Fuel and related compositions – Liquid fuels – Aluminum or heavy metal – other than lead – containing
Patent
1993-04-15
1994-11-29
Bradley, P. Austin
Fuel and related compositions
Liquid fuels
Aluminum or heavy metal, other than lead, containing
445 28, 359888, 313526, 313532, H01J 3150, H01J 944
Patent
active
053685130
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for manufacturing a correction mask for an image intensifier tube of the proximity-focus type having an oblong cathode and anode.
An oblong image intensifier tube of the proximity-focus type is described in the Dutch Patent 183,914. Such oblong image intensifier tubes are frequently used in so-called slit radiography apparatuses. The cathode is in that case sensitive to X-ray radiation, while the anode provides an output image corresponding to the incident X-ray radiation via an anode window which may possibly comprise an optical fibre plate. In such an application, the anode and the cathode may have a length of, for example, 40 cm and a width of, for example, 4 cm.
In practice the problem arises that it is difficult to make such long image intensifier tubes which have a uniform conversion factor over the entire active surface. Conversion factor is understood to mean the ratio between the radiation incident at the cathode side and the resultant output radiation at the anode side. It is also possible for the conversion factor to alter locally during the service life of such an image intensifier tube as a consequence of ageing phenomena.
There is therefore a need for a facility enabling correction of an oblong image intensifier tube so that the conversion factor is, so to speak, equalized.
The object of the invention is to provide such a facility. To this end, a method for manufacturing a correction mask for an image intensifier tube of the proximity-focus type having an oblong cathode and anode is characterized, according to the invention, in that the cathode is essentially uniformly illuminated over the entire surface with radiation to which the cathode is sensitive; in that during the illumination of the cathode, the intensity of the light provided by the anode is measured in at least one narrow strip-type region, extending in the longitudinal direction of the anode, as a function of the distance from one of the ends of the anode; in that the measured values obtained in this way for each strip-type region are reproduced in a graph as an experimental curve; in that a required value line approximating to the experimental curve is determined for each experimental curve; in that the difference between the experimental curve and the required value line is determined as a function of the distance from one of the ends of the anode; in that a transparent carrier is manufactured which is provided, in at least one oblong region, with a blackening which represents the difference between an experimental curve and an associated required value line as a function of the distance from one of the ends of the anode.
A method for correcting an image intensifier tube of the proximity-focus type having an oblong cathode and anode and an anode window matching the anode is characterized, according to the invention, in that a strip-type transparent carrier which is provided with a blackening in at least one oblong region is placed as a mask against the anode window.
The invention will be described in greater detail below with reference to the attached drawing.
FIG. 1 shows diagrammatically an example of an apparatus in which an image intensifier tube of the proximity-focus type having an oblong cathode and anode is used;
FIGS. 2A and 2B shows diagrammatically two examples of graphs which reproduce the output signal of an oblong proximity-focus image intensifier tube as a function of the distance from one end of the tube for a given input signal;
FIG. 3 shows diagrammatically an example of a correction mask for an oblong image intensifier tube.
FIG. 1 shows diagrammatically an example of an apparatus in which an image intensifier tube of the proximity-focus type having an oblong cathode and anode is used. The apparatus shown is an apparatus, known per se, for slit radiography in which a part of a patient 1, for example the thorax, is scanned with a flat fan-shaped X-ray beam 3 via a slit diaphragm 2. To this end, an X-ray source 4 can be used which is rotatable about an axis which is parallel to
REFERENCES:
patent: 3149968 (1964-09-01), Stephens
patent: 4187002 (1980-02-01), Roziere
G. W. Hobgood, Jr., IBM Tech. Discl., vol. 14, No. 11 (Apr. 1972) p. 3324.
Bradley P. Austin
BV Optische Industrie "De Oude Delft"
Knapp Jeffrey T.
Marn Louis E.
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