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Measurements from actinic flux spectroradiometers on board the NASA DC-8 during the Atmospheric Tomography (ATom) mission provide an extensive set of statistics on how clouds alter photolysis rates (J values) throughout the remote Pacific and Atlantic Ocean basins. J values control tropospheric ozone and methane abundances, and thus clouds have been included for more than three decades in tropospheric chemistry modeling. ATom made four profiling circumnavigations of the troposphere capturing each of the seasons during 2016-2018. This work examines J values from the Pacific Ocean flights of the first deployment, but publishes the complete Atom-1 data set (29 July to 23 August 2016). We compare the observed J values (every 3s along flight track) with those calculated by nine global chemistry-climate/transport models (globally gridded, hourly, for a mid-August day). To compare these disparate data sets, we build a commensurate statistical picture of the impact of clouds on J values using the ratio of J-cloudy (standard, sometimes cloudy conditions) to J-clear (artificially cleared of clouds). The range of modeled cloud effects is inconsistently large but they fall into two distinct classes: (1) models with large cloud effects showing mostly enhanced J values aloft and or diminished at the surface and (2) models with small effects having nearly clear-sky J values much of the time. The ATom-1 measurements generally favor large cloud effects but are not precise or robust enough to point out the best cloud-modeling approach. The models here have resolutions of 50-200 km and thus reduce the occurrence of clear sky when averaging over grid cells. In situ measurements also average scattered sunlight over a mixed cloud field, but only out to scales of tens of kilometers. A primary uncertainty remains in the role of clouds in chemistry, in particular, how models average over cloud fields, and how such averages can simulate measurements.

Agroecosystem strategies to enhance agrobiodiversity can curb many of the negative impacts associated with current food production systems. With rising interest in agrobiodiversity and agroforestry as farming interventions that confer ecological and socioeconomic benefits, understanding the intended pathways of interventions is important for successful agroecological transformations. Yet, the patterns of agrobiodiversity introduction and adoption remain elusive. Drawing upon social network research from the regions of Ghana where cocoa (Theobroma cacao) is grown, we synthesize the relationships between agroforestry interventions, information networks, and the adoption of diversified agroecosystems. We illustrate middle-level patterns from independent studies in three regions of Ghana and nearly 500 farmer interviews. Strong structural indicators at the network level are linked to agrobiodiversity; farmers in larger, less dense information networks with ties to external organizations tend to have higher reported and measured agrobiodiversity. Remarkably, these trends were found in environmentally and socio-culturally different contexts in Ghana. However, these trends do not, in all cases, scale to the community level. For example, we did not observe any clear relationship between the density of community networks and the measures of agrobiodiversity at the community scale. This may be on account of the type of agrobiodiversity measure applied (above-ground biomass) to assess community-level outcomes. Selection of environmental attributes with meaningful spillover effects, such as pest management, would more likely uncover nontrivial network effects at the collective level. Our findings support that both innovation and cooperation are indispensable for successful agrobiodiversity interventions, and that networks can operate to overcome negative outcomes of agrobiodiversity. Based on these studies, we conclude that agrobiodiversity adoption via interventions and established farmer-to-farmer networks may trigger the formation of other, observation-based networks that draw in socially distant actors. Our research strategy of ex-post qualitative comparisons allowed for in-depth insight into the complexities of information networks and agrobiodiversity adoption but also generated new hypotheses on the role of social networks in diversified farming systems.

Germanium-based detectors are the standard technology used for gamma-ray spectroscopy when high efficiency and excellent energy resolution are desired. By dividing the electrical contacts on these detectors into segments, the locations of the gamma-ray interaction events within the detectors can be determined as well as the deposited energies. This enables simultaneous gamma-ray imaging and spectroscopy and leads to applications in the areas of astronomy, nuclear physics, environmental remediation, nuclear nonproliferation, and homeland security. Producing the fine-pitched electrode segmentation often required for imaging has been problematic in the past. To address this issue, we have developed an amorphous-semiconductor contact technology. Using this technology, fully passivated detectors with closely spaced contacts can be produced using a simple fabrication process. The current state of the amorphous-semiconductor contact technology and the challenges that remain will be given in this paper.

The successful development of lithium-drifted Ge detectors in the 1960's marked the beginning of the significant use of semiconductor crystals for direct detection and spectroscopy of gamma rays. In the 1970's, high-purity Ge became available, which enabled the production of complex detectors and multi-detector systems. In the following decades, the technology of semiconductor gamma-ray detectors continued to advance, with significant developments not only in Ge detectors but also in Si detectors and room-temperature compound-semiconductor detectors. In recent years, our group at Lawrence Berkeley National Laboratory has developed a variety of gamma ray detectors based on these semiconductor materials. Examples include Ge strip detectors, lithium-drifted Si strip detectors, and coplanar-grid CdZnTe detectors. These advances provide new capabilities in the measurement of gamma rays, such as the ability to perform imaging and the realization of highly compact spectroscopy systems.

At present, the contacts generally used for lithium-drifted silicon detectors consist of a diffused lithium layer (n-type) and a gold surface barrier (p-type). These contacts work well for unsegmented detectors. However, they both have disadvantages if used for segmented detectors. For this reason, we are developing new types of contacts that will be more robust and easier to segment. To replace the lithium n-type contact, we are using a thin layer of amorphous silicon (a-Si) with metalization on top. The new p-type contact consists of boron implanted into the silicon and annealed at the relatively low temperature of 500 degrees C. The implantation and annealing is carried out as the first step in the process, prior to lithium drifting. Detectors have been fabricated using the new contacts both with and without a guard ring. They performed as well as detectors with standard contacts at operating temperatures between 80K and 240K. We will present data on the leakage current vs. temperature, isolation resistance between the guard ring and the center contact versus temperature and bias voltage, electronic noise and energy resolution versus temperature, as well as 57Co spectra.

Gamma-ray spectroscopy is a valuable tool of science and technology. Many applications for this tool are in need of a detector technology capable of achieving excellent energy resolution and efficient detection while operating at room temperature. Detectors based on the material cadmium zinc telluride (CdZnTe) could potentially meet this need if certain material deficiencies are addressed. The coplanar-grid as well as other electron-only detection techniques are effective in overcoming some of the material problems of CdZnTe and, consequently, have led to efficient gamma-ray detectors with good energy resolution while operating at room temperature. At the present time, the performance of these detectors is mainly limited by the degree of uniformity in electron generation and transport. Despite recent progress in the growth of CdZnTe material, small variations in these properties remain a barrier to the widespread success of such detectors. Alpha-particle response characterization of CdZnTe crystals fabricated into simple planar detectors provides an effective tool to accurately study such variations. We have used a finely collimated alpha source to produce two-dimensional maps of detector response. For a number of crystals, a clear correlation has been observed between their alpha response maps and the distribution of tellurium inclusions inside the crystals. An analysis of the induced charge signals indicates that regions of enhanced electron trapping are associated with the inclusions, and that these regions extend beyond the physical size of the inclusions. Such regions introduce non-uniform electron trapping in the material that then degrades the spectroscopic performance of the material as a gamma-ray detector.

The coplanar-grid as well as other electron-only detection techniques are effective in overcoming some of the material problems of CdZnTe and, consequently, have led to efficient gamma-ray detectors with good energy resolution while operating at room temperature. The performance of these detectors is limited by the degree of uniformity in both electron generation and transport. Despite recent progress in the growth of CdZnTe material, small variations in these properties remain a barrier to the widespread success of such detectors. Alpha-particle response characterization of CdZnTe crystals fabricated into simple planar detectors is an effective tool to accurately study electron generation and transport. We have used a finely collimated alpha source to produce two-dimensional maps of detector response. A clear correlation has been observed between the distribution of precipitates near the entrance contact on some crystals and their alpha-response maps. Further studies are ongoing to determine the mechanism for the observed response variations and the reason for the correlation. This paper presents the results of these studies and their relationship to coplanar-grid gamma-ray detector performance.

Environmentally induced farmer migration is an important livelihood strategy, yet little is known of the effects on the destination region agroecosystem information networks and management practices. In the forest-savanna transition zone (Brong Ahafo Region) of Ghana, where migration from northern regions (migrant) and from neighboring regions (settler) is active, we chart the role of migrant famers and the type of agroecosystem management practices embedded in information networks using a social networks approach. Based on empirical network data from 44 respondents across three communities, we illustrate a diffuse information network, with variable tie frequency between settlement categories (local, settler, or migrant) of farmers. The cohesion of this network is dependent on a few strategic bridging ties initiated by migrant farmers, who are thus centrally positioned to exchange agroecosystem management practices between geographically and socially distant groups. At the individual level, migrant and settler farmers are more likely: (1) to have larger networks with more ties between members of their networks, (2) to be brokers positioned between non-migrant farmers, and (3) to tend (although not statistically significantly) to use pro-environmental management regimes, including agroforestry practices, new planting methods, and plot-scale weeding. We conceptualize this phenomenon as extended social and environmental experience and the deployment of social-ecological memory, with migrant farmers as potential agents of innovation and adaptive management.

Discusses the influence of finite surface recombination velocity on the proper interpretation of photoconductive decay (PCD) transients in semiconductors. Consideration of the limitations of simple analytical equations which relate the observed effective lifetime to the material parameters; Proposed methods to extract information from PCD experiments; Conclusion.

Noise in CdZnTe devices with different electrode configurations was investigated. Measurements on devices with guard-ring electrode structures showed that surface leakage current does not produce any significant noise. The parallel white noise component of the devices appeared to be generated by the bulk current alone, even though the surface current was substantially higher. This implies that reducing the surface leakage current of a CdZnTe detector may not necessarily result in a significant improvement in noise performance. The noise generated by the bulk current is also observed to be below full shot noise. This partial suppression of shot noise may be the result of Coulomb interaction between carriers or carrier trapping. Devices with coplanar strip electrodes were observed to produce a 1/f noise term at the preamplifier output. Higher levels of this 1/f noise were observed with decreasing gap widths between electrodes. The level of this 1/f noise appeared to be independent of bias voltage and leakage current but was substantially reduced after certain surface treatments. Index Terms--CdZnTe, gamma-ray detectors, noise, semiconductor radiation detectors.

Germanium orthogonal strip detectors have been produced using amorphous-semiconductor contacts. The amorphous-semiconductor contact fabrication process is relatively simple, and it is capable of producing fine-pitched electrode structures. The bipolar blocking behavior of the amorphous-semiconductor contact permits its use on both sides of a detector, replacing conventional B ion implanted and Li diffused contacts. A 5 x 5 orthogonal strip detector has been produced using this technique. Experimental results from this detector are presented.

Develops an isotope-specific and quantitative technique based on self-detection in a position-sensitive detector for the imaging of radio-carbon clusters in high-purity germanium. Prerequisites for applying such technique; Basis for the position-sensitive detector; Description of the detector.

Focuses on a study which proposed an approach to ionizing radiation detection. Method of measuring the amount of ionization produced by a detector medium; Advantages offered by the approach; Demonstration on the principal operation.