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Linac

A linear accelerator, or “linac,” is basically a long hollow pipe, depleted of nearly all its air, through which electrons are accelerated on the crest of a traveling radio-frequency wave. By using a moving electromagnetic field to accelerate the electrons, the linac achieves a high-energy electron beam without the need for excessively high electrical voltages.

A long metal pipe is divided into sections.
Credit: NIST
The linac consisted of nine accelerating sections of 10 feet each to accelerate electrons.

Overhead view of complex scientific equipment
Credit: NIST
The magnet room for the linac allowed bending magnets to direct the high-energy electrons into beam lines that led to three different experimental facilities. 

When it went into operation in 1965 within Building 245 on the newly built campus in Gaithersburg, Maryland, the linac produced one of the world's most intense high-energy electron beams. Emerging from the end of the accelerator, this well-defined beam was then controlled by magnetic fields so it could interact directly with various materials or strike certain targets to generate other radiation, such as X-rays, positrons and neutrons. Beams of these radiations could be used in a variety of experiments in nuclear physics.

Long tube a few inches above the ground on NIST's campus
Credit: NIST
The neutron time-of-flight tubes located above ground allowed a beam of neutrons created in the linac to impact targets at tens of meters distances. The delay times for neutrons before they hit the target permits greater precision in the nuclear measurements.

The linac design stressed stability, a small spread of electron energies, and other high-quality beam characteristics. 

 

A man in a suit stands next to a piece of equipment with round targets.
Credit: NIST
NIST physicist Roald Schrack adjusts a target array for an experiment with the linac in the 1970s.

A man stands in the far background at the end of a long metal tube
Credit: NIST
NIST physicist H. Thompson Heaton adjusts a target on the linac beam line in the 1970s. 

Over a period of nearly two decades, the research program at the linac contributed to fundamental nuclear physics with a well-coordinated collaboration between theorists, experimentalists and database developers. Its ability to produce a high-intensity beam of neutrons made the linac a major user facility for university-based nuclear physics research. Experiments using the accelerator included measurements of a variety of neutron properties and light-induced nuclear reactions.  

It was decommissioned in the 1980s.

 

Created July 29, 2019, Updated September 20, 2019