Sensitive Semiconductor Detectors Research Articles

AGGREGATION OF MS-MONOPYRIDYL-Β-OCTAALKYLPORPHYRINS IN DICHLOROMETHANE IN PRESENCE OF Pd(II)

Aggregation of 13,17-diethyl-2,3,7,8,12,18-hexamethyl-5-(pyridin-4-yl) porphyrin (I), 13,17-diethyl-2,3,7,8,12,18-hexamethyl-5-(pyridin-3-yl)porphyrin (II) and 13.17-diethyl-2,3,7,8,12,18-hexamethyl-5-(pyridin-2-yl)porphyrin (III) in the presence of trans-bis(benzonitrile)palladium(II) dichloride was studied by dynamic light scattering and electronic absorption spectroscopy in dichloromethane at 293 K. The average aggregate size and the nature of their distribution were determined. Using scanning electron microscopy, it was determined the size and composition of clusters formed by aggregates of complexes of the palladium(II) cation with the studied porphyrins. It was shown that minimal acetic acid additions lead to the destruction of the corresponding clusters. At the same time, complete destruction of the aggregates does not occur even with a 100-fold molar excess of acid.We used the Zetasizer Nano ZS (model ZEN3600, Malvern Instruments), equipped with a 633nm laser and non-invasive backscattering (NIBS) technology when the scattered light detector is positioned at an angle of 173° to the incident light. Confirmation of porphyrin aggregation was performed by additional study of the structure using a Hitachi TM4000Plus desktop electron microscope equipped with a 4-segment highly sensitive semiconductor detector and a secondary electron detector for low vacuum mode. Elemental analysis of the obtained aggregates in the cluster was performed using a silicon drift detector with a working area of 30 mm2, combined with a Hitachi TM4000Plus microscope. It was found that aggregates consisting of a para-pyridyl derivative of alkylporphyrin and trans-bis (benzonitrile) palladium (II) dichloride are formed in dichloromethane at 293 K. The best results of porphyrin structures were observed for mixtures of 13,17-diethyl-2,3,7,8,12,18-5-hexamethyl-5-(pyridine-4-yl)porphyrin with TRANS-bis(benzonitrile)- palladium (II) dichloride in a ratio of 1:3, which is probably due to less spatial shielding of the reaction center of the macrocycle and, as a result, better stabilization of the resulting particles. The size of a cluster consisting of individual aggregates was measured using scanning electron microscopy. An elemental analysis of a single aggregate was obtained.

Fiberless, Multi-Channel fNIRS-EEG System Based on Silicon Photomultipliers: Towards Sensitive and Ecological Mapping of Brain Activity and Neurovascular Coupling.

Portable neuroimaging technologies can be employed for long-term monitoring of neurophysiological and neuropathological states. Functional Near-Infrared Spectroscopy (fNIRS) and Electroencephalography (EEG) are highly suited for such a purpose. Their multimodal integration allows the evaluation of hemodynamic and electrical brain activity together with neurovascular coupling. An innovative fNIRS-EEG system is here presented. The system integrated a novel continuous-wave fNIRS component and a modified commercial EEG device. fNIRS probing relied on fiberless technology based on light emitting diodes and silicon photomultipliers (SiPMs). SiPMs are sensitive semiconductor detectors, whose large detection area maximizes photon harvesting from the scalp and overcomes limitations of fiberless technology. To optimize the signal-to-noise ratio and avoid fNIRS-EEG interference, a digital lock-in was implemented for fNIRS signal acquisition. A benchtop characterization of the fNIRS component showed its high performances with a noise equivalent power below 1 pW. Moreover, the fNIRS-EEG device was tested in vivo during tasks stimulating visual, motor and pre-frontal cortices. Finally, the capabilities to perform ecological recordings were assessed in clinical settings on one Alzheimer’s Disease patient during long-lasting cognitive tests. The system can pave the way to portable technologies for accurate evaluation of multimodal brain activity, allowing their extensive employment in ecological environments and clinical practice.

Application of Timepix3 based CdTe spectral sensitive photon counting detector for PET imaging

Positron emission tomography (PET) is a nuclear medicine functional imaging technique. It is used in clinical oncology (medical imaging of tumors and the search for metastases), and pre-clinical studies using animals. PET uses small amounts of radioactive materials (radiotracers) and a special photon sensitive camera. Most of these cameras use scintillators with photomultipliers as detectors. However, these detectors have limited energy sensitivity and large pixels. Therefore, the false signal caused by a scattering poses a significant problem. In this work we study properties of position, energy and time sensitive semiconductor detector of Timepix3 type and its applicability for PET measurements. This work presents an initial study and evaluation of two Timepix3 detectors with 2 mm thick CdTe sensors used in simplified geometry for PET imaging. The study is performed on 2 samples —a capillary tube and a cylindrical plexiglass phantom with cavities. Both samples are filled with fluodeoxyglucose (FDG) solution that is used as a radiotracer. The Timepix3 offers better properties compared to conventional detectors —high granularity (55μm pixel pitch), good energy resolution (1 keV at 60 keV) and sufficient time resolution (1.6 ns). The spectral sensitivity of Timepix3 together with coincidence/anticoincidence technique allows for significant reduction of background signal caused by Compton scattering and internal X-ray fluorescence of Cd and Te.

Development of a stable and sensitive semiconductor detector by using a mixture of lead(II) iodide and lead monoxide for NDT radiation dose detection

Recently, high-energy radiation has been widely used in various industrial fields, including the medical industry, and increasing research efforts have been devoted to the development of radiation detectors to be used with high-energy radiation. In particular, nondestructive industrial applications use high-energy radiation for ships and multilayered objects for accurate inspection. Therefore, it is crucial to verify the accuracy of radiation dose measurements and evaluate the precision and reproducibility of the radiation output dose. Representative detectors currently used for detecting the dose in high-energy regions include Si diodes, diamond diodes, and ionization chambers. However, the process of preparing these detectors is complex in addition to the processes of conducting dosimetric measurements, analysis, and evaluation. Furthermore, the minimum size that can be prepared for a detector is limited. In the present study, the disadvantages of original detectors are compensated by the development of a detector made of a mixture of polycrystalline PbI2 and PbO powder, which are both excellent semiconducting materials suitable for detecting high-energy gamma rays and X-rays. The proposed detector shows characteristics of excellent reproducibility and stable signal detection in response to the changes in energy, and was analyzed for its applicability. Moreover, the detector was prepared through a simple process of particle-in-binder to gain control over the thickness and meet the specific value designated by the user. A mixture mass ratio with the highest reproducibility was determined through reproducibility testing with respect to changes in the photon energy. The proposed detector was evaluated for its detection response characteristics with respect to high-energy photon beam, in terms of dose-rate dependence, sensitivity, and linearity evaluation. In the reproducibility assessment, the detector made with 15 wt% PbO powder showed the best characteristics of 0.59% and 0.25% at 6 and 15 MV, respectively. Based on its selection in the reproducibility assessment, the 15 wt% PbO detector showed no dependence on the dose-rate changes, with R-SD < 1%. Finally, a coefficient of determination of 1 in the linearity assessment demonstrated very good linearity with regards to changes in dose. These results demonstrate the applicability and usefulness of the proposed detector made from a mixture of PbI2 and PbO semiconductors.

Upgrading of X-ray CT technology for analyses of irradiated FBR MOX fuel

The X-ray CT technology previously developed by JAEA was upgraded. The shape of the X-ray source beam was changed from a circular shape to an elliptical one and the collimator slit width was decreased from 0.3 to 0.1 mm. The X-ray detector was improved by changing a CdWO4 scintillator to a highly sensitive silicon semiconductor detector. The analysis code of X-ray CT image was revised with respect to the number of points by using two kinds of experimental results and taking into account the effects of crack existence and deviation of the central void position from the radial center of a fuel pellet. As a result, high resolution X-ray CT images could be obtained on the transverse cross section of irradiated fuel assemblies. The error of the dimensional measurement was improved from ±0.1 to ±0.03 mm by upgrading the instrument and revising the analysis code of X-ray CT image. The discriminating accuracy of density difference could be increased, and the low density region (undisturbed region) and high density region (equi-axial and columnar regions) in the X-ray CT image on the cross section of irradiated fuel could be discriminated from each other. The reliability of fuel performance analysis improves because a large number of PIE data can be collected, compared with the conventional destructive PIE.

Semiconductor detectors for Compton imaging in nuclear medicine

An investigation is underway at the University of Liverpool to assess the suitability of two position sensitive semiconductor detectors as components of a Compton camera for nuclear medical imaging. The ProSPECTus project aims to improve image quality, provide shorter data acquisition times and lower patient doses by replacing conventional Single Photon Emission Computed Tomography (SPECT) systems. These mechanically collimated systems are employed to locate a radioactive tracer that has been administered to a patient to study specifically targeted physiological processes. The ProSPECTus system will be composed of a Si(Li) detector and a High Purity Germanium (HPGe) detector, a configuration deemed optimum using a validated Geant4 simulation package. Characterising the response of the detectors to gamma irradiation is essential in maximising the sensitivity and image resolution of the system. To this end, the performance of the HPGe ProSPECTus detector and a suitable Si(Li) detector has been assessed at the University of Liverpool. The energy resolution of the detectors has been measured and a surface scan of the Si(Li) detector has been performed using a finely collimated 241Am gamma ray source. Results from the investigation will be presented.

Calculation of a system based on a multihole diaphragm for achromatic attenuation of soft X rays

A technique is proposed for calculating a system for uniform attenuation of soft X rays in a wide range of photon energies using a diaphragm with a large number of small holes. The system for achromatic attenuation is intended for measuring the radiation power and allows matching of high-power (terawatt) radiators with highly sensitive semiconductor detectors. The spectral characteristic of the diaphragm is constant within a wide range of radiation wavelengths.

Quantifying the limitations of small animal positron emission tomography

The application of position sensitive semiconductor detectors in medical imaging is a field of global research interest. The Monte-Carlo simulation toolkit GEANT4 [ http://geant4.web.cern.ch/geant4/] was employed to improve the understanding of detailed γ -ray interactions within the small animal Positron Emission Tomography (PET), high-purity germanium (HPGe) imaging system, SmartPET [A.J. Boston, et al., Oral contribution, ANL, Chicago, USA, 2006]. This system has shown promising results in the field of PET [R.J. Cooper, et al., Nucl. Instr. and Meth. A (2009), accepted for publication] and Compton camera imaging [J.E. Gillam, et al., Nucl. Instr. and Meth. A 579 (2007) 76]. Images for a selection of single and multiple point, line and phantom sources were successfully reconstructed using both a filtered-back-projection (FBP) [A.R. Mather, Ph.D. Thesis, University of Liverpool, 2007] and an iterative reconstruction algorithm [A.R. Mather, Ph.D. Thesis, University of Liverpool, 2007]. Simulated data were exploited as an alternative route to a reconstructed image allowing full quantification of the image distortions introduced in each phase of the data processing. Quantifying the contribution of uncertainty in all system components from detector to reconstruction algorithm allows the areas in need of most attention on the SmartPET project and semiconductor PET to be addressed.

P, d and α particle discrimination in NRA: thin, adjustable sensitive zone semiconductor detectors revisited

Overlapping peaks arising from particles of different types in complex NRA energy spectra may be unscrambled by using partially depleted semiconductor detectors with well chosen sensitive zone thicknesses. The latter should range from ∼ 30 to ∼ 100 μm for removing proton or deuteron peaks from a typical alpha particle energy interval between 1.5 and 12 MeV. It is difficult to find commercial detectors with such characteristics as they are usually made from silicon of too high a resistivity. Special, large area detectors prepared in nominal 500 Ωcm silicon were investigated for their response, both in energy equivalent amplitude and spread, to protons, deuterons and alpha particles as a function of their energy and of the applied bias voltage. The results may be interpreted in terms of charge collection efficiency depth profiles extending behind the depletion region. If turns out that the effective sensitive thickness of such detectors may be varied continuously over a wide range so that it may be tuned, in combination with a well chosen Mylar absorber, to the optimal value required for unscrambling a large variety of complex spectra, arising from deuteron or 3He beam induced reactions. The results suggest that it is possible and desirable to produce detectors with well defined discrimination characteristics. The advantages of this simple method with respect to dE dx telescope based particle identification techniques are discussed. Various applications to the NRA of light isotopes are presented.

New structures for position sensitive semiconductor detectors

Some recent developments in “standard” detectors such as silicon strip detectors are described and a proposal for further improvement is made. In view of future applications in high rate environments we propose completely new detector-amplification structures for two dimensional measurement with gating and fast clearing possibilities. One of them allows local storage of several charge images in sequence and delayed selective readout.

Correlation technique with a new two-dimensional position sensitive detector

A new 2-dimensional position sensitive semiconductor detector was developed. With this detector the correlation between implanted fusion products and their subsequent α decays can be improved. The position resolution of the detector will be described as a function of the position. Measurements with α-particles and a model of the detector will be presented and the results for the correlation technique are demonstrated.

New Structure of Two-Dimensional Position Sensitive Semiconductor Detector and Application

An improved silicon position sensitive detector (PSD) for electron detection has been developed which may have additional application including high energy particle detection as well as light beam detection. The improved PSD device characteristics and construction is presented with a review of other conventional two-dimensional PSDs. A photon counting detector (so-called MCP-PSD tube) is utilized as an application example.

AN ONLINE SENSOR FOR MONITORING OF ETHANOL IN BEER

A modification of previously known online sensors for continuous measurement of ethanol and other volatile compounds using a gas sensitive semiconductor detector, in combination with gas permeable membranes, is presented. The online sensor is provided with a continuous dilution system which dilutes the ethanol samples to a degree necessary to obtain accurate signals from the detector in concentration ranges appearing in beer and other brewery products. The instrument delivers a continuous voltage of 0–10 V, proportional to ethanol concentrations of 0–20% (w/v) with an analysis time of 10–15 min. Disturbances from carbon dioxide and sugars in the medium are small and negligible. Other volatile compounds are only of influence when their concentrations are comparable to that of ethanol.

Discrimination Between Neutrons and Gamma Rays and Evaluation of Dose with a Position Sensitive Semiconductor Detector in a Mixed Field

Discrimination Between Neutrons and Gamma Rays and Evaluation of Dose with a Position Sensitive Semiconductor Detector in a Mixed Field

Discrimination Between Neutrons and Gamma Rays and Evaluation of Dose with a Position Sensitive Semiconductor Detector in a Mixed Field

Abstract The application of a surface barrier position sensitive detector (PSD) for discrimination between neutrons and gamma rays in a mixed field is investigated. A centre part of the sensitive area of PSD is covered with the n-p converter foil and the energy and position signals from the single detector are used for identification of neutrons and gamma rays. Output signals are fed to multichannel analysers and a computer, and dose rates are evaluated separately for neutrons and gamma rays, taking account of energy spectra and reaction efficiencies, by an unfolding calculation in real time.

Position-Sensitive Semiconductor Detector for Gamma Rays

A novel position sensitive semiconductor detector is described using a capacitive coupling method for position sensing. Spatial resolution of 1 mm and energy resolution of 4.2 keV FWHM was achieved (for 137 Cs radiation). The detector is easy to manufacture as compared to conventional position-sensitive detectors. Large area two-dimensional detectors can be made for use as imaging devices.

Some aspects of the use of small needle-shaped semiconductor detectors in the determination of regional distribution and transport of labelled compounds

The use of beta -sensitive semiconductor detectors permits the determination of the regional distribution and turnover rate of any substance which can be labelled with a suitable beta -emitter. The number of counts recorded after a slug injection will be proportional to the amount of mother substance located in the monitored volume, the largest fraction being generated in the regions in the vicinity of the detector surface. The peak activity will be a fairly valid index of the flow to the region studied if the distribution of transit times is less than twice the mean transit time. The accuracy of the analysis will be influenced by the area around the detector damaged by the insertion of the probe, particularly pronounced in the study of multi-compartment systems with low energy beta -emitters.

Precise determination of the shape of the twice forbidden beta spectrum of 137Cs

The shape of the twice forbidden beta spectrum in the decay of 137Cs was measured in a magnetic spectrometer. By employing an energy sensitive semiconductor detector at the focus, it was possible to demand that the recorded particles have the correct energy signature corresponding to the momentum setting of the magnetic field. An extremely high degree of discrimination was thus provided against detection of scattered electrons from the intense, low-energy inner group and the internal conversion lines. The shape of the outer group could be fitted with S∝ q 2+ λ 2 p 2 with λ 2=0.004±0.002 or with S = L 0 q 2+9 λ 2 L 1 with λ 2=0.005±0.002. The endpoint and intensity of the outer group are 1.176±0.001 MeV, 6.0±0.5%. The end-point and intensity of the inner group are 0.514±0.001 MeV, 94.0±0.5%. The K-internal conversion coefficient is α K = 0.101±0.007.