Source Geometry Research Articles

True coincidence summing correction factor for point source geometry with PHITS

In this study, it has been shown that the true coincidence summing correction factor can be obtained for the first time using the PHITS Monte Carlo program. Determining this correction factor using different methods and tools in each laboratory to increase the possibility of achieving high-efficiency measurement conditions is still popular in gamma-ray spectrometry. By using 133Ba, 152Eu, 134Cs, and 60Co point sources, the true coincidence summing factor was investigated in both near and far counting geometries for 15 different energy values. GESPECOR software was used to validate the results obtained with PHITS. A remarkable agreement was obtained between PHITS and GESPECOR, with a discrepancy of less than 3%. With this study, a new tool has been proposed to obtain the true coincidence summing factor, which is one of the significant correction factors investigated/calculated in gamma-ray spectrometric studies.

NA-GCAP: A New Full Moment Tensor Inversion Method Based on the Renewed GRTM and NA Method

Abstract Moment tensor inversion plays a crucial role in determining earthquake types, magnitude, and source geometry. Compared to polarity and amplitude methods, full-waveform approaches provide more comprehensive constraints on the complex full moment tensor (FMT). In this study, we propose a novel FMT inversion method named neighborhood algorithm-generalized cut-and-paste (NA-GCAP) method. Similar to the “cut-and-paste” method, our approach divides seismograms into Pnl and surface-wave segments. To enhance inversion efficiency, we employ the NA in conjunction with a newly developed strategy for efficient Green’s functions computation based on the renewed fast generalized reflection and transmission method (GRTM). Our method requires only a single forward computation and stores ten Green’s functions, significantly improving computational efficiency. We validate the robustness of our approach through synthetic tests using a velocity model perturbed by 5% relative to the input model. Furthermore, we apply the NA-GCAP method to the 2019 Changning earthquake sequence comprising 16 earthquakes, where twelve events exhibit double-couple (DC) components larger than 0.95, indicating a simple dislocation source, and four events display significant non-DC components. Our results align well with the previous studies and demonstrate the potential for widespread application to other earthquake sequences in the future.

Monte Carlo-based identification of electron and proton edges for calibration of miniaturized tissue equivalent proportional counter

Miniaturized tissue equivalent proportional counters (mini-TEPCs) are proper for radiation dosimetry in medical application because the small size of the dosimeter could prevent pile-up effect under the high intensity of therapeutic beam. However, traditional methods of calibrating mini-TEPCs using internal alpha sources are not feasible due to their small size. In this study, we investigated the use of electron and proton edges on Monte Carlo-generated lineal energy spectra as markers for calibrating a 0.9 mm diameter and length mini-TEPC. Three possible markers for each spectrum were calculated and compared using different simulation tools. Our simulations showed that the electron edge markers were more consistent across different simulation tools than the proton edge markers, which showed greater variation due to differences in the microdosimetric spectra. In most cases, the second marker, yδδ, had the smallest uncertainty. Our findings suggest that the lineal energy spectra from mini-TEPCs can be calibrated using Monte Carlo simulations that closely resemble real-world detector and source geometries.

A modified plasma immersed solid-phase impurity assisted doping geometry for the creation of highly fluorescent CVD nanodiamond

In this work, we report on a simple and easy to realize doping geometry by which the color center formation efficiency can be improved significantly in nanocrystalline diamond structures during solid impurity source-assisted microwave plasma enhanced chemical vapor deposition (MWCVD). A vertically aligned solid impurity source immersed into the CVD plasma results in diamond thin film with significantly higher color center related fluorescence signal, than the horizontal and source-free arrangements. Based on the example of negatively charged silicon-vacancy (SiV−) center, we demonstrated that the emission peak intensity of fluorescent nanodiamond structures prepared in such a way can be 7–10 times enhanced without significant alteration of the crystal quality. The observed phenomenon is explained by the increased number of incorporated silicon impurities into the diamond nanocrystals, initiated by the beneficial conditions for the atomization of the vertically aligned impurity source, including the enlarged contact area and the elevated surface temperature. The efficiency of the method was demonstrated for thin films and individual nanocrystal structures as well. The proposed solid-phase doping source geometry can be adapted to other impurities to extend the type or improve the in-situ formation efficiency of impurity related color centers in CVD nanodiamond crystals.

New Late Cretaceous and CAMP Magmatic Sources off West Iberia, From High‐Resolution Magnetic Surveys on the Continental Shelf

AbstractMagma‐poor rifted margins can be affected by magmatic occurrences coeval with rifting and post‐rifting. Understanding the geological processes that originated these magmatic events requires determining their extent, type and size of magmatic bodies and tectonics. This work investigates the distribution and origin of two large magmatic events off SW Iberia, the Late Triassic Central Atlantic Magmatic Province (CAMP) and the West Iberia Late Cretaceous Alkaline Province (WILCAP). Marine magnetic data were densely acquired over ∼4,400 km2 and new magnetic maps reveal a complex heterogeneous anomaly field with different anomaly zones. A wide number and variety of magmatic bodies are interpreted, from km‐scale deeply intruded plutons to small plug‐like and dike‐like intrusions. Integration with bathymetry and seismic reflection data allows discussing the geometry, extent and age of the magmatic sources. The Cabo Raso complex is a densely intruded zone related to the WILCAP event. The Sines complex comprises the offshore prolongation of the on‐land Sines WILCAP magmatic rocks but also the newly mapped Côvo and Milfontes anomalies. Côvo is possibly the largest magmatic intrusion recognized in West Iberia. Milfontes intrudes the non‐rifted Paleozoic crust and is the first known evidence of a plutonic source of the CAMP in Iberia. The intrusion of magmatic bodies was mostly controlled by the crustal tectonic fabric inherited from the Paleozoic Variscan orogeny, which was re‐worked during the Mesozoic rifting and the Cenozoic Alpine collision.

Kaon Femtoscopy with Lévy-Stable Sources from sNN=200 GeV Au+Au Collisions at RHIC

Femtoscopy has the capacity to probe the space-time geometry of the particle-emitting source in heavy-ion collisions. In particular, femtoscopy of like-sign kaon pairs may shed light on the origin of non-Gaussianity of the spatial emission probability density. The momentum correlations between like-sign kaon pairs are measured in data recorded by the STAR experiment, from sNN=200 GeV Au+Au collisions at RHIC, BNL. Preliminary results hint at the possible existence of non-Gaussian, Lévy-stable sources, with the likely presence of an anomalous diffusion process in the signal for the identically charged kaon pairs so produced. More statistically significant studies at lower centre-of-mass energies may contribute to the search for the critical end point of QCD.

Evaluating imaging uncertainty associated with the near surface and added value of vertical arrays using Bayesian seismic refraction tomography

AbstractTraditional tomographic methods do not consider the uncertainties associated with near-surface velocities and static corrections and provide a deterministic solution to the estimation problem. However, these uncertainties significantly affect structural mapping and interpretation of seismic imaging results. On the other hand, Bayesian first-arrival tomography provides multiple near-surface models that fit observed traveltimes equally well and enable the study of potential solution distributions. We demonstrate this approach on a complex synthetic near-surface model, representative of arid environments, to quantify associated velocity and statics uncertainties. We evaluate two different parameterizations for subsurface velocities in the context of near-surface Bayesian tomography: Voronoi tessellation with natural neighbor interpolation and the more conventional Delaunay triangulation with linear interpolation. Our analysis shows that the Voronoi cell parameterization with natural neighbor interpolation is more appropriate for this problem. Finally, the new approach is applied to compare two alternative acquisition geometries comprising conventional surface receivers and surface receivers augmented with vertical receiver arrays. The results demonstrate that adding vertical receiver arrays to conventional surface receivers can significantly reduce the near-surface velocity uncertainty and thus increases the accuracy of the seismic imaging results. Furthermore, the study shows that Bayesian tomography can be used as a tool for evaluating different source and receiver geometries during the acquisition design stage.

Thermofluidic investigations of oil natural transformer: Closed‐loop modelling and experimental validation

AbstractExcessively high temperatures inside a power transformer can accelerate the ageing rate and even cause unplanned outages. Accurately estimating the hot‐spot temperature (HST) of a power transformer is important for regulating the load and ensuring long‐term operation. In this study, a closed‐loop model of a 110‐kV product transformer with an oil natural/air forced (ONAF) cooling mode is built to predict HST, in which the compression ratio of windings, equivalent heat source and radiator geometry are considered. According to the flow field of the winding, the ‘dead oil zone’ and reverse oil flow are observed in the horizontal oil channels. The accuracy of the proposed model is experimentally validated by temperature‐rise tests. The results show that the absolute errors between the measured results and simulation are below 5°C, and the average error is ∼2°C. Furthermore, the arrangements of windings and radiators are studied to enhance the oil circulation. By adding 5 washers to the high‐voltage winding, the average temperature can be decreased by 6°C compared with the case without a washer. Elevating the radiator can also mitigate the characteristic temperatures, and the optimal height difference between the radiator and winding centre is suggested to be 0.66 m.

Estimation of inhomogeneous occupational exposure to the lens of the eyes and the extremities of radiation workers in a research accelerator facility.

We performed an experimental investigation on occupational exposure of the eye lens and the extremity of radiation workers engaged in handling of highly activated materials in a small research accelerator facility. Using a simplified physical phantom to simulate the relevant inhomogeneous radiation exposure situations, the personal dose equivalents obtained at the eye lens and the extremities of radiation workers handling heavily radioactive converters were measured together with the dose measured by personal dosemeters worn on their trunk. Results of mockup experiments and the Monte Carlo calculations suggest that the quantitative estimation of the eye lens doses can be estimated from the trunk dose, while the extremity doses vary considerably from the dose readings from the trunk, depending on the use of simple point-source or volume source geometry.

Characteristics of the far-field source signature and its ghost effect of a marine single air gun

The estimation of the air gun source signature is a crucial topic in marine seismic. Typical approaches such as numerical modelling or near-field measurement-based inversion normally work in practice, but suffer from lack of knowledge on the varying sea surface reflection coefficient, the signature directional consistency and the dynamically changed source geometry. For better understanding of the above uncertainties, real far-field air gun source signatures were acquired. A customized approach combined with sparse f-k transformation and adaptive subtraction is applied to deblend the source signature from the sea-floor reflections. Characteristic of the ghost notch distribution and bubble oscillation period indicate an overall good match to the simulated results, except the latter part due to the unexpected air-leakage. Amplitude decay with incidence-angle increase is observed, indicating that the point-source spherical theory for directional signature estimation may be questionable. The sea-surface reflection coefficient appears time-variant and frequency-dependent which challenges the assumption of flat sea surface in signature estimation. An innovative notional source inversion workflow is adapted to the frequency-dependent reflection coefficient. The notional signature inversed through the adapted approach results in less ghost residuals and weaker spectral notch effect comparing with the normal inversion result, i.e., based on a constant reflection coefficient.

Permeation grouting in soils: numerical discussion of a simplified analytical approach

Permeation grouting – injections at low-pressure values of either microfine cements or chemical products – is frequently adopted to increase the mechanical/hydraulic properties of soils, and standard design approaches are currently either empirical or based on simplified analytical solutions. In this paper, some fundamental hypotheses of these analytical solutions are discussed by carrying out a campaign of finite-element numerical analyses, in which the injection phase in a water-saturated soil is analysed, a Newtonian rheology for the grout is implemented and the hypothesis of immiscibility for the two liquids is assumed. The effect of injection source geometry is discussed, as well as the role of gravity and capillarity. The authors analyse the conditions, in terms of injection flow rate, grout viscosity, soil intrinsic permeability and retention curve, under which the analytical solutions provide reliable results. The numerical results have been compared with the simplified analytical solution herein derived for a one-dimensional spherical geometry, in terms of the ‘characteristic curves’ for the system: the relationship between injection pressure/grout front advancement and injection time.

Multi-planar 2.5D U-Net for image quality enhancement of dental cone-beam CT.

Cone-beam computed tomography (CBCT) can provide 3D images of a targeted area with the advantage of lower dosage than multidetector computed tomography (MDCT; also simply referred to as CT). However, in CBCT, due to the cone-shaped geometry of the X-ray source and the absence of post-patient collimation, the presence of more scattering rays deteriorates the image quality compared with MDCT. CBCT is commonly used in dental clinics, and image artifacts negatively affect the radiology workflow and diagnosis. Studies have attempted to eliminate image artifacts and improve image quality; however, a vast majority of that work sacrificed structural details of the image. The current study presents a novel approach to reduce image artifacts while preserving details and sharpness in the original CBCT image for precise diagnostic purposes. We used MDCT images as reference high-quality images. Pairs of CBCT and MDCT scans were collected retrospectively at a university hospital, followed by co-registration between the CBCT and MDCT images. A contextual loss-optimized multi-planar 2.5D U-Net was proposed. Images corrected using this model were evaluated quantitatively and qualitatively by dental clinicians. The quantitative metrics showed superior quality in output images compared to the original CBCT. In the qualitative evaluation, the generated images presented significantly higher scores for artifacts, noise, resolution, and overall image quality. This proposed novel approach for noise and artifact reduction with sharpness preservation in CBCT suggests the potential of this method for diagnostic imaging.

X-ray radiography of HPGe detectors for Monte Carlo simulations

The results of the development of a radiographic installation that allows to control the size of the internal elements of HPGe detectors' cryostats for simulation by Monte Carlo method, are presented. Calibration and assessment of image quality value of the developed radiographic installation were carried out in accordance with ISO Standards 19232–1 and 19232–5. Simulation of the HPGe detector's registration efficiency in the range of 50 keV-3 MeV with the MCC-MT program showed that the discrepancy between the calculated and experimental results when adjusting the detector model using radiological measurement data does not exceed 3% in geometry for point sources and 5% for the Eu-152 source in the Marinelli beaker geometry.

Collimator design for gamma-ray cascade angular correlations in medical imaging

In recent decades, Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET) have become workhorses of molecular imaging. The main drawback of these modalities is that they resort to statistical methods of image reconstruction, as the location of the individual nuclei emitting radiation is not accessible. To remedy this situation, we embarked on a project to introduce a new modality of nuclear medical imaging which exploits the non-collinear angular correlations of nuclear gamma-ray cascades subsequent to beta decays. This modality, if effective, determines the location of each decay nucleus. We have retrofitted the small animal PET assembly of RIKEN-Kobe (Japan) with tungsten+PLA (polylactic acid) collimators. The chosen material is inexpensive, amenable to three-dimensional (3D) printing, and has good photon attenuation properties. We included the collimator geometry in GATE (Geant4 Application for Tomographic Emission) simulations and developed algorithms for image reconstruction with medical isotope candidates viz., 111In and 43K. Our preliminary simulations show that data acquisition with a 2 MBq source for 900 s is sufficient to reproduce the source geometry with high resolution. This report summarizes our progress to date and the plans for the near future.

True coincidence summing corrections in HPGe detectors

The true coincidence effect is studied in two High Purity Germanium (HPGe) detectors for a variety of isotopes, source geometries and source to detector configurations, via computational tools based on Monte–Carlo simulations. Τhe upgraded patch of MCNP code MCNP–CP and the 2018 version of PENELOPE, which take into account the decay scheme of each cascade emitter, are used to calculate the Full Energy Peak Efficiency (FEPE) for the corresponding gamma-ray energies. The true coincidence correction (TCC) factor is calculated as the ratio of the FEPE derived for each nuclide taking into consideration the true coincidence effect, to the FEPE estimated without considering the phenomenon. In all cases, a satisfactory agreement is observed between the TCC factors calculated using MCNP–CP and PENELOPE 2018. Moreover, the results of the calculations are compared against experimentally derived efficiency values. The correction factors obtained using the TrueCoinc software are applied on experimentally determined FEPE curves, based on measurements performed using reference sources, and consequently the corrected data are compared against the simulations for the "non-coincidence" case. The results of this work contribute to the validation of the computational tools and codes used to study the true coincidence effect and determine the corresponding correction factors, providing useful data for gamma–spectrometry studies of cascade emitters.

Theoretical considerations and supporting evidence for the primary role of source geometry on field potential amplitude and spatial extent.

Field potential (FP) recording is an accessible means to capture the shifts in the activity of neuron populations. However, the spatial and composite nature of these signals has largely been ignored, at least until it became technically possible to separate activities from co-activated sources in different structures or those that overlap in a volume. The pathway-specificity of mesoscopic sources has provided an anatomical reference that facilitates transcending from theoretical analysis to the exploration of real brain structures. We review computational and experimental findings that indicate how prioritizing the spatial geometry and density of sources, as opposed to the distance to the recording site, better defines the amplitudes and spatial reach of FPs. The role of geometry is enhanced by considering that zones of the active populations that act as sources or sinks of current may arrange differently with respect to each other, and have different geometry and densities. Thus, observations that seem counterintuitive in the scheme of distance-based logic alone can now be explained. For example, geometric factors explain why some structures produce FPs and others do not, why different FP motifs generated in the same structure extend far while others remain local, why factors like the size of an active population or the strong synchronicity of its neurons may fail to affect FPs, or why the rate of FP decay varies in different directions. These considerations are exemplified in large structures like the cortex and hippocampus, in which the role of geometrical elements and regional activation in shaping well-known FP oscillations generally go unnoticed. Discovering the geometry of the sources in play will decrease the risk of population or pathway misassignments based solely on the FP amplitude or temporal pattern.

Physical conditions for dust grain alignment in Class 0 protostellar cores

Context. High angular resolution observations of Class 0 protostars have produced detailed maps of the polarized dust emission in the envelopes of these young embedded objects. Interestingly, the improved sensitivity brought by ALMA has revealed wide dynamic ranges of polarization fractions, with specific locations harboring surprisingly large amounts of polarized dust emission. Aims. Our aim is to characterize the grain alignment conditions and dust properties responsible for the observed polarized dust emission in the inner envelopes (≤1000 au) of Class 0 protostars. Methods. We analyzed the polarized dust emission maps obtained with ALMA and compared them to molecular line emission maps of specific molecular tracers, mainly C2H, which allowed us to probe one of the key components in dust grain alignment theories: the irradiation field. Results. We show that C2H peaks toward outflow cavity walls, where the polarized dust emission is also enhanced. Our analysis provides a tentative correlation between the morphology of the polarized intensity and C2H emission, suggesting that the radiation field impinging on the cavity walls favors both the grain alignment and the warm carbon chain chemistry in these regions. We propose that shocks happening along outflow cavity walls could potentially represent an additional source of photons contributing to dust grain alignment. However, some parts of the cores, such as the equatorial planes, exhibit enhanced polarized flux, although no radiation driven chemistry is observed, for example where radiative torques are theoretically not efficient enough. This suggests that additional physical conditions, such as source geometry and dust grain evolution, may play a role in grain alignment. Conclusions. Comparing chemical processes with grain alignment physics opens a promising avenue to develop our understanding of the dust grain evolution (i.e., their origin, growth, and structure) in the interior of Class 0 protostars. The source geometry and evolution can represent important factors that set the environmental conditions of the inner envelope, determining whether the radiation field strength and spectrum can drive efficient dust grain alignment via radiative torques.

Effect of the Fire Modelling on the Structural Temperature Evolution Using Advanced Calculation Models

The main objective of this study is to compare the results in terms of gas temperature and structural elements temperature, using different localized fire models. In particular, with reference to an open car park fire, the simplified Hasemi localized fire model was firstly used for assessing the steel temperature of a typological steel-concrete beam. In the second step, the computational fluid dynamics (CFD) models were applied, also varying the geometry of the fire source; in the first case a 3D flame was considered, in the second case a flat flame source was modelled. The latter represented one of the main research novelties of this work. All the analyses were carried out without and with the activation of a sprinkler system, simulated by varying the Heat Release Rate curve, according to the Italian national fire technical code. The main results show that there was a significant effect of the fire model, indeed the Hasemi model generally overestimated the steel element temperature. Moreover, an effect of fire source modelling was observed, with greater temperature for a 3D fire source modelling in the case of no sprinkler activation. In all the analyses, to consider the sprinkler system leaded to a beneficial effect on temperature.

Modelling continuum reverberation in active galactic nuclei: a spectral-timing analysis of the ultraviolet variability through X-ray reverberation in Fairall 9

ABSTRACT Continuum reverberation mapping of active galactic nuclei (AGNs) can provide new insight into the nature and geometry of the accretion flow. Some of the X-rays from the central corona irradiating the disc are absorbed, increasing the local disc temperature. This gives an additional reprocessed contribution to the spectral energy distribution (SED) which is lagged and smeared relative to the driving X-ray light curve. We directly calculate this reverberation from the accretion disc, creating fully time-dependent SEDs for a given X-ray light curve. We apply this to recent intensive monitoring data on Fairall 9, and find that it is not possible to produce the observed ultraviolet (UV) variability by X-ray reprocessing of the observed light curve from the disc. Instead, we find that the majority of the variability must be intrinsic to the UV emission process, adding to evidence from changing-look AGN that this region has a structure which is quite unlike a Shakura–Sunyaev disc. We filter out this long time-scale variability and find that reprocessing alone is still insufficient to explain even the fast variability in our assumed geometry of a central source illuminating a flat disc. The amplitude of reprocessing can be increased by any vertical structure such as the broad-line region and/or an inner disc wind, giving a better match. Fundamentally though the model is missing the major contributor to the variability, intrinsic to the UV/EUV emission rather than arising from reprocessing.

Monogenetic volcanism in subduction settings: comparative statistical study of the Sierra Chichinautzin and Los Tuxtlas Volcanic Fields in Mexico

Monogenetic fields present significant diversity, yet this diversity has not been fully quantified, and its origin remains elusive. We studied two large subduction-related fields in Mexico, the Sierra Chichinautzin and Los Tuxtlas, that have distinct crustal stress regime and structures, magma compositions, vent types, and climatic conditions. Using recently available 5-m resolution topographical data, we located all the eruptive centers, studied their spatial distribution and analyzed scoria cone shapes in detail, calculating morphometric parameters for the best preserved. We then applied a set of statistical tools to analyze and compare the patterns of vent distribution, vent alignment, and diversity in cone shapes in these two fields. We observe that, despite their distinct setting, the two fields are similar in terms of vent distribution and cone morphology, which shows that this type of data cannot be used alone to infer the tectonic, magmatic, and climatic context of monogenetic fields. It also confirms previous results that the diversity in cone shapes (slope, height-to-diameter ratio) reflects processes that are common to all cones (e.g., ballistic emplacement followed by scoria avalanching on slopes), and hence do not vary significantly (at field-scale) with external parameters. Differences in the crustal stress regime had no apparent impact on vent distribution as the dikes followed active faults, irrespective of their motion. Climatic differences did not affect the shape variety of the studied cones probably because of their young ages (< 50,000 years old) and their location in a vegetated environment. The fields nevertheless differ in size and vent density, as well as scoria cone shape complexity and volume, which can be attributed to differences in the geometry of the magma source for its impact on the closeness of the dikes feeding the activity. Differences in the relative proportion of small cones in both fields are likely due to factors impacting eruptive style such as magma-water interaction, magma composition, and/or fissure lengths.