Thin Silicon Crystals Research Articles

Development of multi-beam optics for time-resolved X-ray tomography: from π-polarization to σ-polarization

A multi-beam X-ray optics that can image a sample from different directions in a large angular range simultaneously without sample rotation is reported. It consists of 28 thin silicon crystals that are arranged in a σ-polarization diffraction geometry so that the diffracted X-rays from an incident white synchrotron radiation beam pass through the sample. A tomogram of a simple test sample was calculated from projection images recorded with the optics, showing that an alignment accuracy sufficient for X-ray tomography can be achieved.

Tronox site in Thann inaugurates sulfuric acid recycling unit

Efficient steering of GeV-energy negatively charged particle beams was demonstrated to be possible with a new generation of thin bent silicon crystals. Suitable crystals were produced at the Sensor Semiconductor Laboratory of Ferrara starting from Silicon On Insulator wafers, adopting proper revisitation of silicon micromachining techniques such as Low Pressure Chemical Vapor Deposition, photolithography and anisotropic chemical etching. Mechanical holders, which allow to properly bend the crystal and to reduce unwanted torsions, were employed. Crystallographic directions and crystal holder design were optimized in order to excite quasi-mosaic effect along (1 1 1) planes. Prior to exposing the crystal to particle beams, a full set of characterizations were performed. Infrared interferometry was used to measure crystal thickness with high accuracy. White-light interferometry was employed to characterize surface deformational state and its torsion. High-resolution X-rays diffraction was used to precisely measure crystal bending angle along the beam. Manufactured crystals were installed and tested at the MAMI MAinz MIcrotron to steer sub-GeV electrons, and at SLAC to deflect an electron beam in the 1 to 10 GeV energy range.

X-ray Dark-Field Imaging (XDFI)-a Promising Tool for 3D Virtual Histopathology.

X-ray dark-field imaging (XDFI) utilizing a thin silicon crystal under Laue case enables visualizing three-dimensional (3D) morphological alterations of human tissue. XDFI uses refraction-contrast derived from phase shift rather than absorption as the main X-ray image contrast source to render 2D and 3D images of tissue specimens in unprecedented detail. The unique features of XDFI are its extremely high sensitivity (approximately 1000:1 compared to absorption for soft tissues under X-ray energy of around 20keV, theoretically) and excellent resolution (8.5μm) without requiring contrast medium or staining. Thus, XDFI-computed tomography can generate 3D virtual histological images equivalent to those of stained histological sections pathologists observe under low-power light microscopy as far as organs and tissues selected as samples in preliminary studies. This paper reviews the fundamental principles and the potential of XDFI, describes two optical setups for XDFI with examples, illustrates features of XDFI that are salient for histopathology, and presents XDFI examples of refraction-contrast images of atherosclerotic plaques, musculoskeletal tissue, neuronal tissue, and breast cancer specimens. Availability of this X-ray imaging in routine histopathological evaluations of tissue specimens would help guide clinical decision making by highlighting suspicious areas in unstained, thick sections for further sampling and analysis using conventional histopathological techniques. XDFI is a promising tool for 3D virtual histopathology.

Investigation of two-photon emission in strong field QED using channeling in a crystal

We investigate the 2nd order process of two photons being emitted by a high-energy electron dressed in the strong background electric field found between the planes in a crystal. The strong crystalline field combined with ultra relativistic electrons is one of very few cases where the Schwinger field can be experimentally achieved in the electron's rest frame. The radiation being emitted, the so-called channeling radiation, is a well studied phenomenon. However only the first order diagram corresponding to emission of a single photon has been studied so far. We elaborate on how the 2 photon emission process should be understood in terms of a two-step versus a one-step process, i.e., if one can consider one photon being emitted after the other, or if there is also a contribution where the two photons are emitted 'simultaneously'. From the calculated full probability we see that the two-step contribution is simply the product of probabilities for single photon emission while the additional one-step terms are, mainly, interferences due to several possible intermediate virtual states. These terms can contribute significantly when the crystal is thin. Therefore, in addition, we see how one can, for a thick crystal, calculate multiple photon emissions quickly by neglecting the one-step terms, which represents a solution of the problem of quantum radiation reaction in a crystal beyond the usually applied constant field approximation. We explicitly calculate an example of 180 GeV electrons in a thin Silicon crystal and argue why it is, for experimental reasons, more feasible to see the one-step contribution in a crystal experiment than in a laser experiment.

Superfocusing and zero-degree focusing in planar channeling of protons in a thin silicon crystal

This is a theoretical study of the superfocusing and zero-degree focusing effects appearing in channeling of protons of energy of 2 MeV in the {1 1 0} channel of a thin silicon crystal. We prove that the ultimate origin of these effects is the crystal rainbow effect, which has been discovered and explored in ion transmission through axial crystal channels, nanotubes and graphene. Moreover, the effect is the origin of the shapes of the whole spatial and angular distributions of channeled protons. The incident proton velocity vector is taken to be parallel to the channel midplane. We use the Molière's approximation of the Thomas-Fermi proton-atom interaction potential and the continuum approximation. The effect of thermal vibrations of the crystal's atoms is included. We solve numerically the proton equation of motion and analyze the spatial and angular proton transmission functions. The extrema of these functions are the spatial and angular rainbow points, respectively. When the whole proton beam is taken into account, a spatial rainbow pattern, composed of the lines emerging from the superfocusing points, and an angular rainbow pattern, consisting of the lines emerging from the origin and the zero-degree focusing points, appear along the channel. We consider the region of crystal thickness comprising the first, second and third superfocusing and zero-degree focusing points. When the effect of thermal vibrations is neglected, each of these rainbow lines look like the bifurcation set of the cusp catastrophe, and when the effect is included, the line resembles the bifurcation set of the butterfly catastrophe. We demonstrate that the spatial and angular distributions of transmitted protons are fully determined by the spatial and angular rainbow lines, respectively. The superfocusing and zero-degree focusing effects weaken with the increase of the crystal thickness. This is a consequence of the anharmonicity of the continuum proton-crystal interaction potential, which makes the proton beam propagation through the channel incoherent. We also explore the influence of the effect of proton collisions with the crystal's electrons on the beam dynamics in the channel. This effect additionally contributes to the incoherence of the beam motion along the channel. Our opinion is that the peaks of the spatial and angular distributions of ions transmitted through the planar channels lying off the origin registered before were in fact the rainbow peaks.

Extravillous trophoblast invasion is accelerated by WNT10B

Efficient steering of GeV-energy negatively charged particle beams was demonstrated to be possible with a new generation of thin bent silicon crystals. Suitable crystals were produced at the Sensor Semiconductor Laboratory of Ferrara starting from Silicon On Insulator wafers, adopting proper revisitation of silicon micromachining techniques such as Low Pressure Chemical Vapor Deposition, photolithography and anisotropic chemical etching. Mechanical holders, which allow to properly bend the crystal and to reduce unwanted torsions, were employed. Crystallographic directions and crystal holder design were optimized in order to excite quasi-mosaic effect along (1 1 1) planes. Prior to exposing the crystal to particle beams, a full set of characterizations were performed. Infrared interferometry was used to measure crystal thickness with high accuracy. White-light interferometry was employed to characterize surface deformational state and its torsion. High-resolution X-rays diffraction was used to precisely measure crystal bending angle along the beam. Manufactured crystals were installed and tested at the MAMI MAinz MIcrotron to steer sub-GeV electrons, and at SLAC to deflect an electron beam in the 1 to 10 GeV energy range.

Innovative remotely-controlled bending device for thin silicon and germanium crystals

Steering of negatively charged particle beams below 1 GeV has demonstrated to be possible with thin bent silicon and germanium crystals. A newly designed mechanical holder was used for bending crystals, since it allows a remotely-controlled adjustment of crystal bending and compensation of unwanted torsion. Bent crystals were installed and tested at the MAMI Mainz MIcrotron to achieve steering of 0.855-GeV electrons at different bending radii. We report the description and characterization of the innovative bending device developed at INFN Laboratori Nazionali di Legnaro (LNL).

Manufacturing and characterization of bent silicon crystals for studies of coherent interactions with negatively charged particles beams

Efficient steering of GeV-energy negatively charged particle beams was demonstrated to be possible with a new generation of thin bent silicon crystals. Suitable crystals were produced at the Sensor Semiconductor Laboratory of Ferrara starting from Silicon On Insulator wafers, adopting proper revisitation of silicon micromachining techniques such as Low Pressure Chemical Vapor Deposition, photolithography and anisotropic chemical etching. Mechanical holders, which allow to properly bend the crystal and to reduce unwanted torsions, were employed. Crystallographic directions and crystal holder design were optimized in order to excite quasi-mosaic effect along (111) planes. Prior to exposing the crystal to particle beams, a full set of characterizations were performed. Infrared interferometry was used to measure crystal thickness with high accuracy. White-light interferometry was employed to characterize surface deformational state and its torsion. High-resolution X-rays diffraction was used to precisely measure crystal bending angle along the beam. Manufactured crystals were installed and tested at the MAMI MAinz MIcrotron to steer sub-GeV electrons, and at SLAC to deflect an electron beam in the 1 to 10GeV energy range.

Total yield of channeling radiation from relativistic electrons in thin Si and W crystals

Orientation dependences of channeling radiation total yield from relativistic 155–855MeV electrons at both 〈100〉 axial and (100) planar channeling in thin silicon and tungsten crystals are studied by means of computer simulations. The model as well as computer code developed allows getting the quantitative results for orientation dependence of channeling radiation that can be used for crystal alignment in channeling experiments and/or for diagnostics of initial angular divergence of electron beam.

Measurements of high energy loss rates of fast highly charged U ions channeled in thin silicon crystals

The results of two channeling experiments show that highly charged heavy ions at moderate velocities ($v\ensuremath{\ll}{\mathit{Zv}}_{0}$) may lose more energy in the traversal of a thin crystal when they are injected along a major crystallographic direction than when they traverse the crystal in random conditions. This is due to the fact that the large reduction of electron capture probabilities allows them to keep their high electronic charge throughout the crystal, which is not the case for projectiles traveling in random conditions. Although channeled projectiles experience reduced electron densities, their energy loss rate, that is, at first order, proportional to the square of the ions charge, is then strongly enhanced. This feature could be used as a step for decelerating highly charged ions from the high energies that are needed to produce them, and also to improve our understanding of the slowing down of very highly charged projectiles at low velocities, for which the current perturbative models are not well suited.

CRYSTAL COLLIMATION STUDIES AT THE TEVATRON (T-980)

Bent-crystal channeling is a technique with a potential to increase beam-halo collimation efficiency in high-energy colliders. First measurements at the Tevatron in 2005 have shown that using a thin silicon crystal to deflect the 1-TeV proton beam halo onto a secondary collimator improves the system performance by reducing the machine impedance, beam losses in the collider detectors and irradiation of the superconducting magnets, all in agreement with simulations. Recent results, obtained with an improved goniometer and enhanced beam diagnostics, are reported here for dedicated beam studies and first full collider stores along with simulation results and plans for substantial enhancement of the T-980 experimental setup.

Time-dependent quantum model of recharge of heavy ions and shell effects in angular distributions at channeling of nuclei in a silicon crystal

The model of recharge of heavy ions, based on the use of a pseudopotential and the three-dimensional time-dependent Schrodinger equation has been developed. The angular distributions of Y ions with initial energies of 60 and 140 MeV, transmitted through a thin silicon crystal in the axial channeling mode, are explained.

Formation of spectral characteristics of channeling radiation from 800 to 2000 MeV electrons and positrons in a thin silicon crystal

The influence of the tails of particle trajectories on planar channeling radiation (CR) spectra from relativistic (800–2000 MeV) electrons and positrons in a thin silicon crystal is investigated. It is shown that the trajectory tails significantly change the CR spectra from electrons and positrons in specific parts of the spectra compared to calculations which do not take into account this effect.

Ion slowing down and charge exchange at small impact parameters selected by channeling: Superdensity effects

In two experiments performed with 20–30MeV/u highly charged heavy ions (Pb56+, U91+) channeled through thin silicon crystals, we observed the original features of superdensity, associated to the glancing collisions with atomic rows undergone by part of the incident projectiles. In particular, the very high collision rate yields a quite specific charge exchange regime, that leads to a higher ionization probability than in random conditions. X-ray measurements show that electrons captured in outer shells are prevented from being stabilized, which enhances the lifetime of the projectile inner shell vacancies. The charge state distributions and the energy loss spectra are compared to Monte-Carlo simulations. These simulations confirm, extend and illustrate the qualitative analysis of the experimental results.

Electron emission induced by fast heavy ions in a thin silicon crystal

We report observations of backward and forward electron emission by a thin silicon crystal target traversed by $29\phantom{\rule{0.3em}{0ex}}\text{MeV}∕\mathrm{u}$ ${\mathrm{Pb}}^{56+}$ incident ions. For each incident ion we have performed measurements of backward and forward electron emission, of the energy loss and of the charge state of the transmitted ion. The crystal target was traversed by incident ions either in random incidence or in axial alignment conditions. In both cases these correlated measurements bring original information on electron emission. In random conditions, using an incident ion species with a charge quite far from equilibrium, we observe correlations between backward and forward electron emission, that we understand when analyzing the associated charge exchange and energy-loss data. In channeling conditions, we added electron emission measurements to simultaneous energy-loss and charge state measurements (that are known to characterize quite precisely the type of trajectory of a projectile transmitted through a thin crystal). This allowed us to observe the reduced electron emission due to hyperchanneled ions, that interact mainly with target valence electrons, and also the enhanced electron emission due to projectiles entering the crystal very close to atomic strings.

Impact parameter dependent electron capture by decelerated U91+ ions at 20 MeV/u using crystal channeling conditions

We present results of an experiment using decelerated U91+ ions, extracted from the GSI-ESR storage ring, and transmitted through a thin silicon crystal in channeling conditions. Charge state at emergence, secondary electron multiplicity and X-rays are measured simultaneously. These conditions allow to study the competition between mechanical electron capture (MEC) and radiative electron capture (REC) as a function of impact parameter. We observe that REC is the dominant charge exchange process for the best channeled ions, i.e. those travelling always far from the silicon target core electrons. For ions with high transverse energy, MEC into highly excited states is counterbalanced by enhanced ionization arising from a succession of close collisions along atomic rows.

High-resolution X-ray diffraction analyses of protein crystals

High–resolution triple–axis X–ray diffraction analyses have been performed on tetragonal crystals of hen egg–white lysozyme (HEWL). In order to perform these analyses in a laboratory setting, an X–ray optical system consisting of a pair of parabolic graded X–ray mirrors and an asymmetric channel–cut crystal was employed. Analyses of thin silicon crystals confirmed the differences between the transmission geometry used for the HEWL crystals and the more common reflection geometry typically used for the characterization of inorganic crystals. Significant differences in the intensity distribution in the vicinity of the HEWL reciprocal lattice points between different reflections of the same crystal and between different crystals have been observed.

Ion optical study of a transmission ion microscope

This paper describes new imaging methods which use a nuclear microprobe lens system placed after the sample to focus the transmitted ions. Recent experimental work has demonstrated how a quadrupole lens multiplet can be used to magnify the angular distribution of unfocused proton beams passing through thin silicon crystals, and also the spatial distribution of unfocused beams of MeV protons passing through free-standing grids. It has also been shown how a highly convergent, focused MeV proton beam which passed through a thin silicon crystal could be used to directly image the defects present. Such experimental work has highlighted the need for new ion optical studies on how MeV ion beams can be manipulated by quadrupole lens multiplets in order to fully understand this previous work, and also to show how the attainable spatial and angular magnification can be further increased. This paper presents such calculations in the form of ion optical trajectory plots using the matrix ray-tracing program PRAM, which takes chromatic and spherical aberrations into account.

Dependence on the incident angle of the electronic energy loss of planarly channeled fast ions

The angular dependence of the electronic energy loss of fast ions was calculated. Models for the transitions from axial to planar channeling and from planar channeling to a random direction are discussed in terms of a simple generalization of the Lindhard–Jin–Gibson Model for the axial–random transition. In order to compare these models with experimental data, the energy loss of 2.0 MeV He ions channeled through a thin silicon crystal into directions that scan the {0 0 1} plane from the [1 1 0] axis to the [1 0 0] axis was measured.

Defect imaging using convergent beam ion channeling patterns

The use of convergent beam ion channeling patterns to observe the lattice rotation around defects in a thin silicon crystal is described here. A 3 MeV proton beam from a nuclear microprobe was focused to a small spot with a large convergence angle in the horizontal direction and a small convergence angle in the vertical direction. With the crystal slightly displaced along the beam axis the convergent proton beam illuminated a 100 μm long line on the crystal surface. The spatial variation of the exiting proton angular distribution along the 100 μm line was projected downstream on to a fluorescent viewing screen, enabling the lattice rotation around circular defects to be directly observed within this illuminated area. A small mosaic spread present in the crystal was also imaged and quantified using convergent beam channeling patterns.