US2129295A - Screen for x-ray photographs - Google Patents

Description

Patented Sept. 6, 1938 PATENT oFFIcE,

SCREEN FOR X-RAY PHOTOGRAPHS 7 Karl Wiirstlin, Berlin-Baumschulenweg, and Karl H Grabbe, Berlin-Niederschoneweide, Germany," assignors to Kali-Chemie Aktiengesellschaft,

Berlin, Germany Application August 29, 1935, Serial No. 38,352 In Germany May 2, 1935 4 Claims.

The invention relates to a new intensifying screen for X-ray photography by means of which the exposure time is shortened and the definition of the picture is also improved.

It is an object of the invention to produce a screen by means of which much better definition can be obtained in X-ray photographs than with the previously known screens.

A further object of our invention is an intensifying screen which includes means for absorbing reflected light and a fluorescent material of such a grain size that the best possible definition can be obtained in X-ray photographs.

It is known in X-ray practice to use intensifying screens for the purpose of shortening the exposure time. The screens consist chiefly of a cardboard sheet or Celluloid film to which calcium tungstate is applied, together with a binder, in the form of crystals subdivided in the most 20 uniform manner possible. The cardboard supports have also been omitted and a gelatine layer containing calcium tungstate, the so-called supportless screen, has been used. The calcium tungstate has the property of fluorescing, that 25 is to say emitting visible light when irradiated tage by mixing with the layer containing the.

fluorescent material a dye or a light absorbing means. This procedure has the disadvantage 35 that the exposure time has to be increased 3 to 4 fold. Attempts have also been made to place a red or dark paper behind a so-called supportless screen. To obtain a sharp picture, close contact between the paper layer and the fluorescent 40 layer is necessary, which cannot be obtained with the separate use of a coloured paper layer and screen.

Finally, it has also been proposed to unite the fluorescent layer and the special layer for the 45 absorption of light or a special layer can be placed between the screen and its carrier, which is steeped in or coated with a light absorbing materi a We have now discovered that the definition of 50 the image, in spite of the use of a light absorb ing layer and even when the fluorescent layer and the light absorbing layer are united together, is very variable, and that in many cases an improvement in the definition is practically non- 55 existent. It is believed that the reason for this is that the effectiveness of this absorbing layer is dependent to a large extent upon the grain size of the material used for making the fluorescent layer, that is to say the calcium tungstate.

We have found that the best results can be 5 obtained with our new screens which contain a fluorescent material, in particular calcium tungstate, the grain size of which is substantially or in greater part of the order of 3 to 5 p. (1 a or micron=0.001 millimeter). If one goes considerably above this grain size the definition of the picture is impaired. If one goes below this grain size the intensification effect of the screen is reduced.

The type of new screen is shown more exactly in the accompanying drawing and in the follow-. ing description.

Figure 1 shows diagrammatically one form of construction of the screen in accordance with the invention;

Figure 2 shows also diagrammatically a modified form of construction.

In the drawing the thickness of the layers has been exaggerated for the purpose of illustration. The subject of the invention is not to be restricted in any way to what is shown in the drawing.

The screen shown in Figure 1 has three layers.

I' is a cardboard supporting layer, 2 is a layer of lac which is dyed with fluorescein and 3 is a layer of gelatine with finely divided calcium tungstate. The calcium tungstate must be in a state of fine subdivision and, most important of all, in a state of very uniform subdivision. The tungstate layer 3 is united with the layer lying beneath it by means of a transparent cement such for example as glue. The grain size of the tungstate is 3 to 5 [.L, but naturally a small proportion can also have a grain size which is somewhat above or below this.

The supporting layer I can also be made of Celluloid. Instead of the layer of lac a gelatine layer can be used which for example is dyed with eosin.

The screen according to Figure 2 only has two layers. A black coloured cardboard serves as the supporting layer 4. On to this is cemented the calcium tungstate layer 3, the grains of which are for the greater part of a diameter of 3 to 5 a. The cementing may be effected in a known manner, for example by means of an acetyl cellulose lacquer.

If the screen is to be flexible, then red coloured paper may be used for example instead of the black coloured cardboard.

colored supporting layer, a second layer firmly united with said black colored supporting layer and consisting of a fluorescent substance with I a grain size from 3 to 5 microns. v

3. In an intensifying scre graphs, in combination, a supporting layer, a second layer united therewith and adapted to absorb reflected light, and a third layer united to said second layer and containing a fluorescent material having a grain size of 3 to 5 4. An intensifying screen for X-ray photographs comprising a sheet of cardboard, a layer oi lac united to the latter and being dyed with fluorescein, and a layer of calcium tungstate united to said lac layer and consisting of calcium 10 tun gstate of a grain size of 3 to 5 KARL WURSTLIN. KARL GRABBE.

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