A new technique in charged particle radiography was invented in 1995 at Los Alamos National Laboratory utilizing the 800MeV proton beam at the Los Alamos Neutron Science Center (LANSCE).At present proton radiography (pRad) has proven to be useful in the study of explosives driven dynamic phenomena, and quasi-static systems such as metal eutectics. For static objects, tomographic imaging has been demonstrated with possible use to study failure mechanism in materials such as nuclear fuel pellets. The basic principles of pRad will be presented along with selected representative results.
We present the design and development of a dual-species, neutron/γ-ray imaging spectrometer for the identification and
location of radioactive and special nuclear materials (SNM). Real-time detection and identification is important for
locating fissile materials. These materials, specifically uranium and plutonium, emit neutrons and γ rays via spontaneous
or induced fission. Co-located neutron and γ-ray emissions are a sure sign of fissile material, requiring very few spatially
correlated events for a significant detection. Our instrument design detects neutrons and γ rays from all sources in its
field of view, constructs images of the emission pattern, and reports the spectra for both species. The detection principle
is based upon multiple elastic neutron-proton scatters in organic scintillator for neutrons, and Compton scattering in
organic scintillator followed by photoelectric absorption in inorganic scintillator for γ rays. The instrument is optimized
for neutron imaging and spectroscopy in the 1-20 MeV range. We recorded images and spectra of a Cf-252 source from
0.5 - 10 MeV, and have done similarly for several γ-ray sources. We report the results of laboratory testing of this
expanded instrument and compare them to detailed Monte Carlo simulations using Geant4.
The 200TW laser system, (Ti:Sapphire CPA system) delivering 5J in 25fs pulse with a 10Hz repetition rate and a contrast ratio of 1:10^-11 at the fundamental 800nm frequency, is used at the Advanced Laser Light Source (ALLS) facility to develop new generation of x-ray and pulsed particle beam sources (electrons, protons, neutrons). Experimental results on the betatron emission and electron emission from high intensity (<10^19 W/cm2) interactions with gas jet targets (1cm long supersonic nozzle) and on proton generation during high intensity (10^20 W/cm2) laser interaction with thin foil (10nm) and thick (several µm) targets will be presented and discussed. With gas jet targets, very high-resolution single shot phase contrast imaging with 10-20 keV X-rays has been demonstrated, and electrons are currently generated in the GeV range. X-ray source characterization will be presented. With foil targets, the target expansion has been measured on both sides of the target as well as proton generation (15 MeV range) at these relativistic intensities with various diagnostics (folding wave interferometer, time of flight, Thomson parabola...) We will describe the progresses we are doing to move from the laboratory experiments system to the application levels with integrated systems and compact light sources, with a special emphasis on medical applications. We are exploring the use of these high power lasers as a basic tool to image in real time with X-rays (betatron emission) tumors during their irradiation by protons (accelerated by the same laser).
+ funded by NSERC, CIPI, CFI, FQRNT, MDEIE, INRS, CRC program.
Conventional diagnostic radiography is limited by the similarity between x-ray absorption coefficients of normal tissue
and carcinoma, which results in poor inherent subject contrast. Differences in x-ray refractive indices are much larger, so
phase imaging has the potential for higher contrast. Unfortunately, the spatial coherence necessary for simple in-line
phase contrast requires small sources at large distances, and hence excessive exposure times. Other schemes such as
grating techniques require multiple images and complex alignment. In this work, polycapillary optics were employed to
increase the intensity of the x-ray beam for simple propagation in-line imaging. Focusing through pinhole apertures
created a small virtual source of high intensity from which phase contrast edge effects were observed with tissueequivalent
Conventional mammography has poor contrast between healthy tissue and carcinoma due to small differences in
attenuation. Since interference of coherently scattered radiation depends on the intermolecular spacing, it can provide
new information with higher contrast. A Monte Carlo simulation was developed for coherent scatter imaging. The
modeled design exploits a conventional scan slot mammography system with an additional anti-scatter grid tilted at the
characteristic angle of carcinoma. Preliminary results are promising and agree with experimental measurements on
phantom systems. The effect of changing grid tilt angle and sample detector distance were studied in order to begin
The system using a wide slot beam and simple anti-scatter grid has been designed to provide a localized map of tissue
type that could be overlaid on the simultaneous conventional transmission image to provide an inexpensive, low dose
adjunct to conventional screening mammography.
The purpose of this work is to explore whether a screening mammography system can be designed to exploit coherent
scatter to provide some tissue type information.
In recent years, the concept of embedding composite scintillators consisting of nanosized inorganic crystals in an organic matrix has been actively pursued. Nanocomposite detectors have the potential to meet many of the homeland security, non-proliferation, and border and cargo-screening needs of the nation and, by virtue of their superior nuclear identification capability over plastic, at roughly the same cost as plastic, have the potential to replace all plastic detectors. Nanocomposites clearly have the potential of being a gamma ray detection material that would be sensitive yet less expensive and easier to produce on a large scale than growing large, whole crystals of similar sensitivity. These detectors would have a broad energy range and a sufficient energy resolution to perform isotopic identification. The material can also be fabricated on an industrial scale, further reducing cost. This investigation focused on designing and fabricating prototype core/shell and quantum dot (QD) detectors. Fourteen core/shell and four QD detectors, all with the basic consistency of a mixture of nanoparticles in a polymer matrix with different densities of nanoparticles, were prepared. Nanoparticles with sizes <10 nm were fabricated, embedded in a polystyrene matrix, and the resultant scintillators’ radiation detector properties were characterized. This work also attempted to extend the gamma energy response on both low- and high-energy regimes by demonstrating the ability to detect low-energy and high-energy gamma rays. Preliminary results of this investigation are consistent with a significant response of these materials to nuclear radiation.
We performed a number of comparative MCNPX simulations of gamma energy depositions of scintillation crystals with smooth and rough surfaces. In the study, nine surface patterns (8 micro-roughness + 1 smooth) were coupled with eight common scintillation crystals for a total of 72 possible combinations. Although this was a preliminary study, the outcome was counterintuitive; results generally favored surfaces with micro-roughness over a conventional smooth surface as measured in terms of average energy depositions. The advantage gained through surface roughness is less significant for CdSe and LaCl3, but is most significant for the common NaI and the glass-like SiO2 scintillators. Based on the results of the 64 rough-surface coupled MCNPX simulations, 57 of the 64 (~89%) simulations showed some improvement in energy deposition. The mean improvement in energy deposition was 2.52%. The maximum improvement was about 8.75%, which was achieved when roughening the surface of a SiO2 scintillator using a micro cutting pattern. Further, for a conventional NaI scintillator, MCNPX results suggest that any roughness pattern would improve the energy deposition, with an average improvement of 3.83%. Although the likely causes remain unclear, we intend to focus on presenting simulation results instead of offering a sound explanation of the underlying physics.
Scintillating nanomaterials are being investigated as replacements for fragile, difficult to synthesize single crystal
radiation detectors, but greater insight into their structural stability when exposed to extreme environments is needed to
determine long-term performance. An initial study using high-Z cadmium tungstate (CdWO4) nanorods and an in-situ
ion irradiation transmission electron microscope (I3TEM) was performed to determine the feasibility of these extreme
environment experiments. The I3TEM presents a unique capability that permits the real time characterization of
nanostructures exposed to various types of ion irradiation. In this work, we investigated the structural evolution of
CdWO4 nanorods exposed to 50 nA of 3 MeV copper (3+) ions. During the first several minutes of exposure, the
nanorods underwent significant structural evolution. This appears to occur in two steps where the nanorods are first
segmented into smaller sections followed by the sintering of adjacent particles into larger nanostructures. An additional
study combined in-situ ion irradiation with electron tomography to record tilt series after each irradiation dose; which
were then processed into 3D reconstructions to show radiation damage to the material over time. Analyses to understand
the mechanisms and structure-property relationships involved are ongoing.
Particle size effects of nano- and polycrystalline metal tungstate MWO4 (M = Ca, Pb, Cd) scintillators were examined
through a comparison of commercially available powders and solution precipitation prepared nanoscaled materials. The
scintillation behaviors of nanoparticles and commercial powders were examined with ion beam induced luminescence
(IBIL), photoluminescence (PL), and cathodoluminescence (CL) spectroscopy techniques. For commercial microns
sized MWO4 powders, spectral emission differences between CL and PL were only observed for Cd and Pb tungstates
when compared to reported single crystals. The IBIL wavelength emissions also differed from the commercial MWO4
CL and PL data and were red shifted by 28 and 14 nm for CaWO4 and CdWO4; respectively, while PbWO4 had no
significant change. IBIL analysis on CaWO4 nanoparticles produced a 40 nm blue shift from the commercial powder
emission. These preliminary results suggest that both size and cation Z may affect the emission properties of the MWO4
The dual-energy computer tomography compared with its traditional single-energy variant ensures substantially higher
contrast sensitivity. The evaluation of the signal ratio from high-energy and low-energy detectors has been carried out
using a simplified model of the dual-energy detector array and accounting for the X-ray tube spectrum. We proposed to
use of a dual-energy receiving–detecting circuit with a detector pair ZnSe/CsI or ZnSe/CdWO that allows efficient
distinction between muscular and bone tissues, which supports our earlier theoretical assumptions that this method could
be successfully used for separate detection of materials differing in their effective atomic number Zeff and local density
(e.g., calcium contents in bone densitometry), so as can be turn to account for new generation instruments. A possibility
of dual energy tomography use for osteoporosis diagnostics was considered. Direct image reconstruction of biological
objects has been carried out, demonstrating details of bones with different density. The density of the bone depends on
the calcium content, which is not more than 20 % for the narrow part and about 18,5 % in the broad part. This results
obtained were in good agreement with the results of the independent chemical analysis.
Energetic electrons generation by longitudinal field acceleration from a laser pulse was demonstrated. The longitudinal field was generated by focusing a radially polarised TM01 ultrashort laser pulse (1,8 microns, 550 uJ, 15 fs) with a high numerical aperture parabola. The created longitudinal field was intense enough to ionised and accelerated electrons with a few tens of keV from a low density oxygen gaz. The energy, spectrum, number of charges per shot and divergence of the generated electron bunches have been measured and will be presented. Electron bunch pulse duration, space charge effects and energy tunability will also be discussed.