kb/data/en.wikipedia.org/wiki/Abram_Alikhanov-1.md

title	chunk	source	category	tags	date_saved	instance
Abram Alikhanov	2/4	https://en.wikipedia.org/wiki/Abram_Alikhanov	reference	science, encyclopedia	2026-05-05T17:41:26.105097+00:00	kb-cron

Alikhanov switched to nuclear physics in 1933, following the discovery of the neutron and the positron in 1932. Abram Ioffe appointed Alikhanov head of the positron laboratory at the Department of Solid-State Physics at the Physical-Technical Institute. His group studied pair production and gamma rays and made observations of positrons using Geiger counters. According to Viktor Frenkel, their work became a "starting point for the application of radio engineering to experimental nuclear physics in the Soviet Union." Abov wrote that in 1933–34 Alikhanov and his colleagues were the "first to study in detail the spectrum of positrons from external pair conversion over the entire energy range. Among other things, they showed that, in accord with relevant theoretical results, the maximum of the spectrum occurs in the vicinity of the positron energy equal to half the endpoint energy." He added, "those investigations made it possible to reveal gamma lines that had previously been unknown, whereby it was possible to reconstruct the diagrams of decays of excited nuclei." They went on to study beta decay using not the usual Wilson cloud chamber, but a spectrometer developed by Alikhanov and Mikhail Kozodayev. It was a "radically improved" version of the "classical magnetic spectrometer with transverse field, fitting it with a system of coincidence-coupled gas-discharge counters. The use of this registration system was an important methodological novelty. It opened the way to development of Soviet nuclear electronics, which has been advanced in many of its aspects by Alikhanov's students. The new magnetic spectrometer was capable of registering the comparatively infrequent processes of positron production and could be used to investigate their energy spectra, the dependence of positron yield on γ-quantum energy and on the atomic number of the element, etc." In 1934 Alikhanov and Igor Kurchatov built a "baby cyclotron", which became the first "cyclotron" operating outside of Berkeley, California where Ernest Lawrence had invented it years earlier. It did not operate for long, though some experiments were conducted. The first proper cyclotron in the Soviet Union was built at the Radium Institute in Leningrad by 1936. Alikhanov "discovered that positrons were present even in the absence of a converter made from a heavy element, and this led him to the discovery of a new phenomenon—production of an electron-positron pair as a result of internal conversion of the energy of the excited nucleus." This was later used in nuclear spectroscopy. Alikhanov's group also studied scattering of fast electrons in matter and beta spectra of radioactive substances. In 1938 Alikhanov discovered a new method of determining the rest mass of the neutrino using decay of the nuclei of 7Be. He was awarded a PhD in Physical and Mathematical Sciences in 1935. He lectured at the St. Petersburg State Transport University in 1939–41 and chaired its Department of Physics.

== Cosmic rays and Armenia (1941–43) == Alikhanov planned to study cosmic rays, the only source of high-energy particles known at that time, in the Pamir Mountains in the summer of 1941, however, due to the approaching Nazi forces, Alikhanov and the Institute for Physical Problems were evacuated to Kazan in October 1941. In April 1942 he moved to Yerevan, Soviet Armenia with the intention to study cosmic rays at Mount Aragats. The expedition to Aragats resulted in the discovery of the "presence of an intense group of protons with comparatively small energies in the soft cosmic-radiation component" and "presence of a stream of fast protons in cosmic radiation." Alikhanov and his group, including his brother Artem Alikhanian, also erroneously concluded in the existence of cosmic radiation particles, called by them varitrons, which supposedly possessed a broad spectrum of masses. Alikhanov-Alikhanian brothers were widely criticized for the claim. Turkevich noted in 1956 that "this claim was questioned in the West and attacked by a group of Soviet physicists, with a subsequent bitter polemic in the Soviet physics journals. The controversy has never been settled officially, and Soviet cosmic ray research has suffered a lack of prestige." Luis Walter Alvarez noted that the brothers received the Lenin Prize for their unverifiable discoveries and "for them to have retracted their claims would have been embarrassing to their government." Alikhanov and his brother Artem established the Yerevan Physics Institute (YerPhI) in 1943 as a branch of Yerevan State University.

== Career in Moscow (1943–68) == After returning to Russia from Armenia, Alikhanov worked at the Institute for Physical Problems in Moscow from 1944 to 1946. Between 1947 and 1951 Alikhanov headed the Department of Structure of Matter at the Faculty of Physics and Technology of Moscow State University. He helped organize the Nuclear Physics Division of the Soviet Academy of Sciences. Among Alikhanov's students were Boris S. Dzhelepov, Venedikt P. Dzhelepov, Mikhail S. Kozodaev, Sergey Ya. Nikitin, Pyotr E. Spivak.

=== Atomic bomb project === Alikhanov was involved in the Soviet atomic bomb project. After the Soviet authorities learned of the German, British and American programs of nuclear weapons in mid-1942, works began on the Soviet project led by Igor Kurchatov. At Laboratory no. 2, Alikhanov was assigned to develop a nuclear pile with heavy water. Lev Artsimovich, Isaak Kikoin, and Anatoly Alexandrov worked on electromagnetic isotope separation, gaseous diffusion process and thermal diffusion process, respectively. While Alikhanov led the research on the construction of a heavy-water reactor. In August 1945 the Special Committee under the Council of Ministers (Council of People's Commissars) was formed to oversee works on uranium, headed by Lavrentiy Beria. The Scientific-Technical Council was headed by Boris Vannikov and included Alikhanov (initially as it scientific secretary), Igor Kurchatov, Pyotr Kapitsa, Abram Ioffe and others.

=== ITEP ===