Collimator for x-ray, gamma, or particle radiation

Abstract

A collimator for x-ray, gamma, or particle radiation has a plurality of collimator elements made of a tungsten-containing material to reduce scattered radiation. At least one collimator element consists of a tungsten alloy having a tungsten content of 72 to 98 wt.-%, which contains 1 to 14 wt.-% of at least one metal of the group Mo, Ta, Nb and 1 to 14 wt.-% of at least one metal of the group Fe, Ni, Co, Cu. The collimator also has very homogeneous absorption behavior at very thin wall thicknesses of the collimator elements.

Claims

1. A collimator for x-ray, gamma, or particle radiation, the collimator comprising: a plurality of collimator elements made of a tungsten-containing material and configured to reduce scattered radiation; at least one of said collimator elements being formed of a tungsten alloy having a tungsten content of 72 to 98 wt.-%, said tungsten alloy containing 1 to 14 wt.-% of at least one metal selected from the group consisting of Mo, Ta, and Nb, and 1 to 14 wt.-% of at least one metal selected from the group consisting of Fe, Ni, Co, and Cu; and wherein a mean number of tungsten grains over a thickness of said at least one collimator element is greater than 5, a thickness of said at least one collimator element is 50 to 250 μm, and a homogeneity factor HF is ≦0.5.

2. The collimator according to claim 1, wherein said tungsten alloy consists of 1 to 14 wt.-% of at least one metal selected from the group consisting of Mo, Ta and Nb; 1 to 14 wt.-% of at least one metal selected from the group consisting of Fe, Ni, Co and Cu, and a remainder of tungsten.

3. The collimator according to claim 1, wherein said tungsten alloy contains 2 to 8 wt.-% of at least one metal selected from the group consisting of Mo, Ta and Nb and 2 to 9 wt.-% of at least one metal selected from the group consisting of Fe, Ni, Co and Cu.

4. The collimator according to claim 3, wherein said tungsten alloy contains 2 to 8 wt.-% Mo and 2 to 9 wt.-% of at least one metal selected from the group consisting of Fe and Ni.

5. The collimator according to claim 1, wherein said tungsten alloy comprises tungsten grains having a mean grain aspect ratio of less than 1.5.

6. The collimator according to claim 5, wherein said tungsten alloy comprises tungsten grains having a globular form.

7. The collimator according to claim 1, wherein the homogeneity factor HF is ≦0.25.

8. The collimator according to claim 1, wherein the mean number of tungsten grains over the thickness of said at least one collimator element is greater than 10.

9. The collimator according to claim 1, wherein said at least one collimator element is a collimator plate.

10. The collimator according to claim 1, configured to form a part of an imaging unit of a computed tomography device.

11. A collimator element, consisting of a tungsten alloy having a tungsten content of 72 to 98 wt.-%, said tungsten alloy containing 1 to 14 wt.-% of at least one metal selected from the group consisting of Mo, Ta and Nb, and 1 to 14 wt.-% of at least one metal selected from the group consisting of Fe, Ni, Co and Cu; and wherein a mean number of tungsten grains over a thickness of the collimator element is greater than 5, a thickness of the collimator element is 50 to 250 μm, and a homogeneity factor HF is ≦0.5.

12. A method for producing a collimator element according to claim 11, the method which comprises carrying out a foil extrusion process or a tape casting process to thereby produce the collimator element according to claim 11.

13. The method according to claim 12, which comprises the following method steps: producing a powder compound with: 45 to 65 vol.-% metal powder, the metal powder containing 72 to 98 wt.-% W, 1 to 14 wt.-% of at least one metal selected from the group consisting of Mo, Ta and Nb, and 1 to 14 wt.-% of at least one metal selected from the group consisting of Fe, Ni, Co and Cu; and 35 to 55 vol.-% of a thermoplastic binder; plasticizing the powder compound to form a plasticized powder compound; producing a green sheet by shaping the plasticized powder compound; debindering the green sheet by a chemical and/or thermal process to form an at least partially debindered green sheet; sintering the at least partially debindered green sheet at a sintering temperature of 1100 to 1500° C. for producing a sintered sheet; processing the sintered sheet to produce a final form of the collimator element having a mean number of tungsten grains over a thickness of the collimator element greater than 5, a thickness of the collimator element is 50 to 250 μm, and a homogeneity factor HF is ≦0.5.

14. The method according to claim 13, wherein the processing step comprises at least one process selected from the group consisting of pickling, stamping, and eroding.

15. The method according to claim 13, which comprises, prior to debindering the green sheet, smoothing the green sheet.

16. The method according to claim 13, which comprises subjecting the sintered sheet to calibration rolling.

17. The method according to claim 13, wherein the powder compound comprises content of up to 5 vol.-% dispersing agent and/or other auxiliary agents.

Description

EXAMPLE

Brief Description of the Several Views of the Drawing

(1) FIG. 1: light microscopy picture of sample number 2 according to table 1, which schematically shows the determination of the homogeneity factor HF.

DESCRIPTION OF THE INVENTION

(2) The invention is described as an example hereafter.

(3) The following powders were used for the experiments: tungsten (grain size according to Fisher 4 μm), nickel (grain size according to Fisher 5 μm), iron (grain size according to Fisher 6 μm), molybdenum (grain size according to Fisher 4 μm), tantalum (grain size according to Fisher 7 μm), niobium (grain size according to Fisher 7 μm), cobalt (grain size according to Fisher 5 μm), copper (grain size according to Fisher 6.5 μm).

(4) Firstly powder mixtures were produced by mixing in a diffusion mixer in the compositions as listed in table 1. The respective powder batches were admixed with polyamide and plasticizer, wherein the powder fraction was respectively 53 vol.-% and the binder fraction was respectively 47 vol.-%.

(5) The binder had the following composition: 30 wt.-% polyamide, 44 wt.-% aromatic carboxylic acid ester of an aliphatic alcohol having a chain length of C8, 26 wt.-% fatty acid having a chain length of C16 to C22.

(6) Powder and binder were mixed in a kneading assembly at 130° C. for 20 min. The powder compound was extruded at 110° C., cooled, and made into a molding compound in granule form having approximately 3 to 4 mm particle diameter. The molding compound was melted by means of a single-screw extruder at barrel zone temperatures of 80° C. to 130° C. and extruded through a slot die. The green body thus produced was smoothed in a smoothing rolling mill with a thickness reduction of 40% and cooled to room temperature. In the next process step, the green body was subjected to chemical partial debinding in acetone at 42° C.

(7) The remaining binder was removed pyrolytically/thermally by heating (heating rate 10° C./minute) and holding for 30 min. at 600° C. The debindered green body was sintered for 15 min. at a temperature 20° C. above the respective liquidus temperature, as can be inferred from the known phase diagrams. The sheet thickness after the sintering was 100 μm. The density was determined by the buoyancy method. The values are again listed in table 1.

(8) A metallographic microsection was then produced and analyzed by quantitative metallography. A line was drawn at 45° C. to the surface and the total route length for the binding phase (SSL) was determined. SSL is to be understood as the sum of all individual route lengths s.sub.1 to s.sub.n, as shown in FIG. 1.

(9) $\mathrm{SSL}=\underset{1}{\overset{n}{.Math.}}s$

(10) This measurement was repeated 20 times, the mean total route lengths SSL (mean value of the 20 measurements) were determined for the binding phase and the total maximum route length SSL.sub.MAX (greatest measured value of the 20 measurements) was determined for the binding phase.

(11) The homogeneity factor HF was then ascertained, where:

(12) $\mathrm{HF}=\frac{{\mathrm{SSL}}_{\mathrm{MAX}}-\stackrel{\_}{\mathrm{SSL}}}{\stackrel{\_}{\mathrm{SSL}}}$

(13) The homogeneity of the beam absorption was classified as follows: HF≦0.25 (high homogeneity=HH) 0.25<HF≦0.5 (moderate homogeneity=MH) HF>0.5 (low homogeneity=LH).

(14) The results are listed in table 1.

(15) TABLE-US-00001 TABLE 1 W (wt.- Mo (wt.- Ta (wt.- Nb (wt.- Ni (wt.- Fe (wt.- Co (wt.- Cu (wt.- Relative No. %) %) %) %) %) %) %) %) density HF  1 92.5 7.5 100 LH NEG  2 92.5 5 2.5 99.8 LH NEG  3 92.5 5 2.5 94.7 LH NEG  4 92.5 4.5 2.5 0.5 99.5 LH NEG  5 92.5 4.5 2.5 0.5 99.8 LH NEG  6 92.5 4.5 2 1 99.1 LH NEG  7 92.5 0.5 4.5 2.5 99.7 LH NEG  8 90 4 4 2 98 HH EG  9 92.5 3 3 1.5 100 HH EG 10 92.5 1.5 4 2 100 MH EG 11 80 11 6 3 97.0 MH EG 12 95 3 2 97.5 MH EG 13 88 6 4 2 97.0 MH EG 14 92.5 3 4 0.5 98.1 HH EG 15 92.5 3 4 0.5 96.2 HH EG 16 77 14 6 3 95.0 HH EG 17 92 2 4 2 97.8 MH EG 18 90 4 4 2 98 MH EG 19 92.5 1.5 4 2 100 MH EG 20 90 3 1 4 2 97.8 HH EG NEG . . . Not according to the invention; EG . . . According to the invention; HH: HF ≦ 0.25 (high homogeneity) MH: 0.25 < HF ≦ 0.5 (moderate homogeneity) LH: HF > 0.5 (low homogeneity)