Timothy Madden

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

Firmware lower-level discrimination and compression applied to streaming x-ray photon correlation spectroscopy area-detector data

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

) 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.

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

We present a data acquisition system to perform on-the-fly background subtraction and lower-level discrimination compression of streaming x-ray photon correlation spectroscopy data from a fast charge-coupled device (CCD) area detector. The system is built using a commercial frame grabber with an on-board field-programmable gate array. The system is capable of continuously processing at least 60 CCD frames per second each consisting of 1024 × 1024 16-bit pixels with ≲ 15,000 photon hits per frame at a maximum compression factor of ≈95%.

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.

2-D scintillation position-sensitive neutron detector

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.

Tomography with energy dispersive diffraction

Thermal kinetic inductance detectors (TKIDs) are promising new detectors for use in X-ray spectroscopy because of the relative ease with which they can be fabricated into large arrays. While initial results have hinted at their resolution capability, the ultimate resolution achievable with these detectors has not been described. Using a bolometer matrix formalism, we examine the parameter space of the detector design (i.e., film critical temperature, detector operating temperature, resonator coupling, etc.) to examine the detectors response to noise sources, including phonon, Johnson, bias, and amplifier noise. Finally, we present the design of TKID optimized for 6-keV X-ray spectroscopy.

Real-time MPI-based software for processing of XPCS data

A new 2-dimensional scintillation position-sensitive neutron detector (PSND) with an active area of 155times155 mm2 was developed for use on the single crystal diffractometer at the intense pulsed neutron source at Argonne National Laboratory. The detector is based on the well-proven Anger camera technique and uses a 6Li glass scintillator as the neutron converter. This PSND incorporates a 6times6 PMT array with 29.6 mm pitch and optimized optics to achieve an average spatial resolution of 1.75 mm full width at half maximum. The detector read-out has separate electronics for each PMT and the neutron position is calculated by a microprocessor during acquisition. A newly developed position extraction algorithm makes use of an analytical calculation to determine the event position. This new method improves the linearity of the calculated position, provides a slight improvement in resolution, and in principle allows for the correct determination of position to the edge of the scintillator. The design of the detector enclosure allows multiple detectors to be tiled with minimal dead space between them. In addition, the design incorporates a means of attaching external shielding plates that minimizes the shielding surface area required

FPGA-based compression of streaming x-ray photon correlation spectroscopy data

X-ray diffraction can be used as the signal for tomographic reconstruction and provides a cross-sectional map of the crystallographic phases and related quantities. Diffraction tomography has been developed over the last decade using monochromatic x-radiation and an area detector. This paper reports tomographic reconstruction with polychromatic radiation and an energy sensitive detector array. The energy dispersive diffraction (EDD) geometry, the instrumentation and the reconstruction process are described and related to the expected resolution. Results of EDD tomography are presented for two samples containing hydroxyapatite (hAp). The first is a 3D-printed sample with an elliptical crosssection and contains synthetic hAp. The second is a human second metacarpal bone from the Roman-era cemetery at Ancaster, UK and contains bio-hAp which may have been altered by diagenesis. Reconstructions with different diffraction peaks are compared. Prospects for future EDD tomography are also discussed.

Microstructure Analysis of Bismuth Absorbers for Transition-Edge Sensor X-ray Microcalorimeters

We describe a software library, called MPIFCCD, based on the Message Passing Interface (MPI) for real-time parallel computing on data continuously streamed from the Frame Store Fast Charge-Coupled Device (FSFCCD) Detector located at the Advanced Photon Source (APS) at Argonne National Laboratory. The FSFCCD is used to collect data for X-ray Photon Correlation Spectroscopy (XPCS) experiments at Sector 8-ID at APS. MPIFCCD is integrated into another software package called CINController, developed at APS and Lawrence Berkeley National Laboratory to serve as a QT-based user interface for control and data collection from the FSFCCD. Real-time calculations performed by MPIFCCD include dark image integration and subtraction, noise image integration, image descrambling, and lower-level discrimination. MPIFCCD allows for continuous real-time data collection of FSFCCD data at image rates of 100 frames- per-second (fps) for 1 mega-pixel images and 1000fps for 10 kilo-pixel images. In the future, more complex computations will be implemented in real time with MPIFCCD.