Method for making sintered cubic halide scintillator material
View Patent ↗A method of making a cubic halide scintillator material includes pressing a powder mixture of cubic halide and at least one activator under conditions of pressure, temperature, residence time and particle size effective to provide a polycrystalline sintered cubic halide scintillator having a pulse height resolution of from about 7% to about 20%. The conditions include a temperature ranging from about ambient temperature up to about 90% of the melting point of the cubic halide, a pressure of from about 30,000 psi to about 200,000 psi, a pressing residence time of from about 5 minutes to about 120 minutes and an average cubic halide particle size of from about 60 micrometers to about 275 micrometers.
1. A method for making a sintered cubic halide scintillator comprising:
pressing a powder mixture of cubic halide and at least one activator under processing conditions of pressure, temperature, residence time and particle size effective to provide a polycrystalline sintered cubic halide scintillator having a pulse height resolution at 662 keV of from about 7% to about 20%, wherein the processing temperature ranges from about ambient temperature up to about 90% of the melting point of the cubic halide in degrees Centigrade, a pressure of from about 30,000 psi to about 200,000 psi, a pressing residence time of from about 5 minutes to about 120 minutes and an average cubic halide particle size of from about 60 micrometers to about 2000 micrometers.
2. The method of claim 1 wherein the cubic halide is a binary cubic halide selected from halides of sodium, potassium, cesium and rubidium.
3. The method of claim 1 wherein the cubic halide is sodium iodide.
4. The method of claim 1 wherein the activator is selected from halides of thallium, cesium and sodium.
5. The method of claim 1 wherein the activator is thallium iodide.
6. The method of claim 1 wherein the activator concentration ranges from about 0.005% to 5.0% by weight.
7. The method of claim 1 wherein the processing temperature ranges from about 20° C. to about 30° C., the pressure ranges from about 100,000 psi to about 200,000 psi, the residence time ranges from about 5 minutes to about 10 minutes and the average particle size ranges from about 60 micrometers to about 90 micrometers.
8. The method of claim 1 wherein the temperature ranges from about 90° C. to about 150° C., the pressure ranges from about 100,000 psi to about 150,000 psi, the residence time ranges from about 5 minutes to about 10 minutes and the average particle size ranges from about 90 micrometers to about 120 micrometers.
9. The method of claim 1 wherein the temperature ranges from about 250° C. to about 450° C., the pressure ranges from about 30,000 psi to about 60,000 psi, the residence time ranges from about 50 minutes to about 60 minutes and the average particle size ranges from about 200 micrometers to about 275 micrometers.
10. The method of claim 1 wherein the pressing is accomplished by cold, warm or hot uniaxial pressing.
11. The method of claim 10 wherein the uniaxial pressing is hot pressing.
12. The method of claim 1 wherein the pressing is accomplished by cold, warm or hot isostatic pressing.
13. The method of claim 1 wherein the activator is substantially uniformly distributed throughout the mixture.
14. The method of claim 1 wherein the activator has a concentration percentage which varies throughout the mixture in accordance with a controlled gradient.
15. The method of claim 1 wherein the mixture comprises at least first and second blends having first and second different activator concentrations and/or first and second different particle size range distributions and said first and second blends are loaded into a compression die in a preselected order for subsequent sintering to provide a scintillator body having a controlled gradient of activator concentration and/or crystal size along a dimension of the scintillator.
16. The method of claim 1 wherein the mixture can include from 25% to about 75% of a first blend of cubic halide and activator having a relatively large first cubic halide average particle size, and from about 25% to about 75% of a second blend of cubic halide and activator having a relatively small second cubic halide average particle size of up to about 30% of the first cubic halide average particle size.
17. The method of claim 16 wherein the relatively large first cubic halide average particle size ranges from about 200 micrometers to about 250 micrometers, and the second relatively small average cubic halide particle size ranges from about 30 micrometers to about 50 micrometers.
18. The method of claim 1 further including pre-treating the mixture prior to pressing to remove moisture and/or other volatile impurities.
19. The method of claim 18 wherein the pre-treating is accomplished by preheating the mixture under an inert atmosphere or vacuum.
20. The method of claim 1 further including annealing the polycrystalline sintered cubic halide scintillator at a temperature sufficient to reduce internal mechanical stresses in the scintillator.