Much of the Marquardt Ramjet engine was made of a Magnesium-Thorium alloy. The magnesium was for machinability. But as you may already know Thorium is an actinide group element. Here is a snippet from webelements.com:

"Thorium is a source of nuclear power. There is probably more untapped energy available for use from thorium in the minerals of the earth's crust than from combined uranium and fossil fuel sources. Much of the internal heat the earth has been attributed to thorium and uranium."

"When pure, thorium is a silvery white metal which is air-stable and retains its lustre for several months. When contaminated with the oxide, thorium slowly tarnishes in air, becoming grey and finally black. Thorium oxide has a melting point of 3300°C, the highest of all oxides. Only a few elements, such as tungsten, and a few compounds, such as tantalum carbide, have higher melting points."

"Thorium is slowly attacked by water, but does not dissolve readily in most common acids, except hydrochloric. Powdered thorium metal is often pyrophoric and should be carefully handled.When heated in air, thorium turnings ignite and burn brilliantly with a white light."

"Thorium is named for Thor, the Scandinavian god of war. It is found in thorite and thorianite in New England (USA) and other sites."

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Consequently, Magnesium-Thorium aircraft engine parts are treated as nuclear waste, along with depleted uranium ammunition and other stuff:

Radiac calibrator sets
Chemical agent detectors
Tritium fire control devices
Tester moisture and density gauges
Magnesium/thorium alloy aircraft engine parts
Depleted uranium ammunition
Thorium fluoride coated optics
Aviation and troop command (ATCOM) industrial radiographic equipment
Electron tubes
Radium used in radioluminescent devices
ATCOM radium commodities
Thorium combustion liners
Vehicle radium dials/gauges
M97 explosive detector
M11 pistols

source

I have to say it, pun intended...... The Marquardt Ramjet was HOT. heh heh.