The experiment B8 at Haigerloch

The relocation of the lab to Haigerloch

Walter Gerlach, who studied physics in Tübingen and had been professor there, probably recalled the area around Hechingen and Haigerloch. He proposed building a laboratory within a bunker in the narrow limestone valley of the Eyach-River, since it was considered safer from air raids. During their visit to Haigerloch, it was pure coincidence that caused the scientists to find the rockhewn beer cellar of the "Schwanen Inn" and they could rent it for their work.

In an adventuresome trip by truck from Berlin to Haigerloch, the uranium and the heavy water was relocated from Berlin to Haigerloch, where the famous "B8"-experiment was able to be carried out at the end of March and the beginning of April.

The setup

The reactor was located in a concrete cylinder. Between the outer concrete shell and the inner aluminium shell normal water was filled in for cooling purposes. The aluminium container had a diameter of 210 cm and a height of 210 cm, and contained another vessel made of magnesium. The space between the two vessels was filled with a 40 cm layer of graphitic carbon bricks. These bricks provided an external shield which prevented the escape of neutrons generated during the fission. The 664 uranium cubes (edge lenght of 5 cm) attached to the lid were then lowered into the inner magnesium vessel. It was a spatial grid, and the distance between the closest was 14 cm. Subsequently, the lid was bolted onto the reactor.

(Bild des Einsatzes)

The execution

A neutron source was inserted into the center of the installation through the so-called chimney. There were openings in the top for the insertion of the so-called neutron probes to determine an exact measurement of the distribution of neutrons inside the apparatus, in the surrounding graphite bricks, and in the light water in the tank. Lastly, the heavy water was poured in slowly and carefully and the proliferation of the neutrons measured during the filling-up operation. If the reactor had become critical, the experiment would have been terminated.

(Bild der Schwerwassertanks)

Tanks for the Heavy Water

The result

Empty: The neutron count was taken without uranium and without heavy water, but with the neutron source inserted, in the exterior filled with graphite and light water.

Full:The neutron count was taken in the exterior with uranium inserted and the heavy water poured in.

The ratio of measurement with to the measurement without uranium and the heavy water is called the multiplication factor. It came to about seven. By this, the reactor didn't become critical. Further calculations showed that a functioning nuclear reactor would have had to be about 1.5 times the size of this reactor. However, expanding the reactor was no longer possible in April 1945 due to the lack of both heavy water and additional quantities of uranium blocks.

Michael.Thorwart@physik.uni-augsburg.de(Aug-11-1997)