V. Perez-Mendez

Magnetostrictive readout for wire spark chambers

Abstract A method for locating track coordinates in a wire spark chamber is described. The transducer is a nickel magnetostrictive ribbon which is coupled to the chamber wires magnetically. Spark coordinates are determined by digitizing the time delay from the chamber trigger signal to the arrival of the magnetostrictive pulse at a pickup coil. Multiple-spark events are readily recorded without ambiguities; the only limitations are the two-spark resolution of the transducer signal and the readout capacity of the digitizing electronics.

PHASE COMPENSATED ELECTROMAGNETIC DELAY LINES FOR WIRE CHAMBER READOUT.

Abstract In this paper a phase-compensated distributed parameter electromagnetic delay line suitable for the readout of the positions of ionizing tracks in multi-wire proportional chambers is described. Delay lines with delays of 40 to 200 ns/cm having a rectangular cross section have been designed. The rectangular cross section enables them to be capacitatively coupled to the wire chamber simply by clamping them on the wire chamber external leads. The coupling coefficients between the chamber and delay line are approximately 3 to 10%. The electronic readout accuracy is better than ±0.1 mm due to the delay line.

ELECTROMAGNETIC DELAY LINE READOUT FOR PROPORTIONAL WIRE CHAMBERS.

Abstract We describe the use of electromagnetic delay lines to read out the position of ionizing events in multi-wire proportional chambers. The delay line used is a ceramic core (non-magnetic) type with a delay of 80 nsec/cm. The readout accuracy achieved depends on the wire plane which is read out: for the positive plane which forms the electron avalanche, the accuracy is ±1 m (half the wire spacing). For the negative plane, which records the induced signal produced on a number of adjacent wires by the positive ions, the interpolation property of the delay line permits an accuracy of ±0.15 mm.

Amorphous silicon pixel layers with cesium iodide converters for medical radiography

We describe the properties of evaporated layers of cesium iodide (thallium activated) deposited on substrates that enable easy coupling to amorphous silicon pixel arrays. The CsI(Tl) layers range in thickness from 65 to 220 /spl mu/m. We used the two-boat evaporator system to deposit CsI(Tl) layers. This system ensures the formation of the scintillator film with homogenous thallium concentration which is essential for optimizing the scintillation light emission efficiency. The Tl concentration was kept to 0.1-0.2 mole percent for the highest light output. Temperature annealing can affect the microstructure as well as light output of the CsI(Tl) film. 200-360/spl deg/C temperature annealing can increase the light output by a factor of two. The amorphous silicon pixel arrays are p-i-n diodes approximately 1 /spl mu/m thick with transparent electrodes to enable them to detect the scintillation light produced by X-rays incident on the CsI(Tl). Digital radiography requires a good spatial resolution. This is accomplished by making the detector pixel size less than 50 /spl mu/m. The light emission from the CsI(Tl) is collimated by techniques involving the deposition process on patterned substrates. We have measured MTF of greater than 12 line pairs per mm at the 10% level. >

X-ray and charged particle detection with CsI(Tl) layer coupled to a Si:H photodiode layers

A compact real-time X-ray and charged-particle imager with digitized position output can be built either by coupling a fast scintillator to a photodiode array or by forming one on a photodiode array directly. CsI(Tl) layers 100-1000- mu m thick were evaporated on glass substrates from a crystal CsI(Tl). When coupled to a crystalline Si or amorphous silicon (a-Si:H) photodiode and exposed to calibrated X-ray pulses, their light yields and speed were found to be comparable to those of a crystal CsI(Tl). Single beta particle detection was demonstrated with this combination. The light spread inside evaporated CsI(Tl) was suppressed by its columnar structure. Scintillation detection gives much larger signals than direct X-ray detection due to the increased energy deposition in the detector material. Fabrication of monolithic-type X-ray sensors consisting of CsI+a-Si:H photodiodes is discussed. >

Axial Tomography and Three Dimensional Image Reconstruction

A number of existing cameras for Nuclear Medicine imaging of radio-isotope distributions give depth information about the distribution. These devices have in common that they provide tomographic images of the object, that is, that images of a given object plane have that plane in focus and all other object planes contribute an out-of-focus background superimposed on the in-focus image. We present here a method for three dimensional reconstruction of these axial tomographic images which removes the blurred off-plane activity from a number of transverse planes simultaneously. The method is applicable to a number of tomographic cameras, such as the multiple single-pinhole camera, the rotating slanted-hole collimator, the Anger focussing tomographic scanner, and the positron camera. The method can be implemented on a small computer having a disc system.

MULTIWIRE PROPORTIONAL CHAMBERS FOR BIOMEDICAL APPLICATION

Abstract Multiwire proportional chambers with delay-line readouts, currently used for particle trajectory measurements in high-energy physics, are being adapted for a variety of biomedical applications including X-radiography, neutron radiography, and radioisotope imaging. This paper describes chamber-design features and gives calculated and measured efficiency and resolution data. Sample radiographic images taken with prototype chambers are shown.

DELAY-LINE READOUT FOR PROPORTIONAL CHAMBERS.

Abstract A simple method for locating the position of particles which produce ionizing events in proportional wire chambers is described. The method involves the use of ferrite-loaded delay cable.

Detection of charged particles in amorphous silicon layers

Abstract The succesful development of radiation detectors made from amorphous silicon coul offer the possibility for relatively easy construction of large area position-sensitive detectors. We have conducted a series of measurements with prototype detectors, on signals derived from alpha particle. The measurement results are compared with simple model calculations, and projections are made of potential applications in high-energy and nuclear physics.

Evidence for a low-energy resonance in the three-neutron system

Abstract A study of the double charge-exchange reaction π − + 3 He π − π + + 3 n indicates resonant behavior in the three-neutron system within a few MeV of threshold. The three-neutron data from this experiment are in good agreement with the resonant behavior obtained in the three-proton system in another reaction.