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Obtaining directional information is required in many applications such as nuclear homeland security, contamination mapping after a nuclear incident and radiological events, or during the decontamination work. However, many directional radiation detectors are based on directional shielding, made of lead or tungsten collimators, introducing two main drawbacks. The first is the size and weight, making those detectors too heavy and irrelevant for utilization in handheld devices, drone mapping, or space applications. The second drawback is the limited field of view (FOV), which requires multiple detectors to cover the whole required FOV or machinery to rotate the detector’s narrow FOV detector. We propose a novel $4\pi $ directional detector based on a segmented hollow cubic detector, which uses the Compton effect interactions with no heavy collimators. The symmetrical cubical design provides both higher efficiency and $4\pi $ detection ability. Instead of the traditional two types of detectors (scatterer and absorber) structure, we use the same type of detector, based on Gd3Al2Ga3O12 (GAGG) (Ce) scintillator coupled to silicon photomultiplier. An additional advantage of the proposed detector is obtained by locating the photon sensors inside the detector, behind the scintillators, which improves the radiation hardness required for space applications. Furthermore, such an arrangement flattens the temperature variation across the detector, providing better gain stability. The main advantage of the proposed detector is an efficient $4\pi $ radiation detection for high-energy gamma rays without the use of heavy collimators. [ABSTRACT FROM AUTHOR]

This article reports the first application of a convolutional neural network (CNN) to in vivo X-ray fluorescence (XRF) images of gold nanoparticles (GNPs) obtained by a benchtop X-ray system to eliminate Compton-scattered photons. The XRF imaging system comprises a 2-D cadmium zinc telluride (CZT) gamma camera, a pinhole collimator, and fan-beam polychromatic X-rays. An architecture of the 2-D CNN model for Compton background elimination was optimally designed and trained with data sets obtained by the measurements of water only and GNP-embedded imaging phantoms. The XRF images generated by the trained 2-D CNN were compared with those generated by the direct subtraction method. The developed 2-D CNN was also applied to generate in vivo XRF images of gold in living mice exposed to GNPs. The in vivo XRF images generated by the two methods were then compared in terms of the difference in GNP concentrations. The results demonstrate that the 2-D CNN model was successfully applied to in vivo XRF images for detecting the concentration and location of GNPs in living mice. This also implies that in vivo XRF images can be acquired using the 2-D CNN without preinjection scanning; thus, the image acquisition time and imaging dose can be reduced by half. Furthermore, in vivo XRF images of GNPs can be acquired at any time after the injection, as the 2-D CNN eliminates the need to restrict a living object during the interscans. [ABSTRACT FROM AUTHOR]

In this paper, we examine the history of detection efficiency measurements of photons (soft to hard X-rays and beyond) with microchannel plates (MCPs). We investigate the detection efficiency as a function of photon energy over a wide energy range, from a few hundred eVs up to 20 MeV. We also investigate detection efficiency as a function of incident angle onto the MCP. We interpreted the published efficiency data measured with a variety of MCPs and the use of MCP coatings for enhancement of X-ray quantum detection efficiency, and discuss theoretical expectations based on the main photon interactions with matter: the photoelectric effect, Compton scattering, and pair production. Contributing to the published literature at the highest end of the energy range, we also discuss our photon detection efficiency experiments from 2.5 to 20 MeV and theoretical implications. [ABSTRACT FROM AUTHOR]

Image-reconstruction with Compton-scattered photons is a nonlinear problem, because it involves both the linear process of scattering and the exponential pre- and post-scatter attenuation. For thin and light objects and with high-energy photons, the exponential terms can be ignored, rendering the problem linear. We show that when attenuation is significant, linearity can also be accomplished by considering scattering as a scaling factor and with subsequent logarithmic transformation, the image-reconstruction problem is converted into a transmission-like problem along the travel lines of incident and scattered radiation. It is shown that this formulation produces images qualitatively reflecting object features in a manner similar to that of backprojection in conventional computed tomography. This is done without the need for calibration or scaling of measurements. The theoretical aspects of the introduced mathematical formulation are developed for idealized pencil-beams, adapted approximately to fan-beam configurations, and applied to imaging with laboratory-acquired measurements. The introduced transmission-like formulation and calibration-free aspects should promote wider use of scatter imaging. [ABSTRACT FROM AUTHOR]

Previously, fixed angle Laser-Compton Scattering (LCS) experiments have been conducted at the terminal of the 100 MeV LINAC of the Shanghai Institute of Applied Physics, using SINAP-I and SINAP-II facility. Sub-MeV energy continuously tunable laser-Compton light source device (SINAP-III) is an updated facility that will allow the collision angle between the laser and electron beam continuously adjustable from 20^\circ to 160^\circ . This new feature will enable convenient control on the maximum energy of the generated X/\gamma ray in a wide energy region, especially when the energy of electrons cannot be momentarily adjusted, e.g. on the storage ring. Keeping the electron beam and laser beam waist coincident at arbitrary angle is crucial for LCS gamma-ray production, an interaction chamber containing a rotatable bracket that holds a series of plane mirrors and convex lens is presented. This work is a summary of its design. The simulation of photon production’s variation caused by the systematic errors is performed using a MC code. The accuracies of installation and adjustment of mirrors and lens are given according to the simulation results. The sizes of these optical devices are also optimized. [ABSTRACT FROM PUBLISHER]

Gamma ray sources with high flux and spectral densities are the main requirements for new nuclear physics experiments to be performed in several worldwide laboratories with dedicated facilities. The paper is focalized on a proposal of experiment on \gamma photons production using Compton collisions between the DA\Phi NE electron beam and a high average power laser pulse, amplified in a Fabry-Pérot optical resonator. The calculations show that the resulting \gamma beam source has extremely interesting properties in terms of spectral density, energy spread and \gamma flux comparable (and even better) with the last generation \gamma sources. The energy of the \gamma beam depends on the adopted laser wavelength and can be tuned changing the energy of the electron ring. In particular we have analyzed the case of a \gamma factory tunable in the 2-9 MeV range. The main parameters of this new facility are presented and the perturbation on the transverse and longitudinal electron beam dynamics is discussed. A preliminary accelerator layout to allow experiments with the \gamma beam is presented with a first design of the accelerator optics. [ABSTRACT FROM PUBLISHER]

To improve the quantitative accuracy of linear attenuation coefficients measured by computed tomography (CT), we used a single scatter model to estimate the Compton scatter distribution and then a polychromatic image reconstruction algorithm, namely the iterative maximum-likelihood polychromatic algorithm for CT (IMPACT), was implemented to include scatter correction (SC). To perform the IMPACT, the X-ray spectra of a tube were estimated via an expectation-maximization (EM) algorithm with SC. To test the accuracy of the estimated spectra, the projection images of cubic phantoms containing different depths of polymethylmethacrylate (PMMA) were acquired. The percentage of root mean square errors (%RMSE) of the measured transmission data and calculated transmission values were used to evaluate the accuracy of the estimated spectra. In addition, a hydroxylapatite (HA) phantom was used to study streak artifacts and evaluate the accuracy of the linear attenuation coefficients estimated using the IMPACT with SC. The %RMSE of the EM-with-SC estimated spectra were all lower than 1% and were also smaller than that without SC. The error in the quantification of the HA linear attenuation was only about 3% after SC. Our results showed that the quantitative accuracy of the linear attenuation coefficients measured with a cone beam CT was improved when the IMPACT with SC was used. [ABSTRACT FROM AUTHOR]

The Rotating Scatter Mask (RSM) system is an inexpensive retrofit that provides imaging capabilities to scintillating detectors. Unlike traditional collimator systems that primarily absorb photons in order to form an image, this system primarily scatters the photons. Over a single rotation, there is a unique, smooth response curve for each defined source position. Testing was conducted using MCNPX simulations. Image reconstruction was performed using a chi-squared reconstruction technique. A simulated 100 uCi, Cs-137 source at 10 meters was detected after a single, 50-second rotation when a uniform terrestrial background was present. A Cs-137 extended source was also tested. The RSM field-of-view is 360 degrees azimuthally as well as 54 degrees above and 54 degrees below the horizontal plane. Since the RSM is built from polyethylene, the overall cost and weight of the system is low. The system was designed to search for lost or stolen radioactive material, also known as the orphan source problem. [ABSTRACT FROM PUBLISHER]

A theoretical analysis is proposed to investigate the Compton scattering as well as the inverse Compton scattering. In this analysis, the incident and scattered electromagnetic (EM) waves are classically described using Maxwell's equations, while the interacting electron is represented quantum mechanically by a wavepacket with a finite spreading length. The density matrix formalism is introduced to analyze the interaction between the electron wave and the EM field in a quantum mechanical manner. The interaction mechanism is caused by the effective coupling between EM and electron waves satisfying the energy and momentum conservation rules. The effects of the electron relaxation time due to Coulomb collisions among electrons, as well as the finite spreading size of an electron, are newly considered. Expressions for the radiated power of the scattered wave are derived for Compton and inverse Compton scattering. [ABSTRACT FROM AUTHOR]

In order to measure atomic number (Z) of materials, we present a Z identification method based on MV X-ray scattering spectra analysis in this paper. Scattering photons, which include positron annihilation photons, bremsstrahlung photons and Compton scattered photons, are generated by interactions of X-rays with matters and carry their Z information. A LaBr3(Ce) detector is used for its short resolving time (<100 ns) to measure scattered photons to alleviate pulse pileup problem in the 5 \mus X-ray pulse duration. ADC with high sampling rate of 120 MHz and high resolution of 14-bit is used to digitize signal waveform from the preamplifier of the LaBr3(Ce) detector. An offline algorithm is designed to reconstruct scattering spectra. Appropriate shielding structure is set up to reduce the number of transmission photons from accelerator target and scattering photons in environment that enter the detector. These designs ensure effective acquisition of scattering photons in the intense pulsed radiation field. We investigated 10 materials with Z from 13 to 82. Preliminary experimental results show that Z of different materials can be determined successfully. [ABSTRACT FROM PUBLISHER]

The detection of radioactive contraband is a critical problem in maintaining national security for any country. Gamma-ray emissions from threat materials challenge both detection and measurement technologies significantly. The development of a sequential, model-based Bayesian processor that captures both the underlying transport physics of gamma-ray emissions including Compton scattering and the measurement of photon energies offers a physics-based approach to attack this challenging problem. The inclusion of a basic radionuclide representation of absorbed/scattered photons at a given energy along with interarrival times is used to extract the physics information available from noisy measurements. It is shown that this representation leads to an “extended” physics-based structure that can be used to develop an effective sequential detection technique. The resulting model-based processor is applied to data obtained from a controlled experiment in order to assess its feasibility. [ABSTRACT FROM AUTHOR]