Receiving credit with Georgy Flyorov, a physicist, for the fundamental discovery of spontaneous fission of uranium in 1940, Petrzhak's career in physics was then spent mostly in the former Soviet program of nuclear weapons.

[4] There is very little information known about his early life and started working at the age of 12 (in 1919) as a painter at a glass-making factory in Malaya Vishera in Russia to provide income to his poor family.

[4] In 1928, Petrzhak was sent to attend the trade school, Rabfak, that was affiliated with the Leningrad State University, where he studied painting which remained his lifelong passion.

[6] In November 1936, Pertzhak eventually earned his diploma certified under Igor Kurchatov[7] from the Leningrad State University.

[14][14] The team created a multilayer ionization chamber to detect decay products originating from the fission of uranium.

The team moved to an underground lab in the Dinamo station of Moscow Metro (about 50 m below the earth surface)[20] in an attempt to rule out the effects of cosmic rays.

[21] The certificate of discovery stated, "the new type of radioactivity with mother nucleus decays into two nuclei, that have kinetic energy of about 160 MeV".

When the Soviet Union entered World War II, Petrzhak was eligible to serve in the Red Army.

Jointly with M. Yakunin, Petrzhak developed methods for the radiochemical determination of plutonium, and found the mean free path of Pu-239 alpha particles.

[32] Petrzhak founded the Saint Petersburg State Institute of Technology department of nuclear physics in 1949,[4] and remained its chair for 22 years.

[4] Konstantin Petrzhak created an express method to detect plutonium and associated radioisotopes in samples of irradiated uranium.

[35][36] From 1973 through 1984, he took part in measuring induced fission cross-sections of U-238, U-235 and Pu-239 when irradiated by monoenergy neutrons[37][38] In 1978, Konstantin Petrzhak co-authored a paper (with Yuri Oganessian and others) about synthesis of hassium performed in Joint Institute for Nuclear Research.