J.E. Bateman

A positron camera for industrial application

Abstract A positron camera for application to flow tracing and measurement in mechanical subjects is described. It is based on two 300 × 600 mm 2 hybrid multiwire detectors; the cathodes are in the form of lead strips plated onto printed-circuit board, and delay lines are used to determine the location of photon interactions. Measurements of the positron detection efficiency (30 Hz μCi −1 for a centred unshielded source), the maximum data logging rate (3 kHz) and the spatial resolving power (point source response = 5.7 mmfwhm) are presented and discussed, and results from initial demonstration experiments are shown.

The Rutherford Appleton laboratory's mark I multiwire proportional counter positron camera

Abstract A small (30 cm × 30 cm) model of a proposed large aperture positron camera has been developed at Rutherford Appleton Laboratory. Based on multiwire proportional counter technology it uses lead foil cathodes which function simultaneously as converters for the 511 keV gamma rays and readout electrodes for a delay line readout system. The detectors have been built up into a portable imaging system complete with a dedicated computer for data taking, processing and display. This has permitted evaluation of this type of positron imaging system in the clinical environment using both cyclotron generated isotopes ( 15 O, 11 C, 18 F, 124 I) and available isotopic generator systems ( 82 Rb, 68 Ga). At RAL we provided a complete hardware system and sufficient software to permit our hospital based colleagues to generate useful images with the minimum of effort. A complete description of the system is given with performance figures and some of the images obtained in three hospital visits are presented. Some detailed studies of the imaging performance of the positron camera are reported which have bearing on the design of future, improved systems.

Two digital X-ray imaging systems for applications in X-ray diffraction

Abstract Two digital X-ray imaging systems developed at the Rutherford Appleton Laboratory are described: the Mark I and the Mark II. Both use a bidimensionally sensitive multiwire proportional counter (MWPC) as the basic X-ray image transducer coupled, in the case of the Mark I to a Digital LSI 11–23 microcomputer system via CAMAC, and in the case of the Mark II to a Digital LSI 11–73 microcomputer system via custom-built data acquisition hardware mounted directly on the Q-bus of the microcomputer. The Mark I system provides the advantages of high speed, high sensitivity digital imaging directly into the computer with the potential for software control of the sample orientation and environment. The Mark II system adds the novel features of signal averaging and multiframe exposures. The dedicated digital memories have a resolution of 512×512 pixels of 16 bits, matching well to the spatial resolution of the xenon-filled MWPC (0.5 mm fwhm over an aperture of 200 mm×200 mm). A 512×512×4 bit video graphics system displays the images in grey scales or colour.

High speed quantitative digital beta autoradiography using a multistep avalanche detector and an Apple II microcomputer

Abstract The development of an electronic, digital beta autoradiography system is described. Using a multistep avalanche/multiwire proportional counter (MSA/MWPC) detector system fitted with delay line readout, high speed digital imaging is demonstrated with submillimeter spatial resolution. In the case of autoradiography with a tritium label, image acquisition requires about one hour compared with several weeks for conventional film techniques. Good proportionality of observed counting rate relative to the known tritium activity is demonstrated. The application of the system to autoradiography in immunoelectrophoresis, histopathology and DNA sequencing is described (using 125I, 14C and 35S labels in addition to 3H).

The development of gas microstrip detectors for high energy physics applications

Abstract Results are presented from the on-going programme of work at Rutherford Appleton Laboratory aimed at the development of high spatial resolution, high rate tracking counters for the next generation of collider experiments.

PETRRA: preliminary experimental results from the first full size detector and dead time simulation of the count rate performance of a unique whole body PET camera

The design and construction of the first of two BaF/sub 2/-TMAE large area detectors to be incorporated in a unique double headed whole body PET system (PETRRA) has been completed. Preliminary experimental work carried out with the first large area detector shows an absolute detection efficiency of 20.5% and a time resolution of 3.5 ns (FWHM) and 8.0 ns (FWTM), using 8 mm thick scintillation crystals. An analytical model of the electronic read-out system has been developed to investigate the rate capability of the new scanner. This model predicts that under typical imaging conditions, with 40 MBq of activity in the field of view, the proposed scanner will acquire coincidence data at 20-25 kcps. >

X-ray and gamma imaging with multiwire proportional counters

The role of the Multiwire Proportional Counter (MWPC) as an X-ray image transducer in integrated digital imaging systems for use in a wide variety of fields (X-ray diffraction, medicine, non-destructive,testing, etc.) is discussed with particular reference to the suitability of the technology for wider application than has been the case up to the present. A survey is given of the mechanical, electrical and electronic aspects of MWPC system design and the integration of this technology with microprocessor systems is examined. After a survey of the newer developments in the field of multiwire gaseous detectors it is concluded that this type of technology offers good potential for routine production of integrated digital X-ray imaging systems, possibly on a commercial basis.

Studies of the gain properties of gas microstrip detectors relevant to their application as X-ray and electron detectors

The microstrip gas counter (MSGC) makes an excellent planar (position-sensitive) amplifier of incident electron clouds because both the anodic and cathodic gain-defining elements are produced lithographically on the same rigid substrate. We have studied the dependence of the gas gain and pulse-height resolution of the plate as a function of various geometric and gas parameters. The results show that an MSGC can be made very insensitive to. the shape of the drift electrode, allowing it to be used in a wide variety of applications. An example of an electron-yield XAFS study is given. The aim of the work reported in this paper is to produce a well-defined technology platform from which to build detectors that meet the requirements of high-flux synchrotron radiation and neutron facilities, both of which are key CLRC facilities.

The pin detector — A simple, robust, cheap and effective nuclear radiation detector

Abstract The development of a series of radiation detectors based on the point anode is reported. Using readily available preformed pins from a variety of electrical connectors as the anodes, a family of devices has been created with useful properties as X-ray detectors, radiation monitors and internal beta counters. A wide variety of gas fillings can be used, argon/CH 4 premix being the most convenient. The stuctures are robust and call for no precision alignments so keeping costs down. Peformance of the devices in respect of sensitivity and pulse height resolution is comparable to that of conventional wire counters.

The effect of beam time structure on counting detectors in SRS experiments

Counting detector systems are increasingly used in X-ray experiments because of their attractive properties as regards linearity, large dynamic range and simple noise properties. In synchrotron radiation source (SRS) applications of X-ray detectors, counting rates are generally high enough to require dead-time correction. The time structure of an SRS beam interacts with the dead-time characteristics of the detector in a way that the simple stochastic dead-time models cannot always handle. This report generates analytical and Monte Carlo mathematical models which describe the rate performance of any given detector system when used with the typical beam structures encountered in an SRS.