Compact Compton Camera for Radiation Distribution Imaging under High Dose Rate Environments (#2454)
Y. Sato1, Y. Terasaka1, M. Kaburagi1, Y. Tanifuji1, H. Usami1, H. N. Miyamura1, S. Ozawa2, R. Izumi2, K. Kawabata1, T. Suzuki3, T. Torii1
1 Japan Atomic Energy Agency, Collaborative Laboratories for Advanced Decommissioning Science, Tokai-mura, Naka-gun, Ibaraki, Japan
The development of quick radiation imaging methods in the high dose rate environments is very important to accelerate decommissioning of the Fukushima Daiichi Nuclear Power Station (FDNPS). We have developed a compact Compton camera for measurement of radioactive contamination inside FDNPS. We conducted a performance evaluation test inside the gamma-ray irradiation facility, and the Compton camera can visualize the 137Cs-irradiation source under the dose rate of 1 mGy/h. We also developed the remote radiation imaging system consisting of the Compton camera and a multicopter-type drone. The drone system succeeded in observing the 137Cs-radioactive source, which was set on the floor surface, remotely. We plan to use the Compton camera and the drone system inside the buildings of FDNPS.
Keywords: Radiation Imaging; Compton camera; Remote Technology; Fukushima Daiichi Nuclear Power Station; Decommissioning
Double-Photon coincidence imaging for cascade sub-MeV gamma-rays with Ce:GAGG scintillator based Compton Camera (#2209)
Y. Mizumachi1, M. Uenomachi1, Y. Yoshihara1, H. Takahashi1, K. Shimazoe1, G. Yabu2, 3, H. Yoneda2, 3, S. Watanabe2, 3, T. Takahashi2, 3, S. Takeda4, T. Orita4, F. Moriyama4, H. Sugawara4
1 The University of Tokyo, Nuclear Engineering and Management, Hongo Bunkyo Tokyo, Japan
A Compton camera is one of gamma-ray imaging method, which has advantage for sub-MeV gamma-ray imaging. It has been utilized for visualizing nuclides, which are environmentally distributed by the Fukushima accident. The three-dimensional gamma-ray imaging of fuel debris is also required, but it is difficult to use Compton camera for 3-D imaging and distributed sources, because of its low signal-to-noise ratio. To solve this problem, we focused on Double-Photon coincidence imaging for cascade gamma-rays. For the imaging of fuel debris, 134Cs and 60Co are important elements, which release multiple cascade gamma-rays with a short delay. Our group are developing double-photon coincidence Compton imaging for the double photon emission nuclides. For Compton imaging, we used 8×8 array of GAGG and SiPM as scatter and absorber, and dynamic Time-over-Threshold method for parallel event detection. We used two Compton cameras, and a function generator as external clock, which synchronize data from two cameras. By using those setups, we took experimental data of a 134Cs point source, and two 22Na point source, and made image by single Compton imaging and double-photon emission imaging. Both of those dataset indicated the drastic improvement of SN ratio and point spread function by using double-photon emission imaging method.
Keywords: Compton imaging, Double photon emission, Double-Photon Emission Computed Tomography
Development of the Pinhole Compton hybrid Camera for the Environmental Radioactivity Survey (#1328)
N. Nakada1, K. Shimazoe1, H. Takahashi1, Y. Shikaze2
1 The University of Tokyo, School of Engineering, Tokyo, Japan
We developed a hybrid detector combining Pinhole camera and Compton camera to measure the dose distribution in Fukushima. We conducted three experiments to evaluate this detector. As a result, we found these followings. (1) It is necessary to improve the detector so that characteristic X-rays can be measured. (2) Ce:GAGG of the scatterer cut off low-energy gamma-rays, and the central hole functioned as Pinhole. (3) We confirmed that the source position is imaged from the Compton scattering event of gamma-ray (662 keV).
Keywords: Pinhole Camera, Compton Camera, Dynamic TOT method, Environmental Radioactivity Survey
Investigation of the 11B(d,n-gamma)12C Discrete Energy Photon Source for Active Interrogation Applications (#3718)
P. B. Rose Jr1, A. S. Erickson1
1 Georgia Institute of Technology, Nuclear and Radiological Engineering Program, Atlanta, Georgia, United States of America
Detecting special nuclear material, especially while in transit, has been identified as "searching for a needle in a haystack" and endures as one of the greatest technical challenges facing national security. Active interrogation can be utilized to probe through shielding, uncovering illicit material when specific techniques are applied. Emerging monoenergetic radiation sources, such as low energy nuclear reaction based sources, show promise for elevating SNM detection capabilities far beyond traditional bremsstrahlung beam interrogation. In this work we report advancements on the understanding of one of these monoenergetic sources, the accelerator driven 11B(d,n-gamma)12C reaction. This source is known to produce intense, highly penetrating gamma rays of 4.4 MeV and 15.1 MeV, but it also produces an abundance of other high energy gamma rays that have not been identified until now. Detailed classification of this source is imperative for our understanding of the physics taking place and how it can be exploited for active interrogation, paving the way for new possibilities in nuclear security and other fields where high energy monoenergetic photons are desired. We present a detailed analysis of experimentally observed gamma rays produced from this low energy nuclear reaction as well as their relative yields based on an incident 3.02 MeV deuteron beam.
Keywords: active interrogation, imaging, nuclear reaction source, snm
Compressive Gamma-Ray Imaging (#2199)
D. A. Boardman1, M. C. Guenette1, A. Sarbutt1, A. Flynn1, D. Prokopovich1
1 ANSTO, Nuclear Stewardship, Lucas Heights, N.S.W, Australia
We describe the development of a novel single pixel gamma-ray imaging system, designed around the theory of compressed sensing. Compressed sensing theory allows for highly undersampled measurements under the conditions that an image is sparse in some basis, and that the sensing matrix and basis are as incoherent as possible. The developed system employs two nested cylindrical masks that independently rotate around a single central detector, which enables a series of quasi-random (incoherent) linear projections of the scene plane to be measured. Compressive gamma-ray images were experimentally obtained for both point sources and extended sources. The spectroscopic gamma-ray imaging of point sources was performed with only 1/10th of the measurements normally required by traditional aperture based imaging techniques. The system design provides a large field of view (360o x 70o) and covers a wide energy range of 40 keV to 1.5 MeV. The development of a compressive gamma-ray imaging technique exploits the sparsity typically found in gamma-ray images and presents a new method for imaging gamma-rays.
Keywords: gamma-ray imaging, compressed sensing, single pixel imager, image reconstruction
Omnidirectional 3D Gamma-ray Imaging with a Free-moving Spherical Active Coded Aperture (#3950)
D. Hellfeld1, P. Barton2, D. Gunter2, A. Haefner2, L. Mihailescu2, K. Vetter1, 2
1 University of California, Berkeley, Nuclear Engineering, Berkeley, California, United States of America
The integration of gamma-ray imaging and visual scene data in 3D has been shown to improve radioactive source localization and mapping capabilities. By constraining the image reconstruction to occupied voxels in the 3D scene model, the localization accuracy can be improved and the reconstruction time can be reduced. Contextual sensors such as visual cameras and light detection and ranging (LiDAR) units aboard mobile imaging systems have been used with Simultaneous Localization and Mapping (SLAM) algorithms to create 3D scene models and to track the position and orientation of the system as it moves freely through an environment in real-time. The tracking information and scene data in conjunction with gamma-ray data facilitates accurate real-time, free-moving, 3D gamma-ray image reconstruction. These concepts have recently been demonstrated with mobile germanium and CdZnTe (CZT) Compton imaging systems. Here we investigate the free-moving 3D imaging capabilities of a hand-portable, CZT-based, omnidirectional spherical active coded aperture system currently being developed at Lawrence Berkeley National Laboratory (LBNL). Akin to previous imagers, the active configuration enables broad-energy dual-mode coded aperture and Compton imaging. However, the spherical arrangement of detectors facilitates omnidirectional imaging with both modalities, overcoming the limited and anisotropic field-of-view inherent in active two-plane systems. We explore the free-moving 3D imaging performance of the low-energy coded aperture modality using both simulations and lab measurements with the prototype system. Iterative algorithms are used to reconstruct coded aperture data in bin-mode (multiple static measurements) and list-mode (continuous motion) operations. GPU-parallelization is also investigated for real-time reconstruction.
Keywords: 3D Gamma-ray Imaging, Spherical Coded Aperture, Free-moving Imaging, Omnidirectional Imaging