Wendi Dreesen

Obtaining material identification with cosmic ray radiography

The passage of muons through matter is dominated by the Coulomb interaction with electrons and nuclei in the matter. The muon interaction with the electrons leads to continuous energy loss and stopping of the muons. The muon interaction with nuclei leads to angular diffusion. Using both stopped muons and angle diffusion interactions allows us to determine density and identify materials. Here we demonstrate material identification using data taken at Los Alamos with a particle tracker built from a set of sealed drift tubes with commercial electronics and software, the Mini Muon Tracker (MMT).

Fielding of a time-resolved tomographic diagnostic

A diagnostic instrument has been developed for the acquisition of high-speed time-resolved images at the Dual-Axis Radiographic Hydrodynamic Test (DARHT) Facility at Los Alamos National Laboratory. The instrument was developed in order to create time histories of the electron beam. Four discrete optical subsystems view Cerenkov light generated at an x-ray target inside of a vacuum envelope. Each system employs cylindrical optics to image light in one direction and collapse light in the orthogonal direction. Each of the four systems images and collapses in unique axes, thereby capturing unique information. Light along the imaging axis is relayed via optical fiber to streak cameras. A computer is used to reconstruct the original image from the four optically collapsed images. Due to DARHTs adverse environment, the instrument can be operated remotely to adjust optical parameters and contains a subsystem for remote calibration. The instrument was deployed and calibrated, and has been used to capture and reconstruct images. Matters of alignment, calibration, control, resolution, and adverse conditions will be discussed.

Design considerations for a time-resolved tomographic diagnostic at DARHT

An instrument has been developed to acquire time-resolved tomographic data from the electron beam at the DARHT [Dual-Axis Radiographic Hydrodynamic Test] facility at Los Alamos National Laboratory. The instrument contains four optical lines of sight that view a single tilted object. The lens design optically integrates along one optical axis for each line of sight. These images are relayed via fiber optic arrays to streak cameras, and the recorded streaks are used to reconstruct the original two-dimensional data. Installation of this instrument into the facility requires automation of both the optomechanical adjustments and calibration of the instrument in a constrained space. Additional design considerations include compound tilts on the object and image planes.

Using Muons to Image the Subsurface.

Muons are subatomic particles that can penetrate the earth’s crust several kilometers and may be useful for subsurface characterization. The absorption rate of muons depends on the density of the materials through which they pass. Muons are more sensitive to density variation than other phenomena, including gravity, making them beneficial for subsurface investigation. Measurements of muon flux rate at differing directions provide density variations of the materials between the muon source (cosmic rays and neutrino interactions) and the detector, much like a CAT scan. Currently, muon tomography can resolve features to the sub-meter scale. This work consists of three parts to address the use of muons for subsurface characterization: 1) assess the use of muon scattering for estimating density differences of common rock types, 2) using muon flux to detect a void in rock, 3) measure muon direction by designing a new detector. Results from this project lay the groundwork for future directions in this field. Low-density objects can be detected by muons even when enclosed in high-density material like lead and even small changes in density (e.g. changes due to fracturing of material) can be detected. Rock density has a linear relationship with muon scattering density per rock volume when this ratio is greater than 0.10. Limitations on using muon scattering to assess density changes among common rock types have been identified. However, other analysis methods may show improved results for these relatively low density materials. Simulations show that muons can be used to image void space (e.g. tunnels) within rock but experimental results have been ambiguous. Improvements are suggested to improve imaging voids such as tunnels through rocks. Finally, a

X-ray radar imaging technique using a 2 MeV linear electron accelerator

X-ray radar imaging, patented in 2013 by James R. Wood, combines standard radar techniques with the penetration power of x-rays to image scenes. Our project strives to demonstrate the technique using a 2 MeV linear electron accelerator (linac) to generate the S-band-modulated x-ray signals. X-ray detectors such as photodiodes and scintillators are used to detect the signals in backscatter and transmission detection schemes. The S-band microstructure is imposed on the variable-width electron pulse, and this modulation carries over to the bremsstrahlung x-rays after the electron beam is incident upon a copper-tungsten alloy target. Using phase/distance calculations and a low-jitter timing system, we expect to detect different object distances by comparing the measured phase differences. The experimental setup, which meets strict jitter requirements, and preliminary experimental results are presented.

Imaging shielded configurations using near-horizontal and near-vertical trajectory cosmic-ray muons

This work will describe the proof-of-concept research applying muon tomography technologies based on drift tube systems to create images using near-horizontal trajectory muons. To date, the majority of imaging studies using cosmic-ray muons have used near-vertical trajectory muons. This work compares imaging results using near-vertical trajectory muons with results using near-horizontal trajectory muons. The muon flux is much lower for the near-horizontal trajectory muons, requiring longer imaging times, but the average muon energy is higher, so the horizontal results are expected to better differentiate high-Z materials. The muon tracking system is easily configurable and can be oriented to capture near-vertical trajectory or near-horizontal trajectory cosmic-ray muons. The software can track each muon passing through the system, and generate 3D images of the scene. The experimental design and preliminary results will be presented, including the comparisons of detection efficiency, image resolution, and integration times.

Detection of petawatt laser-induced muon source for rapid high-Z material detection

A proof-of-concept investigation of a rapid detection system for shielded high-Z material using a petawatt laser-based muon source is presented. Unlike cosmic-ray muons, a laser-induced muon beam has unique characteristics that can be exploited for use in a rapid detection system. These characteristics include: (1) a near-point source of muons, (2) well-characterized muon energies, (3) directionality of the beam, and (4) well-defined timing of the muons. A detector system is being developed that combines multiple muon detection technologies to characterize an active muon source. This detection system and the associated data acquisition and analysis techniques are designed to search for deflections of the muon beam as it passes through high-Z materials. Additionally, the ability of the system to differentiate muons from the expected secondary particles, such as high-energy gammas and electrons, is being explored. The detector systems ability to differentiate muons from other particles, muon angular distribution, and measured muon flux will be discussed.

E-beam electron mobility study on CZT and CsI

There is much interest in developing new scintillator detectors for radiation detection and radiographic imaging applications. The knowledge of the electron mobility (μ) is important in the basic understanding of charge transport and in the selection and optimization of many inorganic scintillator materials such as thallium-doped cesium iodide, CsI(Tl). Performance measures are used to model various scintillator responses in an effort to predict the effect of doping concentrations. Performance models will help in the new scintillator design process. Initial tests are done with cadmium zinc telluride detectors to establish measurement techniques and baselines.