Antonino Miceli

Quantitative 3D elemental microtomography of Cyclotella meneghiniana at 400-nm resolution

X-ray fluorescence tomography promises to map elemental distributions in unstained and unfixed biological specimens in three dimensions at high resolution and sensitivity, offering unparalleled insight in medical, biological, and environmental sciences. X-ray fluorescence tomography of biological specimens has been viewed as impractical—and perhaps even impossible for routine application—due to the large time required for scanning tomography and significant radiation dose delivered to the specimen during the imaging process. Here, we demonstrate submicron resolution X-ray fluorescence tomography of a whole unstained biological specimen, quantifying three-dimensional distributions of the elements Si, P, S, Cl, K, Ca, Mn, Fe, Cu, and Zn in the freshwater diatom Cyclotella meneghiniana with 400-nm resolution, improving the spatial resolution by over an order of magnitude. The resulting maps faithfully reproduce cellular structure revealing unexpected patterns that may elucidate the role of metals in diatom biology and of diatoms in global element cycles. With anticipated improvements in data acquisition and detector sensitivity, such measurements could become routine in the near future.

Picosecond time-resolved laser pump/X-ray probe experiments using a gated single-photon-counting area detector.

The recent developments in X-ray detectors have opened new possibilities in the area of time-resolved pump/probe X-ray experiments; this article presents the novel use of a PILATUS detector to achieve X-ray pulse duration limited time-resolution at the Advanced Photon Source (APS), USA. The capability of the gated PILATUS detector to selectively detect the signal from a given X-ray pulse in 24 bunch mode at the APS storage ring is demonstrated. A test experiment performed on polycrystalline organic thin films of alpha-perylene illustrates the possibility of reaching an X-ray pulse duration limited time-resolution of 60 ps using the gated PILATUS detector. This is the first demonstration of X-ray pulse duration limited data recorded using an area detector without the use of a mechanical chopper array at the beamline.

Synchrotron applications of an amorphous silicon flat-panel detector

A GE Revolution 41RT flat-panel detector (GE 41RT) from GE Healthcare (GE) has been in operation at the Advanced Photon Source for over two years. The detector has an active area of 41 cm x 41 cm with 200 microm x 200 microm pixel size. The nominal working photon energy is around 80 keV. The physical set-up and utility software of the detector system are discussed in this article. The linearity of the detector response was measured at 80.7 keV. The memory effect of the detector element, called lag, was also measured at different exposure times and gain settings. The modulation transfer function was measured in terms of the line-spread function using a 25 microm x 1 cm tungsten slit. The background (dark) signal, the signal that the detector will carry without exposure to X-rays, was measured at three different gain settings and with exposure times of 1 ms to 15 s. The radial geometric flatness of the sensor panel was measured using the diffraction pattern from a CeO(2) powder standard. The large active area and fast data-capturing rate, i.e. 8 frames s(-1) in radiography mode, 30 frames s(-1) in fluoroscopy mode, make the GE 41RT one of a kind and very versatile in synchrotron diffraction. The loading behavior of a Cu/Nb multilayer material is used to demonstrate the use of the detector in a strain-stress experiment. Data from the measurement of various samples, amorphous SiO(2) in particular, are presented to show the detector effectiveness in pair distribution function measurements.

Tungsten silicide films for microwave kinetic inductance detectors

Microwave kinetic inductance detectors are used to detect photons over a large range of wavelengths from submillimeter to X-ray. The common material requirements for this application are: high internal quality factor (Qi), high kinetic inductance fraction, long quasiparticle lifetime, and in the case of X-ray photons stopping power (i.e., dense, high atomic number materials). Superconducting tungsten silicide alloys have a tunable TC with silicon content, a high normal state resistivity, and a high density. In this work, we investigate the properties of thin films of tungsten silicide made of two different stoichiometry: WSi2 and W5Si3 with particular attention to their application to microwave kinetic inductance detectors. We present a study of the structural and transport properties of films deposited under different conditions for both stoichiometry. Quarter wavelength microwave coplanar waveguide resonators have been fabricated from films of both stoichiometry and we present measurements of the microwave properties of these films as well as quasiparticle lifetimes using X-ray photons.

X-ray photon detection using superconducting resonators in thermal quasi-equilibrium

Superconducting resonators have to date been used for photon detection in a non-equilibrium manner. In this paper, we demonstrate that such devices can also be used in a thermal quasi-equilibrium manner to detect x-ray photons. We have used a resonator to measure the temperature rise induced by an x-ray photon absorbed in normal metal and superconducting absorbers on continuous and perforated silicon nitride membranes. We observed two distinct pulses with vastly different decay times. We attribute the shorter pulses to non-equilibrium quasiparticle relaxation and the longer pulses to a thermal relaxation process. In addition, we have measured the temperature dependence of the x-ray induced temperature rise and decay times. Finally, we have measured the resonator sensitivity and energy resolution.

Development of Thick Electroplated Bismuth Absorbers for Large Collection Area Hard X-ray Transition Edge Sensors

Transition edge sensors (TES) offer some of the highest resolutions for solid-state X-ray spectrometers. We are developing TES detectors for use at hard X-ray synchrotron light sources for energy ranges up to 20 keV. Because TES resolving power scales inversely with the square root of heat capacity, it is important to have an absorber with both a small heat capacity and a large X-ray stopping power. We are developing electroplated bismuth (Bi) absorbers to meet these criteria. Although Bi has a smaller X-ray absorption at 20 keV than gold, the specific heat is up to two orders of magnitude smaller, allowing for much larger collection area (up to 1 mm

Eliminating the non-Gaussian spectral response of X-ray absorbers for transition-edge sensors

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Processing of X-ray Microcalorimeter Data with Pulse Shape Variation using Principal Component Analysis

) without significantly increasing the total device specific heat. However, due to its low thermal conductivity, Bi absorbers may have longer thermalization times. Also, some evaporated Bi absorbers may produce spectra with low-energy tails that will hinder X-ray line shape analysis and increase minimum detectability limits of trace metals for X-ray fluorescence microscopy. We examine the impact of plating current density, agitation, film thickness, and seed layer thickness on the grain size, residual resistance ratio, and uniformity of Bi absorbers. Additionally, we discuss processing considerations important for successful electroplating.

Optimization of thermal kinetic inductance detectors for x-ray spectroscopy

Transition-edge sensors (TESs) as microcalorimeters for high-energy-resolution X-ray spectroscopy are often fabricated with an absorber made of materials with high Z (for X-ray stopping power) and low heat capacity (for high resolving power). Bismuth represents one of the most compelling options. TESs with evaporated bismuth absorbers have shown spectra with undesirable and unexplained low-energy tails. We have developed TESs with electroplated bismuth absorbers over a gold layer that are not afflicted by this problem and that retain the other positive aspects of this material. To better understand these phenomena, we have studied a series of TESs with gold, gold/evaporated bismuth, and gold/electroplated bismuth absorbers, fabricated on the same die with identical thermal coupling. We show that the bismuth morphology is linked to the spectral response of X-ray TES microcalorimeters.

Ultra-fast LuI3:Ce scintillators for hard x-ray imaging

We present a method using principal component analysis (PCA) to process x-ray pulses with severe shape variation where traditional optimal filter methods fail. We demonstrate that PCA is able to noise-filter and extract energy information from x-ray pulses despite their different shapes. We apply this method to a dataset from an x-ray thermal kinetic inductance detector which has severe pulse shape variation arising from position-dependent absorption.