Detection Properties Research Articles

Electronic Pulse Shape Formation in Transient Charge and Transient Current Detection Approach in (CdZn)Te Detectors

The transient-charge technique (TChT) and transient-current technique (TCT) belong to basic methods routinely used for the determination of transport properties of semiconductor radiation detectors. In spite of apparently definite correspondence between the charge and current transients via simple differentiation or integration in time, the passing of the signal through real electronic circuits interferes with the evaluation of the transients and hampers the direct relation between TChT and TCT transients. In this paper we use in parallel both TChT and TCT for the characterization of (CdZn)Te detector and compare their output. We show how real TChT and TCT signals deviate from their ideal shape and complicate the evaluation of electron mobility from detected pulses. We conclude that whilst TCT may conveniently be used for the analysis of current waveforms and determination of carrier transit time and mobility in rather highly biased detectors, TChT is mainly useful for determining the total charge collection both at high and low biasing. We also suggest the way to improve the transit time readout in case of TChT method.

Factors influencing the accuracy of beam range estimation in proton therapy using prompt gamma emission

In-vivo imaging is a strategy to monitor the range of protons inside the patient during radiation treatment. A possible method of in-vivo imaging is detection of secondary ‘prompt’ gamma (PG) photons outside the body, which are produced by inelastic proton-nuclear interactions inside the patient. In this paper, important parameters influencing the relationship between the PG profile and percentage depth dose (PDD) in a uniform cylindrical phantom are explored. Monte Carlo simulations are performed with the new Geant4 based code TOPAS for mono-energetic proton pencil beams (range: 100–250 MeV) and an idealized PG detector. PG depth profiles are evaluated using the inflection point on a sigmoid fit in the fall-off region of the profile. A strong correlation between the inflection point and the proton range determined from the PDD is found for all conditions. Variations between 1.5 mm and 2.7 mm in the distance between the proton range and the inflection point are found when either the mass density, phantom diameter, or detector acceptance angle is changed. A change in cut-off energy of the detector could induce a range difference of maximum 4 mm. Applying time-of-flight discrimination during detection, changing the primary energy of the beam or changing the elemental composition of the tissue affects the accuracy of the range prediction by less than 1 mm. The results indicate that the PG signal is rather robust to many parameter variations, but millimetre accurate range monitoring requires all medium and detector properties to be carefully taken into account.

Erratum: Single Shot Coherence Properties of the Free-Electron Laser SACLA in the Hard X-ray Regime

We measured the coherence properties of the free-electron laser SACLA on a single shot basis at an X-ray energy of 8 keV. By analysing small-angle X-ray scattering speckle patterns from colloidal dispersions we found a degree of transverse coherence of βt = 0.79 ± 0.09. Taking detector properties into account, we developed a simulation model in oder to determine the degree of coherence from intensity histograms. Finally we calculated a coherence time of τc = 0.1 fs and a pulse duration of 5.2 fs which corresponds with previous predictions.

Processing properties of ON and OFF pathways for Drosophila motion detection.

The algorithms and neural circuits that process spatio-temporal changes in luminance to extract visual motion cues have been the focus of intense research. An influential model, the Hassenstein-Reichardt correlator, relies on differential temporal filtering of two spatially separated input channels, delaying one input signal with respect to the other. Motion in a particular direction causes these delayed and non-delayed luminance signals to arrive simultaneously at a subsequent processing step in the brain; these signals are then nonlinearly amplified to produce a direction-selective response. Recent work in Drosophila has identified two parallel pathways that selectively respond to either moving light or dark edges. Each of these pathways requires two critical processing steps to be applied to incoming signals: differential delay between the spatial input channels, and distinct processing of brightness increment and decrement signals. Here we demonstrate, using in vivo patch-clamp recordings, that four medulla neurons implement these two processing steps. The neurons Mi1 and Tm3 respond selectively to brightness increments, with the response of Mi1 delayed relative to Tm3. Conversely, Tm1 and Tm2 respond selectively to brightness decrements, with the response of Tm1 delayed compared with Tm2. Remarkably, constraining Hassenstein-Reichardt correlator models using these measurements produces outputs consistent with previously measured properties of motion detectors, including temporal frequency tuning and specificity for light versus dark edges. We propose that Mi1 and Tm3 perform critical processing of the delayed and non-delayed input channels of the correlator responsible for the detection of light edges, while Tm1 and Tm2 play analogous roles in the detection of moving dark edges. Our data show that specific medulla neurons possess response properties that allow them to implement the algorithmic steps that precede the correlative operation in the Hassenstein-Reichardt correlator, revealing elements of the long-sought neural substrates of motion detection in the fly.

Detector to detector corrections: a comprehensive experimental study of detector specific correction factors for beam output measurements for small radiotherapy beams.

The aim of the present study is to provide a comprehensive set of detector specific correction factors for beam output measurements for small beams, for a wide range of real time and passive detectors. The detector specific correction factors determined in this study may be potentially useful as a reference data set for small beam dosimetry measurements. Dose response of passive and real time detectors was investigated for small field sizes shaped with a micromultileaf collimator ranging from 0.6 × 0.6 cm(2) to 4.2 × 4.2 cm(2) and the measurements were extended to larger fields of up to 10 × 10 cm(2). Measurements were performed at 5 cm depth, in a 6 MV photon beam. Detectors used included alanine, thermoluminescent dosimeters (TLDs), stereotactic diode, electron diode, photon diode, radiophotoluminescent dosimeters (RPLDs), radioluminescence detector based on carbon-doped aluminium oxide (Al2O3:C), organic plastic scintillators, diamond detectors, liquid filled ion chamber, and a range of small volume air filled ionization chambers (volumes ranging from 0.002 cm(3) to 0.3 cm(3)). All detector measurements were corrected for volume averaging effect and compared with dose ratios determined from alanine to derive a detector correction factors that account for beam perturbation related to nonwater equivalence of the detector materials. For the detectors used in this study, volume averaging corrections ranged from unity for the smallest detectors such as the diodes, 1.148 for the 0.14 cm(3) air filled ionization chamber and were as high as 1.924 for the 0.3 cm(3) ionization chamber. After applying volume averaging corrections, the detector readings were consistent among themselves and with alanine measurements for several small detectors but they differed for larger detectors, in particular for some small ionization chambers with volumes larger than 0.1 cm(3). The results demonstrate how important it is for the appropriate corrections to be applied to give consistent and accurate measurements for a range of detectors in small beam geometry. The results further demonstrate that depending on the choice of detectors, there is a potential for large errors when effects such as volume averaging, perturbation and differences in material properties of detectors are not taken into account. As the commissioning of small fields for clinical treatment has to rely on accurate dose measurements, the authors recommend the use of detectors that require relatively little correction, such as unshielded diodes, diamond detectors or microchambers, and solid state detectors such as alanine, TLD, Al2O3:C, or scintillators.

Effect of Z1/2, EH5, and Ci1 deep defects on the performance of n-type 4H-SiC epitaxial layers Schottky detectors: Alpha spectroscopy and deep level transient spectroscopy studies

Spectroscopic performance of Schottky barrier alpha particle detectors fabricated on 50 μm thick n-type 4H-SiC epitaxial layers containing Z1/2, EH5, and Ci1 deep levels were investigated. The device performance was evaluated on the basis of junction current/capacitance characterization and alpha pulse-height spectroscopy. Capacitance mode deep level transient spectroscopy revealed the presence of the above-mentioned deep levels along with two shallow level defects related to titanium impurities (Ti(h) and Ti(c)) and an unidentified deep electron trap located at 2.4 eV below the conduction band minimum, which is being reported for the first time. The concentration of the lifetime killer Z1/2 defects was found to be 1.7 × 1013 cm−3. The charge transport and collection efficiency results obtained from the alpha particle pulse-height spectroscopy were interpreted using a drift-diffusion charge transport model. Based on these investigations, the physics behind the correlation of the detector properties viz., energy resolution and charge collection efficiency, the junction properties like uniformity in barrier-height, leakage current, and effective doping concentration, and the presence of defects has been discussed in details. The studies also revealed that the dominating contribution to the charge collection efficiency was due to the diffusion of charge carriers generated in the neutral region of the detector. The 10 mm2 large area detectors demonstrated an impressive energy resolution of 1.8% for 5486 keV alpha particles at an optimized operating reverse bias of 130 V.

Single shot coherence properties of the free-electron laser SACLA in the hard X-ray regime.

We measured the coherence properties of the free-electron laser SACLA on a single shot basis at an X-ray energy of 8 keV. By analysing small-angle X-ray scattering speckle patterns from colloidal dispersions we found a degree of transverse coherence of βt = 0.79 ± 0.09. Taking detector properties into account, we developed a simulation model in oder to determine the degree of coherence from intensity histograms. Finally we calculated a coherence time of τc = 0.1 fs and a pulse duration of 5.2 fs which corresponds with previous predictions.

Synchronized analysis of testbeam data with the Judith software

The Judith software performs pixel detector analysis tasks utilizing two different data streams such as those produced by the reference and tested devices typically found in a testbeam. This software addresses and fixes problems arising from the desynchronization of the two simultaneously triggered data streams by detecting missed triggers in either of the streams. The software can perform all tasks required to generate particle tracks using multiple detector planes: it can align the planes, cluster hits and generate tracks from these clusters. This information can then be used to measure the properties of a particle detector with very fine spatial resolution. It was tested at DESY in the Kartel telescope, a silicon tracking detector, with ATLAS Diamond Beam Monitor modules as a device under test.

Thermodynamics study of laser detector with high rotation speed

In this paper, thermodynamics properties of a laser detector applied in 105 mm shrapnel with high rotation speed have been explored. In outer trajectory, aerodynamic heating usually generates because of viscosity, and this is strengthened by high rotation speed of the shrapnel. Thermal strain may occur, which will influence the overall power of the detector and shrapnel. The temperature has been computed by computational fluid dynamics method, and ANSYS Workbench has been applied to obtain thermal strain. In order to disclose the effect of rotation, comparison among simulation results in different conditions are carried out. It is figured out that the temperature increase does not exceed the limit of optical material (polymethyl methacrylate), so the function of laser detector and the power of shrapnel will not be affected. This paper demonstrates the feasibility of material choice of laser detector optical systems. It has important theoretical meaning and practical application value for the design of conventional ammunition laser detector.

MCNPX Monte Carlo simulations of particle transport in SiC semiconductor detectors of fast neutrons

The aim of this paper was to investigate particletransport properties of a fast neutron detector based on silicon carbide.MCNPX (Monte Carlo N-Particle eXtended) code was used in our study becauseit allows seamless particle transport, thus not only interacting neutronscan be inspected but also secondary particles can be banked for subsequenttransport. Modelling of the fast-neutron response of a SiC detector wascarried out for fast neutrons produced by 239Pu-Be source with the meanenergy of about 4.3 MeV. Using the MCNPX code, the following quantities havebeen calculated: secondary particle flux densities, reaction rates ofelastic/inelastic scattering and other nuclear reactions, distribution ofresidual ions, deposited energy and energy distribution of pulses. Thevalues of reaction rates calculated for different types of reactions andresulting energy deposition values showed that the incident neutronstransfer part of the carried energy predominantly via elastic scattering onsilicon and carbon atoms. Other fast-neutron induced reactions includeinelastic scattering and nuclear reactions followed by production of α-particles and protons. Silicon and carbon recoil atoms, α-particles and protons are charged particles which contribute to thedetector response. It was demonstrated that although the bare SiC materialcan register fast neutrons directly, its detection efficiency can beenlarged if it is covered by an appropriate conversion layer. Comparison ofthe simulation results with experimental data was successfully accomplished.

The preparation and properties of “porous silicon–nickel ferrite” nanoheterocomposites for gas detectors

This paper discusses the preparation and properties of gas detectors based on “porous silicon–nickel ferrite” nanocomposites. Impedance spectroscopy was used to measure sensitivity to ethanol and isopropanol vapours in the presence of an alternating electric field. The results were interpreted with the help of an equivalent electrical circuit. In the analysis of the resistive–capacitive properties in the equivalent circuit a constant phase element was used.

Large area pixel detector WIDEPIX with full area sensitivity composed of 100 Timepix assemblies with edgeless sensors

The superior properties of the single particle countingsemiconductor pixel detectors in radiation imaging are well known. They arenamely: very high dynamic range due to digital counting, absence ofintegration and read-out noise, high spatial resolution and energysensitivity. The major disadvantage of current pixel devices preventingtheir broad exploitation has been their relatively small sensitive area offew cm2. This disadvantage is often solved using tiling method placingmany detector units side by side forming a large matrix. The current tilingtechniques require rather large gaps of few millimeters between tiles. Thesegaps stand as areas insensitive to radiation which is acceptable only insome applications such as diffraction imaging. However standard transmissionradiography requires fully continuous area sensitivity. In this article wepresent the new large area device WIDEPIX composed of amatrix of 10 × 10 tiles of silicon pixel detectors Timepix (each of 256 × 256 pixels with pitch of 55 μm) having fully sensitive area of 14.3 × 14.3 cm2 without any gaps between the tiles. The device contains atotal of 6.5 mega pixels. This achievement was reached thanks to newtechnology of edgeless semiconductor sensors together with precise alignmenttechnique and multilevel architecture of readout electronics. The mechanicalconstruction of the device is fully modular and scalable. This conceptallows replacing any single detector tile which significantly improvesproduction yield. The first results in the field of X-ray radiography andmaterial sensitive X-ray radiography are presented in this article.

Study of the radiation damage of Silicon Photo-Multipliers at the GELINA facility

In this paper we present a study of the neutrons-induced damage in Silicon Photo-Multipliers. Twenty-six devices, produced by AdvanSiD, Hamamatsu and SensL, have been irradiated at the Geel Electron LINear Accelerator (GELINA) in Belgium with a nearly white neutron beam. The total 1 MeV equivalent integrated dose was 6.2 × 109 neq/cm2. Photodetector performances have been measured during the whole irradiation period and a gradual worsening of the detector properties, such as dark current and charge spectra, has been observed.An extensive comparison of the performances of all the tested deviceswill be presented.

TCT measurements with slim edge strip detectors

Transient current technique (TCT) measurements with focused laser light on miniature silicon strip detectors (n+-type strips on p-type bulk) with one inactive edge thinned to about 100µm using the Scribe-Cleave-Passivate (SCP) method are presented. Pulses of focused IR (λ=1064nm) laser light were directed to the surface of the detector and charge collection properties near the slim edge were investigated. Measurements before and after irradiation with reactor neutrons up to 1MeV equivalent fluence of 1.5×1015neq/cm2 showed that SCP thinning of detector edge does not influence its charge collection properties.TCT measurements were done also with focused red laser beam (λ=640nm) directed to the SCP processed side of the detector. The absorption length of red light in silicon is about 3µm so with this measurement information about the electric field at the edge can be obtained. Observations of laser induced signals indicate that the electric field distribution along the depth of the detector at the detector edge is different than in the detector bulk: electric field is higher near the strip side and lower at the back side. This is a consequence of negative surface charge caused by passivation of the cleaved edge with Al2O3. The difference between bulk and edge electric field distributions gets smaller after irradiation.

Matching X-ray beam and detector properties to protein crystals of different perfection.

An analysis is given of the effect of different beam and detector parameters on the sharpness of recorded diffraction features for macromolecular crystals of different quality. The crystal quality parameters include crystal strain, crystal or mosaic block size and mosaic block misorientation. Calculations are given for instrument parameters such as angular resolution of the detector, beam divergence and wavelength bandpass to be matched to the intrinsic diffraction properties from these crystals with the aim of obtaining the best possible data out of each crystal. Examples are given using typical crystal imperfections obtained from the literature for both room-temperature and cryo-cooled crystals. Possible implications for the choice of X-ray source, beamline design, detector specifications, instrument set-up and data processing are discussed, together with the limitations of the approach.

Changes in the thermal properties of PADC film-based nuclear track detectors produced by high doses of γ-radiation

Irradiation effects on the thermal properties of poly allyl diglycol carbonate (PADC) polymer-based nuclear track detectors (in the form of CR-39) have been investigated. PADC films were exposed to γ-rays at high doses ranging from 5.0 × 105 to 1.0 × 106 Gy. The induced modifications were analyzed by means of thermogravimetric analysis, which indicated that the PADC film decomposed in three main stages. The activation energy for thermal decomposition was determined using a type of Arrhenius equation based on the TGA experimental results. This study presents quantitative results showing that the exposed PADC films do not undergo continual further degradation from high-energy γ-photons with increase in dose. The experimental results also provide insight into the specific property changes induced by γ-rays, which may be of use for industrial applications.

Effect of heat treatment on some properties of CR-39 nuclear track detector irradiated by gamma ray

The present study aims to determine the effect of heat treatment on the bulk etch rate of un-irradiated and gamma irradiated CR-39 detector. Track density and the damage in samples surface due to the heat treatment have also studied for the un-irradiated and gamma irradiated CR-39 detector. The samples of CR-39 polymer track detector has been exposed to γ-ray from 60Co source with doses 0, 10, 50, and 100 kGy then exposed to α-particles from the air radon gas. These samples have been annealed at 50, 100 and 150 °C for different annealing times then etched in 6.25 N NaOH solution at 70 °C for 6 h. The variation of bulk etch rate and the track density as a function of annealing temperature have been studied. The bulk etch rate increases with gamma dose and with increasing both of the annealing time and the annealing temperature. The decrease of track density with increasing the annealing time and the damage of annealed gamma irradiated CR-39 samples clarify serious degradation under the effect of heat treatment.

Distinct Roles for Inhibition in Spatial and Temporal Tuning of Local Edge Detectors in the Rabbit Retina

This paper examines the role of inhibition in generating the receptive-field properties of local edge detector (LED) ganglion cells in the rabbit retina. We confirm that the feed-forward inhibition is largely glycinergic but, contrary to a recent report, our data demonstrate that the glycinergic inhibition contributes to temporal tuning for the OFF and ON inputs to the LEDs by delaying the onset of spiking; this delay was more pronounced for the ON inputs (∼340 ms) than the OFF inputs (∼12 ms). Blocking glycinergic transmission reduced the delay to spike onset and increased the responses to flickering stimuli at high frequencies. Analysis of the synaptic conductances indicates that glycinergic amacrine cells affect temporal tuning through both postsynaptic inhibition of the LEDs and presynaptic modulation of the bipolar cells that drive the LEDs. The results also confirm that presynaptic GABAergic transmission contributes significantly to the concentric surround antagonism in LEDs; however, unlike presumed LEDs in the mouse retina, the surround is only partly generated by spiking amacrine cells.

Collimated LaBr3 detector response function in radioactivity analysis of nuclear waste drums

The properties of a Lanthanum bromide(LaBr3)detector and its response functions were investigated via experiments and simulations in this paper.The LaBr3detector had good relative energy resolution and higher efficiency than a high-purity germanium detector.Monte Carlo and other numerical methods were used to calculate the efficiencies of a LaBr3detector with a square collimation window.A model of the numerical method was established based on a pure geometric model that was consistent with the experimental situation.The results showed that the detector response functions calculated by these methods were in great agreement with experimental results.

Effect of 14 MeV neutrons on the optical properties of CR-39 detector

This study is carried out to establish a correlation between optical absorbance and track density in CR-39 detectors exposed to different fluences of D-T (14 MeV) neutrons. This can be useful in estimating the neutron fluence and hence the dose without involving the tedious track counting procedure, especially when the track density is extremely high. Variation in the optical properties is studied using UV-VIS-NIR (ultraviolet-visible-near infrared) spectroscopic technique. The neutron-induced recoil tracks are developed by chemical etching and the track density is determined. The optical transmission spectra are obtained for pristine and neutron irradiated detectors before and after etching. A linear relationship is obtained between the track density and the optical absorbance with increasing neutron fluence. Another objective of this work is to study the effect of etching on the optical properties such as transmittance and absorbance of irradiated CR-39 detectors. The optical properties are found to be changing due to the development of tracks in the detector.