i recently heard that when us scientist tested fat boy in new mexico, many of them though that the bomb may wipe out the entire world.

When i heard this is thought: OMG!!!! Testing a weapon than can erase manking, even if the chances were 1% u cant take that risk
What do you think??

There was a theory that the chain reaction might spread to the atmosphere and essentially incinerate the earth. But quantum math equations did not bear this theory out and, in fact, indicated that the chances of such an occurrence approached absolute zero (in other words the chances were much, much less than 1%). The idea did cause some anxiety among the scientists who checked and rechecked their calculations on this matter over and over. I understand that some small scale lab experiments tended to discredit the theory, as well.

The scientists were much more concerned that the bomb would not work at all. I have read that a betting pool was set up regarding the potential results; the predictions ranging from a complete dud, up through a range of kiloton yields, to destruction of the state of New Mexico, and finally the incineration of the earth. The unfortunate bettor who drew either of the last two options must have been disappointed as he or she would not be able to collect the pot, if they "won".

Make your decision, Little Boy or Fat Man?

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I recall from Tibbets´book that the last practice bomb´s fuse before dropping the real A-bomb did not work but the again we all know what a bad last practice means...Then again it would have been an interesting situation if the Japanese had gotten an actual A-bomb that failed to work.

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Was the trigger on the practice bombs similar to those on the atomic bombs? I thought the "pumpkin" practice bombs were just high explosive which I believe would have used a quite different fusing mechanism. Even the two atomic bombs dropped on Hiroshima and Nagasaki had different types of fuses due to the fact that the Little Boy bomb used a "gun" type trigger which utilized explosive charges at each end of a closed tube to propel two masses of fissionable material into contact with each other thereby achieving critical mass. The Fat Man plutonium bomb achieved critical mass by implosion; an explosive "lens" surrounding a plutonium shell was triggered to force the shell to collapse, thus achieving critical mass. About the only thing each had in common was the use of conventional explosive to force fissionable material into a critical mass. However, due to the very different configuration of the explosives used, the initiating fuses must have been quite different. In addition, I believe there were a number of redundant fuses in each bomb to avoid just such circumstances as you postulate.

Well that's all a bit over my head!
But I do know that there is a whole lot of radio active soil still out there! At least that's what a friend told me! That could be just one of those old wives tales!!

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This is a pair of Dutch resistance crystal radios, built into a small metal can, and a matchbox. The image is from a postcard bought at a Dutch Resistance Museum in Amsterdam. The matchbox is marked in Swedish, but Swedish matches were sold in Holland for many years..
Scott

That must be checked from the book. I just recall what the author mentioned that the last practice session did not go very well. I believe the system measuring the height was suspected of being faulty ( I guess my word choice of fuse in my previous posting is not correct sorry about that ) with the last practice version. But they did have several practice bombs dropped successfully so all in all it was pretty well tested that it worked. Definitely the explosion system worked, but at what height the bomb would explode needed another mechanism, I think.

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And the book I am actually referring to is:

Amazon.com: Enola Gay: Mission to Hiroshima: Gordon Thomas, Max Morgan-Witts: Books

In the Finnish version the details of the flight are on p. 302-306.

( translated from the Finnish text )

Sweeney was ordered on 5th August to perform the last flight before the Atomic bomb attack. Tibbets had given an order to fly the "Great Artiste" and from 30,000 feet drop a concrete bomb to the ocean , which would be followed by scientists from Tinian. This was the same kind of detonator test as was done by Sweeney´s crew in Wendower, and back then the mechanim had worked prematurely.

One of the scientists following the test was Luis Alvarez, the son of the famous surgeon working in the Mayo clinic. Alavarez knew every step that would happen if the mechanism worked perfectly. Once the bomb would fall out from the bomber, also a wire would fall out which would cut the signal Alvarez was listening to, and would close the switch inside the bomb - the first switch in line of several switches. These switches would have to close in certain order before the battery´s current would reach the electrical detonator.

The signal Alvarez was listening to ended. He knew the bomb had started falling.One of the switches would close once a certain height had been reached, i.e. 5,000 feet. After that the most sensitive part of the system would be activated, the mini radar, which would reveive the waves it sends coming back from the ground below, and the radar was adjusted to close the last switch at 1,850 feet. As a sign of the last switch being closed there would be a puff of smoke.

However, no smoke puff was noticed and the bomb fell into the ocean. Alvarez turned to his colleagues. " Great, just great! Tomorrow we´re going to drop one of those to Japan, even if we haven´t managed to make the mechanism work properly!"

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That's an interesting story of which I wasn't aware. Apparently the test you are referring to used a different kind of practice bomb from the "pumpkins" which were large metal spheres painted orange (hence the name) and loaded with high explosive. I do know that the actual atomic bombs used radar altimeter devices as their primary triggers because maximum damage depended on the bombs exploding at a specific altitude. I also understand that there was some question about the exact altitude at which one of the bombs exploded (I forget which, but I think it was the Nagasaki bomb) and that the radar altimeter may have been at fault. There were however other types of fuses used as back-ups including an impact fuse, so that it was unlikely the Japanese would be able to recover an unexploded atomic bomb.