LOS ALAMOS, N.M. - Louis Rosen, a Los Alamos National Laboratory scientist who worked on the Manhattan Project and later created an influential neutron center at the facility, died Thursday. He was 91.

Rosen was sent to an Albuquerque hospital after an apparent fall at his home Aug. 15. A granddaughter, Ambyr Hardy, said he was transferred to a Los Alamos rehabilitation center shortly before he died.

The Lujan Neutron Scattering Center at LANSCE credits Rosen with leading the way in developing the world's most powerful linear accelerator, culminating in construction of the Los Alamos Meson Physics Facility, known today as the Los Alamos Neutron Science Center, or LANSCE.

Rosen directed the center until 1986.

Rosen went to work at Los Alamos in 1944 as a member of the Manhattan Engineering District's Project Y that led to the world's first atomic bomb in World War II. He worked during the war in neutron cross-section measurements and nuclear test diagnostics.

Rosen was born in New York City on June 10, 1918. He received his bachelor's and master's degrees from the University of Alabama and his Ph.D. from Penn State University. He taught at both universities.

Rosen in 2002 received the prestigious Los Alamos National Laboratory Medal, the lab's highest award.