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July 27, 1998


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So, it was an H-Bomb after all

India's first test at Pokhran on May 11 comprised a hydrogen bomb and the yield was closer to 60 kilotons, it has been confirmed following the release of data collected by 125 seismic stations across the world.

There had been scepticism about India's claim that it had exploded a hydrogen bomb as initial data from seismic stations had recorded only 25 kilotons.

The respected New Scientist magazine confirmed the near 60 kiloton yield and set at rest the controversy whether or not India exploded a thermonuclear device.

In Parliament, the government recently described as ''erroneous'' the conclusions that the Pokhran tests did not comprise a hydrogen bomb.

New Scientist said the tests could have had their seismic signals muffled, possibly by ''decouping'' the devices -- suspending them within caverns in the ground or burying them in sand.

In theory, ten kilotons of explosive force can be completely hidden in this way.

There could be peculiarities in Rajasthan's geology that may have weakened the signals, New Scientist says.

Sceptics say the Comprehensive Test Ban Treaty will fail because secret nuclear explosions cannot always be detected. New Scientist says the recent nuclear tests by India and Pakistan appear to prove them wrong.

Before dawn on May 11, a seismograph in a research institute outside Washington DC recorded a disturbance deep in the earth on the other side of the world. Over the next few minutes, dozens of other seismographs all over the planet recorded the same event and transmitted their data automatically to the institute, the Prototype International Data Centre.

A computer analysed the signals and gave its interpretation: an ''event'' of magnitude 5.0 on the Richter Scale under Rajasthan in India. Later that morning, seismologists at the PIDC studied the signals and recognised the event as a nuclear test.

The job of the institute is to test the technology for detecting nuclear bomb tests around the world. From next year its successor, the Real International Data Centre in Vienna, will be charged with policing the CTBT, which outlaws all nuclear explosions.

Whether the RIDC can actually police the CTBT has become the subject of a fierce debate. For it emerged that the seismic monitoring network under trial by the PIDC failed to ''diagnose'' India's tests accurately.

In particular, PIDC failed to detect the second explosion, which India claims yielded between 0.2 and 0.6 kilotons.

The reliability of the monitoring system is vital to the success of the CTBT. The treaty is opposed by some in the US who say that testing is necessary to maintain a nuclear deterrent.

They claim the flaws in the monitoring system prove that CTBT cannot work. Such accusations are ''already damaging prospects for US ratification of the CTBT,'' New Scientist quoted Christopher Paine of the Natural Resources Defence Council, and the American Pressure Group that supports the treaty, as having said.

The CTBT has been signed by 149 countries since it was agreed upon in 1996, but to come into force it must be ratified by all 44 nations in the UN Conference on Disarmament that have nuclear reactors.

So far, only 13, including two ''bomb'' states, Britain and France, have ratified it. US ratification, as well as being essential for the treaty to come into force, is crucial to encouraging others to ratify.

The CTBT calls for four separate global networks to listen for nuclear explosions. None is yet complete, but the seismic network -- which includes stations that automatically transmit data as well as some that can be used as necessary -- is the most developed.

In addition, there will be hydroacoustic monitors to listen for undersea tests, atmospheric sensors to detect the radioactive particles and rare gases, such as xenon, that are released by nuclear explosions, and infrasound receivers to listen for near-surface explosions. All are being tested by the PIDC.

The technology at the centre of the current dispute is seismic. New Scientist quoted Frank Gaffney, former US assistant secretary of defence under President Reagan and now head of the Center for Security Policy, an anti-disarmament think-tank in Washington DC, who argues that because the seismic network failed to pick up all of India's tests, ''nuclear testing can be conducted in ways that will be unverifiable, if not undetectable.''

Roger Clarke, a seismologist at the University of Leeds, argues that the problem such as with regard to the peculiarities in Rajasthan's geology that weakened the signals would diminish with experience of monitoring earthquakes.

''The more stations we have feeding seismic data into the system, the more details like that we will understand,'' he says. Seismologists point out that the network detected both of Pakistan's tests.

But Gaffney's team maintains that the waveforms that allow seismologists to distinguish earthquakes from explosions are not always clear.

''If the Indians hadn't announced their tests, CTBT supporters would have claimed the seismic events that were recorded were natural,'' he says.

"Nonsense," says Clarke. The wave forms of the explosions in India's first test and those in both of Pakistan's were clearly caused by explosions.


India may not have an H-bomb, says scientist

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