Cover Story: Is India's H-Bomb a Dud? Pg 2

Indian scientists dismiss such assessments as erroneous. R. Chidambaram, Atomic Energy Commission (AEC) chairman and chief designer of the Pokhran 1998 tests, believes that western researchers did not take into account vital local parameters including the location of the shafts in Pokhran and the geology of the region that could have a significant impact on calculations. Chidambaram says emphatically, "The yields we estimated match our calculations." Adds Anil Kakodkar, a key member of the tests team and director of the Bhabha Atomic Research Centre (BARC), India's premier nuclear establishment: "We are not perturbed. In the coming months we will produce evidence that thermonuclear fusion did take place. We will prove it scientifically and through peer review."

Other Indian nuclear scientists are livid over the charges that the Indian H-bomb was a dud. They had considered designing the H-bomb "the most complex and challenging of the series". It certainly is. The atom bomb works on the principle of imploding plutonium the size of a tennis ball till it reaches critical mass, then triggering a chain reaction of fissioning atoms that releases enormous explosive energy. A hydrogen bomb works in two stages and is based on the principle of the sun generating energy. The secret is to harness the enormous heat generated by an atomic blast -- equivalent to temperatures found on the sun -- to fuse hydrogen atoms and cause a truly titanic release of energy.

The world's first Hydrogen bomb, exploded by the US on November 1, 1952, rose like a dark sun. An immense, blinding white fireball, 5-km across, blotted the horizon and all but obliterated Eniwetok Atoll in the Pacific. Those who watched it realised that it marked a decisive moment in human history. A bomb had been built whose power was boundless.

If an atom bomb could flatten a small city like Nagasaki, a powerful H-bomb could wipe out the entire New York metropolis in minutes, killing millions of people. In military circles the bomb was known as the city buster. Till the Indian test, apart from the US only four other countries -- the former Soviet Union, Britain, France and China -- had exploded H-bombs.

The Indians, it is learnt, mastered the technology of designing the H-bomb only in 1996. Chidambaram, in fact, terms their device "98 vintage". They have no doubts that the device worked and as a measure of their openness, India Today was allowed access to their major findings and permitted to interview top scientists including S.K. Sikka, director of BARC's solid state physics group and head of the team that made the physics design of the nuclear devices (see interview).

The reason why Indian scientists appear confident is that they have a wealth of data from various techniques to estimate explosive yields which no foreign researcher has. On the seismic front, they have records from seven accelerometers and five geophones placed close to the shafts (see diagram) that give accurate information on the shockwaves produced. Apart from that they have data from four highly sensitive regional seismic stations, over 40 recorders of the Meteorological Department and access to international seismic records.

Since Indian equipment are notorious for failing at critical times, the Pokhran team had to ensure that all the key seismic stations in the country were active. To avoid suspicion that India was planning a test, they told the station chiefs to be on full alert as Pakistan was expected to conduct one. The ploy worked. The team also had access to data from a Corrtex recorder -- a sensing cable lowered into each shaft for accurate readings of the shockwaves. And critically, they know the geology of the region. Seismic results could vary if an explosion occurred in a sand dune or on a hard rock terrain and compensations have to be made for accurate results.

Based on the range of the data, India put the seismic magnitude of the tests at 5.4 while the CTBT's provisional International Data Centre pegged it at a much lower 5.0 and the US geological stations at 5.2. These differences may seem small but the Indian scientists say it could skew the yield figures by as much 20-30 kt. Sikka says other factors need to be taken into account. On May 11, apart from an H-bomb explosion, India conducted two other tests simultaneously: an atom bomb and a low-yield fission weapon with sub-kilotonne yields (below 1,000 tonnes of TNT equivalent). The Indian scientists now put the yield from the fission bomb at 15 kt and the hydrogen bomb at 45 kt.

The simultaneous tests made interpretation of data difficult but the scientist say they had no option as they feared that a single explosion would damage the shafts containing the other two bombs. Since the two shafts which contained the bigger explosions were only a kilometre apart some of the shockwaves could have interfaced and caused distortions in seismic readings. Also the shafts were aligned on an east-west plane. On plotting seismic findings Sikka and his team found that the recorders on this azimuth across the globe had much lower readings indicating distortions. The recorders to the north, which were subjected to less attenuation of shockwaves, showed consistently higher readings in keeping with Indian estimates.

International seismologists disagree with the Indians on the significance of such factors as alignment of shafts and simultaneous tests in causing faulty estimates. Says John Murphy of Maxwell Technologies, a Virginia-based private institution in the US, who was part of the team of researchers that assessed India's tests: "Our findings took into account all these variations and are based on 40 years experience of using seismic records to estimate nuclear explosive yields. Our studies show the yields were nowhere close to what India is claiming."

Indian scientists angrily point out that the foreign researchers haven't revealed their methodology for arriving at such estimates. Murphy, for instance, did not want to say in writing what he told India Today because he explained that he was sub-contracted to do the study for the US Department of Defence. Some Indian scientists suspect that the spate of studies on India's tests is a ploy to make them come out with more details on the devices tested.

While the battle over seismic results is unlikely to be settled early, it is, as Marshall points out, "only a war of words over whether the explosion was 10 kt or 20 kt. To prove that a thermo-nuclear device was exploded you need radio chemical evidence from the site." One definite indicator that the H-bomb did go off would be deposits of high amounts of tritium -- which is produced during the fusion process -- at the blasts sites.

The Indian team has already started drilling in the area and has reportedly extracted samples from midway down the deep shaft which was used for the blasts. The BARC team refuses to divulge the findings but India Today has reliably learnt that the initial results from radio-chemical analysis positively points to thermonuclear fusion having occurred. Even P.K. Iyengar, former AEC chairman who had initially doubted India's H-bomb test, says, "They have definitely done it. I know the team well and they are unlikely to be wrong."

Sikka says Indian scientists are soon going to present conclusive findings that show the measured acceleration of the shockwaves and yield estimates of the May 11 tests match US tests in Rio Blanco and Rulison done under similar rock types.

Yet, even if the final results point to the H-bomb exploding as planned, charges can be made that BARC tailored the results, especially since independent observers are not allowed access to the blast sites. The joke doing the rounds is that since there is a moratorium on tests, unless BARC holds a public display of the H-bomb, doubts would continue to be raised over whether India exploded one or not.

For now, the Indians seem confident that they are right. In the interview Sikka makes a dramatic revelation: the first stage of India's H-bomb was not the usual atomic bomb but a boosted fission device. In such a device the core of the atom bomb is filled with a few grams of hydrogen fuel and when it is detonated fusion reaction also takes place, increasing the yield by as much as four times. It is the first time that the Pokhran team is revealing that it had tested a boosted fission device.

Experts say if true it is a significant development. Says Ray Kidder, a nuclear weapons physicist at the Lawrence Livermore Laboratory in the US with over 40 years of bomb-designing experience: "To me the headline is the boosted fission device but funnily no one is talking about it. If the Indians have done it then it is a very significant advance. It is a next generation weapon compared to atom bombs and would give them the confidence to develop a hydrogen bomb of any size." A boosted fission device also reduces the amount of plutonium needed for bigger yields apart from making the device lighter -- a big plus for India which does not have a huge stock of nuclear explosive material.

The Indian scientists even ridicule the foreign experts' inability to detect the two sub-kilotonne tests on May 13. "It is their bother and it casts doubts on their CTBT verification system and not on our capabilities," says Sikka. He is unwilling to divulge what the team tested on May 13 but India Today has learnt from reliable sources that one of the tests was to use what is known as dirty plutonium. Atom bombs require plutonium of a high degree of purity which are refined by a special process. India's nuclear power reactors generate plutonium in their fuel rods but it is considered unreliable for use in weapons.

If the Indians have developed the art of using reactor grade plutonium for bombs, it would significantly enhance India's fissile or nuclear explosive material stocks. This is particularly important because the UN has begun negotiating a treaty to limit fissile material stocks of countries. The sub-kilotonne tests have also enabled India to generate enough computer data that would help simulate tests. It would obviate the need for further nuclear explosive testing and possibly allow India to sign the CTBT. The team's estimate: the five tests were equivalent in value to about 50 of them.

Meanwhile, the debate over whether India detonated the H-bomb is unlikely to be settled in a hurry. Many think it is a futile one. As Kidder says, "It gives me no comfort to know that the Indians may have failed. What's important is they now have advanced capability for nuclear explosions." His point: even a dozen atom bombs will deter a country with hostile intentions.

Other experts too acknowledge that after these five tests India has a range of nuclear weapons capability that puts it far ahead of Pakistan. While Pakistan has demonstrated that it is capable of exploding atomic bombs, its claims of having tested a boosted fission device are in doubt after the reduced yields. Also unlike India, much of Pakistan's weapons capability has reportedly come clandestinely from other countries, mainly China and North Korea. Its fissile material stock too is considered much less than what India has.

The H-bomb, of course, puts India in a different league. The technology learnt would help make India's nuclear bombs much more compact, lighter and efficient. Although one H-bomb test will validate what is known as "proof of concept", whether India proceeds to make weapons with it will depend on just how good its computer simulations are. So it is important that scientists clear the doubts whether India's H-bomb was a dud or a truly deadly one.

"Our H-Bomb is not a fizzle and we are not afraid of peer review"

S K Sikka Satinder Kumar Sikka, 55, jokes that he could have easily ended up ploughing wheat fields in Ferozepore, Punjab, where he grew up. AEC chief R. Chidambaram, who was his Ph D guide, says it was fortunate for the country that he didn't. For as director of BARC's solid state and spectroscopy group, Sikka heads a team that is credited with the physics design of all the nuclear devices tested in May. He also played a key role in the 1974 Pokhran explosion. Last week the soft-spoken Sikka, in a rare interview to Deputy Editor
Raj Chengappa, revealed some secrets of India's H-bomb. Excerpts:

What is your response to the charge by international scientists that the yields of the 1998 Pokhran tests are far less than what India claims?
They have just not done their analysis properly. They have underestimated the yield by as much as a factor of four. Part of the reason is that they have taken the average of seismograph readings across the world without compensating for interference that could have distorted the results. Especially because factors such as location of the shafts, geology of the region and the fact that the three tests were done simultaneously could seriously affect calculations on yield. Seismic waves are like sound waves. And everyone knows that when you blare two loudspeakers placed close to each other the sound is usually distorted. Our hydrogen bomb test was certainly not a fizzle. Our device worked successfully.

But western researchers say they took all these distortions into account?
They never reveal how they came to such conclusions saying it is classified. Our findings are on the basis of sound scientific analysis. So let them refute it scientifically. We are not afraid of peer review. We have data from monitors close to the tests site which are far more sensitive and accurate. There are also other methods to measure the results of our tests. All of them clearly indicate that our thermonuclear device was successful.

The explosive yields for H-bombs are usually in megatons. Isn't India's claim of 45 kilotons a bit low for such devices?
That isn't true. The yields for a hydrogen bomb can vary from as little as 1 kilotonne to over 60 megatons. We kept our yield deliberately low to minimise damage to villages which are just 5 km from the blast site. Controlling yields does require a certain sophistication in design. Ours was a two-stage thermonuclear device. In early models the first stage was usually an atom bomb. We never revealed this before but our first stage was a boosted fission bomb which uses far more advanced technology.

Why test an H-bomb when experts maintain that bombs with such explosive force are not needed any more?
There was a similar debate even in the US in the 1950s when it was first exploded. All I can say is that it demonstrates our enhanced nuclear capability. The advantage with a hydrogen bomb is that with a small inventory of fissile material you can produce large yields. Whether we use it or not, it is good for us to have such a capability.

Are these five tests enough?
That's for the country to decide. All I can say is that these tests are worth about 50 in terms of experience and have enhanced our capability.