Montage of our solar system

The High Energy Astrophysics Division of the American Astronomical Society has named Jet Propulsion Laboratory astrophysicist Dr. Allan S. (Bud) Jacobson the winner of the 1985 Rossi Prize.

The prize, named in honor of Professor Bruno Rossi, was awarded for Dr. Jacobson's discoveries of radioactive aluminum-26 in the interstellar medium of the Milky Way Galaxy, and the discovery of variability of the 0.511 MeV (mega-electron volt) line from the direction of the center of the galaxy.

The prize consists of certificate and $500. Dr. Jacobson will make presentation of his work, for which the prize was awarded, at the June meeting of the American Astronomical Society in Ames, Iowa.

In 1980, Dr. Jacobson was awarded the NASA Medal for Exceptional Scientific Achievement for development of high resolution gamma-ray spectrometer launched the previous year aboard NASA's High Energy Astronomy Observatory (HEAO 3). This instrument, with which the discoveries were made, was designed and proposed in 1969, his first year at JPL.

Dr. Jacobson is native of Chattanooga, Tenn. He was graduated from UCLA in 1962 with Honors and elected to Phi Beta Kappa. He received his Master's degree (1964) and Doctorate in Physics (1968) from University of California, San Diego.

His discovery of radioactive aluminum-26 was the first direct evidence that elements of intermediate weight are presently being produced in our galaxy.

The element is unstable and spontaneously decays to another element, magnesium-26. "It is during this decay process that the characteristic gamma-ray is emitted which allowed the material to be detected," he said.

Dr. Jacobson's experiment also determined the variations in the 0.511 MeV line observed from the direction of the center of the galaxy. It has unique energy characteristic of the process in which an electron and an anti-electron, or positron, collide and mutually annihilate in burst of gamma-radiation.

In two HEAO 3 observations, six months apart, the experiment determined the intensity of the line had decreased by about one-third. This variation, he said, indicates the emission region must be relatively small when compared to expected scales of galactic structure.

"This lends support to the idea that there is black hole at the center of our galaxy," Dr. Jacobson said.

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