J. Andrew Green

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).

A new method for imaging nuclear threats using cosmic ray muons

Muon tomography is a technique that uses cosmic ray muons to generate three dimensional images of volumes using information contained in the Coulomb scattering of the muons. Advantages of this technique are the ability of cosmic rays to penetrate significant overburden and the absence of any additional dose delivered to subjects under study above the natural cosmic ray flux. Disadvantages include the relatively long exposure times and poor position resolution and complex algorithms needed for reconstruction. Here we demonstrate a new method for obtaining improved position resolution and statistical precision for objects with spherical symmetry.

A range muon tomography performance study

Soft cosmic ray tomography has been shown to successfully discriminate materials with various density levels due to their ability to deeply penetrate matter, allowing sensitivity to atomic number, radiation length and density. Because the multiple muon scattering signal from high Z-materials is very strong, the technology is well suited to the detection of the illicit transportation of special and radiololgical nuclear materials. In addition, a recent detection technique based on measuring the lower energy particles that do not traverse the material (range radiography), allows to discriminate low and medium Z-materials. We have demonstrated it first using Monte Carlo simulations. More recently, using a Mini-Muon Tracker developed at Los Alamos National Laboratory, we performed various experiments to try out the radiation length technology. This paper presents the results from real experiments and evaluates the likelihood that soft cosmic ray tomography may be applied to detect high-explosives.

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

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.

Charged particle energy loss radiography for homeland security applications

We discuss an innovative low-dose approach for detecting shielded strategic nuclear materials (SNM) based on measuring the energy-loss of energetic protons penetrating an object.