Xunliang Ding

Focusing synchrotron radiation using a polycapillary half-focusing X-ray lens for imaging.

An imaging system based on a polycapillary half-focusing X-ray lens (PHFXRL) and synchrotron radiation source has been designed. The focal spot size and the gain in power density of the PHFXRL were 22 microm (FWHM) and 4648, respectively, at 14.0 keV. The spatial resolution of this new imaging system was better than 5 microm when an X-ray charge coupled device with a pixel size of 10.9 x 10.9 microm was used. A fossil of an ancient biological specimen was imaged using this system.

Performance of polycapillary X-ray optics for confocal energy-dispersive small-angle X-ray scattering

A confocal energy-dispersive small-angle X-ray scattering (EDSAXS) setup based on polycapillary optics was designed. In this confocal EDSAXS setup, a polycapillary slightly focusing X-ray lens (PSFXRL) and a polycapillary parallel X-ray lens (PPXRL) with a long input focal distance were placed confocally in the excitation channel and detection channel, respectively. This confocal configuration was helpful in improving the signal-to-noise ratio of the EDSAXS. The high gain in power density of the PSFXRL and PPXRL decreased the power requirement of the X-ray source for EDSAXS. The confocal EDSAXS technology could be used to perform nondestructive and in situ analysis of samples such as milk powder in its packaging.

Photochemistry and electron-transfer mechanism of transition metal oxalato complexes excited in the charge transfer band

The photoredox reaction of trisoxalato cobaltate (III) has been studied by means of ultrafast extended x-ray absorption fine structure and optical transient spectroscopy after excitation in the charge-transfer band with 267-nm femtosecond pulses. The Co–O transient bond length changes and the optical spectra and kinetics have been measured and compared with those of ferrioxalate. Data presented here strongly suggest that both of these metal oxalato complexes operate under similar photoredox reaction mechanisms where the primary reaction involves the dissociation of a metal–oxygen bond. These results also indicate that excitation in the charge-transfer band is not a sufficient condition for the intramolecular electron transfer to be the dominant photochemistry reaction mechanism.

Application of confocal X-ray fluorescence micro-spectroscopy to the investigation of paint layers

A confocal micro X-ray fluorescence (MXRF) spectrometer based on polycapillary X-ray optics was used for the identification of paint layers. The performance of the confocal MXRF was studied. Multilayered paint fragments of a car were analyzed nondestructively to demonstrate that this confocal MXRF instrument could be used in the discrimination of the various layers in multilayer paint systems.

Size-Resolved Source Apportionment of Aerosol Particles with a Confocal Micro X-Ray Fluorescence Spectrometer

A laboratory confocal micro X-ray fluorescence (micro-XRF) spectrometer based on a polycapillary focusing X-ray lens (PFXRL) in the excitation channel and a polycapillary parallel X-ray lens (PPXRL) in the detection channel was used to carry out the size-resolved source apportionment of aerosol particles. The PPXRL in the detection channel both increased the collection angle of the detector and improved the signal-to-noise ratio of the X-ray spectrum. When this confocal micro-XRF spectrometer was used to carry out the quantitative XRF analysis of single aerosol particles with smaller size than that of the overlapping foci of the PFXRL and the PPXRL, the sensitivity was corrected by using a Gaussian function. The size-resolved “fingerprint database” for the air pollution sources was established based on the quantitative XRF results for single aerosol particles. The size-resolved aerosol particles on hazy-foggy days in Beijing were apportioned.