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Nuclear resonance fluorescence has significant potential in the identification and measurement of isotopes due to its specificity for different nuclei. This study explored the NRF pinhole imaging technique through Monte Carlo simulations in the detection of $^{239}$Pu samples. By designing and optimizing key parameters of the pinhole imaging system, including the direction of incident photons, geometric aperture, acceptance angle, pinhole thickness, object distance and magnification factor, high spatial resolution of 1.2cm with good signal-to-noise ratio of 1.63 have been achieved. Simulation results preliminarily demonstrate the capability of NRF pinhole imaging to effectively distinguish $^{239}$Pu samples with different concentrations and sizes and obtain direct imaging results without the need for further data processing. However, challenges such as high-energy noise photons and low count rate of NRF photons limit the image quality. Further investigations are warranted to develop imaging correction algorithms that can compensate for these effects and enhance the accuracy of NRF pinhole imaging.
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