Running Hard Radiation X-Ray Experiments in the Lab

This article will explore the different benefits of analyzing materials using hard radiation. The majority of powder XRD systems use copper anodes to produce X-rays. However, for some applications using molybdenum or silver anodes, which produce radiation of a shorter wavelength, can provide more benefits and enabling new experiments, such as those involving a wide Q range.

When hard radiation is required the use of synchrotrons is common. However, this is no longer always needed as advances in x-ray generators, detectors and optics means some types of hard radiation experiments can be performed in the labs. This article explores six different advantages of conducting research using hard radiation.

A Greater Penetration Depth

The use of softer X-rays, such as those from copper anodes, can result in penetration depths for inorganic materilas of only several micrometers (Table 1). Hard radiation sources can be used to analyze samples to a deeper level, increase the sampled volume and facilitating transmission experiments on thicker samples.

Table 1. Example of penetration depth in μm for different materials and different X-ray wavelengths.

This increased degree of penetration facilitates the crystallographic analysis of real devices such as lithium-ion batteries and the execution of high-pressure experiments using e.g. diamond anvil cells.

Better Crystallographic Data

The favorite setup for crystallographic measurements of powder sample is to use glass capillaries in a Debye-Scherrer geometry, in order to minimize preferred orientation effects.

Figure 1. Rietveld refinement of Fe(IO₃)₃ carried out with the HighScore suite [1] Space group P6₃ with cell parameters a = b = 9.2361(1) Å, c = 5.23882(7) Å; Rwp = 2.4, GoF =3.4

Using molybdenum radiation with X-ray focusing optics facilitates the use of capillaries with a large diameter without the problem of excessive absorption or reduced angular resolution, thanks to the fact that the radiation is focused to the detector position.  In addition, hard radiation facilitates a more comprehensive determination of atomic thermal parameters such as B_iso.

Reliable Data on Material Local Structure (PDF Analysis)

Previously, Pair Distribution Function (PDF) analysis has only been possible using synchrotron-generated X-rays. However, now, this is possible using a lab multipurpose diffractometer, such as Panalytical’s Empyrean, thanks to a carefully optimized beam path, resulting in low and featureless background.

Figure 2. Structure function S(Q)comparison between two synchrotron beamlines and the Empyrean with GaliPIX^3D(both Mo as well as Ag radiation)

When using a molybdenum (Mo) X-ray source a maximum Q range of 17 Å^-1 can be attained, silver (Ag) sources can achieve a Q range of up to 21 Å^-1, see Figure 2.

X-Ray Imaging and Computed Tomography for A Wide Range of Materials

The use of hard radiation means that X-ray imaging and computed tomography can be used to analyze a wider range of materials. As X-rays from a molybdenum or silver sources are more penetrating it means that samples which are denser, or thicker, can be analyzed.

Figure 3. Porous concrete. Top row with small pores, bottom row with large pores. a) picture of the concrete slab, b) 3D view using Isosurface render, c) cross section of the sample showing in more detail the pores (blue) and the concrete framework related to the selected area where the pores are determined in.

Rapid Data Collection

Using hard radiation, as opposed to using copper radiation, means that the 2θ range needed to collect a set number of reflections is lower. A 2θ range of 100° for copper radiation is equivalent to approximately 30° with silver, meaning that a full pattern can be taken in just few seconds.

Figure 4. Hyper-speed full pattern snapshot (33 deg with Ag radiation, equivalent to ~100 deg with Cu radiation) recorded in just 2 seconds.

Better Preparation for Synchrotron Beam Time

Whilst lab-based hard X-ray systems have a much lower flux than synchrotrons they are far more available. Lab-based systems allow the testing of samples before they are measured in the much more expensive synchrotron system. This is more time and cost efficient, and it increases the likelihood of project approval.

Figure 5. Four complete charge-discharge cycles of a commercial prismatic battery cell, measured with Ag radiation (5 minutes per scan, 14 hours total measuring time)

Who Benefits from Research with Hard Radiation

Researchers who want to investigate amorphous state. Improvements in hard radiation hardware and software mean that PDF analysis is now possible in labs that do not have synchrotron access. PDF analysis allows researchers to determine the interatomic distances in amorphous and nano-crystalline materials.

Researchers who want to investigate chemical reactions. As hard radiation from molybdenum and silver sources is more penetrating it means that chemical reactions taking place in sealed containers can be observed. A good example of this is research into the reactions occurring inside lithium-ion batteries. Spatially resolved information can be collected by using 2D X-ray detector and pencil-like beam.

Crystallographers. Using hard radiation sources alongside specialized focusing optics and advanced detectors allows crystallographers to observe fine detail about crystal structures without having to use a synchrotron source.

Leaders of Educational and Commercial Research Facilities. As explored above the use of hard radiation in research is beneficial to a wide number of applications. Using Empyrean’s PreFIX concept users can easily switch between different experimental set ups to extract rich information on a wide range of samples including electrochemical cells, biomaterials, metals and pharmaceuticals.

2. Malvern Panalytical are Experts in Hard Radiation Analysis

The Empyrean can provide high quality data even for more challenging applications using hard radiation. High quality data is guaranteed because of:

• An instrument made for continuous operation at an excitation voltage of 60 kV to produce high molybdenum and silver K-alpha radiation flux. The instrument automatically determines which X-ray tube is being used and stores this information in the .xrdml files.
• A 4 kW X-ray generator – meaning using a molybdenum source (3 kW max) is easily within the limits.
• Highly precise X-ray mirrors for transmission geometry experiments. Using focusing mirrors allows data at high angular resolutions to be collected facilitating imaging of working devices, e.g. batteries, and measurements inside glass capillaries
• An optical path which provides a low noise background, as required for sensitive applications such as PDF. The Empyrean as proven this in the many dedicated installation around the world for this type of analysis.
• X-ray detectors designed to work with hard radiation. Experiments involving hard radiation require detectors that are high absorbing. Conventional detectors (gas or silicon-based) can only absorb some of the radiation, with the remainder collected by read out circuitry – potentially causing damage.
• A volume of experience of using hard radiation at non-ambient conditions. The applications team has performed hard radiation tests in most available non-ambient chambers and asked for improvements from suppliers when needed. Malvern Panalytical works with chamber manufacturers and can help provide custom non-ambient chambers.
• Malvern Panalytical’s novel Pixirad technology uses state-of-the-art CdTe sensors which are opaque to a limit of 90 keV (see Figure 6) and provide high quality images with a resolution of 60 microns per pixel. Sharp images are provided by a point spread function of only one pixel, which prevents blooming, and limits background noise. The high dynamic range of the detector facilitates computed tomography, radiography and X-ray imaging. Exposure of the detector to the direct beam will not cause damage if done infrequently.
• The X-ray tubes have a high anode stability.  As hard radiation has tighter diffraction angles than copper x-ray radiation the optical path stability is of greater importance. Malvern Panalytical has ensured stable results over a long lifetime by several modifications to conventional tube designs.
• Malvern Panalytical’s instruments are designed to be flexible and future-proof. The PreFIX design of the system means new experimental needs can be fulfilled by easily changing the instrument configuration, for example:
  • Changing between reflection and transmission modes (with a horizontal sample) and capillary modes
  • Changing between hard radiation and copper-based radiation
  • Changing between non-ambient sample chambers and different optical components
• Malvern Panalytical has a solid reputation of innovating and bringing the latest techniques to their existing instrumentation, in some cases even to systems that are more than 10 years old.
• Malvern Panalytical’s instruments are extremely safe, fitting to all regulations. Every individual instrument is safety tested using hard radiation prior to sale. Third party safety checks are used to oversee design and production.
• Analysis of .xrdml data produced (which includes the wavelength) via the provided HighScore software allows the analysis of powder diffraction and more using hard radiation. This follows an algorithm developed at the Rutherford Appleton Laboratories for the calculation of the PDF. Computed tomography data can be ran through VG StudioMax software from Volume Graphics.

Figure 6. Detection efficiency as a function of photon energy for Si and CdTe with different thicknesses (h).

This information has been sourced, reviewed and adapted from materials provided by Malvern Panalytical.

For more information on this source, please visit Malvern Panalytical