1. We report a new chemical thermal diffusion method for permeating 45 steel with zirconium.

2. In February the Alpha racetracks began receiving slightly enriched (1.4%) feed from the new S-50 thermal diffusion plant.

3. Oppenheimer wrote to Groves suggesting that the output of a thermal diffusion plant could be fed into Y-12.

4. Groves contracted with the H. K. Ferguson Company of Cleveland, Ohio, to build the thermal diffusion plant, which was designated S-50.

5. The most obvious technology, the centrifuge, failed, but electromagnetic separation, gaseous diffusion, and thermal diffusion technologies were all successful and contributed to the project.

6. By April 1945, K-25 had attained a 1.1% enrichment and the output of the S-50 thermal diffusion plant began being used as feed.

7. This procedure makes it possible to regulate precisely the energy and the electron flux and to adjust the dopage effect, something which is not possible using thermal diffusion alone .

8. However, this process makes it possible to control precisely the energy and the flux of the electrons and thereby to adjust exactly the dopage effect, a result which is not possible using thermal diffusion alone .

9. Simultaneous measurements with a thermal diffusion chamber and an Aitken nucleus counter show that in fine weather situations a high percentage of the Aitken nuclei (average 69%) is also active as cloud nuclei (supersaturation <1%).