S.M. Owens

Focusing of synchrotron radiation with polycapillary optics

Abstract Polycapillary optics are arrays of thousands of hollow capillary tubes. Focal spots are produced from the overlap of outputs from multiple channels at distances of 10–100 mm from the output of the optic. Synchrotron focusing was performed with two polycapillary X-ray optics. The spot size for the monolithic optic was 80 μm, which yielded a measured gain in photon flux through a 350 μm pinhole of nearly 100. Gains up to an order of magnitude larger are expected for smaller pinholes. White beam focusing was also demonstrated.

Stationary Crystal Diffraction with a Monochromatic Convergent X-ray Source and Application for Macromolecular Crystal Data Collection

A diffraction geometry utilizing convergent X-rays from a polycapillary optic incident on a stationary crystal is described. A mathematical simulation of the resulting diffraction pattern (in terms of spot shape, position and intensity) is presented along with preliminary experimental results recorded from a lysozyme crystal. The effective source coverage factor is introduced to bring the reflection intensities onto the same scale. The feasibility of its application to macromolecular crystal data collection is discussed.

Polycapillary x-ray optics for macromolecular crystallography

Polycapillary x-ray optics have found potential application in many different fields, including antiscatter and magnification in mammography, radiography, x-ray fluorescence, x-ray lithography, and x-ray diffraction techniques. In x-ray diffraction, an optic is used to collect divergent x-rays from a point source and redirect them into a quasi-parallel, or slightly focused beam. Monolithic polycapillary optics have been developed recently for macromolecular crystallography and have already shown considerable gains in diffracted beam intensity over pinhole collimation. Development is being pursued through a series of simulations and prototype optics. Many improvements have been made over the stage I prototype reported previously, which include better control over the manufacturing process, reducing the diameter of the output beam, and addition of a slight focusing at the output of the optic to further increase x-ray flux at the sample. We report the characteristics and performance of the stage I and stage II optics.

Concentration of synchrotron beams by means of monolithic polycapillary X-ray optics

Abstract Capillary optics are valuable tools for concentrating synchrotron radiation [D.J. Tiel, A.E. Stern, D.H. Bilderback and A. Lewis, Physica B 158 (1989) 314]. Single tapered capillaries are used at several facilities. However, most of these optics collect only over a small area. This can be overcome by using larger capillary structures. Polycapillary optics can deflect X-rays by larger angles than other X-ray optics that use only one or two reflections. Conventional X-ray optics that achieve similar deflections are much more energy selective than capillaries. Therefore, capillaries can achieve very short focal distances for a wide range of energies. The measurements shown here represent first tests performed with polycapillaries with large collection area. The performance with respect to transmission efficiency and spot size was evaluated for a set of four very different prototypes. It is shown that for these prototypes a significant gain may be achieved if a spot size of the order of 0.1 mm is required. Further, some characteristics of the different optics are discussed.

Ferromagnetism in a New Structural, Phase of [Fe(C5Me5)2] [TCNQ]

Abstract The five integrated-stack charge-transfer salts [M(C5Me5)2][TCNQ] (M═Mn,Cr) and [M(C5Me5)2][TCNE] (M═Fe, Mn, Cr) are bulk ferromagnets, whereas [Fe(C5Me5)2][TCNQ] was reported to exist as two different phases, a metamagnet and a paramagnet. We now report that with careful control of the crystallization conditions, it is possible to isolate a new structural phase of [Fe(C5Me5)2][TCNQ] which is a bulk 3-D ferromagnet with Tc = 3.1 K. Thus [Fe(C5Me5)2][TCNQ] is the first example of a single compound giving rise to three distinctly different magnetic phenomena, a finding that will permit an assessment of the subtle structural features that control magnetic ordering in this class of materials.

Effects of intense x-ray radiation on polycapillary fiber performance

Several applications of Kumakhov polycapillary optics require extended exposure to intense x- ray radiation. No degradation of performance has been observed when using polycapillary x- ray optics with laboratory sources. As part of an ongoing study to develop an understanding of damage mechanisms and performance limitations, borosilicate glass polycapillaries have been exposed to white beam bending magnet synchrotron radiation with peak energies of 5 and 11 keV, and focused broad band energy centered at 1.4 keV synchrotron radiation. In situ and ex situ measurements of degradation of x-ray transport efficiency have been performed at doses up to 1.8 MJ/cm2 at ambient and elevated temperatures. No decrease in transmission was observed for in situ measurement of fibers exposed to 1.4 keV photons at doses up to 1.4 MJ/cm2. Ambient temperature exposure to higher photon energies causes degradation that can be recovered by low temperature annealing. Exposure at elevated temperatures prevented any measurable damage to rigid fibers, at doses up to 800 kj/cm2.

Measurements of a prototype CdZnTe array for direct digital mammography

Measurements have been performed on a prototype CdZnTe linear array designed for direct digital mammography. Direct detection of x-ray photons without conversion to visible light avoids the trade-off between resolution and efficiency with phosphor thickness inherent in the conversion process. Polycapillary x-ray optics can be used to shape the x-ray image in a manner similar to the use of fused fiber optic tapers with visible light. The polycapillary optics also provide significant scatter rejection and resultant contrast enhancement. The theoretical detector quantum efficiency of CdZnTe at mammographic energies (20 keV) is quite high. Measurements were performed of DQE values and uniformity from 13 - 256 keV in large single pixel detectors. Uniformity and imaging measurements were also performed on a prototype 1 cm long linear detector array with 50 micrometer pixels attached to read-out electronics using indium bump bonding technology.