Tuesday, September 13, 2016

Interesting article by Dr. Pervez Hoodbhoy

The story of Riazuddin.

I didn't know this for a fact but I had suspected it,

Soon thereafter, perhaps around September 1972, Salam summoned Riazuddin to his office at the International Center for Theoretical Physics in Trieste, Italy. He had decided that Riazuddin was to design the bomb and, immediately upon his return to Islamabad, must create a group of theoretical physicists who would explore various technical aspects: the conceptual design for a nuclear device, calculation of the critical size of the fissile core, working out of a triggering mechanism, and finding the explosive yield for a variety of theoretical designs. Salam had already discussed the matter with Munir Ahmad Khan, with whom he had a warm relationship. Riazuddin should be given this task, Salam said. Khan agreed; and Riazuddin dutifully complied.

Another detail that I was unaware of

Some weeks after the 1998 tests, Riazuddin wrote to Sharif pleading that Pakistan should now sign the Comprehensive Test Ban Treaty and the Fissile Material Cutoff Treaty. The first would prohibit more test explosions, which in any case were not essential, while the second would limit the size of the nuclear arsenal and prevent a sharp upward spiral in warhead numbers, costs, and dangers. As quid pro quo, he said, Pakistan should insist on nuclear-power technology transfer from the West. He received no reply. Quite possibly Sharif did not know how much the bomb owed to Riazuddin.

This part is simply intriguing

The calculations Riazuddin carried out were tedious and complex. The plutonium route had been closed for now and Munir Ahmad Khan had tasked him with the following problem: his bomb must use the absolute minimum amount of highly-enriched uranium, and certainly no more than 20 kilograms. As a particle physicist he had a reasonable understanding of nuclear physics, but knew no hydrodynamics or how matter behaved under extreme compression. This knowledge is crucial for designing an implosion bomb because the high explosive surrounding the bomb’s core creates a shockwave that makes jelly out of even the toughest metal. These unfamiliar things had to be learned from books and papers. Like any good theoretical physicist, Riazuddin refused to accept what the computer churned out until he could verify it by using some clever analytical techniques.

What Pervez is describing here is the computation of the neutron absorption cross-sections by Dr. Masud Ahmad and Dr. Tufail Naseem. Those can be verified against physical experiments ("analytical techniques").  Those numbers by themselves are important but mean nothing without control over flow and compression.

A pity - it would be good to know who  the lead hydrodynamicist and the lead high pressure physicist was in Pakistan.

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