Systems, methods, and apparatuses to determine an operation gas pressure in a neutron radiation generator are described. In certain aspects, a method to determine the operation gas pressure includes receiving an operation radiation signal from a radiation generated by electrons backstreaming in a radiation generator, and determining from the operation radiation signal an operation gas pressure in a chamber of the radiation generator. An operation radiation signal may be received from a radiation detector associated with a neutron radiation generator. A radiation detector may detect radiation produced by particles (e.g., electrons) striking a portion (e.g., a cathode) of the neutron radiation generator.