The answer's basically the dull one: the space was large, available and convenient.
It had actually already been in use for earlier sub-critical experiments for quite some time. One method for progress following the discovery of fission had been to study larger and larger assemblies of uranium. While these couldn't sustain a permanent chain reaction, essentially by studying how fast a chain reaction took to die out in them allowed insight into the reactions and a measure of how much bigger your pile was going to have to be to go critical. But these still involved tons of uranium and so required fairly large spaces in which to work. Bigger than the average university physics lab. Joliot-Curie had been doing that sort of experiment on the outskirts of Paris until interrupted in 1940 and Fermi had been doing the same at Columbia. Smaller versions had started under Stagg Field even prior to Fermi's arrival, when he used this space to continue what he'd started at Columbia.
Such experiments weren't much more radioactive than a pile of uranium ore sitting in a warehouse and were inherently stable, so didn't provoke any particular safety worries about doing them in the heart of the South Side. People were much more cautious initially about CP-1 and thus the original plan was to build it out at the new site at Argonne. However there was a labour strike by construction unions there that delayed the construction of the buildings. Rather than be delayed by the wait for them to be finished, Fermi proposed that it was now realised that the experiment was safe enough to be done in the existing space. (In particular, that delayed neutrons meant that while the pile could run-away with nasty consequencies once critical, this would happen so slowly that the experimenters would have plenty of time to intervene first.) This argument prevailed.
Arthur Compton made quite a bit of fuss in his postwar memoir
Atomic Quest about how he deliberately hid the decision from other university officials. His view being that Robert Hutchins wasn't in a position to judge how safe the experiment was and so he'd just have to have trusted Compton anyway. I suspect that - as quite often with Compton - there's an element of grandstanding (no pun intended) here.
As
this old Reader article from 1987 discusses, CP-1 eventually wound up out at Argonne and was buried there. I seem to recall a controversy in the Chicago papers back in the early Nineties about whether the burial was safe, but as I understand things it's still down there.
01-16-2009, 01:02 PM
Linear Mode
