The L X-ray photons emitted by transuranic (TRU) elements are expected to be useful for developing nondestructive TRU monitors. Energy spectra of L X-rays emitted by 241Am, 238Pu and 239Pu sources were measured by a transition edge sensor (TES) microcalorimeter, which allowed precise peak identification with high energy resolution. In the measurements using the TES microcalorimeter, the full width at half-maximum energy resolution was 62.6 eV at 17.222 keV for 239Pu source, 62.5 eV at 17.222 keV for 238Pu source and 60.9 eV at 17.751 keV for 241Am source. This study demonstrates the separation of 241Am and plutonium isotopes by L X-ray spectroscopy using a TES microcalorimeter.
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