The Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory

CAMS operates an HVEC FN tandem accelerator for use in both basic research and technology development. The accelerator is operated under a distributed computer control system with sophisticated auto-scaling, beam flat-topping, archiving, and recall capabilities, which makes possible rapid and precise switching between experimental configurations daily. Using the spectrometer, the AMS group can routinely measure the isotopes {sup 3}H, {sup 9}Be, {sup 10}Be, {sup 14}C, {sup 26}Al, {sup 36}Cl, {sup 41}Ca, and {sup 129}I at abundances as low as 1 part in 10{sup 16}

Methodological approaches to determining the marine radiocarbon reservoir effect

The marine radiocarbon reservoir effect is an offset in 14C age between contemporaneous organisms from the terrestrial environment and organisms that derive their carbon from the marine environment. Quantification of this effect is of crucial importance for correct calibration of the <sup>14</sup>C ages of marine-influenced samples to the calendrical timescale. This is fundamental to the construction of archaeological and palaeoenvironmental chronologies when such samples are employed in <sup>14</sup>C analysis. Quantitative measurements of temporal variations in regional marine reservoir ages also have the potential to be used as a measure of process changes within Earth surface systems, due to their link with climatic and oceanic changes. The various approaches to quantification of the marine radiocarbon reservoir effect are assessed, focusing particularly on the North Atlantic Ocean. Currently, the global average marine reservoir age of surface waters, R(t), is c. 400 radiocarbon years; however, regional values deviate from this as a function of climate and oceanic circulation systems. These local deviations from R(t) are expressed as +R values. Hence, polar waters exhibit greater reservoir ages (δR = c. +400 to +800 <sup>14</sup>C y) than equatorial waters (δR = c. 0 <sup>14</sup>C y). Observed temporal variations in δR appear to reflect climatic and oceanographic changes. We assess three approaches to quantification of marine reservoir effects using known age samples (from museum collections), tephra isochrones (present onshore/offshore) and paired marine/terrestrial samples (from the same context in, for example, archaeological sites). The strengths and limitations of these approaches are evaluated using examples from the North Atlantic region. It is proposed that, with a suitable protocol, accelerator mass spectrometry (AMS) measurements on paired, short-lived, single entity marine and terrestrial samples from archaeological deposits is the most promising approach to constraining changes over at least the last 5 ky BP

Single-nanoparticle phase transitions visualized by four-dimensional electron microscopy

The advancement of techniques that can probe the behaviour of individual nanoscopic objects is of paramount importance in various disciplines, including photonics and electronics. As it provides images with a spatiotemporal resolution, four-dimensional electron microscopy, in principle, should enable the visualization of single-nanoparticle structural dynamics in real and reciprocal space. Here, we demonstrate the selectivity and sensitivity of the technique by visualizing the spin crossover dynamics of single, isolated metal–organic framework nanocrystals. By introducing a small aperture in the microscope, it was possible to follow the phase transition and the associated structural dynamics within a single particle. Its behaviour was observed to be distinct from that imaged by averaging over ensembles of heterogeneous nanoparticles. The approach reported here has potential applications in other nanosystems and those that undergo (bio)chemical transformations

What determines how we see nature? Perceptions of naturalness in designed urban green spaces

1. The multiple benefits of ‘nature’ for human health and well-being have been documented at an increasing rate over the past 30 years. A growing body of research also demonstrates the positive well-being benefits of nature-connectedness. There is, however, a lack of evidence about how people's subjective nature experience relates to deliberately designed and managed urban green infrastructure (GI) with definable ‘objective’ characteristics such as vegetation type, structure and density. Our study addresses this gap.2. Site users (n = 1411) were invited to walk through woodland, shrub and herbaceous planting at three distinctive levels of planting structure at 31 sites throughout England, whilst participating in a self-guided questionnaire survey assessing reactions to aesthetics, perceived plant and invertebrate biodiversity, restorative effect, nature-connectedness and socio-demographic characteristics.3. There was a significant positive relationship between perceived naturalness and planting structure. Perceived naturalness was also positively related to the perceived plant and invertebrate biodiversity value, participants’ aesthetic appreciation and the self-reported restorative effect of the planting. A negative relationship was recorded between perceived naturalness and perceived tidiness and care. Our findings showed that participants perceived ‘naturalness’ as biodiverse, attractive and restorative, but not necessarily tidy. Perceived naturalness was also related to participants’ educational qualifications, gender and nature-connectedness, with women and more nature-connected participants perceiving significantly greater levels of naturalness in the planting.4. These findings are highly significant for policymakers and built environment professionals throughout the world aiming to design, manage and fund urban GI to achieve positive human health and biodiversity outcomes. This applies particularly under austerity approaches to managing urban green spaces where local authorities have experienced cuts in funding and must prioritise and justify GI maintenance practices and regimes