[en] A long-time detection of the 870.73 keV gamma ray emitted from two PuO₂ samples of 100 g recycle powder and of 8 g pure powder has been respectively conducted using a high resolution HPGe spectrometer in a lead-shielded chamber. None of the characteristic gamma-rays related to the existence of oxygen shows up except the expected 870.73 keV gamma-ray which transit from the first exited state of ¹⁷O to the ground state. The analysis of the detection lower limit and the quantificational lower limit indicates that the minimum time for a credible detection of the 870.73 keV from the 8 g pure PuO₂ powder sample without any shield chambers is 4.6 h. From the pointview of on-site inspection, the mass of 8 g is inadequate, there must be more amount of PuO₂ presented so that the detection time can be controled within the permitted inspection ranges. It is still ambiquous whether the mass of 100 g recycled PuO₂ powder sample is adequate or not for on-site inspection of 870.73 keV gamma ray. (authors)