A method for detailed simulations of neutron diffraction from imperfect crystals

Abstract An upgraded version of the McStas Monochromator-curved module is presented. The new component, called Monochromator-reflect, is based on the use of input files for interpolating the neutron reflection and transmission probabilities according to the theoretical reflectivity of the crystal. These probabilities depend on the energy and angle at the crystal surface and also on the crystal mosaicity, geometry, material scattering cross-section, attenuation coefficient, and Bragg planes. We present details of the algorithm and definitions which are essential for a correct use of the module and show the improvements that it offers.

Precision scans of the pixel cell response of double sided 3D pixel detectors to pion and x-ray beams

hree-dimensional (3D) silicon sensors offer potential advantages over standard planar sensors for radiation hardness in future high energy physics experiments and reduced charge-sharing for X-ray applications, but may introduce inefficiencies due to the columnar electrodes. These inefficiencies are probed by studying variations in response across a unit pixel cell in a 55μm pitch double-sided 3D pixel sensor bump bonded to TimePix and Medipix2 readout ASICs. Two complementary characterisation techniques are discussed: the first uses a custom built telescope and a 120GeV pion beam from the Super Proton Synchrotron (SPS) at CERN; the second employs a novel technique to illuminate the sensor with a micro-focused synchrotron X-ray beam at the Diamond Light Source, UK. For a pion beam incident perpendicular to the sensor plane an overall pixel efficiency of 93.0±0.5% is measured. After a 10o rotation of the device the effect of the columnar region becomes negligible and the overall efficiency rises to 99.8±0.5%. The double-sided 3D sensor shows significantly reduced charge sharing to neighbouring pixels compared to the planar device. The charge sharing results obtained from the X-ray beam study of the 3D sensor are shown to agree with a simple simulation in which charge diffusion is neglected. The devices tested are found to be compatible with having a region in which no charge is collected centred on the electrode columns and of radius 7.6±0.6μm. Charge collection above and below the columnar electrodes in the double-sided 3D sensor is observed

"m=1" coatings for neutron guides

A substantial fraction of the price for a supermirror neutron guide system is the shielding, which is needed because of the gamma radiation produced as a result of neutron absorption in the supermirror layers. Traditional coatings have been made of nickel-titanium heterostructures, but Ni and Ti also have a fairly high absorption cross section for cold and thermal neutrons. We examine a number of alternatives to Ni as part of a study to reduce the gamma radiation from neutron guides. Materials such as diamond and Be have higher neutron scattering density than Ni, smaller absorption cross section, and when a neutron is absorbed they emit gamma photons with lower energies. We present reflectivity data comparing Ni with Be and preliminary results from diamond coatings showing there use as neutron guide coatings. Calculations show that Be and diamond coatings emit two orders of magnitude fewer gamma photons compared to Ni, mainly because of the lower absorption cross section

"m=1" coatings for neutron guides

A substantial fraction of the price for a supermirror neutron guide system is the shielding, which is needed because of the gamma radiation produced as a result of neutron absorption in the supermirror layers. Traditional coatings have been made of nickel-titanium heterostructures, but Ni and Ti also have a fairly high absorption cross section for cold and thermal neutrons. We examine a number of alternatives to Ni as part of a study to reduce the gamma radiation from neutron guides. Materials such as diamond and Be have higher neutron scattering density than Ni, smaller absorption cross section, and when a neutron is absorbed they emit gamma photons with lower energies. We present reflectivity data comparing Ni with Be and preliminary results from diamond coatings showing there use as neutron guide coatings. Calculations show that Be and diamond coatings emit two orders of magnitude fewer gamma photons compared to Ni, mainly because of the lower absorption cross section

Development of neutron optical components at ILL

The neutron optics laboratory at ILL carries out an innovative research program in various fields of neutron optics with the aim of developing new and improved tools for neutron instrumentation. An overview of some recent highlights is presented, indicating the breadth of the potential applications

Tensile deformation of a Cu mosaic crystal along the [1 1 0] direction studied by time of flight neutron transmission

We studied the plastic deformation of a Cu monochromator loaded in tension along the [I 10] direction between 0 and 4% equivalent shear strain. We tracked the changes in the orientation and mosaicity of the specimen at several locations simultaneously by analysing the neutron spectra transmitted by the sample. We found that an initial misalignment between different regions of the specimen decreases as deformation proceeds, to reach a minimum at 2% shear strain. On the other hand, the mosaicity of most reflections changes linearly from 10 to 30 min, except for the [2 0 0] reflection, which presents a more complex behaviour. The experiments used a novel transmission technique involving a polychromatic neutron beam and a pixellated time of flight detector. The technique exploits sharp dips in intensity present in the transmitted neutron spectrum, corresponding to the neutrons removed from the beam after being diffracted by the crystal planes

Optical configurations for X-ray imaging by projection

Several optical configurations aiming to create images of sub-millimetre objects with magnification from 1 to 100 have been experimentally tested at the ESRF BM5 beamline. A Kirkpatrick-Baez (KB) System is used for focusing the beam into a 30 microns spot and then direct projection images are recorded. Some results using a spherical crystal downstream from the KB System are presented. The possibility to focus the synchrotron beam into a 40 microns spot using an spherical crystal in quasi-normal incidence is demonstrated and its use for projection microscopy is discussed.