Multiple-Coincidence Active Neutron Interrogation of Fissionable Materials

In an extension of the Associated Particle Imaging technique that is used for the detection and imaging of hidden explosives, the present measurements use a beam of tagged 14.1 MeV neutrons in coincidence with two or more gammas to probe for the presence of fissionable materials. We have measured neutron-gamma-gamma coincidences with targets of depleted uranium, tungsten, lead, iron, and carbon and will present results that show the multiple-coincidence counting rate for the depleted uranium is substantially higher than any of the non-fissionable materials. In addition, the presence of coincidences involving delayed particle spectra provides a signature for fissionable materials that is distinct from that for non-fissionable ones. Information from the tagged neutron involved in the coincidence event is used to compute the position of the fissionable material in all three dimensions. The result is an imaging probe for fissionable materials that is compact and portable, and produces relatively low levels of background radiation. Simultaneous measurements on packages of interest for both explosives and fissionable materials are now feasible

Fission Detection Using the Associated Particle Technique

A beam of tagged 14 MeV neutrons from the deuterium-tritium (DT) reaction is used to induce fission in a target composed of depleted uranium. The generator yield is 107 neutrons/second radiated into a 4π solid angle. Two 4 in.×4 in. NaI detectors are used for gamma-ray detection. The fission process is known to produce multiple gamma-rays and neutrons. Triple coincidences (α-γ-γ) are measured as a function of neutron flight time up to 90 ns after fission, where the α-particle arises from the DT reaction. A sudden increase in the triple coincidence rate at the location of the material is used to localize and detect fission in the interrogated target. Comparisons are made with experiment runs where lead, tungsten, and iron were used as target materials. The triple coincidence response profile from depleted uranium is noted to be different to those observed from the other target materials. The response from interrogation targets composed of fissile material is anticipated to be even more unique than that observed from depleted uranium

Multiple-Coincidence Active Neutron Interrogation of Fissionable Materials

Using a beam of tagged 14.1 MeV neutrons to probe for the presence of fissionable materials, we have measured n-γ-γ coincidences from depleted uranium (DU). The multiple coincidence rate is substantially above that measured from lead, tungsten, and iron. The presence of coincidences involving delayed gammas in the DU time spectra provides a signature for fissionable materials that is distinct from non-fissionable ones. In addition, the information from the tagged neutron involved in the coincidence gives the position of the fissionable material in all three dimensions. The result is an imaging probe for fissionable materials that is more compact and that produces much less radiation than other solutions

Mass-luminosity relation for FGK main sequence stars: metallicity and age contributions

The stellar mass-luminosity relation (MLR) is one of the most famous empirical "laws", discovered in the beginning of the 20th century. MLR is still used to estimate stellar masses for nearby stars, particularly for those that are not binary systems, hence the mass cannot be derived directly from the observations. It's well known that the MLR has a statistical dispersion which cannot be explained exclusively due to the observational errors in luminosity (or mass). It is an intrinsic dispersion caused by the differences in age and chemical composition from star to star. In this work we discuss the impact of age and metallicity on the MLR. Using the recent data on mass, luminosity, metallicity, and age for 26 FGK stars (all members of binary systems, with observational mass-errors <= 3%), including the Sun, we derive the MLR taking into account, separately, mass-luminosity, mass-luminosity-metallicity, and mass-luminosity-metallicity-age. Our results show that the inclusion of age and metallicity in the MLR, for FGK stars, improves the individual mass estimation by 5% to 15%.Comment: 7 pages, 4 figures, 1 table, accepted in Astrophysics and Space Scienc

Characterising current agroecological and regenerative farming research capability and infrastructure, and examining the case for a Living Lab network [Final report]

Agriculture is a major cause of greenhouse gas (GHG) emissions, biodiversity loss, and pollution. Agroecological and regenerative farming have been advocated as alternative approaches that may have fewer negative (or even net positive) environmental impacts than conventional agriculture at farm- and landscape-scales, leading to considerable interest in these approaches (Newton et al. 2020; Bohan et al. 2022; Prost et al. 2023). This report forms the third part of a Defra-funded project Evaluating the productivity, environmental sustainability and wider impacts of agroecological and regenerative farming systems compared to conventional systems. The first part of this project was a rapid evidence review of agroecological and regenerative farming systems and their impacts (Burgess et al. 2023), and the second reported interview findings to examine farmer and stakeholder perspectives on barriers and enablers in agroecological and regenerative farming (Hurley et al. 2023). This third part of the project characterised the current research capability in agroecology and regenerative farming, and explored the potential role of a new ‘living lab’ trial network. Three objectives are addressed in this report: 1) Characterise the existing agroecological and regenerative farming research capability and infrastructure in the UK. 2) Explore lessons from recent research initiatives and identify key research gaps, to inform a potential UK living labs trials network in agroecology/regenerative farming. 3) Develop recommendations for a new living lab trial or research network in agroecology/regenerative farming. Objective 1 was addressed through an online survey to gather quantitative and qualitative data on current research initiatives and networks in regenerative farming and agroecology. There were 22 respondents from 20 organisations (Section 2.2). Key findings from the survey: • The size and the timescales of research initiatives varied substantially from single sites to networks of 50-100 sites and with agroecological/regenerative practices applied from one to over 20 years. • All the survey respondents applied multiple agroecological/regenerative processes and had multiple target outcomes. • Just under 40% of respondents are not currently collecting data from their network. • Three-quarters of the survey participants not currently collecting data stated they would like to collect data, given more funding, knowledge or support. • Biodiversity was one of the most frequent target outcomes, and data collection most frequently focussed on biodiversity. • Face-to-face and email communication was most frequently used between farms in a network. Around two-thirds of respondents also held farm demonstration days as a means of knowledge exchange. • Most of the research initiatives and networks were funded by charities, NGOs or funded themselves, with a smaller number funded by UK or EU government funding. • Growing to incorporate more farms and researchers and developing knowledge exchange further were prioritised as future aspirations by survey respondents. Incorporating more researchers and applying for funding were also a focus for many research initiatives. • Targeted funding was seen as very important in achieving future aspirations by most respondents, along with improved connections with farmers and landowners and improved skills and information for knowledge exchange. Improved infrastructure and monitoring tools were emphasised less, but still considered important. The online survey results illustrate the wide range of current research initiatives in agroecology and regenerative farming, which vary from small-scale trials on a few farms to robust, repeatable data collection across a large network. To illustrate the range of approaches in more details, five case studies were described (Section 2.3) which included an ongoing living lab network, three research project and a long-term demonstration farm. Key characteristics of eight European living labs were also summarised through a network of EU agroecology living labs (the ALL-Ready project; Section 2.4). Objective 2 was addressed through an online workshop, at which participants responded to questions about research gaps and priorities, infrastructure needs, and the barriers and enablers to data sharing and access (Section 3). Participants views were gathered through online discussion boards and facilitated verbal discussion (Figure 1). Key themes and conclusions from the workshop: • Many of the impacts of agroecology and regenerative practices remain poorly understood, with biodiversity and greenhouse gas emissions highlighted. • Impacts on multiple potential benefits and trade-offs (e.g. yield vs. biodiversity vs. greenhouse gas emissions) need to be understood. The variation in responses (e.g. between soil types or regions) was seen as a priority area for research to improve the understanding of scaling-up. • Research needs to be conducted at adequate temporal and spatial scales given the timescales needed for impacts of these practices to become apparent. • There may be a bias in farmer participation in agroecological and regenerative agriculture research (those who can afford the time and money). • Understanding transitions to agroecology and regenerative farming across different types of farm business was raised as a research gap along with investigating the role of knowledge in these types of practice. This was reflected in the discussion of infrastructure and skills, with support (better guidance, input from advisors) and upskilling/improvements in education seen as priorities to support transitions. • The role of economic drivers, including subsidies and supply chain structures, is a research priority to understand why and how farmers may transition to these farming practices. • Standardised assessments and monitoring tools (including farmer apps) were highlighted to support future research, in particular standardised soil carbon assessments. Hubs to loan monitoring equipment to farmers were also suggested. • The time commitment needed was seen as an impediment to data collection by farmers, with comments that research initiatives worked better with someone external collecting data. • Data quality and formats were raised as barriers to data sharing in agroecology/regenerative farming. Formats that can be easily read across a range of software were suggested as a solution, along with more standardised approaches in data collection. • Integration and sharing of data across platforms were another solution, in particular for regulatory data (e.g. pesticide usage). • A potential tension was raised between standardising monitoring approaches and data collection, and constraining innovation by farmers. • Our understanding of how widespread agroecological and regenerative farming practices are, and which are being used / in what combinations, is constrained by lack of uptake data. Practices are being implemented with or without subsidies, and in varying combinations with more conventional approaches. Without these uptake data, larger scale research and modelling may be constrained. The online survey findings, case studies and lessons learnt from the workshop participants informed the development of recommendations for a future living labs network in the UK (Objective 3, Section 4). Four options were proposed: i) Develop a standardised methodology or protocol for each of the 12 attributes listed for assessment within the Global Farm Metric, to support consistency of farm measurements. ii) New research projects funded to collect standardised data on impacts and trade-offs across existing networks of farms applying agroecological / regenerative practices. This would maximise research synergies with existing networks. iii) New research network set up to apply agroecological / regenerative practices on commercial farms, co-designed between farmers and researchers. Standardised data collection on impacts and trade-offs. iv) Long-term living lab UK network set up, within which facilitation roles and research projects funded. These options could be applied in combination (e.g. a standardised methodology (i) developed within (iv) a long-term living lab network ). Which options are taken forward will depend on funding and factors such as the structure of available funding and timescales. Indicative costs were provided for field surveys of greenhouse gases and biodiversity, two of the impacts identified as research priorities in the workshop

Probing the Nature of Short Swift Bursts via Deep INTEGRAL Monitoring of GRB 050925

We present results from Swift, XMM-Newton, and deep INTEGRAL monitoring in the region of GRB 050925. This short Swift burst is a candidate for a newly discovered soft gamma-ray repeater (SGR) with the following observational burst properties: 1) galactic plane (b=-0.1 deg) localization, 2) 150 msec duration, and 3) a blackbody rather than a simple power-law spectral shape (with a significance level of 97%). We found two possible X-ray counterparts of GRB 050925 by comparing the X-ray images from Swift XRT and XMM-Newton. Both X-ray sources show the transient behavior with a power-law decay index shallower than -1. We found no hard X-ray emission nor any additional burst from the location of GRB 050925 in ~5 Ms of INTEGRAL data. We discuss about the three BATSE short bursts which might be associated with GRB 050925, based on their location and the duration. Assuming GRB 050925 is associated with the H II regions (W 58) at the galactic longitude of l=70 deg, we also discuss the source frame properties of GRB 050925.Comment: 13 pages, 13 figures, accepted for publication in ASR special issue on Neutron Stars and Gamma Ray Bursts, full resolution of Fig 5 is available at http://asd.gsfc.nasa.gov/Takanori.Sakamoto/GRB050925/integral_ibis_images.ep

WD + MS systems as the progenitor of SNe Ia

We show the initial and final parameter space for SNe Ia in a ($\log P^{\rm i}, M_{\rm 2}^{\rm i}$) plane and find that the positions of some famous recurrent novae, as well as a supersoft X-ray source (SSS), RX J0513.9-6951, are well explained by our model. The model can also explain the space velocity and mass of Tycho G, which is now suggested to be the companion star of Tycho's supernova. Our study indicates that the SSS, V Sge, might be the potential progenitor of supernovae like SN 2002ic if the delayed dynamical-instability model due to Han & Podsiadlowski (2006) is appropriate. Following the work of Meng, Chen & Han (2009), we found that the SD model (WD + MS) with an optically thick wind can explain the birth rate of supernovae like SN 2006X and reproduce the distribution of the color excess of SNe Ia. The model also predicts that at least 75% of all SNe Ia may show a polarization signal in their spectra.Comment: 6 pages, 2 figures, accepted for publication in Astrophysics & Space Science (Proceeding of the 4th Meeting on Hot Subdwarf Stars and Related Objects, edited by Zhanwen Han, Simon Jeffery & Philipp Podsiadlowski

The mass-to-light ratio of rich star clusters

We point out a strong time-evolution of the mass-to-light conversion factor eta commonly used to estimate masses of unresolved star clusters from observed cluster spectro-photometric measures. We present a series of gas-dynamical models coupled with the Cambridge stellar evolution tracks to compute line-of-sight velocity dispersions and half-light radii weighted by the luminosity. We explore a range of initial conditions, varying in turn the cluster mass and/or density, and the stellar population's IMF. We find that eta, and hence the estimated cluster mass, may increase by factors as large as 3 over time-scales of 50 million years. We apply these results to an hypothetic cluster mass distribution function (d.f.) and show that the d.f. shape may be strongly affected at the low-mass end by this effect. Fitting truncated isothermal (Michie-King) models to the projected light profile leads to over-estimates of the concentration parameter c of delta c ~ 0.3 compared to the same functional fit applied to the projected mass density.Comment: 6 pages, 2 figures, to appear in the proceedings of the "Young massive star clusters", Granada, Spain, September 200

A pilgrimage to gravity on GPUs

In this short review we present the developments over the last 5 decades that have led to the use of Graphics Processing Units (GPUs) for astrophysical simulations. Since the introduction of NVIDIA's Compute Unified Device Architecture (CUDA) in 2007 the GPU has become a valuable tool for N-body simulations and is so popular these days that almost all papers about high precision N-body simulations use methods that are accelerated by GPUs. With the GPU hardware becoming more advanced and being used for more advanced algorithms like gravitational tree-codes we see a bright future for GPU like hardware in computational astrophysics.Comment: To appear in: European Physical Journal "Special Topics" : "Computer Simulations on Graphics Processing Units" . 18 pages, 8 figure

Habitable Zones of Host Stars During the Post-MS Phase

A star will become brighter and brighter with stellar evolution, and the distance of its habitable zone will become farther and farther. Some planets outside the habitable zone of a host star during the main sequence phase may enter the habitable zone of the host star during other evolutionary phases. A terrestrial planet within the habitable zone of its host star is generally thought to be suited to life existence. Furthermore, a rocky moon around a giant planet may be also suited to life survive, provided that the planet-moon system is within the habitable zone of its host star. Using Eggleton's code and the boundary flux of habitable zone, we calculate the habitable zone of our Solar after the main sequence phase. It is found that Mars' orbit and Jupiter's orbit will enter the habitable zone of Solar during the subgiant branch phase and the red giant branch phase, respectively. And the orbit of Saturn will enter the habitable zone of Solar during the He-burning phase for about 137 million years. Life is unlikely at any time on Saturn, as it is a giant gaseous planet. However, Titan, the rocky moon of Saturn, may be suitable for biological evolution and become another Earth during that time. For low-mass stars, there are similar habitable zones during the He-burning phase as our Solar, because there are similar core masses and luminosities for these stars during that phase.Comment: 6 pages, 7 figures. Accepted by Ap & S