Alvin Martin Weinberg (/ˈwaɪnbɜːrɡ/; April 20, 1915 – October 18, 2006) was an American nuclear physicist who was the administrator of Oak Ridge National Laboratory (ORNL) during and after the Manhattan Project.

A graduate of the University of Chicago, which awarded him his doctorate in mathematical biophysics in 1939, Weinberg joined the Manhattan Project's Metallurgical Laboratory in September 1941.

The following year he became part of Eugene Wigner's Theoretical Group, whose task was to design the nuclear reactors that would convert uranium into plutonium.

[12] In early 1942, Arthur Compton concentrated the Manhattan Project's various teams working on plutonium at the University of Chicago.

This brought in many top scientists including Herbert Anderson, Bernard Feld, Enrico Fermi, Leó Szilárd and Walter Zinn from Columbia, and Edward Creutz, Gilbert Plass, Eugene Wigner and John Wheeler from Princeton University.

[13] Wigner led the Theoretical Group at the Metallurgical Laboratory that included Alvin Weinberg, Katharine Way, Gale Young and Edward Creutz.

In July 1942, Wigner chose a conservative 100 MW design, with a graphite neutron moderator and water cooling.

[15] After the United States Army Corps of Engineers took over the Manhattan Project, it gave responsibility for the detailed design and construction of the reactors to DuPont.

The discovery of spontaneous fission in reactor-bred plutonium due to contamination by plutonium-240 led Wigner to propose switching to breeding uranium-233 from thorium, but the challenge was met by the Los Alamos Laboratory developing an implosion-type nuclear weapon design.

Later, he wrote: In these early days we explored all sorts of power reactors, comparing the advantages and disadvantages of each type.

[23] In 1945, Wigner accepted a position as the director of research at the Clinton Laboratories in Oak Ridge, Tennessee, which then had a staff of about 800.

[25] But after the Atomic Energy Commission took over responsibility for the laboratory's operations from the Manhattan Project at the start of 1947, Wigner, feeling unsuited to a managerial role in the new environment, left Oak Ridge at the end of summer in 1947 and returned to Princeton University.

He often sat in the front row at ORNL division information meetings and he would ask the first, often very penetrating, question after each scientific talk.

When asked how he found the time to attend every meeting, Weinberg replied jokingly, "We didn't have a DOE in those days.

That the project had little chance of success was not overlooked, but it provided employment and allowed ORNL to stay in the reactor development business.

Due to the radiation hazard posed to aircrew, and people on the ground in the event of a crash, new developments in ballistic missile technology, aerial refueling and longer range jet bombers, President Kennedy canceled the program in June 1961.

Despite its leaks and corrosion, valuable information was gained from its operation and it proved a simple and safe reactor to control.

[34] During the time the HRE was online, Senators John F. Kennedy and Albert Gore, Sr. visited ORNL and were hosted by Weinberg.

[25] Under Weinberg, ORNL shifted its focus to a civilian version of the meltdown-proof Molten Salt Reactor (MSR) away from the military's "daft"[35] idea of nuclear-powered aircraft.

The Molten-Salt Reactor Experiment (MSRE) set a record for continuous operation and was the first to use Thorium irradiated to produce uranium-233 as fuel.

The MSR was known as the "chemist's reactor" because it was proposed mainly by chemists (ORNL's Ray Briant and Ed Bettis (an engineer) and NEPA's Vince Calkins),[34] and because it used a chemical solution of melted salts containing the actinides (uranium, thorium, and/or plutonium) in a carrier salt, most often composed of beryllium (BeF2) and lithium (LiF) (isotopically depleted in Lithium-6 to prevent excessive neutron capture or tritium production) – FLiBe.

Weinberg's firing effectively halted development of the MSR, as it was virtually unknown by other nuclear laboratories and specialists.

[43] There was a brief revival of MSR research at ORNL as part of the Carter administration's nonproliferation interests, culminating in ORNL-TM-7207, "Conceptual Design Characteristics of a Denatured Molten-Salt Reactor with Once-Through Fueling", by Engel, et al., which is still considered by many to be the "reference design" for commercial molten salt reactors.

From 1976 to 1984, the Institute for Energy Analysis was a center for study of diverse issues related to carbon dioxide and global warming.

[47] In June, 1977, Weinberg testified at a congressional hearing of the House Subcommittee on the Environment and the Atmosphere concerning the impact of increasing carbon dioxide emissions on global average temperatures.