Radiant energy – Invisible radiant energy responsive electric signalling – With or including a luminophor
Patent
1998-03-16
2000-06-27
Hannaher, Constantine
Radiant energy
Invisible radiant energy responsive electric signalling
With or including a luminophor
25036301, 25036302, 25037009, G01T 1169
Patent
active
060809892
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to arrangements for detecting and/or imaging gamma radiation especially using a Compton camera.
The detection and/or imaging of gamma emitting radioactive materials whose distribution is unknown requires one of a broad range of techniques which include:
Collimation--where a gamma radiation image is produced on a position sensitive gamma radiation detector or on film coated with gamma radiation sensitive emulsion by heavy (e.g. lead or tungsten) collimators. The collimators allow only gamma photons passing along certain pre-determined trajectories to pass readily towards the detectors or films. Gamma photons and scattered radiation passing along all other pathways are, as far as possible, prevented from progressing towards the detectors or films.
Anti Collimation--where a gamma radiation image appears when two images from a position sensitive gamma radiation detector are compared; one image being taken whilst a small gamma attenuating object (e.g. lead or tungsten) is used to cast a gamma radiation shadow onto the position sensitive gamma radiation detector.
Compton Camera--where a gamma radiation image can be formed by detecting many near coincident events on pairs of gamma radiation detectors in an array of such gamma radiation detectors. A coincident event is assumed to comprise an incident gamma photon detected on one detector by releasing a Compton scattered electron, the photon being detected a short time later on the second detector. The energies measured in the two events are used with the standard Compton scatter equation to back-calculate the trajectory of the original incident gamma photon, which can be placed somewhere on the surface of a hollow cone whose apex is positioned at the centre of the first detector.
Compton cameras employed in the prior art are large, heavy, delicate devices which employ heavy shielding material, (e.g. lead or tungsten) as part of the outer casing of the device. Such shielding material encloses various of the gamma radiation detector elements and position sensitive gamma radiation detectors as a means of improving the rejection of unwanted detection events. The gamma radiation detectors used also usually require to be cooled below room temperature, involving more bulk and weight.
Most prior art Compton Cameras have been developed for medical application in 3D imaging of injected radio-nuclides where a single gamma photon energy is involved. Although portable to a degree they would, because of their size, weight and delicate nature be limited to use in only a limited number of applications in which it is desirable to image radioactive materials. For example, whilst some gamma radiation imaging devices for the Nuclear Power Industry may be required in fixed installations, such as imaging the content of waste sentencing cells, many other applications within the Nuclear Power Industry will require highly mobile gamma radiation imaging systems. These will need to be small, light and rugged as they may be needed for remote deployment deep within nuclear facilities, often where man-access is prohibited and/or where it is necessary to carry out remote investigations or remote manipulative operations. Conventional Compton cameras are not suitable for such uses.
The present invention aims to provide a solution to the problem of imaging gamma emitting sources within a radioactive or otherwise inaccessible cell, where conventional Compton cameras or other gamma radiation imaging systems are not suitable.
According to the present invention there is provided apparatus for determining a source of gamma radiation using the Compton effect by detecting gamma photons emitted by the source, comprising: from the first and second detectors, the signal recorder and processor comprising means for recording coincidences between outputs from the first detector and outputs from the second detector; incident on the first detector when coincidences are recorded between the outputs of the first and second detectors; co-ordinates of source of the gamma photons inciden
REFERENCES:
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patent: 5567944 (1996-10-01), Rohe et al.
Redus, R.H., Nagarkar, V., Cirignano, L.J., McGann, W., and Squillante, M.R., A Nuclear Survey Instrument with Imaging Capability, vol. 2, Watertwon, MA, pp. 1354-1357, published Nov. 2, 1991.
Royle, G.J. and Speller, R.D., Design of a Compton Camera for Imaging 662 keV Radionuclide Distributions, Nuclear Instruments & Methods in Physics Research, Section A, 1994, pp. 623-626.
Royle Gary John
Speller Robert David
British Nuclear Fuels PLC
Hannaher Constantine
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