Understanding Warm Dense Matter (WDM), the state of planetary interiors, is a new frontier in scientific research. There exists very little experimental data probing WDM states at the atomic level to ...test current models and those performed up to now are limited in quality. Here, we report a proof-of-principle experiment that makes microscopic investigations of materials under dynamic compression easily accessible to users and with data quality close to that achievable at ambient. Using a single 100 ps synchrotron x-ray pulse, we have measured, by K-edge absorption spectroscopy, ns-lived equilibrium states of WDM Fe. Structural and electronic changes in Fe are clearly observed for the first time at such extreme conditions. The amplitude of the EXAFS oscillations persists up to 500 GPa and 17000 K, suggesting an enduring local order. Moreover, a discrepancy exists with respect to theoretical calculations in the value of the energy shift of the absorption onset and so this comparison should help to refine the approximations used in models.
Purpose
Current techniques and procedures for dosimetry in microbeams typically rely on radiochromic film or small volume ionization chambers for validation and quality assurance in 2D and 1D, ...respectively. Whilst well characterized for clinical and preclinical radiotherapy, these methods are noninstantaneous and do not provide real time profile information. The objective of this work is to determine the suitability of the newly developed vM1212 detector, a pixelated CMOS (complementary metal‐oxide‐semiconductor) imaging sensor, for in situ and in vivo verification of x‐ray microbeams.
Methods
Experiments were carried out on the vM1212 detector using a 220 kVp small animal radiation research platform (SARRP) at the Helmholtz Centre Munich. A 3 x 3 cm2 square piece of EBT3 film was placed on top of a marked nonfibrous card overlaying the sensitive silicon of the sensor. One centimeter of water equivalent bolus material was placed on top of the film for build‐up. The response of the detector was compared to an Epson Expression 10000XL flatbed scanner using FilmQA Pro with triple channel dosimetry. This was also compared to a separate exposure using 450 µm of silicon as a surrogate for the detector and a Zeiss Axio Imager 2 microscope using an optical microscopy method of dosimetry. Microbeam collimator slits with range of nominal widths of 25, 50, 75, and 100 µm were used to compare beam profiles and determine sensitivity of the detector and both film measurements to different microbeams.
Results
The detector was able to measure peak and valley profiles in real‐time, a significant reduction from the 24 hr self‐development required by the EBT3 film. Observed full width at half maximum (FWHM) values were larger than the nominal slit widths, ranging from 130 to 190 µm due to divergence. Agreement between the methods was found for peak‐to‐valley dose ratio (PVDR), peak to peak separation and FWHM, but a difference in relative intensity of the microbeams was observed between the detectors.
Conclusions
The investigation demonstrated that pixelated CMOS sensors could be applied to microbeam radiotherapy for real‐time dosimetry in the future, however the relatively large pixel pitch of the vM1212 detector limit the immediate application of the results.
Energy dispersive X-ray absorption spectroscopy (ED-XAS), in which the whole XAS spectrum is acquired simultaneously, has been applied to reduce the real-time for acquisition of spectra of ...photoinduced excited states by using a germanium microstrip detector gated around one X-ray bunch of the ESRF (100 ps). Cu K-edge XAS was used to investigate the MLCT states of Cu(dmp)2+ (dmp =2,9-dimethyl-1,10-phenanthroline) and Cu(dbtmp)2+ (dbtmp =2,9-di-n-butyl-3,4,7,8-tetramethyl-1,10-phenanthroline) with the excited states created by excitation at 450 nm (10 Hz). The decay of the longer lived complex with bulky ligands, was monitored for up to 100 ns. DFT calculations of the longer lived MLCT excited state of Cu(dbp)2+ (dbp =2,9-di-n-butyl-1,10-phenanthroline) with the bulkier diimine ligands, indicated that the excited state behaves as a Jahn–Teller distorted Cu(II) site, with the interligand dihedral angle changing from 83 to 60° as the tetrahedral coordination geometry flattens and a reduction in the Cu–N distance of 0.03 Å.
Microbeam radiotherapy is a novel type of radiotherapy in which narrow beams of radiation (typically less than 500μm) are spatially fractionated, delivering a non-uniform distribution to the target ...tumour volume. Due to the very high dose gradients and very small beams involved, new dosimetric techniques are required for translation into clinical practise. Current real-time beam monitoring is typically performed using 1 dimensional silicon strip detectors or wire chambers, with 2D beam information measured offline using radiochromic film (requiring a minimum of 24 h to self-develop).
Using an Xstrahl SARRP X-ray irradiation device with a bespoke microbeam collimator at the Technical University of Munich, Germany, the newly developed vM1212 detector was exposed to a variety of microbeams (220 kV, nominal slit widths 0–100μm) for evaluation of in vivo real time verification.
The performance of the detector was assessed by changing the collimator slit width (and thus microbeam FWHM) mid-irradiation. Microbeam FWHMs of 130–190μm could be measured in this manner in addition to temporally monitoring other basic parameters such as the radiation intensity. More advanced parameters could be calculated as the tungsten slits within the microbeam collimator opened and closed such as the rate of change of FWHM; the peak–valley-dose-ratio (PVDR); and the sub-pixel movement of each microbeam peak.
This work demonstrates the potential of radiation hard CMOS sensors in radiotherapy for in vivo real-time monitoring of X-ray microbeams FWHM, intensity and position.
Microsecond (μs) time-resolved extended X-ray absorption fine structure spectroscopy (EXAFS) has been developed using an energy-dispersive EXAFS (EDE) setup equipped with a silicon Quantum Detector ...ULTRA. The feasibility was investigated with a prototypical thermally driven redox reaction, the thermal decomposition of (NH₄)₂PtCl₆. EXAFS data were collected with snapshots every 60 μs during the course of the thermolysis reaction, then averaged for 100 times along the reaction to get better signal to noise ratio which reduces the time resolution to 6 millisecond (ms). Our results provide direct structural evidence of cis-PtCl₂(NH₃)₂ as the intermediate, together with continuous electronic and geometric structure dynamics of the reactant, intermediate and final product during the course of the thermolysis of ((NH₄)₂PtCl₆. The thermal effect on EXAFS signals at high temperatures is considered in the data analysis, which is essential to follow the reaction process correctly. This method could also be applied to other reaction dynamics.
The Cherwell is a 4T CMOS sensor in 180 nm technology developed for the detection of charged particles. Here, the different test structures on the sensor will be described and first results from ...tests on the reference pixel variant are shown. The sensors were shown to have a noise of 12 e- and a signal to noise up to 150 in 55Fe.
The Cherwell is a 4T CMOS sensor in 180nm technology developed for the detection of charged particles. Here, the different test structures on the sensor will be described and first results from tests ...on the reference pixel variant are shown. The sensors were shown to have a noise of 12 e− and a signal to noise up to 150 in 55Fe.
Using a fast silicon strip detector, a multi‐frame acquisition scheme was implemented to perform energy‐dispersive X‐ray magnetic circular dichroism at the iron K‐edge in pulsed high magnetic fields. ...The acquisition scheme makes use of the entire field pulse. The quality of the signal obtained from samples of ferrimagnetic erbium iron garnet allows for quantitative evaluation of the signal amplitude. Below the compensation point, two successive field‐induced phase transitions and the reversal of the net magnetization of the iron sublattices in the intermediate phase were observed.
Detectors for energy-dispersive EXAFS (EDE) experiments Salvini, Giuseppe; Headspith, Jon; Thomas, Stephen L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2005, Volume:
551, Issue:
1
Journal Article
Peer reviewed
EXAFS, X-ray absorption spectroscopy fine structure, has been an important tool within synchrotron radiation science for some years. It has been used extensively in step scanning mode to provide ...information on the local environment within both static and slowly changing samples.
Energy-dispersive EXAFS (EDE) allows similar information to be collected in a significantly shorter time frame, enabling the study of truly dynamically changing samples. The technique uses a bent crystal monochromator to focus an energy-dispersed X-ray beam onto a sample which then impinges upon an array detector positioned behind the sample. This allows the absorption over a range of energies to be collected in a very short period. Until recently only few systems have existed for this technique, typically employing commercially available detectors originally constructed for other applications. These presented limitations in speed, energy resolution, linearity and dynamic range and could only follow changes in the millisecond range.
Using UK ESPRC grant funds, a new detector has been developed (XSTRIP) which shows great improvements over the above limitations and has demonstrated the potential to open new areas of science to researchers.
This paper will present the technique, some of the historical limitations, the performance increase afforded by the XSTRIP system and an overview of the future direction of detectors for this most exciting and important technique.
The challenges facing the application of X-ray absorption spectroscopy to the study of electrochemically initiated processes in solution are discussed. The results from a feasibility study of the ...diffusion of Cu
2+ from a planar electrode are described. These show that millisecond time resolution can be achieved at a 3rd generation source, but delivery of the full potential of the experiment rests upon the availability of suitable detectors.
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