Progress 07/01/18 to 02/28/19

Outputs
Target Audience:One target audience for this effort was hydrologists and other researchers interested in the advancement of cosmic-ray neutron sensing (CRNS) methods and instruments. We shared our findings through informal conversations and emails. We presented the findings formally at the European Geosciences Union conference in Vienna, Austria on 10 April 2019 (after the end of the period of performance). A second target audience for the effort was stakeholders in commercial agriculture and others interested in commerical applications of CRNS. This includes providers of farm management software, agricultural hardware manufacturers, and owners/operators of remote sensing equipment that could be validated with CRNS as ground truth. Our efforts reached this audience through ongoing conversations about how to integrate a CRNS product with existing hardware and software, data needs, and commericalization opportunities. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project provided the opportunity for the PI to assist another scientist in gaining proficiency with neutron transport physics and simulation tools. How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Impact: Quantifying changes in water content at the earth's surface is critical for a number of applications: efficient use of agricultural inputs, particularly water, management of crop and grazing land, weather and climate modeling, and drought and flood forecasting. Soil moisture is also an important link between the land and atmosphere. Despite the necessity of accurate, timely measurements of soil moisture for these and other applications, the tools currently available to collect those data are inadequate. Cosmic-Ray Neutron Sensing (CRNS) is a promising technology that improves upon existing soil moisture sensors by providing an accurate, large-area measurement with a rugged, non-invasive system. There are, however, several challenges facing its widespread adoption. Two of these are the cost of neutron detectors, and control over the size of the measurement area. Silverside's lithium-based neutron detector, and the CRNS systems that integrate it, address those challenges. Silverside's detector panels cost almost 4 times less than the incumbent technology, and the rectangular form-factor offers the potential of directional measurement, allowing the user to "aim" the detector at a target area of soil. The research conducted for this Phase I SBIR demonstrated the feasibility of using Silverside's detector panels for CRNS, and established a method to improve the CRNS system for directional measurement. In particular, we investigated focusing the sensor's field of view for wide-area or local-area measurement, which will improve the quality of the soil moisture signal. This research lays the foundation for future efforts to develop a prototype CRNS system that uses lithium detectors in an optimized design to enable high-quality soil moisture data collection at a lower cost, making the technology more accessible and useful to both hydrology researchers and stakeholders in commercial agriculture. This outcome has important economic and environmental implications: agriculture currently accounts for about 70% of worldwide water use, and population growth and changing weather and rainfall patterns are expected to both increase agriculture's reliance on irrigation in the future, and exacerbate overall water scarsity. Tools that provide accurate soil moisture measurment, such as the technology at the heart of this Phase 1 effort, are critical for enabling efficient water use. Objective 1: Run simulations to determine the optimal configuration of detector/moderator configurations for a wide-area footprint and for a close-in footprint. Activities: We devised a new approach to modeling detector and moderator geometry for environmental neutrons using two existing Monte Carlo-based simulation tools. This enabled us to collect data to compare the efficiency of different moderator and shield designs for different CRNS use cases. Note that the moderator and shield are the materials, usually high-density plastic, that surround the detector chamber to slow down or stop neutrons Data collected: We collected three types of data: First, we ran simulations to better understand the behavior of cosmic-ray neutrons (also referred to as environmental neutrons) near ground level. Second, we simulated the detection efficiency of different detector, moderator and shield configurations to find an optimal design for a future prototype. Lastly, we recreated empirical tests with traditional moderators to obtain simulated results to compare with the empirical results and help explain findings. Summary & Discussion: The new URANOS-Geant4 method can be used to compare the efficiency of different detector, shield, and moderator geometries and materials in realistic environmental conditions. This is a powerful new methodology that was received with interest by the research community, and that forms the foundation of our proposed Phase II work. Key Outcomes: The key outcome was the development of a method for simulating both detector geometry and environmental neutrons. This will enable simulations to build on traditional moderator design by adding spatial selectivity to improve the quality of the measurement. Objective 2: Design and prototype the detector/moderator configurations, based on simulation results from Objective 1. Activity: We created a moderator and shield design based on URANOS and Geant4 simulations. We also constructed new moderator configurations based on empirical test results and ongoing simulations, which we then field-tested for Objective 3. Data Collected: We investigated the cost and availability of various materials, and discussed the feasibility of building and integrating different design concepts. Summary & Discussion: We learned through the work on Objective 1 that simulating detector geometry is more complex than we initially expected. We therefore focused more on method development, and developed one simple prototype design based on the final optimization tool. Throughout the project, however, we constructed and tested different moderator designs based on empirical findings and preliminary test results. Key Outcomes: The key outcome was an optimized system design to be imporoved upon and field-tested in Phase II. Objective 3: Perform laboratory and field tests to measure the performance of the detector/moderator configurations. Compare results to the simulation results from Objective 1. Activity: We conducted extensive field tests of CRNS systems using different detector technologies and various moderator configurations. These tests included a stationary comparison of lithium with other detectors, and a roving (i.e. driving) test. We also carried out a water tank transect test to assess directionality of moderated lithium panels. Data: The data collected includes side-by-side comparisons of lithium-based CRNS systems with those using other, older detector technologies in different use-cases. We also measured detection efficiency for different detector orientations to determine if measurement with the lithium panel is, or could be made, directional. Summary & Discussion: The results from the field tests showed that lithium-based detectors have the same sensivity to changes in soil moisture as older, more expensive detector technologies. The water tank test results did not show the directionality we expected, and our simulations confirmed this finding, raising new questions about the behavior of ground-level neutrons which we will address in Phase II. Key outcomes: We established that lithium detectors are interchangeable with older detector technologies (primarily helium-3) for CRNS. This is important because helium-3 is scarce and expensive, so there is an effort to find suitable alternatives for a range of applications that include CRNS. Objective 4: Preliminary Design Review (PDR) for the CRNS system, including detector size and moderator configuration. Activity: We conducted a PDR of the CRNS system. Data collected: This assessment involved analysis of the cost and feasibility of design options, as well as how the finished product could be integrated into current systems or adapted for future applications. Summary & Discussion: The design reviewed in this PDR was relatively simple (i.e. all right angles, made from familiar materials). We concluded that it would be feasible to make, but also that additional simulations, using the new tool finalized at the end of the period of performance, are required to explore other design options before building a prototype. We also compared our design with those from other researchers and companies. Key Outcomes: Initial design for an advanced CRNS system, and a demonstration of the utility of the tool developed under Objective 1.

Publications

• Type: Conference Papers and Presentations Status: Accepted Year Published: 2019 Citation: A. Raymond, A. Inglis, and M. Zreda. Advances in CRNS with Lithium-Based Neutron Detectors. Poster and Presentation on 10 April 2019 at the European Geosciences Union annual conference in Vienna, Austria. Abstract available at https://meetingorganizer.copernicus.org/EGU2019/posters/31219.