Optically-stimulated luminescent (OSL) nanoDot dosimeters, commercially available from Landauer, Inc. (Glenwood, IL), were assessed for use in computed tomography (CT) for erasure and reusability, linearity and reproducibility of response, and angular and energy response in different scattering conditions. Following overnight exposure to fluorescent room light, the residual signal on the dosimeters was 2%. The response of the dosimeters to identical exposures was consistent, and reported doses were within 4% of each other. The dosimeters responded linearly with dose up to 1 Gy. The dosimeter response to the CT beams decreased with increased tube voltage, showing up to a -16% difference when compared to a 0.6-cm(3) NIST-traceable calibrated ionization chamber for a 135 kVp CT beam. The largest range in percent difference in dosimeter response to scatter at central and peripheral positions inside CTDI phantoms was 14% at 80 kVp CT tube voltage, when compared to the ionization chamber. The dosimeters responded uniformly to x-ray tube angle over the ranges of increments of 0° to 75° and 105° to 180° when exposed in air, and from 0° to 360° when exposed inside a CTDI phantom. While energy and scatter correction factors should be applied to dosimeter readings for the purpose of determining absolute doses, these corrections are straightforward but depend on the accuracy of the ionization chamber used for cross-calibration. The linearity and angular responses, combined with the ability to reuse the dosimeters, make this OSL system an excellent choice for clinical CT dose measurements.

Because of their high electrical resistivity and high magnetic permeability, nickel-zinc ferrites are among the best soft magnetic materials for high-frequency applications. In this work, a precursor of nanostructured (Ni 0.5 Zn 0.5)Fe 2 O 4 was obtained by a sol-gel method modified for large quantity production. Six heat-treated samples were produced by calcining the precursor for 3 h at 450, 500, 600, 650, 700, and 1100°C, respectively. X-ray diffraction peak width data have been used to estimate the particle sizes of the calcined samples. Room-temperature and low-temperature 57 Fe Mössbauer effect experiments allowed us to determine whether the heat-treated nanoparticles are crystalline or amorphous, whether there is a superparamagnetic phase, and which calcining temperature is optimum for obtaining a large magnetic hyperfine field and a homogeneous magnetic phase. Room-temperature Mössbauer spectra revealed that the precursor is paramagnetic, while the heat-treated samples have the ferrimagnetic phase. The samples heat treated at a calcining temperature of 650°C or higher showed no residual paramagnetic phase, indicating that 650°C is the threshold calcining temperature for homogeneous (Ni 0.5 Zn 0.5)Fe 2 O 4 nanoparticles. A comparison between low-temperature and room-temperature Mössbauer spectra demonstrated that the precursor is paramagnetic, whereas the heat-treated (500°C) sample has a component that shows superparamagnet relaxation.

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