Lindsay Helmholz (November 11, 1909 – March 17, 1993) was an American physicist who participated in the Manhattan Project during World War II that created the atomic bomb.

He earned a PhD in chemistry at Johns Hopkins University before studying under Linus Pauling at California Institute of Technology and becoming a professor at Dartmouth College.

After World War II, he joined the faculty at Washington University in St. Louis where he continued his work with X-ray diffraction and retired in 1978.

[1] He then went to Johns Hopkins University, where he submitted his PhD thesis on "Lattice energies of rubidium bromide and sodium chloride and electron affinities of their halogens" in 1933,[3] writing under the supervision of Joseph E. Mayer.

Helmholz was a National Research Council postdoctoral fellow from 1934 to 1936, and he studied crystallography at the California Institute of Technology, working under Linus Pauling.

He was part of the committee that oversaw the RaLa Experiments, and worked out the chemical procedures for separating 100 curies (3.7 TBq) of lanthanum-140 from barium chloride.