Radiation Detector Arrays Research Articles

Modular 64×64 CdZnTe Arrays With Multiplexer Readout for High-Resolution Nuclear Medicine Imaging

AbstractWe are developing modular arrays of CdZnTe radiation detectors for high-resolution nuclear medicine imaging. Each detector is delineated into a 64×64 array of pixels; the pixel pitch is 380 ptm. Each pixel is connected to a corresponding pad on a multiplexer readout circuit. The imaging system is controlled by a personal computer. We obtained images of standard nuclear medicine phantoms in which the spatial resolution of approximately 1.5 mm was limited by the collimator that was used. Significant improvements in spatial resolution should be possible with different collimator designs. These results are promising for high-resolution nuclear medicine imaging.

A novel ASIC for readout electronics in semiconductor γ-ray detection

A low-power low-noise multichannel integrated circuit is implemented in 1.2 μm CMOS technology. This circuit is designed for space γ-ray spectrometer using arrays of CdTe radiation detectors in the 20–750 keV range. The space environment needs rad-tolerant specifications for the technology like 20 krad of total integrated dose and consumption limited to 2 mW/channel. Each channel includes a low-noise charge-sensitive preamplifier, fitted band-pass filters, peak amplitude and rise-time measurements; these enable a remote rise-time corrected γ-ray energy spectral analysis. The circuit includes an associated logic block, dedicated to the internal timing, functional organization, external communication and data transfer.

Analysis of multidimensional spectra

Coincidence spectra obtained from arrays of radiation detectors can be analyzed without resorting to projecting lower dimensional spectra. The techniques for two-dimensional analysis (peak searches and peak fitting) are described, and extensions to higher dimensions are discussed. Even for two-dimensional analysis it is most efficient to compare predictions from a model, such as a scheme for radioactive decay, with the data by backcalculating the data from the model.

Imaging devices based on pyroelectric radiation detector arrays

This paper deals with the major factors affecting the resolving power of imaging devices employing pyroelectric radiation detector arrays. These include thermal and electrical crosstalk between discrete elements of the array. The role and effect of the number of sensitive elements per unit of length and dimension of spacing between them on array resolution magnitude have been analysed.

Local plasma radiation loss rate determination in tokamaks and stellarators

A modified tomography technique was developed to provide, from two radiation detector arrays covering an entire plasma cross section at a fixed toroidal angle, the local distribution of the time rate of change of the radiated power. The radiated power is the least unambiguously measured of all the components involved in plasma thermal equilibrium and its time evolution could be the most indicative of any perturbation of such equilibrium. The tomography technique has been checked by using simulated thermal perturbations, assuming a 1D transport model for the resulting transport. Experimental setups are presented for the TJ-I tokamak and TJ-IU stellarator.

New radiation hodoscope developments for arms control treaty verification

It is pointed out that new developments in hodoscope radiation detection technology offer a wide range of capabilities for arms control treaty verification (ACTV) applications. This concept uses an array of radiation detectors to image or detect objects inside opaque containments. Hodoscope systems can detect neutrons and/or gamma-rays. The systems can be based on transmission of radiation through the objects, can detect radiation stimulated in the objects, or can detect intrinsic object radiation. Laboratory measurements to demonstrate a range of potential applications have been performed. Gamma-ray transmission hodoscopes can be used to inspect canisters, rail cars, etc. to monitor objects such as rocket motors. The use of relatively weak isotopic radiation sources makes it unnecessary to employ expensive and high-intensity accelerators. The heavy metal of nuclear warheads is characterized by strong gamma-ray absorption, and these materials could be counted by low-resolution tomography. Absorbers located in line with objects will themselves be detected, and sources located in the object region will be subtracted out as background. Intrinsic gamma-ray radiation from warheads can also be detected in a passive-instrument mode. >

A 3 × 3 silicon drift chamber array for application in an electronic collimator

The mechanical collimator, used in combination with an Anger camera in nuclear-medical imaging studies, can be replaced with a radiation detector, which performs the function of electronic collimation. The two-detector system is based on the Compton scattering of incident gamma-photons. Although germanium is more efficient in the absorption of gamma-photons by the Compton process than silicon, silicon has advantages which cannot be overlooked when choosing a substrate material on which to fabricate the radiation detector to be used in the electronic collimator system. The semiconductor drift chamber (SDC) principle offers advantages in the construction of a two-dimensional radiation detector array. Simulations of the potential field within the detector array will be shown, as well as the design and processing sequence used in the fabrication of a 3 × 3 SDC array.

Turbulent fluctuations and confinement in JET

High frequency fluctuations are observed in JET by edge magnetic probes and arrays of visible radiation detectors even in the absence of Mirnov activity (typical frequency: ∼1 kHz); cross-correlation techniques are applied in order to study the broadband activity. Magnetic fluctuations (b̃θ) in the range of 1 to 20 kHz are strongly correlated along a direction parallel to the edge magnetic field lines; above ∼10 kHz, a substantial fraction of these fluctuations (30-60%) have low wavenumbers (m ≤ 5, n ∼ 1). Fluctuations in visible radiation coming from the edge are detected by soft X-ray diodes (without absorptive foil) up to ∼ 100 kHz: correlation analysis indicates the presence of rather high m numbers (m ∼ 10-100) with a correlation time of τc ∼ 100 μs. This type of activity is also seen by the magnetic probes and a good correlation between the two diagnostics is observed. The edge magnetic root mean square level is continuously monitored with eight hardware filters over the 5 to 60 kHz frequency range. Database analysis of additionally heated discharges shows a proportionality between b̃θN = |b̃θ|BT/Bθ and the inverse energy confinement time, .

Real time monitor of radiation field shape and intensity

The design and performance of a low-cost, real-time shape and intensity monitor for the AFRRI LINAC radiation fields is described. The system projects the individual outputs of a rectangular array of radiation detectors onto a baseline CRT display to produce a continuous three-dimensional representation of the field. The radiation detectors can be of any type, such as ion chambers, charge sensitive devices or diodes, from which the radiation induced charge can be collected. In addition to the detector array, three waveform and pulse generators, a multiplexor and an oscilloscope are used. The capability of monitoring the field at several points is an advantage over wire plane monitors which only produce beam profiles and are insensitive to certain beam inhomogeneities.