Ruffino we crowd six-and-three-quarter millions of these, two-hundred-and-forty into each of twenty-eight-thousand twelve-foot rods, into the nuclear reactor core. This we figure to be the optimum critical mass for fissioning, a process controlled by huge supplies of cooling water and one that can be stopped altogether by dropping boron rods between the uranium tubes.’
Jeff said: ‘What would happen if the water supply stopped and you couldn’t activate the boron rods or whatever? Bang?’
‘No. The results would be bad enough – clouds of radio-active gas that might cause some thousands of deaths and poison tens, perhaps thousands of square miles of soil – but it’s never happened yet, and the chances of it happening have been calculated at five billion to one. So we don’t worry too much about it. But a bang? A nuclear explosion? Impossible. For that you require U-235 over ninety per cent pure, the stuff we dropped on Hiroshima. Now that is nasty stuff. There was a hundred-and-thirty-two pounds of it in that bomb, but it was so crudely designed – it really belonged to the nuclear horse-and-buggy age – that only about twenty-five ounces of it fissioned: but was still enough to wipe out the city. Since then we have progressed – if that’s the word I want. Now the Atomic Energy Commission reckons that a total of five kilograms – eleven pounds – is the so-called “trigger” quantity, enough for the detonation of a nuclear bomb. It’s common knowledge among scientists that the AEC is most conservative in its estimate – it could be done with less.’
Ryder said: ‘No U-238 was stolen. You used the word “understandably”. Couldn’t they have stolen it and converted it into U-235?’
‘No. Natural uranium contains a hundred-and-forty atoms of U-238 to each atom of U-235. The task of leaching out the U-235 from the U-238 is probably the most difficult scientific task that man has ever overcome. We use a process called “gaseous diffusion” – which is prohibitively expensive, enormously complicated and impossible to avoid detection. The going cost for a gaseous diffusion plant, at today’s inflated rates, is in the region of three billion dollars. Even today only a very limited number of men know how the process works – I don’t. All I know is that it involves thousands of incredibly fine membranes, thousands of miles of tubes, pipes and conduits and enough electrical power to run a fair-sized city. Then those plants are so enormous that they couldn’t possibly be built in secret. They cover so many hundreds of acres that you require a car or electric cart to get round one. No private group, however wealthy or criminally-minded, could ever hope to build one.
‘We have three in this country, none located in this State. The British and French have one apiece. The Russians aren’t saying. China is reported to have one in Langchow in Kansu Province.’
‘It can be done by high-speed centrifuges, spinning at such a speed that the marginally heavier U-238 is flung to the outside. But this process would use hundreds of thousands of centrifuges and the cost would be mind-boggling. I don’t know whether it’s ever been done. The South Africans claim to have discovered an entirely new process, but they aren’t saying what and US scientists are sceptical. The Australians say they’ve discovered a method by using laser beams. Again, we don’t know, but if it were possible a small group – and they’d all have to be top-flight nuclear physicists – could make U-235 undetected. But why bother going to such impossible lengths when you can just go to the right place and steal the damned stuff ready-made just as they did here this afternoon?’
Ryder said: ‘How is it all stored?’
‘In ten-litre steel bottles each containing seven kilograms of U-235, in the form of either an oxide or metal, the oxide in the form of a very fine brown powder, the metal in little lumps known as “broken buttons”. The bottles are placed in a cylinder five inches wide that’s braced with welded struts in the centre of a perfectly ordinary fifty-five-gallon steel drum. I needn’t tell you why the bottles are held in suspension in the airspace of the drum – stack them all together in a drum or box and you’d soon reach the critical mass where fissioning starts.’
Jeff said: ‘This time it goes bang?’
‘Not yet. Just a violent irradiation which would have a very nasty effect for miles around, especially on human beings. Drum plus bottle weighs about a hundred pounds, so is easily moveable. Those drums are called “bird-cages”, though Lord knows why: they don’t look like any bird-cage I’ve ever seen.’
Ryder said: ‘How is this transported?’
‘Long distance by plane. Shorter hauls by common carrier.’
‘Common carrier?’
‘Any old truck you can lay your hands on.’ Ferguson sounded bitter.
‘How many of those cages go in the average truck shipment?’
‘That hi-jacked San Diego truck carries twenty.’
‘One hundred and forty pounds of the stuff. Right?’
‘Right.’
‘A man could make himself a fair collection of nuclear bombs from that lot. How many drums were actually taken?’
‘Twenty.’
‘A full load for the van?’
‘Yes.’
‘So they didn’t touch your plutonium?’
‘More bad news, I’m afraid. When they were being held at gunpoint but before they were locked up some of the staff heard the sound of another engine. A diesel. Heavy. Could have been big – no one saw it.’ The telephone on his desk rang. He reached for it and listened in silence except for the occasional ‘who?’, ‘where?’ and ‘when?’ He hung up.
‘Still more bad news?’ Jablonsky asked.
‘Don’t see it makes any difference one way or another. The hi-jacked van’s been found. Empty, of course, except for the driver and guard trussed up like turkeys in the back. They say they were following a furniture van round a blind corner when it braked so sharply that they almost ran into it. Back doors of the van opened and the driver and the guard decided to stay just where they were. They say they didn’t feel like doing much else with two machine-guns and a bazooka levelled six feet from their windscreen.’
‘An understandable point of view,’ Jablonsky said. ‘Where were they found?’
‘In a quarry, up a disused side road. Couple of young kids.’
‘And the furniture van is still there?’
‘As you say, Sergeant. How did you know?’
‘Do you think they’d have transferred their cargo into an identifiable van and driven off with it? They’d have a second plain van.’ Ryder turned to Dr Jablonsky. ‘As you were about to say about this plutonium –’
‘Interesting stuff and if you’re a nuclear bomb-making enthusiast it’s far more suitable for making an atom bomb than uranium although it would call for a greater deal of expertise. Probably call for the services of a nuclear physicist.’
‘A captive physicist would do as well?’
‘What do you mean?’
‘They – the villains – took a couple of visiting physicists with them this afternoon. From San Diego and Los Angels, I believe they were.’
‘Professor Burnett and Dr Schmidt? That’s a ludicrous suggestion. I know both men well, intimately, you might say. They are men of probity, men of honour. They’d never co-operate with the blackguards who stole this stuff.’
Ryder sighed. ‘My regard for you is high, Doctor, so I’ll only say that you lead a very sheltered life. Men of principle? Decent men?’
‘Our regard is mutual so I’ll just content myself with saying that I don’t have to repeat myself.’
‘Men of compassion, no doubt?’
‘Of course they are.’
‘They took my wife, and a stenographer