Argonne at 50

Argonne-developed alpha source probed lunar surface

ARGONNE, Ill. (Sept. 11, 1996) — More than 30 years ago, as the "space race" was nearing its climax, materials and techniques developed at Argonne National Laboratory helped scientists analyze for the first time in history the surface of another world.

Argonne scientists helped prepare an "alpha scattering instrument" carried to the moon aboard the Surveyor 5 spacecraft and first lowered to the lunar surface on Sept. 11, 1967. The instrument conducted the first direct analysis of the lunar surface.

The Surveyor series was designed to test soft-landing techniques that would be needed later for the Apollo manned space program. As the program was being developed, the University of Chicago's Anthony Turkevich conceived the idea of analyzing the lunar surface with alpha radiation -- charged helium nuclei emitted from some radioactive materials.

Turkevich had strong ties with Argonne, and was a former member of the University of Chicago's Metallurgical Laboratory, which developed the first nuclear reactor and later was renamed Argonne National Laboratory. The instrument would require a small, extremely intense source of alpha radiation. The particles, "scattering" from the nuclei of atoms in the lunar soil, would retain characteristic energies that could be registered by a sensitive detector. The energies of the scattered alpha particles would reveal the composition of the moon's surface.

In December 1960, Turkevich began working with James Patterson of Argonne's Chemistry Division to develop a source of alpha particles. To get high-quality data, the alpha-emitter had to be both extremely pure and produce large numbers of particles. Turkevich and Patterson settled on the isotope curium-242.

Argonne's role was the preparation of the radioactive material to be used in the instrument. The isotope was prepared by mixing the oxide of another, more common isotope, americium-241 (commonly used in ionizing-type smoke detectors) with aluminum powder inside a capsule. The capsule was welded shut and irradiated inside a nuclear reactor for several weeks.

Inside the reactor, americium-241 atoms captured neutrons, then decayed to the desired curium-242. Separating the desired isotope from the many other fission products and impurities that formed during the radioactive bombardment proved to be a complex and difficult job.

The work was carried out under the direction of E. Philip Horwitz, now a senior scientist, using methods he largely developed and special containment equipment built for the project. The highly radioactive mixture had to be handled remotely in shielded "hot cells." Radiation interfered with reagents, eroded and darkened the inner surfaces of glass containers, caused streams of bubbles and other problems.

The finished pellets of curium-242 were personally loaded into the scattering instrument aboard the Surveyor probe by Turkevich or Patterson. The five-pound instrument was about the size and shape of a toaster and contained six alpha sources.

On Sept. 10, 1967, Surveyor 5 came to rest at a slight angle on the side of a crater in the Sea of Tranquillity -- the same area of the moon where Apollo 11 astronauts would land less than two years later. After tests of on-board equipment, the alpha analyzer was lowered to the lunar surface on Sept. 11.

The instrument revealed that the moon's surface was similar in composition to basalt, a common terrestrial volcanic rock.

Alpha scattering devices were also carried by Surveyors 6 and 7, which produced similar results.

Surveyor 6 was launched Nov. 7, 1967, and landed Nov. 10 in Sinus Medii, a region in the center of the Moon's visible hemisphere. The alpha scattering instrument was toppled when the spacecraft was moved a short distance after landing for stereoscopic viewing and photogrammetric mapping of the surrounding terrain. Making the best of a bad situation, the scientists operated the instrument anyway for about a week afterward to measure cosmic radiation.

Surveyor 7 launched Jan. 7, 1968, and landed Jan. 10 north of the crater Tycho in the lunar highlands. A robot arm aboard Surveyor 7 was used to move the analyzer around the lunar surface near the probe.

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For more information, please contact Dave Jacqué (630/252-5582 or info@anl.gov) at Argonne.