The neutron-gamma Feynman variance to mean approach: gamma detection and total neutron-gamma detection (theory and practice)

Two versions of the neutron-gamma variance to mean (Feynman-alpha method or Feynman-Y function) formula for either gamma detection only or total neutron-gamma detection, respectively, are derived and compared in this paper. The new formulas have a particular importance for detectors of either gamma photons or detectors sensitive to both neutron and gamma radiation. If applied to a plastic or liquid scintillation detector, the total neutron-gamma detection Feynman-Y expression corresponds to a situation where no discrimination is made between neutrons and gamma particles. The gamma variance to mean formulas are useful when a detector of only gamma radiation is used or when working with a combined neutron-gamma detector at high count rates. The theoretical derivation is based on the Chapman-Kolmogorov equation with inclusion of general reactions and passage intensities for neutrons and gammas, but with the inclusion of prompt reactions only. A one energy group approximation is considered. The comparison of the two different theories is made by using reaction intensities obtained in MCNPX simulations with a simplified geometry for two scintillation detectors and a 252Cf-source enclosed in a steel container. In addition, the variance to mean ratios, neutron, gamma and total neutron-gamma, are evaluated experimentally for a weak 252Cf neutron-gamma source in a steel container, a 137Cs random gamma source and a 22Na correlated gamma source. Due to the focus being on the possibility of using neutron-gamma variance to mean theories for both reactor and safeguards applications, we limited the present study to the general analytical expressions for Feynman-Y formulas

Shaping the propagation of light in complex media

The main obstacle for optical imaging or for sending information through turbid media such as paint, clouds and biological tissue is the random scattering of light. Owing to its immense complexity, the process of multiple scattering has long been described by the diffusion equation, which ignores the interference of scattered light. Recent developments in optical wavefront shaping and phase recording techniques have enabled the breaking of the diffusion limit and the control of coherent light transport in complex media, including strongly scattering tissues and multimode optical fibres with random mode mixing. Great advances have been made in focusing and controlling the transmission of light through such complex systems and in performing various tasks behind them, such as optical micro-manipulation. Here, we summarize the amazing power and the fundamental limits of controlling multiple light scattering, which lay the physical foundation to harness multiply-scattered light for imaging and communication purposes. Connections to practical applications are illustrated, in particular in those areas covered in the companion articles in this issue

Disordered Crystal Structure and Anomalously High Solubility of Radium Carbonate

XRD measurements of RaCO3 revealedthat it isnot isostructural with witherite, and direct-space ab initio modeling showed that the carbonate oxygens are highly disordered.It was found that the solubility of RaCO3 is unexpectedlyhigher than the solubility of witherite (log(10) K (sp) (0) = -7.5 and -8.56,respectively), supporting the disordered nature of RaCO3. EXAFS data revealed an ionic radius of Ra2+ of 1.55 & ANGS;. Radium is the only alkaline-earth metal which forms disorderedcrystals in its carbonate phase.Radium-226 carbonate was synthesized from radium-bariumsulfate ((Ra0.76Ba0.24SO4)-Ra-226) at room temperature and characterized by X-ray powder diffraction(XRPD) and extended X-ray absorption fine structure (EXAFS) techniques.XRPD revealed that fractional crystallization occurred and that twophases were formed the major Ra-rich phase, Ra(Ba)CO3, and a minor Ba-rich phase, Ba(Ra)CO3, crystallizingin the orthorhombic space group Pnma (no. 62) thatis isostructural with witherite (BaCO3) but with slightlylarger unit cell dimensions. Direct-space ab initio modeling shows that the carbonate oxygens in the major Ra(Ba)CO3 phase are highly disordered. The solubility of the synthesizedmajor Ra(Ba)CO3 phase was studied from under- and oversaturationat 25.1 & DEG;C as a function of ionic strength using NaCl as thesupporting electrolyte. It was found that the decimal logarithm ofthe solubility product of Ra(Ba)CO3 at zero ionic strength(log(10) K (sp) (0)) is-7.5(1) (2 & sigma;) (s = 0.05 g & BULL;L-1). This is significantly higher than the log(10) K (sp) (0) of witheriteof -8.56 (s = 0.01 g & BULL;L-1), supporting the disordered nature of the major Ra(Ba)CO3 phase. The limited co-precipitation of Ra2+ within witherite,the significantly higher solubility of pure RaCO3 comparedto witherite, and thermodynamic modeling show that the results obtainedin this work for the major Ra(Ba)CO3 phase are also applicableto pure RaCO3. The refinement of the EXAFS data revealsthat radium is coordinated by nine oxygens in a broad bond distancedistribution with a mean Ra-O bond distance of 2.885(3) & ANGS;(1 & sigma;). The Ra-O bond distance gives an ionic radius ofRa(2+) in a 9-fold coordination of 1.545(6) & ANGS; (1 & sigma;)

Disordered Crystal Structure and Anomalously High Solubility of Radium Carbonate

Radium-226 carbonate was synthesized from radium-barium sulfate (226Ra0.76Ba0.24SO4) at room temperature and characterized by X-ray powder diffraction (XRPD) and extended X-ray absorption fine structure (EXAFS) techniques. XRPD revealed that fractional crystallization occurred and that two phases were formed─the major Ra-rich phase, Ra(Ba)CO3, and a minor Ba-rich phase, Ba(Ra)CO3, crystallizing in the orthorhombic space group Pnma (no. 62) that is isostructural with witherite (BaCO3) but with slightly larger unit cell dimensions. Direct-space ab initio modeling shows that the carbonate oxygens in the major Ra(Ba)CO3 phase are highly disordered. The solubility of the synthesized major Ra(Ba)CO3 phase was studied from under- and oversaturation at 25.1 \ub0C as a function of ionic strength using NaCl as the supporting electrolyte. It was found that the decimal logarithm of the solubility product of Ra(Ba)CO3 at zero ionic strength (log10 Ksp0) is −7.5(1) (2σ) (s = 0.05 g\ub7L-1). This is significantly higher than the log10 Ksp0 of witherite of −8.56 (s = 0.01 g\ub7L-1), supporting the disordered nature of the major Ra(Ba)CO3 phase. The limited co-precipitation of Ra2+ within witherite, the significantly higher solubility of pure RaCO3 compared to witherite, and thermodynamic modeling show that the results obtained in this work for the major Ra(Ba)CO3 phase are also applicable to pure RaCO3. The refinement of the EXAFS data reveals that radium is coordinated by nine oxygens in a broad bond distance distribution with a mean Ra-O bond distance of 2.885(3) \uc5 (1σ). The Ra-O bond distance gives an ionic radius of Ra2+ in a 9-fold coordination of 1.545(6) \uc5 (1σ)

Strategy for instant neutralisation and metal immobilisation in ARD

Abstract For ARD filters, reactive barriers are often the methods of choice. Some problems are recognised though; iron precipitation cause hydraulic changes and inhibition of neutralising phases. Instead of filter/barrier installation alkalinity is suggested to be added in an aqueous phase (leach beds). Addition of a highly alkaline solution to different ARD results in a rapid, almost instant neutralisation, precipitation of metals (Fe, Al) as well as almost quantitative coprecipitation and sorption of trace metals at near neutral pH. Generation of alkalinity on-site, added to ARD as an aqueous phase, would be a fast and simple ARD treatment method

Charge Transport in High-Mobility Field-Effect Transistors Based on Inkjet Printed Random Networks of Polymer Wrapped Single-Walled Carbon Nanotubes

Printed random networks of polymer-wrapped multi-chiral semiconducting carbon nanotubes (s-SWCNTs) are an opportunity for mass-manufacturable, high-performance large-area electronics. To meet this goal, a deeper understanding of charge-transport mechanisms in such mixed networks is crucial. Here, charge transport in field-effect transistors based on inkjet-printed s-SWCNTs networks is investigated, obtaining direct evidence for the phases probed by charge in the accumulated channel, which is critical information to rationalize the different transport properties obtained for different printing conditions. In particular, when the fraction of nanotubes with smaller bandgaps is efficiently interconnected, the sparse network provides efficient charge percolation for band-like transport, with a charge mobility as high as 20.2 cm(2) V-1 s(-1). However, when the charges are forced by a less efficient morphology, to populate also higher bandgap nanotubes and and/or the wrapping polymer, thermally activated transport takes place and mobility drops. As a result, a trade-off between network density and charge transport properties is identified for device current optimization, in both p- and n-type regimes. These findings shed light on the fundamental aspects related to charge transport in printed s-SWCNT mixed networks and contribute to devise appropriate strategies for the formulation of inks and processes towards cost-effective mass production schemes of high-performance large-area electronics

Software-recorded and self-reported duration of computer use in relation to the onset of severe arm–wrist–hand pain and neck–shoulder pain

Objectives: In both science and media, the adverse effects of a long duration of computer use at work on musculoskeletal health have long been debated. Until recently, the duration of computer use was mainly measured by self-reports, and studies using more objective measures, such as software-recorded computer duration, were lacking. The objective of this study was to examine the association between duration of computer use at work, measured with software and self-reports, and the onset of severe arm-wrist-hand and neck-shoulder symptoms. Methods: A 2-year follow-up study was conducted between 2004 and 2006 among 1951 office workers in The Netherlands. Self-reported computer duration and other risk factors were collected at baseline and at 1-year follow-up. Computer use at work was recorded continuously with computer software for 1009 participants. Outcome questionnaires were obtained at baseline and every 3 months during follow-up. Cases were identified based on the transition within 3 months of no or minor symptoms to severe symptoms. Results: Self-reported duration of computer use was positively associated with the onset of both arm-wrist-hand (RR 1.9, 95% CI 1.1 to 3.1 for more than 4 h/day of total computer use at work) and neck-shoulder symptoms (RR 1.5, 95% CI 1.1 to 2.0 for more than 4 h/day of mouse use at work). The recorded duration of computer use did not show any statistically significant association with the outcomes. Conclusions: In the present study, no association was found between the software-recorded duration of computer use at work and the onset of severe arm-wrist-hand and neck-shoulder symptoms using an exposure window of 3 months. In contrast, a positive association was found between the self-reported duration of computer use at work and the onset of severe arm-wrist-hand and neck-shoulder symptoms. The different findings for recorded and self-reported computer duration could not be explained satisfactorily

Customizing the Polarity of Single-Walled Carbon-Nanotube Field-Effect Transistors Using Solution-Based Additives

Polarity control in semiconducting single-walled carbon-nanotube field-effect transistors (s-SWNT FETs) is important to promote their application in logic devices. The methods to turn the intrinsically ambipolar s-SWNT FETs into unipolar devices that have been proposed until now require extra fabrication steps that make preparation longer and more complex. It is demonstrated that by starting from a highly purified ink of semiconducting single-walled carbon nanotubes sorted by a conjugated polymer, and mixing them with additives, it is possible to achieve unipolar charge transport. The three additives used are benzyl viologen (BV), 4-(2,3-dihydro-1,3-dimethyl-1H-benzimidazol-2-yl)-N,N-dimethylbenzenamine (N-DMBI), which give rise to n-type field-effect transistors, and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F-4-TCNQ) which gives rise to p-type transistors. BV and N-DMBI transform the s-SWNTs transistors from ambipolar with mobility of the order of 0.7 cm(2) V-1 s(-1) to n-type with mobility up to 5 cm(2) V-1 s(-1). F-4-TCNQ transform the ambipolar transistors in p-type with mobility up to 16 cm(2) V-1 s(-1)

Enhancing Quantum Dot Solar Cells Stability with a Semiconducting Single-Walled Carbon Nanotubes Interlayer Below the Top Anode

Semiconducting single-walled carbon nanotubes (s-SWNTs) are used as a protective interlayer between the lead sulfide colloidal quantum dot (PbS CQD) active layer and the anode of the solar cells (SCs). The introduction of the carbon nanotubes leads to increased device stability, with 85% of the initial performance retained after 100 h exposure to simulated solar light in ambient condition. This is in sharp contrast with the behavior of the device without s-SWNTs, for which the photoconversion efficiency, the open circuit voltage, the short-circuit current, and the fill factor all experiencing a sharp decrease. Therefore, the inclusion of s-SWNT as interlayer in CQD SCs, give rise to SCs of identical efficiency (above 8.5%) and prevents their performance degradation

Subpicosecond exciton dynamics in polyfluorene films from experiment and microscopic theory

The authors acknowledge financial support from the UK EPSRC (Grants EP/E065066/1, EP/E062636/1, EP/J009318/1 and EP/J009019/1), from the EPSRC Scottish Centre for Doctoral training in Condensed Matter Physics and from the European Union Seventh Framework Programme under Grant Agreement 321305.Electronic energy transfer (EET) in organic materials is a key mechanism that controls the efficiency of many processes, including light harvesting antennas in natural and artificial photosynthesis, organic solar cells, and biological systems. In this paper we have examined EET in solid-state thin-films of polyfluorene, a prototypical conjugated polymer, with ultrafast photoluminescence experiments and theoretical modeling. We observe EET occurring on a 680 ± 300 fs time scale by looking at the depolarisation of photoluminescence. An independent, predictive microscopic theoretical model is built by defining 125 000 chromophores containing both spatial and energetic disorder appropriate for a spin-coated thin film. The model predicts time-dependent exciton dynamics, without any fitting parameters, using the incoherent Förster-type hopping model. Electronic coupling between the chromophores is calculated by an improved version of the usual line-dipole model for resonant energy transfer. Without the need for higher level interactions, we find that the model is in general agreement with the experimentally observed 680 ± 300 fs depolarisation caused by EET. This leads us to conclude that femtosecond EET in polyfluorene can be described well by conventional resonant energy transfer, as long as the relevant microscopic parameters are well captured. The implications of this finding are that dipole-dipole resonant energy transfer can in some circumstances be fully adequate to describe ultrafast EET without needing to invoke strong or intermediate coupling mechanisms.PostprintPeer reviewe