Category Archives: ManhattanProject

Plutonium Scale

Seederer-Kohlbush scale @ Hanford B Reactor

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.

Hanford B Reactor

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.

T Plant located in 200 West Area of Hanford. (T Plant @

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.

Building D, Tech Area, Los Alamos (Tech Area Gallery @

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:

Chicago Pile-1

December 2, 1942

Henry Moore’s sculpture, Nuclear Energy, at the site of the first controlled nuclear fission reaction on the University of Chicago campus.

On this day on December 2, 1942, Enrico Fermi and colleagues conducted the first controlled nuclear fission reaction at the University of Chicago (Chicago Pile-1). The site was designated a National Historic Landmark in 1965. This Henry Moore sculpture, Nuclear Energy, was placed at the site on the 25th anniversary in 1967.

Atomic Snapshots: 109 E Palace

109 E Palace

In a nondescript arcade of shops in Santa Fe, New Mexico, was the unassuming front face of the Manhattan Project for Los Alamos and the Hill: 109 E Palace.

Dorothy McKibbin, the “Gatekeeper to Los Alamos,” would process each of the scientists and families and keep the overwhelming secretarial work in order, essentially ensuring the top-secret access to Los Alamos.

The entrance to the old offices was off the patio, in back, where men and women entered through the alleyway, and the townsfolk never saw them come out. They were whisked away out the back and spirited to Los Alamos. 

Today, the building has been rezoned and numbered, and the current 109 E Palace is a chocolatier with an entrance on the street.

Go to the back of the courtyard to see the historical marker. And don’t forget to visit the Los Alamos History Museum to see the original door, history, and a tribute to Dorothy McKibbin.