Abstract: The present invention concerns a monitor for measuring both the gamma spectrum and neutrons emitted by an object such as a spent nuclear fuel pin or pin assembly or nuclear waste material. According to the invention, it comprises a lead block (1) presenting a front face (8) intended to be brought close to said pin (7) or assembly to be measured and incorporatinga gamma detector (2) for gamma spectroscopy located close to a rear face of said block and associated with a collimator (4) extending from said front face to said gamma detector,two neutron detectors (3) which extend parallelly to each other and to said front face and are disposed symmetrically on either side of the axis of said collimator (4) close to said front face (8).