One of the fission products decayed into an element, I think it was xenon 135, a violent neutron absorber. But that saved the day because due to its strong neutron absorption it was destroyed rapidly. But if you close down the reactor, let xenon 135 accumulate, then you could not start it up again, a difficulty that took care of itself by waiting a while, but you have to understand it. At any rate, enough of the plutonium was made that together with our work on implosion there would not be a really bad shortage of it at the end- well when it became the end- at the end of the Second World War. All this work in Chicago was concluded by the end of 1944 and at that time, much to my pleasure, Fermi transferred to Los Alamos. He was put in charge of various things, among other things of the group with which I worked. And at that time I had a privilege which I share with very few people. I became the teacher of Fermi. I had to tell him what everybody in Los Alamos was doing and even excellent people- excellent student as Fermi was, and I claim not to have been a poor teacher, it took, it took almost a week before Fermi understood everything he wanted to know and that was just a little mot- bit more than everything that we knew. These were the conditions under which we were working. I, to some extent outside Los Alamos and a part of it of course was, what I already mentioned, the safety from nuclear explosions in other places like Oak Ridge. And one detail about that that I think is worth, worth mentioning, that I had a slightly ticklish job because I was not allowed to answer any questions, but people working on the other projects were instructed to answer all my questions. It says a lot about the character of the effective people who worked at that time, like Manson Benedict, that under these very unfavorable conditions, we worked well together and in fact established all the necessary mutual information.