Preamplifier Circuitry Research Articles

Agata detector technology: recent progress and future developments

gamma -ray tracking is based on a new generation of position sensitive high-purity germanium (HPGe) detectors. A novel type of cluster detector was successfully developed and assembled for the high-resolution gamma -ray spectrometer Advanced Gamma Tracking Array AGATA. The core part of the detector consists of three encapsulated, 36-fold segmented HPGe detectors which are operated in a common cryostat. The Ge crystal is hermetically sealed inside an aluminium can. All energy channels provide best energy resolution of core and segment signals for an extended energy range well above 50 MeV. A low cross-talk level was determined for the HPGe detectors and its preamplifier circuitry. Related cross-talk corrections are essential for highest energy resolution and improved position dependent pulse shape information. Recently a new encapsulation technology was put into operation which is based on a renewable metal elastic seal. HPGe detector developments are concerned with technologies for the production of p+ and n+ contacts, the segmentation and passivation of encapsulated HPGe crystals. Semiconductor processing research specifically aimed to develop a stable, thin and easy to segment n+ contact. A novel process, based on pulsed laser melting PLM, was successfully employed to produce very thin n+ and p+ contacts preserving the Ge purity. The contacts were segmented using a photolithographic process and then the intrinsic surface between contacts was passivated to assure the electrical insulation between them. A small detector prototype with three segments was made using these new techniques and then successfully tested.

The Research and Design of a Room-Temperature Nuclear Radiation CdZnTe Detector

Cadmium zinc telluride (CZT) material is one of the preferred materials for the fabrication of X-ray and gamma-ray detector. In this paper, it is presented a room-temperature nuclear radiation detector system based on CZT material with planar electrode and ohmic-contact. The experimental validation and analysis of the designed system is carried out. At the same time, some research and design on the surface signal-readout method、the charge sensitive preamplifier circuit、pulse signal processing circuit and soft processing program is made. The signal from the CZT material exposed to the radiation through the experiment is successfully required. The signal from the experiment is correspondingly processed and validated. The potential factors that influence the detector performance are discussed. The conductive adhesive is the joint of the ohmic-contact electrode and the preamplifier circuitry. The preamplifier circuitry has high gain, rise time in the nanosecond level and little equivalent charge-noise. The research and experimental design base for the development of subsequent gamma spectrometer.

Experiments and Evaluation Based Pixellated CZT Semiconductor Detector

Cadmium zinc telluride (CZT) material is one of the preferred materials for the fabrication of X-ray and gamma-ray detector. In this paper, it is presented an experimental detector system based on pixellated CZT semiconductor detector. At the same time, some research and design on the surface signal-readout method and the preamplifier circuitry is made. The signal coming from the CdZnTe material exposed to the radiation through the experiment is successfully required. The collection-efficiency between the electron and the hole in the anode is test when the different bias is applied in the pixellated CZT semiconductor detector. The parameter of the CZT detector and validate the responsive effect for the radiation is evaluated.The experiments and evaluation basis for the development of subsequent gamma spectrometer.

An implanted 8-channel array coil for high-resolution macaque MRI at 3T.

An 8-channel receive coil array was constructed and implanted adjacent to the skull in a male rhesus monkey in order to improve the sensitivity of (functional) brain imaging. The permanent implant was part of an acrylic headpost assembly and only the coil element loop wires were implanted. The tuning, matching, and preamplifier circuitry was connected via a removable external assembly. Signal-to-noise ratio (SNR) and noise amplification for parallel imaging were compared to single-, 4-, and 8-channel external receive-only coils routinely used for macaque fMRI. In vivo measurements showed significantly improved SNR within the brain for the implanted versus the external coils. Within a region-of-interest covering the cerebral cortex, we observed a 5.4-, 3.6-fold, and 3.4-fold increase in SNR compared to the external single-, 4-, and 8-channel coils, respectively. In the center of the brain, the implanted array maintained a 2.4×, 2.5×, and 2.1× higher SNR, respectively compared to the external coils. The array performance was evaluated for anatomical, diffusion tensor and functional brain imaging. This study suggests that a stable implanted phased-array coil can be used in macaque MRI to substantially increase the spatial resolution for anatomical, diffusion tensor, and functional imaging.

The AGATA triple cluster detector

The AGATA triple cluster (ATC) detector consists of three asymmetric, 36-fold segmented, hexagonal shaped, encapsulated tapered high-purity germanium (HPGe) detectors. The cluster detector comprises 111 high resolution spectroscopy channels which are operated in one common cryostat. All 111 energy signal channels are equipped with a preamplifier stage based on a cold FET technology in order to provide best energy resolution of core and segment signals. The three average energy resolution values of the segments at low γ - ray energies of 60 and 122 keV were measured to be in the range of 965–1040 eV. For γ - ray energies of 1332.5 keV the average energy resolution of the 36 segments is between 2.10 and 2.19 keV for the three detectors. Crosstalk properties of the highly packed analog preamplifier circuitry and detector assembly were investigated. The crosstalk level between different detectors was found to be negligible on a level below 10 −5. A low crosstalk level of 10 −3 was found for the segment signals within the same HPGe detector caused by the interplay of the core coupling capacitor and the capacitances of the 36 segments. The measured values compare well with expected calculated contributions.

Analysis and simulation of the SLD WIC PADS hybrid preamplifier circuitry

Computer simulation techniques are used to analyze critical performance parameters of the SLD PADS preamplifier hybrid, including its interactions with the detector system. Simulation results are presented and verified with measured performance. The use of the computer simulation of the detector/preamplifier combination is shown to be a reasonably accurate predictor of preamplifier performance, but more importantly, it allows one to demonstrate, analyze, and quantify selected aspects of the hybrid's behavior in the system. In particular, the analysis confirms wide tolerances on system timing and demonstrates that self-calibration can compensate for the effects of large variation in detector capacitance. The selection of 6 mu s for fixed time sampling is shown to be entirely reasonable for this system. >

Active hearing protectors

A hearing protective device consisting of a headset having opposite earmuff and/or earplug assemblies resiliently connected by a headband assembly including a normally open power switch closed when the headband assembly is put on the user's head. The switch controls the energizing of the electrical circuitry of the device. Each earmuff and/or earplug assembly has an outwardly-facing microphone and an inwardly-facing sound reproducer, connected to circuitry defining respective stereo channels, each channel including preamplifier circuitry and a respective power amplifier drivingly connected to one of the sound reproducers. The circuitry also includes a hyper AGC circuit which receives and sums signals from the amplifier chain and derives attenuation signals therefrom which are fed back to the amplifier circuitry and which reduces the gain of this circuitry when the input sound exceeds a certain level. This causes the inputs to the power amplifiers to fall when the input to the preamplifiers increases beyond a certain level. A balanced attenuation circuit arrangement is employed which reduces the size of too-large sound waves without altering their shape, whereby the volumes of the two stereo channels are maintained in the proper relation to each other to preserve binaural hearing.

Hydrophone measurements in diagnostic ultrasound fields

Some of the methods, calculations, and problems associated with making hydrophone measurements in diagnostic ultrasound fields are considered. Several organizations have proposed definitions of various peak and average intensities that need to be specified when characterizing medical ultrasound fields. All of these can be determined from hydrophone measurements, but the bandwidths encountered (>50 MHz), along with the small focal diameters achievable ( approximately 1 mm), can place great demands on hydrophone performance. Two general types of hydrophones are available-the spot-poled membrane and needle types. Both employ the piezopolymer polyvinylidine fluoride (PVDF), and for the most part they have effective dimensions in the 0.5-1.0-mm range. Hydrophones can be made with useful bandwidths extending beyond 50 MHz. However, above approximately 15 MHz the nature of the response becomes highly dependent on the method of construction and PVDF film thickness used, as well as the characteristics of any associated preamplifier circuitry. Other factors that can affect measurement accuracy are discussed.

An eight-channel computer-controlled scanning electromyograph

A measurement system is described for the computerized detection, digitizing, and storage of electromyographic (EMG) signals from up to eight muscle groups. The use of a channel scanning technique allows almost simultaneous multichannel recording with minimal circuit redundancy. Specifically, the scanning electromyograph allows several EMG preamplifiers to share expensive isolation, signal-conditioning, and interface circuitry. The design incorporates monolithic integrated circuit preamplifiers and includes optical isolation of the preamplifier circuitry for protection of the subject. Hybrid active filter modules allow convenient selection of system bandpass characteristics. Key measurement parameters are software programmable. The scanning electromyograph is inexpensively constructed from readily available componentry. Specifications for all functional blocks within the instrument are comparable to those of commercial instrumentation.

The design and operation of a fast 2$\pi$ gas-flow counter for alpha particles

The accurate measurement of high emission rates of alpha radioactive sources has been neglected up to the present time. In order to resolve this difficulty a new 2? proportional counter was developed, capable of measurement up to at least 5?105 alpha particles per second into 2? geometry. Careful attention was placed on the factors limiting counting speed, notably mechanical and electrical design of the counter and preamplifier circuitry. The choice of counting gas was also critical for high speed applications. The calibration of the counter was checked using a certified standard source from the Radiochemical Centre emitting 1?029?105 alpha particles per minute. The measured emission rate of the source agreed to within ?0?1% of this figure.