Characterization of a submicro-X-ray fluorescence setup on the B16 beamline at Diamond Light Source.

An X-ray fluorescence setup has been tested on the B16 beamline at the Diamond Light Source synchrotron with two different excitation energies (12.7 and 17 keV). This setup allows the scanning of thin samples (thicknesses up to several micrometers) with a sub-micrometer resolution (beam size of 500 nm × 600 nm determined with a 50 µm Au wire). Sensitivities and detection limits reaching values of 249 counts s-1 fg-1 and 4 ag in 1000 s, respectively (for As Kα excited with 17 keV), are presented in order to demonstrate the capabilities of this setup. Sample measurements of a human bone and a single cell performed at B16 are presented in order to illustrate the suitability of the setup in biological applications.

Development of a multi-lane X-ray mirror providing variable beam sizes.

Grazing incidence mirrors are used on most X-ray synchrotron beamlines to focus, collimate or suppress harmonics. Increasingly beamline users are demanding variable beam shapes and sizes at the sample position. We have now developed a new concept to rapidly vary the beam size and shape of a focused X-ray beam. The surface of an elliptically figured mirror is divided into a number of laterally separated lanes, each of which is given an additional longitudinal height profile calculated to shape the X-ray beam to a top-hat profile in the focal plane. We have now fabricated two prototype mirrors and present the results of metrology tests and measurements made with one of the mirrors focusing the X-rays on a synchrotron beamline. We envisage that such mirrors could be widely applied to rapid beam-size switching on many synchrotron beamlines.

Nanofocusing optics for synchrotron radiation made from polycrystalline diamond.

Diamond possesses many extreme properties that make it an ideal material for fabricating nanofocusing x-ray optics. Refractive lenses made from diamond are able to focus x-ray radiation with high efficiency but without compromising the brilliance of the beam. Electron-beam lithography and deep reactive-ion etching of silicon substrates have been used in a transfer-molding technique to fabricate diamond optics with vertical and smooth sidewalls. Latest generation compound refractive lenses have seen an improvement in the quality and uniformity of the optical structures, resulting in an increase in their focusing ability. Synchrotron beamline tests of two recent lens arrays, corresponding to two different diamond morphologies, are described. Focal line-widths down to 210 nm, using a nanocrystalline diamond lens array and a beam energy of E = 11 keV, and 230 nm, using a microcrystalline diamond lens at E = 15 keV, have been measured using the Diamond Light Source Ltd. B16 beamline. This focusing prowess is combined with relatively high transmission through the lenses compared with silicon refractive designs and other diffractive optics.

X-ray submicrometer phase contrast imaging with a Fresnel zone plate and a two dimensional grating interferometer.

The application of a two dimensional (2D) grating interferometer-Fresnel zone plate combination for quantitative submicron phase contrast imaging is reported. The combination of the two optical elements allows quick recovery of the phase shift introduced by a sample in a hard X-ray beam, avoiding artifacts observed when using the one dimensional (1D) interferometer for a sample with features oriented in the unsensitive direction of the interferometer. The setup provides submicron resolution due to the optics magnification ratio and a fine sensitivity in both transverse orientations due to the 2D analysis gratings. The method opens up possibilities for sub-micro phase contrast tomography of microscopic objects made of light and/or homogeneous materials with randomly oriented features.

High efficiency nano-focusing kinoform optics for synchrotron radiation.

Modern synchrotron sources have provided for decades intense beams of photons over a large energy spectrum. The availability of improved optics and detectors has opened up new opportunities for the study of matter at the micrometre and nanometre scale in many disciplines. Whilst exploitation of micro-focused beams occurs almost daily in many beamlines, the production of beams of 100 nm is achieved on few instruments which use specialised optics. Refractive lenses, zone plates, curved mirrors, multilayers, and multilayer Laue lenses, can all focus x-rays to less than 50 nm under strict beam stability conditions. Focusing the synchrotron radiation to beam sizes smaller than 10 nm is considered the ultimate goal for the current decade. Silicon micro-technology has so far provided some of the most advanced x-ray refractive lenses; we report on design and characterisation of a novel silicon kinoform lens that is capable of delivering nano-beams with high efficiency.

[Perioperative management of laparoscopic cholecystectomy in children with homozygous sickle cell disease]. / Prise en charge périopératoire de la cholécystectomie par voie laparoscopique chez l'enfant drépanocytaire homozygote.

OBJECTIVE: Sickle cell disease is a public health problem in Africa. The aim of this prospective study was to evaluate per and post-operative complications of laparoscopic cholecystectomy in sickle cell children in Senegal. METHODS: from January 1999 to December 2006, an anesthetic protocol was applied to 39 sickle cell children undergoing a cholecystectomy. Among them, 20 experienced laparoscopic cholecystectomy. RESULTS: All these 20 patients had previously suffered from sickle cell visceral complications and were classified as ASA II (11 cases) and as ASA III (9 cases). Blood transfusion program aimed at sustaining haemoglobin level between 10 and 12 g/dl was implemented. The preoperative monitoring and anesthesia management were the same for these patients. During perioperative period, the prevention of pain, hypovolemia, hypothermia and acidosis was achieved. The mean insufflation duration of laparoscopy was 23 min (17-60 min), the mean surgery duration was 55 min (40-110 min), and the mean anesthesia duration was 78 min (88-135 min). Postoperative complications occurred in 9 patients: acute chest syndrome (n=2), postoperative hemolysis (n=5), vaso-occlusive crisis (n=2). CONCLUSION: Laparoscopic cholecystectomy can be carried out in sickle cell children affected with gallstones, provided that general anaesthetic rules were respected. An appropriate pre-, per- and postoperative anaesthesia is mandatory to reduce postoperative complications in children with sickle cell disease. Searching for early diagnosis of gallstones before occurrence of visceral complications should allow further optimal laparoscopic surgery.

Critical fluctuations and quenched disordered two-dimensional charge stripes in La(5/3)Sr(1/3)NiO4

Using high-resolution x-ray scattering, we have demonstrated the existence of quenched disordered charge stripes in a single crystal of La (5/3)Sr (1/3)NiO (4) at low temperatures. Above the second-order transition critical scattering was observed due to fluctuations into the charge stripe phase. The charge stripes are shown to be two dimensional in nature both by measurements of their correlation lengths (xi(a) approximately 185 A, xi(b) = 400 A, and xi(c) approximately 25 A) and by the critical exponents of the charge strip transition. The charge stripe ordering did not develop long-range order even at low temperatures, indicating that the charge stripes are disordered and that the length scale of the disorder is quenched.