This Seederer-Kohlbusch scale, circa 1944, is found in a side room of the B Reactor at Hanford along with displays of other artifacts and mementos of the Manhattan Project. This is the original scale used to weigh the first milligrams of plutonium (Pu) produced at the facility.
In October 1943, construction began on the B Reactor at the Hanford Site in Washington, with the purpose of producing plutonium. Fuel slugs — uranium billets extruded into slugs and sealed in aluminum jackets — were then placed in the reactor for several weeks to a year. The reactor went critical on September 26, 1944. The first irradiated slugs were discharged from the reactor on December 25, 1944.
Fuel slugs were then removed from the reactor and placed in a 90-day underwater cooling off period before being transported by train to the Hanford T Plant, which began operations on December 26, 1944. Next, the bismuth phosphate process was used on the fuel slugs to separate the plutonium from uranium and other fission products. The final processed product was plutonium nitrate, which made for safer shipping to Los Alamos.
In late January, 1945, the first milligrams of plutonium produced at Hanford were weighed on this scale then sent by courier to Los Alamos for testing. Los Alamos received its first plutonium from Hanford on February 2, 1945.
Subsequently, Building D in the Tech Area at Los Alamos would purify and fabricate the plutonium nitrate received from Hanford into the highly purified metallic hemispheres used in the Trinity and Nagasaki devices.
For further reading:
- Grant, V. (2021, December 12). Atomic number 94. Los Alamos National Laboratory.
- Plutonium. (2014, June 5). Atomic Heritage Foundation.
- Shannon, J.M. & Shannon, G.C. (1999). Seederer-Kohlbush (SeKo). Robert A. Paselk Scientific Instrument Museum, Humboldt State University.
- T Plant. (2022, April 26). Manhattan Project National Historical Park. National Park Service.
- Center for Disease Control. (2009, June). Draft final report of the Los Alamos Historical Document Retrieval and Assessment (LAHDRA) Project. National Center for Environmental Health, Division of Environmental Hazards and Health Effects, Radiation Studies Branch. (See Chapter 4: Plutonium Processing at Los Alamos)
