Having studied the works by Holland physicist C.Ya.Gorter on paramagnetic relaxation, who also attempted to determine magnetic moments of atomic nuclei, Ye. K. Zavoisky decided to reproduce his experiments in spring 1941. For the purpose he employed not the Gorter's "calorimeter" technique, but a more sensitive method of grid current.
The experiments, aimed at the nuclear magnetic resonance, gave hopeful results, but the war impeded the investigations. Yevgeny Konstantinovich had to work for war industry and develop the mass radiator of ultra-Hertzian waves in Arkadyev's laboratory.
At the end of 1943 he continued his researches on magnetic moments of atomic nuclei, applying the method of magnetic modulation on more sensitive equipment. On November 25, according to the documents, he began experimenting for his second doctoral thesis, that marked the end of his forced "creativity delay":
"From 1942 to the end of 1943 I have practice in radiolocation, being a member of home guard subdivision on the assignment of the State Defense Committee. I give lectures at the Department of Physics and Mathematics of Kazan University and go to the subsidiary farm for field-work together with university students in summer" (extract from the scientist's memories).
According to the documents, Yevgeny K. Zavoisky registered the first EPR-signal on oscillograph screen on January 21, 1944. The EPR signals appeared on the screen, were recorded on celluloid films, which are still retained. The device, designed by Zavoisky, consisted of welding transformer, solenoidal coil, ammeter, autodyne generator, Abbot Roughness indicator and oscillograph. The variable magnetic audio-frequency field (50Hz) was established in the 12-centimeter-diameter 6-turn coil.
The coil was energized from the transformer secondary winding, connected with the alternating current source through the rheostat, which regulated the current. The magnetic field of the solenoid was measured by the alternating current value. The Hartmann-Braun ammeter of 200A was series-connected with the solenoid for the purpose. The proportionality factor of the magnetic field and current was determined experimentally.
A radio-frequency coil of the radio-frequency generator (10MHz, wave length 30 m) was placed in the solenoid magnetic field. It was connected in the P-5 valve circuit, which was assembled on valve P-5 on the analogy of the Esau circuit. The paramagnetic under study, brazed in hermetic celluloid ampoule, was located in the coil.