Detector Axis Research Articles

Optical vortex detector as a basis for a data transfer system: Operational principle, model, and simulation of the influence of turbulence and noise

The principle of determining the topological charge of an optical vortex is suggested based on measuring the light field intensity and designing the corresponding detector. A mathematical model of the performance of the detector of topological vortex charge is presented. Results of numerical experiments imitating the vortex recognition in the presence of turbulence or (amplitude or phase) noise in registered radiation as well as of the displacement of the optical beam source and detector axes are presented. Principles are formulated of designing the position finder for an optical vortex (that is, the detector of vortex coordinates) that allows us to consider its realization in the form of mathematical and numerical model. Conditions of reliable operation of the vortex detector and singular optical communication line constructed on its basis are estimated. Dependencies of the probability of error in data transfer on the turbulence intensity, photodetector noise amplitude, and displacement of the optical axes are investigated for different coding algorithms (absolute and differential with fixed or adaptive threshold). The data of modeling confirm the results of analytical calculations.

SU‐E‐T‐390: Real‐Time Measurement of Urethral Dose and Position Using a RADPOS Array during Permanent Seed Implantation for Prostate Brachytherapy

Purpose: The new in vivo dosimetry tool, RADPOS, combines MOSFET dosimetry with an electromagnetic positioning sensor. It has recently been modified to include a MOSFET array rather than a single MOSFET for dose monitoring at five points along the detector axis. The detector is in use as part of a clinical trial which is the first to measure both urethral dose and internal motion concurrently during permanent seed implantation for prostate brachytherapy using a single probe. Methods: The RADPOS detector was secured inside a Foley catheter inside the patientˈs urethra. Spatial coordinates of the RADPOS detector were read every 0.5 s and the timing of events such as needle insertion was noted. MOSFET readings were taken over two ten minute periods once all seeds had been implanted both before and after the TRUS probe was removed. Results: Locations of the dosimeters could be inferred using a marker located at the end of the detector wire which is visible on fluoroscopy images. Although detector position varied slightly between patients, on average one dose point was inside the bladder, two/three dose points were within the prostatic urethra, and one/two dose points were at or inferior to the apex of the prostate. Maximum integral dose in the prostatic urethral ranged from 110–195 Gy, and it was found that the dose can change up to 63 cGy depending on whether the rectal probe is in place. The average change in displacement from the beginning of the procedure to the end for all patients was Δr=(5.5 ± 2.2) mm, with changes in individual coordinates of Δx (right/left) = (0.1–2.6) mm, Δy (superior/inferior) = (0.3–8.7) mm, and Δz (anterior/posterior) = (1.2–5.0) mm. Conclusions: The modified RADPOS is a powerful tool that can provide accurate real time dose and position information for use during prostate brachytherapy.This project has been supported by grants from The Health Technology Exchange, Ontario Research Funds RE‐04‐026, The Ottawa Hospital Cancer Centre Foundation and by financial and technical support from Best Medical Canada and Ascension Technology Corporation.

The liquid nitrogen fill level meter for the AGATA triple cluster detector

A novel liquid nitrogen fill level meter has been put into operation for the all-position dewar of the triple cluster detector of the Advanced GAmma Tracking Array. The new device is based on a capacitance measurement between a metallic cylindrical tube inside the dewar and the inner wall of the cryostat. The fill level dependent capacitance is converted by a C/ V-transducer into a DC voltage signal. Direct monitoring of the LN 2 level inside the detector dewar has been performed with several AGATA detectors at various inclinations and rotation angles of the detector axis. The time-dependent LN 2 consumption is an additional quantity used to survey the status of the cryostat. Supplementary results are the investigations of the LN 2 consumption and the heat loss of the detector during different modes of operation.

DETECTION OF GRB 090618 WITH THERT-2 EXPERIMENT ON BOARD THECORONAS-PHOTONSATELLITE

We present the results of an analysis of the prompt gamma-ray emission from GRB 090618 using the RT-2 Experiment onboard the Coronas-Photon satellite. GRB 090618 shows multiple peaks and a detailed study of the temporal structure as a function of energy is carried out. As the GRB was incident at an angle of 77 degree to the detector axis, we have generated appropriate response functions of the detectors to derive the spectrum of this GRB. We have augmented these results using the publicly available data from the Swift BAT detector and show that a combined spectral analysis can measure the spectral parameters quite accurately. We also attempt a spectral and timing analysis of individual peaks and find evidence for a systematic change in the pulse emission characteristics for the successive pulses. In particular, we find that the peak energy of the spectrum, E_p, is found to monotonically decrease with time, for the successive pulses of this GRB.

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.

디지털 방사선시스템에서 영상증강 파라미터의 영상특성 평가

Digital imaging detectors can use a variety of detection materials to convert X-ray radiation either to light or directly to electron charge. Many detectors such as amorphous silicon flat panels, CCDs, and CMOS photodiode arrays incorporate a scintillator screen to convert x-ray to light. The digital radiography systems based on semiconductor detectors, commonly referred to as flat panel detectors, are gaining popularity in the clinical & hospital. The X-ray detectors are described between a-Silicon based indirect type and a-Selenium based direct type. The DRS of detectors is used to convert the x-ray to electron hole pairs. Image processing is described by specific image features: Latitude compression, Contrast enhancement, Edge enhancement, Look up table, Noise suppression. The image features are tuned independently. The final enhancement result is a combination of all image features. The parameters are altered by using specific image features in the different several hospitals. The image in a radiological report consists of two image evaluation processes: Clinical image parameters and MTF is a descriptor of the spatial resolution of a digital imaging system. We used the edge test phantom and exposure procedure described in the IEC 61267 to obtain an edge spread function from which the MTF is calculated. We can compare image in the processing parameters to change between original and processed image data. The angle of the edge with respect to the axes of detector was varied in order to determine the MTF as a function of direction. Each MTF is integrated within the spatial resolution interval of 1.35-11.70 cycles/mm at the 50% MTF point. Each image enhancement parameters consists of edge, frequency, contrast, LUT, noise, sensitometry curve, threshold level, windows. The digital device is also shown to have good uniformity of MTF and image parameters across its modality. The measurements reported here represent a comprehensive evaluation of digital radiography system designed for use in the DRS. The results indicate that the parameter enables very good image quality in the digital radiography. Of course, the quality of image from a parameter is determined by other digital devices in addition to the proper clinical image.

SU-GG-T-414: Directional Dependence of the Response of Plastic Scintillation Detectors in Photon Beams

Purpose: The plastic scintillation detector(PSD) is a promising dosimeter for in vivodosimetry due to its high spatial resolution and excellent water equivalency. The arbitrary orientation of PSD, when placed inside a patient body, may affect its relative response. This study investigates the directional dependence of the response of PSD in photon beams by Monte Carlo simulations.Method and Materials: Two PSDs (BC‐400 and BCF‐12), each coupled to an optical fiber stem, are modeled. The directional dependences of the response of both PSDs in a water phantom are studied for a 6 MV spectral photon beam and a 300 keV mono‐energetic photon beam. Different optical fiber core materials (plastic, glass, and air) are used in the calculation model to study the influence of the optical fibermaterials upon the directional dependence of the detector response. Results: For the majority of angles between the detector axis and the incident beam direction, the response of the PSDs is within 1∼2 % irrespective of the photon energy or the optical fibermaterial used. For the case when the optical fiber stem is pointing to the source, the PSDs with glass or air cored optical fibers show larger deviations (6 % for 6 MV beam and 15 % for 300 keV beam) while the response for the PSDs with plastic cored optical fibers is still within 2 %. Conclusion: If plastic is used for the fiber core, the directional dependence is not of concern at 2 % level in photon beams. If glass or air is used for the fiber core, the PSD response has a 6 % deviation or more when the optical fiber stem is pointing to the source, which is probable for in vivo applications as the orientation of the detector cannot be guaranteed. Supported by the NCI (1R01CA120198‐01A2)

New numerical algorithm method to calibrate the HPGe cylindrical detectors using non-axial extended source geometries

The knowledge of the full-energy peak efficiency for a specific source-detector arrangement is often required in various fields of research and applications, such as the analysis of nuclear waste or environmental samples, where both require modeling because it is not practical to prepare a standard that matches the physical and nuclear properties of every waste or environmental item. Therefore, a new numerical algorithm method (NAM) is proposed in the present work to calibrate the co-axial HPGe cylindrical detectors. Cylindrical sources are used in the calibration process placed perpendicularly to the detector's axis. The self-attenuation and the coincidence summing effects at low source-detector distance are also included in the algorithm. A remarkable agreement between the measured and the calculated efficiencies is achieved with discrepancies less than 3%.

Physical Characterization of a New Concept Design of an Elekta Radiation Head with Integrated 160-leaf Multi-leaf Collimator

Physical Characterization of a New Concept Design of an Elekta Radiation Head with Integrated 160-leaf Multi-leaf Collimator

A Bragg curve counter with an internal production target for the measurement of the double-differential cross-section of fragment production induced by neutrons at energies of tens of MeV

A Bragg curve counter equipped with an internal production target was developed for the measurements of double-differential cross-sections of fragment production induced by neutrons at energies of tens of MeV. The internal target permitted a large detection solid angle and thus the registration of processes at low production rates. In this specific geometry, the detection solid angle depends on the emission angle and the range of the particle. Therefore the energy, atomic number, and angle of trajectory of the particle have to be taken into account for the determination of the solid angle. For the selection of events with tracks confined within a defined cylindrical volume around the detector axis, a segmented anode was applied. The double-differential cross-sections for neutron-induced production of lithium, beryllium, and boron fragments from a carbon target were measured at 0° for 65 MeV neutrons. The results are in good agreement with theoretical calculation using PHITS code with GEM and ISOBAR model.

Study of the performance of HPGe detectors operating in very high magnetic fields

A new generation of high-resolution hypernuclear γ-spectroscopy experiments using high-purity germanium (HPGe) detectors is presently designed for the FINUDA spectrometer at DAΦNE, the Frascati Φ-factory, and for PANDA, the p–p¯ hadron spectrometer at the future FAIR facility. In both spectrometers the HPGe detectors have to be operated in strong magnetic fields. In this paper we report on a series of measurements performed on a HPGe detector inserted in a magnetic field of intensity up to 2.5T, the highest ever reached for operations with a HPGe, and with different orientations of the detector's axis with respect to field direction. A significant worsening of the energy resolution was found, but with a moderate loss of the efficiency. The most relevant features of the peak shapes, described by bi-Gaussian functions, are parametrized in terms of field intensity and energy: this allows to correct the spectra measured in magnetic field and to recover the energy resolution almost completely.

A fast, primary-interaction Monte Carlo methodology for determination of total efficiency of cylindrical scintillation gamma-ray detectors

A primary-interaction based Monte Carlo algorithm has been developed for determination of the total efficiency of cylindrical scintillation g-ray detectors. This methodology has been implemented in a Matlab based computer program BPIMC. For point isotropic sources at axial locations with respect to the detector axis, excellent agreement has been found between the predictions of the BPIMC code with the corresponding results obtained by using hybrid Monte Carlo as well as by experimental measurements over a wide range of g-ray energy values. For off-axis located point sources, the comparison of the BPIMC predictions with the corresponding results obtained by direct calculations as well as by conventional Monte Carlo schemes shows good agreement validating the proposed algorithm. Using the BPIMC program, the energy dependent detector efficiency has been found to approach an asymptotic profile by increasing either thickness or diameter of scintillator while keeping the other fixed. The variation of energy dependent total efficiency of a 3'x3' NaI(Tl) scintillator with axial distance has been studied using the BPIMC code. About two orders of magnitude change in detector efficiency has been observed for zero to 50 cm variation in the axial distance. For small values of axial separation, a similar large variation has also been observed in total efficiency for 137Cs as well as for 60Co sources by increasing the axial-offset from zero to 50 cm.

Measurement of the range component directional signature in a DRIFT-II detector using 252Cf neutrons

The Directional Recoil Identification From Tracks (DRIFT) collaboration utilizes low-pressure gaseous detectors to search for Weakly Interacting Massive Particle (WIMP) dark matter with directional signatures. A 252Cf neutron source was placed on each of the principal axes of a DRIFT detector in order to test its ability to measure directional signatures from the three components of very low-energy (∼keV/amu) recoil ranges. A high trigger threshold and the event selection procedure ensured that only sulfur recoils were analyzed. Sulfur recoils produced in the CS 2 target gas by the 252Cf source closely match those expected from massive WIMP induced sulfur recoils. For each orientation of the source, with a threshold of ∼50 keV, a directional signal from the range components was observed, indicating that the detector has directional capability along all three axes, though in one direction the directionality was marginal. An analysis of these results yields an optimal orientation for DRIFT detectors when searching for a directional signature from WIMPs. Additional energy dependent information is provided to aid in understanding this effect.

Laser plasma interaction in copper nano-particle targets

AbstractIn this paper, we present the results of studies on ion emission characteristics of a laser plasma produced from a copper nano-particle layer of 1–3 µm thickness coated over polished surface of a solid copper target. Laser intensity of 1013–1014 W/cm2 was produced on the targets by a 2 J Nd:glass laser having a variable pulse duration of 300–800 ps. Nano-particle size was in the range of 15–25 nm. Ion emission from the nano-particle plasma was compared with plasma generated from a polished copper target. Ion emission from the nano-structured target was observed to depend on the polarization of the incident laser beam. This effect was stronger for a shorter laser pulse. X-ray emission was measured in the soft and hard X-ray region (0.7 to 8 keV) using various X-ray filters. A nano-particle coated target is found to yield a larger flux as well as velocity of ions as compared to polished target when the laser polarization is parallel to the plane containing target normal and detector axis. However, no X-ray enhancement has been observed in the wavelength range 1.5 to 20 Å.

Monte Carlo Modeling of the Wall Effect in Cylindrical Tissue-Equivalent Proportional Counters from Heavy Ions

Heavy ions constitute a significant part of radiation in space, they are used for radiation therapy and laboratory experiments with accelerators. The useful instrument for measurement of radiation dose and investigation radiation quality factor for heavy ions is tissue equivalent proportional counter (TEPC). It was found previously [1,2] that response of spherical wall TEPC shows distortions at the wall/cavity interface due to enhanced entry of secondary electrons into the sensitive volume of counter. In this study it was theoretically investigated whether similar effect is expected in cylinder TEPC. The Monte Carlo code [1] originally designed for spherical TEPC was updated by extension with cylindrical shape of internal gas cavity. It was tested the following three geometries of irradiation: ion tracks are parallel-, perpendicular to cylindrical detector axis and µ-randomness superposition. The coordinates of track segments in the wall and gas cavity were calculated using stochastic track structure code PITS to score the energy deposition in the counter. The internal gas cavity with a 0.635 cm radius, 1.27 cm height contains tissue equivalent gas at 7.87 e-5 g/cm**3 density and wall plastic density - 1.0 g/cm**3. Liquid water cross sections were chosen as a target to approximate the plastic and gas. The stochastic tracks of 20-Ne ions with energy 46 MeV/nucleon and LET=167 keV/µm were used for modeling of TEPC response. The linear energy for three mentioned beam geometries was calculated and plotted against impact parameter which is the perpendicular distance from the center of counter to the ion track. In contract to spherical counter [1,2] for the cylindrical TEPC was found no clear occurrence of the peak at the interface between the wall and the gas for all three tested geometries. Nothing but in the case when ion beam is parallel to TEPC axis the weak effect as a small height peak succeeded resulted from grazing events. This findings lead to the conclusion that wall effect like [1] observed in spherical TEPC hardly is expected in experiments with cylindrical proportional counters. References. 1. Rademacher S. E. et al. (1998) Radiat. Res. 149, 387-395. 2. Nikjoo H., Khvostunov I. K., Cucinotta F. A. (2002) Radiat. Res. 157, 435-445.

An analytical calculation of the peak efficiency for cylindrical sources perpendicular to the detector axis in gamma-ray spectrometry

An analytical expression for the so-called full-energy peak efficiency ε( E) for cylindrical source with perpendicular axis to an HPGe detector is derived, using point-source measurements. The formula covers different measuring distances, matrix compositions, densities and gamma-ray energies; the only assumption is that the radioactivity is homogeneously distributed within the source. The term for the photon self-attenuation is included in the calculation. Measurements were made using three different sized cylindrical sources of 241Am, 57Co, 137Cs, 54Mn, and 60Co with corresponding peaks of 59.5, 122, 662, 835, 1173, and 1332 keV, respectively, and one measurement of radioactive waste drum for 662, 1173, and 1332 keV.

Determination of zero‐field size percent depth doses and tissue maximum ratios for stereotactic radiosurgery and IMRT dosimetry: Comparison between experimental measurements and Monte Carlo simulation

In this study, zero-field percent depth dose (PDD) and tissue maximum ratio (TMR) for 6 MV x rays have been determined by extrapolation from dosimetric measurements over the field size range 1 x 1-10 x 10 cm2. The key to small field dosimetry is the selection of a proper dosimeter for the measurements, as well as the alignment of the detector with the central axis (CAX) of beam. The measured PDD results are compared with those obtained from Monte Carlo (MC) simulation to examine the consistency and integrity of the measured data from which the zero-field PDD is extrapolated. Of the six most commonly used dosimeters in the clinic, the stereotactic diode field detector (SFD), the PTW Pinpoint, and the Exradin A14 are the most consistent and produce results within 2% of each other over the entire field size range 1 x 1-40 x 40 cm2. Although the diamond detector has the smallest sensitive volume, it is the least stable and tends to disagree with all other dosimeters by more than 10%. The zero-field PDD data extrapolated from larger field measurements obtained with the SFD are in good agreement with the MC results. The extrapolated and MC data agree within 2.5% over the clinical depth range (dmax-30 cm), when the MC data for the zero field are derived from a 1 X 1 cm2 field simulation using a miniphantom (1 x 1 x 48 cm3). The agreement between the measured PDD and the MC data based on a full phantom (48 x 48 x 48 cm3) simulation is fairly good within 1% at shallow depths to approximately 5% at 30 cm. Our results seem to indicate that zero-field TMR can be accurately calculated from PDD measurements with a proper choice of detector and a careful alignment of detector axis with the CAX.

SU‐FF‐T‐340: Neutron Spectra Measurements For Fast Neuron Brachytherapy Effective Dose Evaluation

Purpose: We are developing a miniature neutron generator capable of brachytherapy, contact therapy and perioperative therapy applications. The neutrons are produced at 14MeV in a thermonuclear reactant target located at the end of a needle. The fast neutron effective dose depends on the lineal spectrum of charged particles produced by neutron interactions in tissue. Neutron interaction probabilities, cross sections, vary with neutron energy and the neutron spectra change with transmission through tissue. The change in spectra of initially 14MeV neutrons with tissue depth in brachytherapy is in itself not dramatic because the neutron mean free path is 10cm. But more seriously, the LET of neutron scattered protons increases with the inverse of proton energy and higher LET protons (bellow 120keV/micron) have increased relative biological effectiveness. The measurement of neutron spectra below 2 MeV is therefore important for understanding the mechanism of effective dose. In this paper, we will describe our development of a double scatter neutron spectrometer (DSNS) that has proven effective in low energy neutron spectral measurements. Method and Materials: The DSNS consists of detector planes of two liquid organic scintillators separated by 18cm. A neutron that scatters in the first plane starts a timer which is stopped by a coincident neutron detection signal for the same neutron in the second detector plane. Energy of the scattered neutron is determined by time‐of‐flight over the distance between detectors, which is the incident energy when the source is aligned with the detector axis. Results: The useful energy range of the DSNS is 0.3MeV to 5MeV and is dependent on the separation distance of the detector planes. Conclusion: The DSNS should be useful for measuring the low energy neutron component of our brachytherapy accelerator based source.

Monte Carlo efficiency transfer method for full energy peak efficiency calibration of three type HPGe detectors: A coaxial N-type, a coaxial P-type and four BEGe detectors

Monte Carlo efficiency transfer method was used to determine full energy peak efficiency of three type high-purity germanium (HPGe) detectors: a coaxial N-type, a coaxial P-type and four broad energy germanium detectors (BEGe). The comparisons between calculations and point source experiments showed that the relative deviations were mostly within ±5% for BEGe detectors in the energy range 13.9–1332 keV, within ±3% for the coaxial N-type detector in the energy range 17.5–662 keV, and within ±3% for the coaxial P-type detector in the energy range 59.5–1332 keV, respectively. An evaluation of Monte Carlo efficiency transfer method at different source-to-detector geometry configurations indicates that peak efficiency may be underestimated when point sources are placed nearer than the reference position to detector on the detector axis, and may be overestimated when point sources are placed far from the detector axis, especially for low-energy photons. Some discussions about direct Monte Carlo calculation method and Monte Carlo efficiency transfer method for full-energy peak efficiency calculation are also presented in this paper.

Measurement of Residual Strains with High Depth Resolution by Energy-Variable Diffraction on Synchrotron Beam Lines

ABSTRACTAn energy-variable synchrotron diffraction technique is established as a novel method for depth-resolved measurements of d-spacings and residual strains in polycrystalline structures. The depth sensitivity is achieved by the controlled changing the x-ray energy and, hence, the x-ray penetration into the sample. Quasi-parallel synchrotron radiation being diffracted at different depths deviates differently from the detector axis. As a result, the maximum diffraction intensity recorded in the detector is coming from a certain depth, which is energy dependent. This finding opens a way for strain measurements with high depth resolution by changing the x-ray energy in small enough steps. The developed technique is applied to characterize the electrodeposited Cu/Ni multilayers.