Liverpool University (1939-43)
Rotblat travelled to England alone in 1939 as he could not afford to support Tola there. He was surprised at the poor state of the facilities at Liverpool with the physics teaching laboratory even lacking an AC electricity supply. He later became active in the Polish community and did fire watching at the University tower as Liverpool became subject to Air attacks.
Chadwick set him some problems connected with measurements on short lived radio-nuclide life times. One of his earliest experiments was the application of two Geiger radiation detectors to measure radioactive lifetimes between 1/10 second and 1/10 of a microsecond, demonstrating his skills as an experimental physicist and was to become part of his Liverpool P.hD thesis and a significant contribution to the subject (Rotblat, 1941).
Chadwick was so impressed with his work that he awarded him the Oliver Lodge Fellowship at £120 per year. Now, with sufficient funds, he returned home to Warsaw in the summer of 1939 with the intention of bringing his wife back to England. He planned to return to England in late August 1939 but Tola fell ill with appendicitis and he returned to Liverpool alone with the expectation that she would follow. However, war broke out as Poland was invaded by Germany on September 1 1939 (the day he arrived back in England) and Tola was stranded. Rotblat made increasingly desperate attempts to bring her out of Poland through Belgium, Denmark or Italy but these attempts failed as borders closed across Europe. She died in Majdanek concentration camp. This event affected him deeply for the rest of his life.
After the outbreak of war, the stipend that he received from Poland was stopped and he suffered considerable financial hardship. His personal relationship with Chadwick was good, visiting his house, going fishing together as well as holidays. As a mark of his regard for Rotblat, Chadwick appointed him lecturer in nuclear physics. This spurred him on to rapidly improving his English so as to deliver undergraduate lectures.
Rotblat’s prime motivation to work with Chadwick in Liverpool was to conduct experiments on the cyclotron that was just becoming operational when he arrived. This 37 inch cyclotron accelerated charged particles, such as protons to an energy of up 4.1 MeV and if then these particles collided with other nuclei, nuclear reactions can occur. The applications include the production of radioactive isotopes and studies of radioactive decay. However, at the outbreak of war, work on the bomb consumed almost all of the time available on the cyclotron until the end of 1943.
In November 1939, he presented to Chadwick plans for a Uranium fuelled bomb. This prompted Chadwick to encourage him to make measurements on the energy of neutrons generated by fission and the proportion of neutrons absorbed by other nuclei without producing fission. He was joined by Otto Frisch (Frisch, 1979) Rotblat went on to work on 235 U and made fundamental measurements on the cross-section of 235 U for fission neutrons, the scattering cross-section for neutrons and the energy spectrum of fission neutrons These experiments demonstrated that the nuclear bomb was feasible but would require a massive technological and industrial effort to produce sufficient quantities of the 235 U isotope required to manufacture a bomb.
What must be stressed here is the ingenuity and brilliance of Rotblat as an experimentalist. Together with Cecil Powell of Bristol University (who went on to win the Nobel Prize for Physics) he pioneered the use of sensitive photographic emulsions to detect neutrons and measure the associated energy and angular distribution of emissions. The neutrons collide with protons in the emulsion that recoil and leave tracks of silver grains, the length of which that can be measured using a microscope. Work he performed, that was subsequently declassified, became part of his Liverpool P.hD thesis. He also did fundamental work on spontaneous fission in Uranium and showed that the number of neutrons emitted was about the same as under induced fission. Again, this work involved difficult experiments (Rotblat, 1942).
Rotblat was wrestling with his conscience during the period back in England from saying, in interview, ‘What should I do? Should I begin to work on it?’ clearly meaning working on the bomb. What is central to Rotblat’s view is that he considered himself a ‘pure scientist’ and it was not his job to work on weapons of mass destruction. However, he was well aware that other scientists need not necessary share his convictions and in particular German scientists. Put simply, if Hitler had the bomb he would win the war.
When Poland was overrun he decided to work on the bomb. His belief was that we needed to work on the bomb in order that it should not be used. In other words, if Hitler can have the bomb, then the only way in which we can prevent him from using it against us would be if we also had it (Rotblat, 1985).
The USA was becoming increasingly more interested in the work going on within the UK and a summit was held in 1942 with Churchill and Roosevelt in attendance. The Americans had centered its efforts to manufacture a bomb at The Los Alamos Laboratory in New Mexico and the decision was taken that Chadwick’s team would relocate there. There was a problem, however, as only British citizens were allowed to work on the Project. Rotblat was adamant that he wanted to retain his Polish citizenship. Chadwick and others left for the US in December 1943 and Rotblat was allowed to join them two weeks later, retaining his Polish citizenship. Rotblat traveled by sea to New York and on to Washington where he was to meet General Groves, Head of the Bomb, or Manhattan Project as it was code named. He was given permission to go to Los Alamos, with Grove’s waiving the requirement for him to be a British citizen. When he arrived, Chadwick was there and he was impressed by the beauty of New Mexico, his accommodation and pay! He was to return to Liverpool in late 1944 and in 1945 to become Director of Research in nuclear physics following a series of dramatic and life changing events.