Monolithic active pixel sensors featuring a time-invariant front-end channel have been fabricated in a quadruple well CMOS process in the frame of an R&D project aiming at developing low material budget, radiation hard detectors for tracking applications. MAPS prototypes have been exposed to integrated fluences up to 10^14 1 MeV neutron equivalent / cm^2 to test the device tolerance to bulk damage also for different values of the epitaxial layer resistivity. Moreover, samples of the same device have been irradiated with y-rays from a 60Co source, reaching a final dose exceeding 10 Mrad, to study ionizing radiation effects. This work discusses the test results, obtained through different measurement techniques, and the mechanisms underlying performance degradation in irradiated quadruple well CMOS MAPS.
