An imaging spectrometer based on high resolution microscopy of fluorescent aluminum oxide crystal detectors

Fluorescent Nuclear Track Detector (FNTD) technology was tested as an imaging, spectroscopic tool for radionuclide analysis. This investigation intended to distinguish between characteristic α-particles of 239Pu (5.2 MeV), 234U (4.8 MeV) and 238U (4.2 MeV). FNTDs are Al2O3:C,Mg single crystals with color centers that undergo radiochromic transformation. FNTD readout is non-destructive and is performed with fluorescence laser scanning confocal microscopy. Ionization events register in the detector as bright fluorescent features on a weak fluorescent background. Images were acquired at several incrementing depths in the detector to produce 3D datasets. Spectroscopic information was obtained by measuring α-particle range in the detector after 3D image reconstruction. The resolution of this technique is fundamentally limited by particle range straggling (about 3.8% (k = 1) at these α-particle energies). The spectroscopic line-width as full width at half maximum (FWHM) was determined to be 0.4 MeV enabling discrimination between the isotopes of interest. ► FNTD technology was investigated as a tool for radionuclide imaging spectroscopy. ► Particle energies were determined using 3D image processing of fluorescent tracks. ► The α-particle energy line-width for 241Am was determined to be 0.4 MeV. ► Range straggling fundamentally limits the resolution of the range measurement technique.