S J Pfauntsch

A Focused Ultrasoft X-Ray Microbeam for Targeting Cells Individually with Submicrometer Accuracy

Abstract Folkard, M., Schettino, G., Vojnovic, B., Gilchrist, S., Michette, A. G., Pfauntsch, S. J., Prise, K. M. and Michael, B. D. A Focused Ultrasoft X-Ray Microbeam for Targeting Cells Individually with Submicrometer Accuracy. Radiat. Res. 156, 796–804 (2001). The application of microbeams is providing new insights into the actions of radiation at the cell and tissue levels. So far, this has been achieved exclusively through the use of collimated charged particles. One alternative is to use ultrasoft X rays, focused by X-ray diffractive optics. We have developed a unique facility that uses 0.2–0.8-mm-diameter zone plates to focus ultrasoft X rays to a beam of less than 1 μm diameter. The zone plate images characteristic K-shell X rays of carbon or aluminum, generated by focusing a beam of 5–10 keV electrons onto the appropriate target. By reflecting the X rays off a grazing-incidence mirror, the contaminating bremsstrahlung radiation is reduced to 2%. The focused X rays are then aimed at selected subcellular targets using rapid automated cell-finding and alignment procedures; up to 3000 cells per hour can be irradiated individually using this arrangement.

Broad angular multilayer analyzer for soft X-rays

Using numerical optimization algorithm, non-periodic Mo/Si, Mo/Be, and Ni/C broad angular multilayer analyzers have been designed. At the wavelength of 13 nm and the angular range of 45~49 degrees , the Mo/Si and Mo/Be multilayer can provide the plateau s-reflectivity of 65% and 45%, respectively. At 5.7 nm, the s-reflectivity of Ni/C multilayer is 16% in the 44~46 degrees range. The non-periodic Mo/Si broad angular multilayer was also fabricated using DC magnetron sputtering, and characterized using the soft X-ray polarimeter at BESSY. The s-reflectivity is higher than 45.6% over the angular range of 45~49 degrees at 13 nm, where, the degree of polarization is more than 99.98%.

Soft x-ray spectromicroscopy of wood fibre composites

Understanding the structural properties of wood fibre composites, widely used in building and other applications, is an important area of research in devising robust new materials for a range of environmental conditions, including those encountered in developing countries. Wood fibre composites are prepared by mixing fibres with prescribed amounts of glue, but exactly where the glue distributes in relation to the fibre components is unclear. Characterisation of the bonding conditions has largely been a matter of trial and error, which is time consuming and imprecise. In soft x-ray spectromicroscopy experiments carried out at the NSLS, a range of wood fibre composites, with different glues and glue loadings, was studied in order to attempt to quantify the relative glue content in different components of the composite.

Smart X-Ray Optics

This paper describes reflective adaptive/active optics for applications including studies of biological radiation damage. The optics work on the polycapillary principle, but use arrays of channels in thin silicon. For optimum performance the x-rays should reflect once off a channel wall in each of two successive arrays. This reduces aberrations since then the Abbe sine condition is approximately satisfied. Adaptivity is achieved by flexing the arrays via piezo actuation, providing further aberration reduction and controllable focal length.

The King’s College laboratory scanning x-ray microscope

The King’s College laboratory scanning x-ray microscope has been used on the laser plasma source at the Rutherford Appleton Laboratory, which has been extensively characterized. Resolution and contrast in the initial images are limited by electrical noise in the detector system.

Applications of wavelet analysis to study growth characteristics of x-ray multilayer mirrors

Transmission electron microscopy images and hard x-ray reflectivity curves are used to obtain information on the growth characteristics of x-ray multilayer mirrors. A multi-resolution approach based on wavelet analysis is used to decompose the interface profiles obtained from transmission electron microscopy images into a number of different spatial frequency ranges. The replication factor (vertical) and the characteristic length (lateral) of the interfacial roughness are determined in these spatial frequency ranges. By changing the upper or lower limits of the wavelet transform of the x-ray reflectivity curves, the structure uniformity (lateral) and evolution of the surface damage (vertical) are determined. These results are significant for the study of the growth characteristics of ultrathin x-ray multilayer mirrors and enable more effective methods to determine their imperfections.

The x-ray microprobe for studies of cellular radiation response

An x-ray microprobe, which utilizses a small laboratory x-ray source with a carbon target and a zone plate to form a fine focus, has been used for initial studies of cellular radiation response. It is not yet clear whether carbon K x-rays exhibit the hypersensitivity at very low doses for 240 kVp x-rays, which manifests itself predominately with sparsely ionizing radiation. There is some evidence to support the phenomenon of radiation induced bystander effects whereby unexposed neighbors of irradiated cells also exhibit a response.

A modified electron multiplier X-ray detector for synchrotron and laser plasma sources

A 129EM electron multiplier has been modified to detect soft x-rays by coating the first dynode with CsI. The prototype detector was tested at the X1a beamline of the NSLS synchrotron source at Brookhaven Lab and at the laser plasma source at the Rutherford Lab. Initial tests have shown that the detector type is suitable for use in soft x-ray microscopy.

Applications of Laboratory Soft X-Ray Systems

Three systems which use laboratory scale X-ray sources and zone plate optics are under development: a dark field microscope, a scanning microscope and a microprobe for studies of cellular radiation response. Both microscopes are designed for use on a laser plasma source, but the dark field system can also be utilised at a storage ring. The microprobe uses either a micro focus source with a carbon target or a laser plasma source.