Geometric Efficiency Research Articles

Measurements of Fission and Radioactive Capture Reaction Rates Inside the Fuel of the Ipen/MB-01

This work presents the measures of the nuclear reaction rates along the radial direction of the fuel pellet by irradiation and posterior gamma spectrometry of a thin slice of fuel pellet of UO2 at 4.3% enrichment. From its irradiation, the rate of radioactive capture and fission had been measured as a function of the radius of the pellet disk using a Ortec GMX HPGe detector. Lead collimators had been used for this purpose. Simulating the fuel pellet in the pin fuel of the IPEN/MB-01 reactor, a thin UO2 disk is used, being inserted in the interior of a dismountable fuel rod. This fuel rod is then placed in the central position of the IPEN/MB-01 reactor core and irradiated during 1 h under a neutron flux of 5 ×108 n/cm2 s. In gamma spectrometry, 10 collimators with different diameters have been used; consequently, the nuclear reactions of radioactive capture that occurs in atoms of 238U and the fission that occurs on both 235U and 238U are measured in function of 10 different regions (diameter of collimator) of the UO2 fuel pellet disk. Nuclear fission produces different fission products such as 143Ce with a yield fission of 5.9% which decay is monitored in this work. Corrections in geometric efficiency due to introduction of collimators on HPGe detection system were estimated using photon transport of MCNP-4C code. Some calculated values of nuclear reaction rate of radioactive capture and fission along the radial direction of the fuel pellet obtained by Monte Carlo methodology, using the MCNP-4C code, are presented and compared to the experimental data showing very good agreement.

Geometric Performance and Efficiency of an Optical Tracking System for Daily Pre-treatment Positioning in Pelvic Radiotherapy Patients

The purpose of this study was to characterize the accuracy of a novel in-house optical tracking system (OTS), and to determine its efficiency for daily pre-treatment positioning of pelvic radiotherapy patients compared to conventional optical distance indicator (ODI) methodology. The OTS is comprised of a passive infrared stereoscopic camera, and custom control software for use in assisting radiotherapy patient setup. Initially, the system was calibrated and tested for stability inside a radiation therapy treatment room. Subsequently, under an ethics approved protocol, the clinical efficiency of the OTS was compared to conventional ODI setup methodology through 17 pelvic radiotherapy patients. Differences between orthogonal source-to-skin distance (SSD) readings and overall set-up time resultant from both systems were compared. The precision of the OTS was 0.01 ± 0.01 mm, 0.02 ± 0.02 mm, and -0.01 ± 0.06 mm in the left/right (L/R), anterior/posterior (A/P), and cranial/caudal (C/C) directions, respectively. Discrepancies measured between the linac radiographic center in the treatment room and the calibrated origin of the camera (OTS) by two independent observers was submillimeter. Analysis of 146 fractions from 17 patients showed a high correlation between the SSD readings of the OTS and ODI setup methodologies (r = 0.99). The average time for pre-treatment positioning using the OTS couch shift calculation was 2.60 ± 0.69 minutes, and for conventional ODI setup, 3.62 ± 0.82 minutes; the difference of 1.02 minutes was statistically significant (p < 0.001). In conclusion, the OTS is a precise and robust tool for use as an independent check of treatment room patient positioning. The system is indicated as geometrically equivalent to current methods of daily pre-treatment patient positioning with potential for gains in efficiency by decreasing setup times in the treatment room.

Geometric efficiency for a circular detector and a ring source of arbitrary orientation and position

Two distinct axisymmetric radiation vector potentials are derived for a circular ring source, both of which are given in terms of elliptic integrals. In combination with Stokes's theorem these potentials reduce the surface integral for the geometric efficiency of a ring source and a general detector to a line integral, though only a circular detector is analyzed in detail here. One of the potentials is bounded as the axis of symmetry is approached and it can also be expressed as an integral of Bessel functions. It is used to derive the ring source analogue of Ruby's formula and its noncoaxial generalization. A trigonometric integral is given for the general noncoaxial case and closed form solutions are given for the coaxial case and the case where the ring source is in the detector plane. Numerical data is given for these cases. The second potential is singular along the entire ring axis and Stokes's theorem must be modified when using it whenever the ring axis intersects the detector or its boundary. This potential is used to derive a trigonometric integral for the geometric efficiency of the ring source and a circular detector in the general case where the source and the detector have arbitrary relative position and angular orientation. Numerical data is given for selected geometric parameters when the planes of the ring and disk are perpendicular and for the general case. The intersection of some results for point source radiation vector potentials with vector potentials arising in diffraction theory is given in an Appendix.

Probability correction for the analytical simulation approach to calibrating γ-ray cylindrical detectors for environmental measurements

Marinelli beakers increase geometric efficiency of detection in the γ-spectrometry of low-activity environmental samples by positioning the sample in close proximity to the detector. A probability correction has been introduced to the analytical simulation approach proposed previously (Nafee et al., 2009) for calculating detection efficiencies of γ-ray cylindrical detectors using extended low- and high-volume Marinelli beakers. Improved expressions for the self-attenuation and the coincidence summing effects at short source-detector distances have also been included in the analytical algorithm. A remarkable agreement between the measured and calculated efficiencies was observed as a result. Deviations of results calculated in this way from experimental values are twice as small as were observed with the previously reported analytical methods (Abbas, 2001; Nafee et al., 2009).

Hit probability of a disk shaped detector with particles with a finite range emitted by a point-like source

An analytical analysis of the geometrical efficiency of a circular detector for particles with a finite range, emitted from a point-like source, is given. Several different cases were determined, depending on the particle range, radius of the detector and the position of the source with respect to the detector. These cases were analyzed separately and different expressions for calculating the hit probability were obtained for each of them. Results were compared with Monte Carlo calculations and good agreement was found. The problem considered here might be relevant for alpha-particle detection under specific conditions.

Improved electron probe microanalysis of trace elements in quartz

Quartz occurs in a wide range of geologic environments throughout the Earth's crust. The concentration and distribution of trace elements in quartz provide information such as temperature and other physical conditions of fomation. Trace element analySes with modern electron-probe microanalysis (EPMA) instruments can achieve 99% confidence detection of - 100 ppm with fairly minimal effort for many elements in samples of low to moderate aVerage atomic number such as mauy common oxides and silicates. HoweVer, trace element measurements below 100 ppm in many materials are limited, not ouly by the precision of the background measurement, but also by the accuracy with which background levels are determined. A new correction algorithm has been developed and tested on both Cameca and JEOL instruments, which applies a quantitative correction to the emitted X-ray intensities duriug the iteration of the sample matrix correction based on a zero level (or known trace) abundance calibration standard. This iterated blank correction, when combined with improved background fit models, and an aggregate'' intensity calculation utilizing multiple spectrometer intensities in software for greater geometric efficiency, yields a detection limit of 2 to 3 ppm for Ti and 6 to 7 ppm for AI in quartz at 99% t-test confidence with similar levels for absolute accuracy.

Formula omitted] and charm at STAR

Gluon saturation effects and Color Glass Condensate models become important at a scale Q S 2 ( x ) . If the saturation scale can be raised to above the charm-quark mass, saturation effects can influence charm production and it is expected, based on CGC models, that charm particle production will follow similar patterns to those found in light quarks. This scale can potentially be reached in the charm sector by going to forward rapidities at RHIC and using nuclear “targets”. The large acceptance and pseudorapidity coverage ( 2.5 < η < 4 ) of the Forward Meson Spectrometer (FMS) at STAR provide excellent geometric efficiency to measure high- x F J / ψ production in p+p and d+Au collisions. A significant observation of high- x F J / ψ in p+p collisions has been obtained. Measurements of forward open charm production also look to be feasible based on initial simulation studies. By comparing d+Au measurements to p+p measurements in both charmonium and open charm productions, the FMS at STAR has the potential to test several predictions of CGC/Saturation models in the charm sector.

Porous Pd films as effective ethanol oxidation electrocatalysts in alkaline medium

Porous Pd films are successfully electrodeposited within hydrogen bubble dynamic templates for the first time, characterized by SEM, EDS, XRD, cyclic voltammetry and chronoamperometry. The effects of the NH 4Cl concentration and deposition time on the morphology are studied. The real surface area and pore size can be controlled easily by modulating the electrolyte composition and deposition time. The as-prepared Pd films have a high geometric efficiency, ensuring a large number of active sites and rapid reaction rates. The porous Pd films with different pore size show different electrocatalytic stability. Amperometric current of ethanol oxidation decays fast on the films with small pores. Porous Pd films with a larger pore size show high electrochemical activity and stability for ethanol electro-oxidation in an alkaline medium.

Study of Shear Capacity in Brazilian Prestressed Hollow Core Slabs

Hollow core slabs have a bold design and can be used in a wide variety of structural systems, performing like floor slabs or wall panels. These slabs are economical due to geometrical and mechanical efficiency of its cross sections, allowing the rationalization of materials consumption (concrete and prestressed strands). The increase of the use of hollow core slabs within the Brazilian construction market has caused a significant boost of production, demanding the assessment of the actual strength capacity of these elements. This paper presents results relative to several hollow core slabs produced in a Brazilian factory, subjected to shear tests according to FIB recommendations. The experimental results were compared with those obtained with the equations from the Guide to Good Practice: Special Design Considerations for Precast Prestressed Hollow Core Floors, published by FIB in 2000.

Evaluation of geometric efficiency and radiation exposure in z-axis for volume scan

The International Electrotechnical Commission (IEC) recommended that a display be provided on the operating console of medical computed tomography (CT) scanners when the geometric efficiency (GE) in the z-axis is 70% or less. Taking into account the increase in the number of detector rows and the changes in the scanning method, the present study was conducted to review the GE and to evaluate the exposure dose in the z-axis direction. The GE for a single-rotation scan was calculated in accordance with IEC-606024 Ed. 2. The findings of the present study suggest that 320-row area detector computed tomography volume scan (single axial scan with no table movement in which it just happened to use a very large beam width) extends 18.8 mm beyond the nominal beam collimation, even when the GE is >70%. However, compared with the helical scan, which is the present mainstream of CT examinations, the dose beyond the scan length is narrower in volume scan for a limited scan length of 160 mm or less.

High efficiency microfluidic beta detector for pharmacokinetic studies in small animals

Abstract New radiotracers are continuously being developed to improve diagnostic efficiency using Single Photon Emission Computed Tomography (SPECT) or Positron Emission Tomography (PET). The characterization of their pharmacokinetics requires blood radioactivity monitoring over time during the scan and is very challenging in small animals because of the low volume of blood available. In this work, a prototype microfluidic blood counter made of a microchannel atop a silicon substrate containing PIN photodiodes is proposed to improve beta detection efficiency in a small volume by eliminating unnecessary interfaces between fluid and detector. A flat rectangular-shaped epoxy channel, 36 μm×1.26 mm cross section and 31.5 mm in length, was microfabricated over a die containing an array of 2×2 mm 2 PIN photodiodes, leaving only a few micrometers of epoxy floor layer between the fluid and the photodiode sensitive surface. This geometry leads to a quasi 2D source, optimizing geometrical detection efficiency that was estimated at 41% using solid angle calculation. CV – IV measurements were made at each fabrication step to confirm that the microchannel components had no significant effects on the diodes’ electrical characteristics. The chip was wire-bonded to a PCB and connected to charge sensitive preamplifier and amplifier modules for pulse shaping. Energy spectra recorded for different isotopes showed continuous beta distribution for PET isotopes and monoenergetic conversion electron peaks for 99m Tc. Absolute sensitivity was determined for the most popular PET and SPECT radioisotopes and ranged from 26% to 33% for PET tracers ( 18 F, 13 N, 11 C, 68 Ga) and more than 2% for 99m Tc. Input functions were successfully simulated with 18 F, confirming the setup’s suitability for pharmacokinetic modeling of PET and SPECT radiotracers in animal experiments. By using standard materials and procedures, the fabrication process is well suited to on-chip microfluidic functionality, allowing full characterization of new radiotracers.

Geometric efficiency for a circular detector and a linear source of arbitrary orientation and position

A new axisymmetric radiation vector potential which is singular along its entire axis of symmetry is derived for a spherically symmetric point radiation source. This potential and a previously given non-singular point source potential are integrated to give radiation vector potentials for a straight linear source of constant strength. Analytical solutions are given for the geometric efficiency G of a line source and a circular disk detector when the line source is parallel to the detector axis. The analytical solution is also given for the case where the line source is parallel to the disk surface, such that the source axis and the detector axis intersect. All other cases are given as simple one-dimensional trigonometric integrals. Numerical results for G are given for all cases considered, and results given previously by Pommé for a line source parallel to the detector plane have been verified. The methods and vector potentials presented here can be adapted for calculations with many different geometries, and many results are applicable in other fields such as electromagnetism, gravity and fluid mechanics.

Monte Carlo calculation for the geometrical efficiency of a multi-detector system for heavy ion reaction products

The Monte Carlo method is employed to calculate the geometrical efficiency of a multi-detector system for fragments produced in heavy ion reactions. This efficiency is defined as a quotient of the number of fragments intercepted by the system and the total number of fragments emitted by the fissioning nucleus in all directions. The multi-detector system consists of six parallel-plate avalanche counters in a hexagonal configuration around the target. Its geometrical efficiency was calculated with respect to the 36Ar + 238U reaction at a 7 MeV/u projectile energy.

Strength and Stiffness of Circular Concrete-Filled Tubes

Concrete-filled tubes (CFTs) are composite structural members that consist of a steel tube and concrete infill. CFTs optimize the contributions of both components by improving their geometric efficiency and fully using their inherent strengths. The concrete infill is confined by the steel tube, resulting in a triaxial state of compression that increases the strength and strain capacity of the concrete. The perimeter steel is at its optimal location, and the concrete infill delays local and global buckling of the tube. CFTs are easily and rapidly constructed and provide significant compression, bending, and shear resistance. They may be used for bridge piers and building columns. However, current design specifications for CFTs vary significantly, thereby limiting the current understanding and use of these components. This study addresses combined axial and flexural loading and determines the best models for predicting the stiffness and resistance of circular CFT. A database of 122 test specimens was compiled and evaluated. The results indicate that the plastic stress method is a simple yet effective method to predict the resistance of circular CFT components under combined loading. These data show that current specifications provide inaccurate predictions of the flexural stiffness, and a new stiffness expression is proposed. The proposed models permit simple yet accurate predictions of stiffness and resistance and allow engineers to use CFT components routinely in structural design.

Geometric efficiency of a two-stage fully absorbing collimation system in single-pass linacs

Collimators are commonly used in particle accelerators to prevent particles traveling at large amplitudes from hitting the vacuum chamber. We derive here, for a single-pass linac, a one-dimensional analytical expression for the efficiency of a two-stage fully absorbing collimation system (CS), based on the CS geometrical and optical properties only. We show that, in the presence of physical space or optics constraints, the best betatron phase advance in between the first and the second collimation stage may differ from the usually prescribed $\ensuremath{\pi}/2$. The analytically computed collimation efficiency is then compared to particle tracking results.

PET systems: the value of added length

The past decade has brought unbelievable advances in CT technology. These have been reflected in a progressive widening of the radiation beam in the axial direction (from “fan beam” to “cone beam” geometry) and in a corresponding increase in the number of detector rings. From the four detectors and 2 cm axial field of view (AFOV), acquired in half a second, that characterised the systems of a decade ago, we now have, with the present technology, 256/312 multi-row detectors that allow the acquisition of an 8/16 cm axial field in less than a third of a second. In addition, dual-source CT is offering a wealth of new possibilities. These new systems, whose realisation demanded the solution of complex mechanics, electronics and information technology problems, have opened up a completely new field of medical investigation: the four-dimensional study of the heart and the vascular system. The past few years have also seen evolutions in the field of PET/CT. Indeed, this combined modality has benefitted not only from improved CT technology, but also from gradual advances in the PET sphere—advances prompted by the introduction of new crystal detectors (such as LSO, GSO, LYSO), new iterative reconstruction algorithms, faster electronics, the “gating” technique (synchronisation of data acquisition with respiratory motion) and, especially, “time of flight” PET technology (TOF) [1–4]. Yet despite these significant improvements, the length of the detector cylinder, or length of the system’s sensitive volume (“field of view”), has remained essentially the same (15–18 cm). With this acquisition geometry, only a very small fraction of the radiation emitted at any given instant is acquired (geometric efficiency ≤0.2). Therefore, to obtain, for example, a “whole-body” study of about 80 cm in length (from the temples to the bladder of the patient), a series of six to eight static scans (“views”) need to be acquired. The adjacent single views, obtained with the movement of the bed, must, of course, also provide an appropriate region of overlap. Obviously, the acquisition time increases in proportion to the number of views. A “standard study” with the injection of 10 mCi of F-FDG takes about 3 min per view and, therefore, approximately 25 min per entire study. To this about a minute should be added for the CT scan. However, when used for wholebody studies in diagnostic oncology—this use accounts for approximately 90% of all PET scans—this procedure presents major limitations. The limited length of the sensitive volume not only imposes the need for multiple views, and thus prolongs the overall duration of the examination, it also (and this is particularly important) limits the maximum “line of response” (LOR) angle (with G. Borasi (*) : F. Fioroni Medical Physics Department, Santa Maria Nuova Hospital, V. le Risorgimento 80, 42100 Reggio Emilia, Italy e-mail: giovanni_borasi@libero.it

Validation of analytical formula for the efficiency calibration of gamma detectors using coaxial and off-axis extended sources

In this paper, we introduce a direct analytical mathematical method for calculating the geometrical and absolute total efficiencies of gamma NaI scintillation detectors using an arbitrarily positioned point source. Generalizing, the geometrical and absolute total efficiencies are extended to include coaxial and off-axis sources with plane and volumetric shapes. The efficiencies are deduced into straightforward mathematical expressions. The current theoretical and the published efficiency values are in good agreement.

Slit-Slat and Multi-Slit-Slat Collimator Design and Experimentally Acquired Phantom Images From a Rotating Prototype

We have previously found and validated expressions for slit-slat (SS) geometric efficiency and resolution. These expressions have suggested that SS may be a good choice for imaging mid-size objects or objects that are long axially since (i) the geometric efficiency increases near the slit as h(-1) (instead of h(-2) for pinhole (PIN) and either decreases near the collimator for fan-beam (FB) or remains constant for parallel-beam (PB)), where h is the distance from a point to the slit plane; (ii) the transverse resolution is comparable to that of PIN, which is better than that of FB and PB for small objects; (iii) the axial resolution is worse than that of PIN since there is no axial magnification; (iv) there is a large axial FOV, unlike PIN, which is likely to be useful when imaging mid-size or long objects; and (v) there is no need for 3D orbits (e.g., helical) since each slice is complete (like PB and FB).We have developed a rotating prototype SS collimator that is capable of single-slit or multi-slit acquisition of data. The focal length (FL) is shorter than that of a typical PIN since increasing the FL requires taller slats to maintain resolution; taller slats reduce geometric efficiency. A lead rectangular box was used to provide support and shielding around the slit-slat collimator. Lead slats, spaced with Rohacell foam, were mounted in an assembly with 3 mm pitch.We have performed preliminary characterization with point sources and acquired micro hot- and cold-rod phantoms and a Deluxe Jaszczak phantom. The projections have been reconstructed using an MLEM algorithm and show good resolution.Comparisons indicate that SS is more sensitive than PB and FB for the same resolution for smaller-diameter objects. The advantage of SS over PB and FB increases as the desired resolution improves. SS can also be used in configurations that yield projections that have non-isotropic resolution; it is possible for SS to achieve transverse resolutions that are unreachable by PB, since PB does not magnify, and by FB, since its magnification factor for small objects is much smaller than that of SS. Experimental results show that the resolution of the reconstructed phantoms is consistent with theoretical expectations.

Quadtree-array-based workpiece geometric representation on three-axis milling process simulation

A workpiece hybrid representation method based on quadtree-array is presented to improve the geometric simulation efficiency on three-axis milling process. The method takes the advantages both of Z-Map and quadtree in simulation model representation. The discrete points managed by using Z-Map algorithm is to represent the whole model, while the points used to represent the simulated surface detail are managed with quadtree-array. The method can reduce the levels of a quadtree without losing simulation accuracy. A dynamic optimization algorithm to the quadtree structure is highlighted to reduce its total nodes in simulation process. As a result, the simulation efficiency can be improved significantly. A three-axis milling process simulation system based on quadtree-array representation was developed and used to evaluate the performance of the presented method. The evaluated results show that quadtree-array-based hybrid representation method of workpiece can improve the simulation efficiency significantly, and reasonable division number of array cells is also recommended.

Energy minimum theorem based on AGA, Lyapunov and force field for CADD techniques

This paper employs the energy minimum to enhance drug docking efficiency in a computer aided drug design (CADD) system. The energy minimum application is used to enhance CADD docking performance. The proposed method is discussed in three aspects, adaptive genetic algorithms (AGA), Lyapunov stability theorem and molecular force field. As in previous researches, docking is the crucial component in drug development. The number of docking sites affects the drug docking speed. Reducing the scope of the geometric search is the key task. This paper proposes AGA to improve geometric molecular docking search efficiency. The Lyapunov stability theorem forwards the stability state identification. Protein folding intention generally finds the most appropriate stability state when the thermodynamic and molecular mechanical free energy has reached the lowest point. The AMBER force field simulation is used to discover the molecular statistical mechanics in a drug-ligand. AGA was found better in terms of processing the geometric graphic search operation. The AGA and Lyapunov algorithms were utilized to sieve out the global energy minimum approach from the numerous, raw docking sites.