An all-digital associated particle imaging system for the 3D determination of isotopic distributions

Associated particle imaging (API) is a non-destructive nuclear technique for the 3D determination of isotopic distributions. By detecting the alpha particle associated with the emitted neutron in the deuterium-tritium fusion reaction with a position- and time-resolving detector, the direction of the 14.1 MeV neutron and its time of emission can be determined. Employing this method, isotope characteristic gamma rays emitted in inelastic neutron scattering events can be correlated with the neutron interaction location. An API system consisting of a sealed-type neutron generator, gamma detectors, and a position-sensitive alpha detector was designed, constructed, and characterized. The system was tested with common soil elements and shown to be sensitive to 12C, 16O, 28Si, 27Al, and 56Fe. New aspects of our approach are the use of a yttrium-aluminum-perovskite (YAP) scintillator, using a sapphire window instead of a fiber-optic faceplate for light transport to the photomultiplier, and the all-digital data acquisition system. We present a description of the system with simulations and experimental results that show a position resolution on the alpha detector of 1 mm, a depth resolution using a LaBr3 detector of 6.2 cm, and an angular resolution of 4.5 degrees. Additionally, we present single-element gamma response measurements for the elements mentioned above together with a comparison to Monte Carlo simulations (MCNP6)

Design, construction, and characterization of a compact DD neutron generator designed for 40Ar/39Ar geochronology

A next-generation, high-flux DD neutron generator has been designed, commissioned, and characterized, and is now operational in a new facility at the University of California Berkeley. The generator, originally designed for 40Ar/39Ar dating of geological materials, has since served numerous additional applications, including medical isotope production studies, with others planned for the near future. In this work, we present an overview of the High Flux Neutron Generator (HFNG) which includes a variety of simulations, analytical models, and experimental validation of results. Extensive analysis was performed in order to characterize the neutron yield, flux, and energy distribution at specific locations where samples may be loaded for irradiation. A notable design feature of the HFNG is the possibility for sample irradiation internal to the cathode, just 8 mm away from the neutron production site, thus maximizing the neutron flux (n/cm2/s). The generator's maximum neutron flux at this irradiation position is 2.58e7 n/cm2/s +/- 5% (approximately 3e8 n/s total yield) as measured via activation of small natural indium foils. However, future development is aimed at achieving an order of magnitude increase in flux. Additionally, the deuterium ion beam optics were optimized by simulations for various extraction configurations in order to achieve a uniform neutron flux distribution and an acceptable heat load. Finally, experiments were performed in order to benchmark the modeling and characterization of the HFNG.Comment: 31 pages, 20 figure

An Associated Particle Imaging System for the Determination of 3D Isotopic Distributions

Associated Particle Imaging (API) is a nuclear technique that allows for the non-destructive determination of 3D isotopic distributions. The technique is based on the detection of the alpha particle associated with the neutron emitted in the deuterium-tritium (DT) fusion reaction, which provides information regarding the direction and time of emission of the 14 MeV neutron. Inelastic neutron scattering leads to characteristic gamma-ray emission from certain isotopes, which can be correlated with the neutron interaction location. An API system consisting of a sealed-type neutron generator, gamma detectors, and a position-sensitive alpha detector was designed, constructed, and tested at Lawrence Berkeley National Laboratory (LBNL) for the non-destructive quantification of 12C distribution in soils. Additionally, the system is also sensitive to other elements present in the soil such as O, Si, Al, Fe, etc. It is capable of quantifying 12C at the percent level with a resolution of 2 cm x 2 cm x 7 cm for an hour of measurement. The first half of the dissertation describes the design of the system (using the simulation packages MCNP6, SPICE, and COMSOL Multiphysics) and the characterization of its components including the neutron generator, the position-sensitive alpha detector (YAP), the lanthanum bromide (LaBr) and sodium iodide (NaI) gamma detectors, and the systems used to observe the alpha and gamma signal. The second half focuses on data analysis techniques and presents initial experimental data benchmarked against simulations

An Associated Particle Imaging System for the Determination of 3D Isotopic Distributions

Associated Particle Imaging (API) is a nuclear technique that allows for the non-destructive determination of 3D isotopic distributions. The technique is based on the detection of the alpha particle associated with the neutron emitted in the deuterium-tritium (DT) fusion reaction, which provides information regarding the direction and time of emission of the 14 MeV neutron. Inelastic neutron scattering leads to characteristic gamma-ray emission from certain isotopes, which can be correlated with the neutron interaction location. An API system consisting of a sealed-type neutron generator, gamma detectors, and a position-sensitive alpha detector was designed, constructed, and tested at Lawrence Berkeley National Laboratory (LBNL) for the non-destructive quantification of 12C distribution in soils. Additionally, the system is also sensitive to other elements present in the soil such as O, Si, Al, Fe, etc. It is capable of quantifying 12C at the percent level with a resolution of 2 cm × 2 cm × 7 cm for an hour of measurement. The first half of the dissertation describes the design of the system (using the simulation packages MCNP6, SPICE, and COMSOL Multiphysics) and the characterization of its components including the neutron generator, the position-sensitive alpha detector (YAP), the lanthanum bromide (LaBr) and sodium iodide (NaI) gamma detectors, and the systems used to observe the alpha and gamma signal. The second half focuses on data analysis techniques and presents initial experimental data benchmarked against simulations

An all-digital associated particle imaging system for the 3D determination of isotopic distributions.

Associated particle imaging (API) is a non-destructive nuclear technique for the 3D determination of isotopic distributions. By detecting the alpha particle associated with the emitted neutron in the deuterium-tritium fusion reaction with a position- and time-resolving detector, the direction of the 14.1 MeV neutron and its time of emission can be determined. Employing this method, isotope characteristic gamma rays emitted in inelastic neutron scattering events can be correlated with the neutron interaction location. An API system consisting of a sealed-type neutron generator, gamma detectors, and a position-sensitive alpha detector was designed, constructed, and characterized. The system was tested with common soil elements and shown to be sensitive to 12C, 16O, 28Si, 27Al, and 56Fe. New aspects of our approach are the use of a yttrium-aluminum-perovskite scintillator, using a sapphire window instead of a fiber-optic faceplate for light transport to the photomultiplier, and the all-digital data acquisition system. We present a description of the system with simulations and experimental results that show a position resolution on the alpha detector of 1 mm, a depth resolution using a LaBr3 detector of 6.2 cm, and an angular resolution of 4.5°. Additionally, we present single-element gamma response measurements for the elements mentioned above together with a comparison to Monte Carlo simulations (MCNP6)

Beam-induced back-streaming electron suppression analysis for an accelerator type neutron generator designed for 40Ar/39Ar geochronology.

A facility based on a next-generation, high-flux D-D neutron generator has been commissioned and it is now operational at the University of California, Berkeley. The current generator designed for 40Ar/39Ar dating of geological materials produces nearly monoenergetic 2.45MeV neutrons at outputs of 108n/s. The narrow energy range is advantageous relative to the 235U fission spectrum neutrons due to (i) reduced 39Ar recoil energy, (ii) minimized production of interfering argon isotopes from K, Ca, and Cl, and (iii) reduced total activity for radiological safety and waste generation. Calculations provided show that future conditioning at higher currents and voltages will allow for a neutron output of over 1010n/s, which is a necessary requirement for production of measurable quantities of 39Ar through the reaction 39K(n,p)39Ar. A significant problem encountered with increasing deuteron current was beam-induced electron backstreaming. Two methods of suppressing secondary electrons resulting from the deuterium beam striking the target were tested: the application of static electric and magnetic fields. Computational simulations of both techniques were done using a finite element analysis in COMSOL Multiphysics®. Experimental tests verified these simulations. The most reliable suppression was achieved via the implementation of an electrostatic shroud with a voltage offset of -800V relative to the target