Element Specific Imaging Using Muonic X-rays

Abstract

The RIKEN-RAL facility provides a source of negative muons that can be used to non-destructively determine the elemental composition of bulk samples. A negative muon can replace an electron in an atom and subsequently transition to lower orbital positions. As with conventional X-ray fluorescence, an X-ray photon is emitted with a characteristic energy to enable the transition between orbitals of an atom. As the mass of a negative muon is much greater than that of an electron, a higher energy X-ray photon is emitted when the negative muon transitions between orbitals compared to conventional X-ray fluorescence. The higher energy muonic X-rays are able to escape large samples even when they are emitted from lower Z atoms, making muonic X-rays fluorescence a unique method to characterize the elemental content of a sample. In a typical experiment a section of a sample will be probed with negative muons with the muon momentum tuned to interact at a desired depth in the sample. A small number of single element high purity Ge detectors are positioned to capture up to one photon each from each of the forty muon pulses per second at the RIKEN-RAL facility. This can provide a high resolution and high dynamic range X-ray energy spectrum when collected for several hours but can only provide a spatial average or single point elemental distribution per collection. Here, an STFC developed CdTe detector with 80 x 80 energy resolving channels has been used to demonstrate the ability to image the elemental distribution of a test sample. A test sample of C, Al and Fe 2 O 3 was positioned close to the detector surface and each of the 250 µm pitch pixels recorded a muonic X-ray energy spectrum. Results are presented to show the principal of this new technique and potential improvements to provide higher resolution and larger area elemental imaging using muonic X-rays are discussed.

HEXITEC: A High-Energy X-ray Spectroscopic Imaging Detector for Synchrotron Applications

“…The system has been used at synchrotrons in applications which wish to discern mechanical, structural or chemical information from within thick samples or to determine the chemical composition of samples containing multiple high Z materials which, typically, have closely spaced K-line X-ray emissions. While originally developed for materials science applications [2], [3], the system has been successfully used across a diverse range of fields including pure science [4], [5], solar physics [6], medical imaging [7] and security applications [8]. This article will review the current status of the technology, the performance of the latest system and demonstrates the use of the system on a synchrotron beamline.…”

A Novel Non-Destructive Technique for Cultural Heritage: Depth Profiling and Elemental Analysis Underneath the Surface with Negative Muons

“…By placing a detector behind the sample, information about the spatial distribution of the sample can be obtained, especially for light elements. In Hillier et al [53] and Yabu et al [54], feasibility studies of muon imaging are reported. In both works, a highly pixelated CdTe detector is used to collect the signal (cadmium telluride is a rather good material for detection, especially in the range of hard X-rays).…”

“…In both works, a highly pixelated CdTe detector is used to collect the signal (cadmium telluride is a rather good material for detection, especially in the range of hard X-rays). In [53], a proximity image (Figure 12) was obtained by placing the detector behind the sample holder and measuring it at 40 MeV/c. In [54], instead, a pinhole setup was used.…”

Feasibility study of a coded aperture imaging technique for position-sensitive muonic X-ray atomic ratio reconstruction

“…Due to the high flux of muon beam enhancement in this century, 𝜇-XES element analysis has been recently applied in many fields, such as archaeological investigations [10,11], extraterrestrial material characterization [12][13][14], lithium battery development [15] and other applications [16][17][18]. Additionally, 𝜇-XES was used to study the spatial distribution of elements inside materials [19][20][21]. Hillier and collaborators placed a CdTe detector behind a sample consisting of C, Al and Fe 2 O 3 blocks to image the distribution of different elements in the sample [19].…”

“…Additionally, 𝜇-XES was used to study the spatial distribution of elements inside materials [19][20][21]. Hillier and collaborators placed a CdTe detector behind a sample consisting of C, Al and Fe 2 O 3 blocks to image the distribution of different elements in the sample [19]. Katsuragawa et al developed a pinhole camera by placing a single-hole collimator between the sample and the CdTe detector to obtain the reversed image of element distributions in the sample [20].…”