolve the issue by placing all the pre-test and post-test data before a group of Indian scientists qualified to judge all elements involved — the pre-test instrumentation sensitivity and calibration methods and the post-test data and charts — to come to the relative correctness of the two estimates.
It is interesting to compare the Indian and Pakistani reaction to the foreign estimates of the yields. As was the case with India, the foreign critics estimated the Pakistani yields to be far less than what was claimed by Pakistan. However, unlike in the case of India, there has not been, so far, any response from Pakistani scientists about the foreign estimates of their test yields. The Pakistani armed forces, of course, have kept quiet all along.
G. Balachandran is a Visiting Fellow at the Institute for Defence Studies and Analyses (IDSA) and Research Consultant, National Maritime Foundation (NMF).