In Sweden, Meitner continued her research as best she could. She measured the neutron cross sections of thorium, lead and uranium using dysprosium as a neutron detector, an assay technique pioneered by George de Hevesy and Hilde Levi. She was able to arrange for Hedwig Kohn, who faced deportation to Poland, to come to Sweden, and eventually to emigrate to the United States, travelling via the Soviet Union. She was unsuccessful in bringing Stefen Meyer out of Germany, but he managed to survive the war. She declined an offer to join Frisch on the British contribution to the Manhattan Project at the Los Alamos Laboratory, declaring "I will have nothing to do with a bomb!" She later said that the atomic bombings of Hiroshima and Nagasaki had come as a surprise to her, and that she was "sorry that the bomb had to be invented". After the war, Meitner acknowledged her own moral failing in staying in Germany from 1933 to 1938. She wrote: "It was not only stupid but very wrong that I did not leave at once." She regretted her own inaction during this period, and was also bitterly critical of Hahn, Max von Laue, Werner Heisenberg, and other German scientists. In a June 1945 letter addressed to Hahn, that he never received, she wrote: