Hitler's Terror Weapons by Brooks, Geoffrey (life books to read .txt) 📗

The thickness of lead required to reduce the initial intensity of gamma radiation by a factor of ten is 1.8 inches. The thickness of the walls, lid and base of the lead containers described by Hirschfeld would have provided an interior volume for each container sufficient for about 19 kilos of uranium metal powder, multiply by eighty = 1520 kilos: divide by 750 kilos = enough for two small-scale atom bombs.

The Implosion Fuses

A final twist to the U-234 story has been suggested.139 The German small-yield device could not have been properly detonated without an effective implosion fuse. For eighteen months the scientists at Los Alamos had failed to develop such a fuse. In October 1944 Robert Oppenheimer created a three-man committee to look into the problem. Luis Alvarez was on this team and became one of the heroes of the American A-bomb story when he solved it in the final days before the Trinity test at Alamogordo in July 1945.

The need was for a fusing system that could fire multiple detonators simultaneously. Harlow Russ, who worked on the plutonium bomb team, stated in his book Project Alberta that improvements were made to the detonator at the last moment. A new type of implosion fuse suddenly becoming available to the Manhattan Project gave a result four times better than expected at the Trinity A-test.

But did the real impetus for this success come from Luis Alvarez or German technology? Germany could not have detonated small-scale atom bombs without the most superior implosion fuse. According to the CI0S-BI0S/FIAT 20 report published by the US authorities in October 1946, by May 1945 Germany already had every kind of fuse known to the Americans –; “and then some”. Professor Heinz Schlicke, one of the passengers aboard U-234, was an expert in fuse technology. Infra-red proximity fuses were discovered to be aboard U-234 on 24 May 1945, apparently as a result of the interrogation of Dr Schlicke in which he mentioned that he had fuses which worked on the principles that govern light. A memorandum by Jack H. Alberti dated 24 May 1945 states:

“Dr Schlicke knows about the infra-red proximity fuses which are contained in some of these packages. Dr Schlicke knows how to handle them and is willing to do so.”

Schlicke and two others were then flown to Portsmouth NH to retrieve the fuses. It is not suggested that these were the fuses used to explode the American plutonium bomb, but rather confirms that Schlicke knew more about fuses than the Manhattan Project did. From a transcript of a lecture given by Dr Schlicke to the Navy Department in July 1945, there seems to have been a close cooperation for some reason between Dr Schlicke and Luis Alvarez. And it is in the fact that the technological side of the Manhattan Project failed them that the real weakness of the American project is exposed.

CHAPTER 13

The Manhattan Project

THE MANHATTAN PROJECT was founded in order that the United States should have a nuclear capability in the event that Hitler developed the atom bomb. By the end of hostilities in Europe in May 1945 the United States did not have a bomb which worked, and, as that was the Project’s raison d’être, it obviously failed. The American failure was in technology, for they were unable to devise an efficient implosion fuse.

How the Implosion Bomb Works

As any physicist will explain, the only economical way to detonate a Pu239 or plutonium bomb is by the implosion method. The bomb core is made as a sub-critical sphere surrounded by a layer of non-fissile U238. A uniform layer of high explosive surrounds the tamper. When the thirty-two fuses are triggered simultaneously, the explosive detonates, creating a massive uniform pressure of millions of pounds per square inch which compresses the core to a supercritical density, causing the implosion. The implosion method is essential for plutonium-type bombs because the radioisotope Pu240, being more fissile than Pu239, would otherwise cause a premature detonation of the material known as a ‘fizzle’. The least speed required for assembly of the critical mass by implosion is in the region of 3500 feet/sec.

The U235 bomb is more fissile than the plutonium device and the speed of assembly of the critical mass can be as low as 1000 feet/sec. For this reason an implosion fuse is not necessary for this type of bomb, but the amount of uranium material required is vastly greater.

In order to conceal the failure of the Manhattan Project, General Groves and his associates wanted people to continue to believe that ideally a plutonium bomb is detonated by an implosion fuse, while ideally the U235 bomb is detonated by a ‘gun-type’ device. The ‘gun-type’ detonator is, of course, what they say was used to detonate the so-called ‘Thin Man’ device used to devastate Hiroshima and which works in principle in the following manner: since one cannot assemble a critical mass without there being a reaction from it, two sub-critical lumps of highly enriched U235 are kept apart until detonation when they are fired together within a howitzer barrel with a breech at each end. The supercritical mass assembles at a reasonably fast speed in sub-atomic terms and so achieves the explosion.

The Development of the Manhattan Project without an Implosion Fuse

Since the Americans had no effective implosion fuse to hand before the end of May 1945, no question ever arose of detonating a plutonium bomb in the preceding period. The U235 bomb was the only possibility. Although the actual information regarding the Hiroshima bomb is probably still classified half a century later, it is known that the critical mass in the most favourable configuration as calculated by Richard Feyman was 50 kilos of U235. Robert Oppenheimer put it at double that. This is an awful lot of U235 to expend in one bomb. Of course, nobody in his right mind would dream of putting half a field gun into a