Device for manufacturing scintillator crystals with uniform distribution of dopant

Abstract

Disclosed herein is a device for manufacturing a scintillator comprising a furnace that includes a furnace wall; a crucible with a shelf disposed on an outer periphery of the crucible; where the shelf comprises a channel that is operative to hold a molten material and deliver the molten material to the crucible through a porous wall; a first delivery arrangement that is operative to deliver a scintillation material precursor to the shelf; a second delivery arrangement that is operative to deliver a dopant precursor directly to the crucible; where the scintillation material precursor and the dopant precursor do not contact each other prior to being delivered to the crucible; and a heating coil disposed inside the furnace wall and outside both the crucible and the shelf; where the scintillation material precursor and the dopant precursor are melted via resistance heating of the crucible and the shelf.

Description

DEVICE FOR MANUFACTURING SCINTILLATOR CRYSTALS WITH UNIFORMDISTRIBUTION OF DOPANTBACKGROUND

[0001] This disclosure relates to a device for manufacturing scintillator crystals that have a uniform distribution of the dopant between successive manufacturing runs.

[0002] Halide crystals (e g., sodium iodide, cesium iodide, lanthanum bromide, lanthanum chloride, strontium iodide, or a combination thereof) are used in medical imaging devices such as gamma cameras, positron emission tomography (PET) scanners and single photon emission computed tomography (SPECT). They can detect gamma rays emitted by radioactive tracers injected into the body for diagnostic purposes or may be used as scintillators in imaging processes such as positron emission tomography (PET) and single photon emission computed tomography (SPECT). Dopants are added to the halide crystals to modify their properties for specific applications, such as improving their efficiency as scintillators. Dopants such as, for example, thallium, cerium, lithium, potassium, sodium, europium, calcium, or a combination thereof are added to halide crystals to improve their scintillation properties.

[0003] Scintillator crystals can be produced by a Czochralski growth process, where a seed crystal contacts a melt located in a crucible and is then drawn away from the melt to produce a crystal boule. For example, raw materials can be loaded into a crucible before the start of the growth process, or the mixture of raw materials can be added into the crucibles during the growth process. FIG. 1 depicts a device 100 that is used to produce a crystalline boule. The device 100 comprises a furnace 102 that contains cooling tubes (not shown) disposed in its walls. Fluid flowing through the cooling tubes can be used to extract heat from the furnace. The furnace 102 contains a crucible 104 having a shelf 105 into which a combination of the desired halide along with the dopant are fed.

[0004] Both the halide along with the dopant (both typically in powder form or in granulated form) are simultaneously fed to shelf 105 via a single delivery tube 1 16. The furnace 102 contains only a single delivery tube 116 with a single inlet port 118 that is in contact with a single feeder or a pair of alternating feeders (not shown). This delivery arrangement is used for delivering both the halide and the dopant to the furnace.

[0005] The shelf 105 as well as the crucible 104 are heated via heating coils 106 and 108 respectively. Heating occurs via resistance heating. The heating promotes melting of the halide and dopant, which then flow from the shelf 105 to the crucible 104 through holes (not shown)located in a wall 107 between the shelf 105 and the crucible 104. The melt 202 located in the crucible is used to produce a crystal boule as detailed below. The crucible 104 is surrounded by bricks or loose ceramic material (also referred to as ceramic beads) 1 14 that is added to the furnace lining to improve its insulation properties. The porous nature of the bricks or beads creates gas pockets within the lining, which reduces heat transfer and helps maintain a stable and uniform temperature inside the furnace. This insulation is crucial for controlling the temperature gradient during crystal growth and ensuring the stability of the process.

[0006] A pull rod 110 having a crystal holder 208 and a seed crystal 206 affixed to its lower end is dipped into the melt 202 and then slowly moved away from the melt (moved vertically) while undergoing rotary motion. The rotary motion of the pull rod 110 is obtained by rotary communication with a first motor (not shown). The rotary motion either clockwise or counterclockwise is used to control the interface shape of the crystal boule 204 while it is in the melt. The translation motion is used to control the pull rate of the boule by extracting the boule from the melt under a controlled translation rate. The translational motion refers to the linear movement of the pull rod (or boule) either upward or downward, which controls the rate at which the boule is extracted from the melt. This means that the pull rod moves vertically in a straight line to pull the crystal boule 204 out of the melt at a controlled speed.

[0007] During the drawing of the crystal boule 204, the crucible 104 may be rotated in a direction opposite to the direction of rotation of the pull rod 110. The rotary motion of the crucible 104 is brought about by a shaft 112 that derives its rotary motion from a second motor (also not shown).

[0008] One of the drawbacks of the aforementioned method (of manufacturing crystal boules) is that some of the dopant evaporates during the process. During the simultaneous addition of the dopant and the halide, some of the dopant evaporates from the shelf 105 and gets deposited on the inside walls of the furnace. This evaporation results in a waste of the dopant material. Another drawback is uneven mixing of the dopant in the feeder filled with halide raw material. In addition, each successive boule produced in the furnace contains varying amounts of dopant, which is undesirable. It is therefore desirable to devise a method and a device that can produce scintillators with minimal variations in the amount of dopant in the melt, in the crystal, which in turn leads to minimal property variations.SUMMARY

[0009] Disclosed herein is a device for manufacturing a scintillator comprising a furnace that includes a furnace wall; a crucible with a shelf disposed on an outer periphery of the crucible; where the shelf comprises a channel that is operative to hold a molten material and deliver the molten material to the crucible through a porous wall; a first delivery arrangement that is operative to deliver a scintillation material precursor to the shelf; a second delivery arrangement that is operative to deliver a dopant precursor directly to the crucible; where the scintillation material precursor and the dopant precursor do not contact each other prior to being delivered to the crucible; and a heating coil disposed inside the furnace wall and outside both the crucible and the shelf; where the scintillation material precursor and the dopant precursor are melted via resistance heating of the crucible and the shelf.

[0010] Disclosed herein is a method for manufacturing a scintillator crystal boule, the method comprising charging a scintillation material precursor to a shelf via a first delivery arrangement; charging a dopant precursor directly to the crucible via a second delivery arrangement; where the shelf disposed on an outer periphery of the crucible; where the shelf comprises a channel that is operative to hold a molten material and deliver the molten material to the crucible through a porous wall; heating the shelf and the crucible via resistance heating; melting the scintillation material precursor causing it to flow to the crucible; contacting a melt in the crucible with a pull rod fitted with a seed crystal; and removing the pull rod from the melt at a rate effective to manufacture the scintillator crystal boule.

[0011] Disclosed herein is a scintillator crystal comprising a scintillator material and a dopant; where the dopant has a standard deviation of less than 0.04 in dopant concentration along the crystal draw direction; where the crystal draw direction is a direction in which a crystal is pulled or drawn from a melt during a crystal growth process.BRIEF DESCRIPTION OF THE FIGURES

[0012] FIG. 1 depicts a prior art device that is used to produce a crystalline boule; the device uses a single delivery inlet port and tube for feeding both the dopant precursor and the scintillation crystal precursor;

[0013] FIG. 2 depicts a device that is used to produce the crystalline boule with minimal dopant losses; the device uses a first delivery inlet port and tube for feeding the scintillation crystal precursor to the shelf and a second delivery inlet port and tube for feeding the dopant precursor to the crucible;

[0014] FIG. 3 is a graph of dopant concentration along the crystal growth axis for a scintillator crystal manufactured by the method disclosed with reference to the FIG. 1; and

[0015] FIG. 4 is a graph of dopant concentration along the crystal growth axis for a scintillator crystal manufactured by the method disclosed with reference to the FIG. 2.DETAILED DESCRIPTION

[0016] Disclosed herein is a device for manufacturing halide scintillator crystal boules that have minimal variation in dopant concentration across the volume of the boule (or across the length of the crystal along the crystal growth axis). The crystal growth axis is the direction in which the pull rod is drawn away from the melt to produce the crystal boule. The device also produces boules that have minimal dopant concentration variation between successive boules that are manufactured in the device. In short, there is minimal variation between a large number of boules produced over a period of time when compared with boules manufactured in the device of the FIG. 1 depicted above.

[0017] The device comprises a plurality of inlet ports, where each inlet port introduces a different ingredient (either a scintillator crystal precursor or a dopant precursor) into the melt. At least one of the inlet ports introduces a dopant precursor directly into the crucible, while the other inlet port introduces a scintillator crystal precursor directly into a shelf where it is melted and then introduced into the crucible to form a melt from which the crystal boule is produced. This method of introduction of the dopant prevents dopant evaporation in the furnace and results in the incorporation of a constant amount of dopant into the crystal boule and in the resulting scintillator crystals that are fabricated from the crystal boule.

[0018] FIG. 2 depicts an embodiment of the device 1000 that comprises a furnace 1102 that is used to produce a crystalline boule. The device 1000 comprises a furnace 1102 that contains cooling tubes (not shown) disposed in its walls. Fluid flowing through the cooling tubes can be used to extract heat from the furnace. The furnace 1102 contains a crucible 1104 having a shelf 1 105 into which only the desired scintillator crystal precursor (e.g., a halide such as, for example, sodium iodide) is directly fed via a first delivery arrangement 3000. In one embodiment, the dopant precursor (such as for example, thallium iodide) is fed directly to the melt in the crucible via a second delivery arrangement 4000. The device 1000 therefore contains a delivery system that comprises a first delivery arrangement 3000 and a second delivery arrangement 4000 that supply the crucible with different raw materials.

[0019] In this embodiment, the desired scintillator crystal precursor is never mixed with the dopant precursor prior to contacting it in the crucible. In another embodiment, most of the dopant precursor is fed directly to the crucible via the second delivery arrangement 4000 while a small portion of the dopant precursor is mixed with the scintillator crystal precursor and fed to the shelf 1105 via the first delivery arrangement 3000. The respective delivery systems are described in detail below.

[0020] The shelf 1105 is a walled channel that lies around the upper periphery of the crucible 1104. The inner wall of the shelf 1121 is porous and permits molten scintillator crystal precursor (or a combination of the scintillator crystal precursor and a portion of the dopant precursor) to enter the crucible 1104. The crucible 1104 and the shelf 1105 lie on a bed of ceramic beads or on refractory bricks 1114. The ceramic beads or refractory bricks 1114 help with temperature control in the furnace I 102. The refractory bricks or ceramic beads 11 14 are added to the furnace lining to improve its insulation properties. The porous nature of the bricks or ceramic beads creates air pockets within the lining, which reduces heat transfer and helps maintain a stable and uniform temperature inside the furnace. This insulation is crucial for controlling the temperature gradient during crystal growth and ensuring the stability of the process.

[0021] The shelf 1105 as well as the crucible 1104 are heated via heating coils 1106 and 1108 respectively. Heating occurs via resistance heating. The heating promotes melting of the scintillator crystal precursor (or a combination of the scintillator crystal precursor and a portion of the dopant precursor), which then flow from the shelf 1105 to the crucible 1104 through holes (not shown) located in a wall 1 121 between the shelf 1 105 and the crucible 1104. The melt 1202 located in the crucible 1104 is used to produce the crystal boule. The melt 1202 contained in the crucible 1104 is a combination of the dopant precursor (or a combination of the scintillator crystal precursor and a portion of the dopant precursor) obtained from the first delivery arrangement 3000 and the dopant precursor obtained from the second delivery arrangement 4000.

[0022] A pull rod 1110 having a crystal holder 1208 and a seed crystal 1206 affixed to its lower end is dipped into the melt 1202 and then slowly moved away from the melt (moved vertically) while undergoing rotary motion. The rotary motion of the pull rod 1110 is obtained by rotary communication with a first motor (not shown). The rotary motion either clockwise or counterclockwise is used to control the interface shape of the crystal boule 1204 while it is in the melt. The translation motion is used to control the pull rate of the boule by extracting the boulefrom the melt under a controlled translation rate. The translational motion refers to the linear movement of the pull rod (or boule) either upward or downward, which controls the rate at which the boule is extracted from the melt. This means that the pull rod moves vertically in a straight line to pull the crystal boule 1204 out of the melt at a controlled speed.

[0023] During the drawing of the crystal boule 1204, the crucible 1104 may be rotated in a direction opposite to the direction of rotation of the pull rod 1110. For example, if the pull rod is rotated in a first direction, then the crucible is rotated in a second direction that is opposite to the first direction. The rotary motion of the crucible 1104 is brought about by a shaft 1112 that derives its rotary motion from a second motor (also not shown).

[0024] In an embodiment, the device 1000 contains two delivery arrangements 3000 and 4000 each with respective feeding tube inlets 1118A and 1118B. The inlets 1118A and 1 1 18B are both located outside the furnace wall. Each inlet 1 1 18A and 1 1 18B is in communication with a delivery tubing 1116A and 1116B respectively. The delivery tubes 1116A and 1116B are partially located outside the furnace wall with the remainder being located inside the furnace wall. Both delivery arrangements - the first delivery arrangement 3000 and the second delivery arrangement 4000 - continuously deliver raw material (e.g., the halide and the dopant respectively) to the crucible 1104 and a crystal boule is continuously drawn from the melt in the crucible 1104 using the pull rod 1110 as detailed above. The respective delivery arrangements will now be described in detail.

[0025] The first delivery arrangement 3000 (shown in the ellipse) is used only for feeding the scintillator crystal precursor to the crucible 1104. The first delivery arrangement 3000 contains a first hopper 1 1 18A (also referred to herein as a first inlet port) that is in communication with a first delivery tubing 1116A. The first delivery tubing 1116A has an outlet 1120A that opens to the shelf 1105. The shelf 1105 lies on the outer periphery of the crucible 1104 and is separated from the crucible 1104 by a porous wall 1121.

[0026] The first delivery arrangement is primarily used for delivering the scintillator crystal precursor to the crucible 1 104 via the shelf 1 105. In an embodiment, it may be used to deliver a mixture of scintillator crystal precursor and dopant precursor to the shelf 1105. When a mixture of dopant precursor and scintillator crystal precursor is delivered to the shelf 1105 via delivery arrangement 3000, the amount of dopant is typically less than 50 wt%, preferably 0 to 40 wt% of the total dopant contained in the scintillator crystal. The remaining portion of the dopant precursor is delivered to the crucible 1 104 via the delivery arrangement 4000.

[0027] In an embodiment, the scintillator crystal precursor (or a mixture of the scintillator crystal precursor along with a portion of the total dopant precursor) is delivered to the first inlet port 1 1 18A. The scintillator crystal precursor (or the mixture of the scintillator crystal precursor along with a portion of the total dopant precursor) are fed via gravity through the first tubing 1116A to the shelf 1105. The contents of the first delivery arrangement 3000 that are delivered first to the shelf 1105 are melted by resistance heating. As may be seen in the FIG. 2, the shelf 1105 is heated via heating coil 1106. The crucible 1104 is heated via heating coil 1108. The heating coils 1106 and 1108 are used to heat the shelf and crucible respectively along with their contents and to produce the melt from which the crystal boule is manufactured. The molten contents of the shelf 1105 are then fed via gravity to the crucible 1104 through holes (not shown) in the wall 1121 that separates the shelf 1105 from the crucible 1104. The heating coils 1108 heat the melt while it is in the crucible 1 104.

[0028] The second delivery arrangement 4000 comprises a metering device 5000 that contains a separate feeder vacuum container 1140, a feed funnel 1150 that is used primarily for delivering dopant precursor, and a screw feeder 1160 that delivers the dopant to a second hopper port 1118B (also called the second inlet port 1118B). The second inlet port 1118B is in communication with a second delivery tube I 1 16B that has an outlet port 1 120B that opens directly to the crucible 1104.

[0029] The second delivery arrangement 4000 is used only for delivering dopant precursor directly to crucible 1104 into the melt 1202. It delivers the dopant precursor without any other materials (such as, for example, the scintillator crystal precursor). In an embodiment, the dopant precursor is not mixed with any other materials (such as, for example, the scintillator crystal precursor) when delivered via the second delivery arrangement 4000.

[0030] In a preferred embodiment, the dopant precursor is not mixed with the scintillator crystal precursor when delivered via the delivery arrangement 4000. In an embodiment, the dopant precursor in an amount of 50 to 100 wt%, preferably 60 to 100 wt%, and more preferably 80 to 100 wt% of the total dopant weight of the halide scintillator crystal is delivered by the second delivery arrangement 4000 to the crucible 1104. In an embodiment, a major portion of the dopant precursor present in the halide scintillator crystal is delivered directly to the crucible 1104 via the second delivery arrangement, while a minor portion of the dopant precursor is delivered indirectly to the crucible 1104 via the first delivery arrangement. Indirect delivery implies that the dopant is delivered to the crucible 1 104 via the shelf 1 105. In an embodiment, no dopant precursor is delivered indirectly to the crucible 1104.

[0031] The feeder vacuum container 1140 also known simply as a “feeder container”, is a type of vessel used in crystal growth processes, particularly in the Czochralski (CZ) method. In an embodiment, the feeder container 1 140 comprises an enclosure that contains the feed funnel 1150 and the screw feeder 1160 within it. The feeder container serves the purpose of providing a controlled atmosphere, often under vacuum conditions, to supply the dopant precursor to the crystal growth zone. The feeder container is a vessel in communication with the crucible that holds the dopant precursor. It ensures a continuous supply of the dopant precursor to the growth zone. The feeder container is designed to maintain the desired atmosphere, such as a controlled vacuum or inert gas environment, to prevent contamination and control the growth conditions. Maintaining a controlled atmosphere within the feeder container is useful for ensuring the quality and purity of the crystal being grown. Vacuum conditions are often used to minimize impurities and reduce the risk of gas bubbles or inclusions in the crystal boule and the scintillator crystals derived therefrom.

[0032] The feeder container may also be designed to maintain the dopant precursor at a specific temperature to ensure proper flow and consistency during the crystal growth process. Temperature control is useful for achieving uniform crystal growth and desired material properties. The feeder container is at room temperature. Both first and second feeders, like the growth furnace, are at about 60 to 100 mm of mercury (Hg) of argon (Ar) gas pressure throughout the growth process.

[0033] The dopant precursor is introduced through the feed funnel 1150 into the screw feeder 1160 via an inlet port (not shown). The feed funnel 1150 and the screw feeder 1160 are located in the feeder vacuum container 1 140. This prevents contamination of the dopant precursor with atmospheric moisture during the delivery of the dopant precursor to the crucible.

[0034] The screw feeder 1160 is typically a single screw extruder that transports the dopant precursor from the inlet port (located at the feed funnel 1150) to an outlet port (not shown) located above the second inlet port 1118B. The screw of the screw feeder 1160 is operated at a speed sufficient to permit the addition of a desired amount of dopant precursor into the crucible. The screw feeder delivers granulated or powdery raw material to the growth zone by controlling the rate of material flow. This flow rate is carefully regulated to achieve a desired concentration of the dopant in the melt 1202 and subsequently in the crystal 1204.

[0035] The second inlet port 1118B may be inside the feeding container or lie below the outlet port of the screw feeder 1 160 and is in communication with a second tube 1 1 16B that has an outlet port 1120B that opens directly to the crucible 1104.

[0036] In one embodiment, in one method of using the device 1000, the first delivery arrangement 3000 delivers raw materials (scintillator crystal precursor) to the shelf 1105. These raw materials are loaded into the first inlet port and are delivered to the shelf 1 105 via the first delivery tube. The heating coils 1106 and 1108 heat the raw materials to melt them. Simultaneously, but separately, the second delivery arrangement 4000 delivers dopant precursor directly to the crucible 1104. The dopant precursor is metered and delivered via the screw feeder to the second inlet port and the second delivery tube.

[0037] The heating coils heat the shelf and the crucible to melt the scintillator crystal precursor. The dopant precursor is delivered directly into the melt 1202 via the feeding tube 1116B and gets mixed into the melt. The dopant precursor and scintillator crystal precursor are miscible with each other in the melt and blend in the melt to form a homogeneous doped scintillator crystal material. The pull rod with seed crystal disposed thereon is introduced into the melt and withdrawn upwards and away from the melt under rotation in a first direction. The crucible may also be rotated in a second direction that is opposite to the first direction. The drawing of the pull rod from the melt results in the formation of the crystal boule as the homogeneous doped scintillator crystal material solidifies. The crystal boule may be cooled and then divided into pixels or crystal plates for use in PET and SPECT devices. In an embodiment, the crystal boule comprises a single crystal.

[0038] Exemplary scintillator crystal precursors include sodium iodide, cesium iodide, lanthanum bromide, lanthanum chloride, strontium iodide, or a combination thereof. Exemplary dopants include thallium, cerium, lithium, potassium, europium, calcium, or a combination thereof. A preferred scintillator crystal precursor is sodium iodide.

[0039] The dopants are added to scintillator crystal precursors to improve their scintillation properties. The dopant upon addition to the scintillator crystal precursor produces the scintillator crystal. The dopants may be added directly to the crucible in elemental form or in the form of a salt. Exemplary dopant precursors include halides of thallium, cerium, lithium, potassium, europium, calcium, or a combination thereof. Exemplary halides include iodides, chlorides, fluorides or bromides of thallium, cesium, lithium, potassium, europium, calcium, or a combination thereof.

[0040] The scintillator crystals produced by this method have significantly smaller concentration variations across the volume of the crystal or across different crystals manufactured during successive production runs using the device. In an embodiment, scintillator crystals produced by the device 1000 depicted in the FIG. 2 have a dopant variation acrosssuccessively produced batches of less than or equal to 0.034, preferably less than or equal to 0.03, preferably less than or equal to 0.025. Scintillator crystals (having the same intended composition) produced by the prior art device 1000 depicted in the FIG. 1 have a dopant variation of greater than or equal to 0.138. Dopant variation is expressed as a standard deviation of the dopant concentration from the mean value along the entire crystal length.

[0041] The device and the method detailed herein are exemplified by the following nonlimiting examples.EXAMPLEExample 1

[0042] This example was conducted to demonstrate the difference in dopant concentration between the conventional method of mixing the scintillation crystal precursor and the dopant precursor and delivering the mixture to the shelf and the method disclosed herein where the scintillation crystal precursor and the dopant precursor are delivered separately to the melt. Both methods used the same concentration of dopant precursor in the scintillator crystal. The only difference is the method of delivery of the ingredients to the crucible.

[0043] This example uses sodium iodide scintillators doped with thallium. The scintillation crystal precursor (the halide) is sodium iodide, while the dopant precursor is thallium iodide. Equivalent compositions were manufactured using the method detailed in the FIG. 1 (where both the dopant and the halide were mixed together prior to melting and added to the shelf) and the method detailed in the FIG. 2 (where the halide and the dopant were added separately). In FIG. 1, the molten material containing the halide (sodium iodide) and the dopant (thallium iodide) were mixed and delivered first to the shelf. They were melted while in the shelf and then transported from the shelf to the crucible under the influence of gravity. In FIG. 2, the halide is delivered to the shelf where it is melted and then fed to the crucible under the influence of gravity, while the dopant is added separately and independently of the halide directly to the melt in the crucible.

[0044] Both crystal boules were drawn and were then tested to determine dopant concentration. The melt temperature in the crucible is above the melting point, 651°C. The pull rod is rotated at a speed of 1.5 rpm and pulled away from the melt at a rate of 2.5 millimeters per hour.

[0045] FIG. 3 depicts dopant concentration variation along the crystal growth axis when the halide and dopant are mixed together and added jointly to the crucible as detailed in theFIG. l, while FIG. 4 depicts dopant concentration variation along the crystal growth axis when the halide and dopant are added separately to the crucible as detailed in the FIG.2. Measurement of the thallium concentration along the crystal growth axis reveals nonuniformity of thallium distribution (FIG. 3). In crystals grown with the separate screw feeding system, dopant concentration appears to be more uniform (FIG. 4).

[0046] Inductively coupled plasma mass spectrometry (ICP-MS) was used to measure dopant concentration. Small crystal samples were extracted from the crystal boule along the length. The samples were digested in a solvent and injected into the mass spectrometer analyzer of the test machine to measure the concentration of the dopant against a standard reference sample.

[0047] The aforementioned device (of FIG. 2) and the method involved therein permits precisely controlled dopant precursor feeding rates. This results in a more consistent delivery of the dopant precursor into the melt of the halide precursor (the scintillation crystal precursor) and in a more uniform impurity distribution along the crystal boule.

[0048] This method of separately feeding the scintillator crystal precursor and the dopant results in reduced evaporative loss of the dopant. As noted above, the dopant is added directly into the melt during axial growth, so there is no evaporation of the dopant from the crucible shelf. When thallium iodide is used as the dopant in a halide scintillator crystal (according to calculations based on the model of thallium distribution and experimental measurement), the evaporative loss of thallium iodide from the shelf is around 33 weight percent of the total thallium iodide raw material used during mixed feeding.

[0049] Observed consumption of thallium iodide per one full crystal changed from 2.3 kilogram (kg) with mixed feeding to 1.5-1.6 kg with separate feeding. About 700 g of dopant is saved per each full-size crystal.

[0050] This method (disclosed with respect to the FIG. 2) is advantageous in that the addition of the dopant to the crucible may be continued when halide feeding is stopped due to a production problem and crystal pulling is on hold. With the conventional mixed feeding method (as shown in the FIG. 1), if there is a problem with the scintillator crystal precursor feeding setup (e.g., the sodium iodide feeding setup), the growth process is stopped and the partially manufactured crystal discharged. With the feeding method disclosed in the FIG. 2 (the disclosed method), the growth process can be kept on hold for hours and continue when the production issue is resolved.

[0051] The method is advantageous because of the ability to re-dry the scintillator and dopant precursor materials independently from one another. If the scintillator crystal precursor is not mixed with the dopant precursor, then hydrated scintillator crystal precursor can be re-dried using a standard heating-drying procedure.

[0052] Multiple steps in the raw material preparation procedure may also be eliminated using the disclosed method (as described with regards to the FIG. 2). In addition, the steps that are used in the new disclosed method are simpler and less difficult to perform. The list of preparation steps includes loading and weighing of the scintillator crystal precursor and dopant precursor, transfer of the dopant precursor into evacuated ampules with dry scintillator crystal precursor powder, shaking and mixing of the loaded ampules, and so on. The disclosed method includes 3 simpler preparation steps involved with the separate feeding setup: (1) weighing of the dopant precursor granules used for a full boule growth, (2) loading of the dopant precursor charge into the separate feeder funnel 1150; and (3) vacuum pumping the separate feeder container 1140 for 10 minutes and then connecting it to the crystal growth furnace.

[0053] While the invention has been described with reference to some embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A device for manufacturing a scintillator comprising: a furnace that includes a furnace wall; a crucible with a shelf disposed on an outer periphery of the crucible; where the shelf comprises a channel that is operative to hold a molten material and deliver the molten material to the crucible through a porous wall; a first delivery arrangement that is operative to deliver a scintillation material precursor to the shelf; a second delivery arrangement that is operative to deliver a dopant precursor directly to the crucible; where the scintillation material precursor and the dopant precursor do not contact each other prior to being delivered to the crucible; a heating coil disposed inside the furnace wall and outside both the crucible and the shelf; where the scintillation material precursor and the dopant precursor are melted via resistance heating of the crucible and the shelf.

2. The device of Claim 1, where the first delivery arrangement comprises a first tube inlet port and a first delivery tube; where the first tube inlet port lies outside the furnace.

3. The device of Claim 1 , where the second delivery arrangement comprises a screw feeder, a second tube inlet port and a second delivery tube; where the second tube inlet port lies outside the furnace and where the screw feeder delivers the dopant to the second tube inlet port.

4. The device of Claim 1, further comprising a pull rod having a seed crystal at an end; where the pull rod is operative to contact the melt in the crucible.

5. The device of Claim 4, where the pull rod is drawn away from the crucible to form a crystal boule.

6. The device of Claim 3, where the screw feeder is disposed in a feeder vacuum container.

7. The device of Claim 6, where the screw feeder meters the dopant that is delivered into the crucible.

8. The device of Claim 6, where the feeder vacuum container controls temperature and pressure at a feed funnel that delivers dopant to the screw feeder.

9. The device of Claim 1, where the first delivery arrangement is operative to further deliver a portion of the dopant precursor to the shelf.

10. The device of Claim 9, where the portion of the dopant precursor delivered to the shelf is smaller than a remainder portion of the dopant precursor delivered directly to the crucible.

11. A method for manufacturing a scintillator crystal boule, the method comprising: charging a scintillation material precursor to a shelf via a first delivery arrangement; charging a dopant precursor directly to the crucible via a second delivery arrangement; where the shelf disposed on an outer periphery of the crucible; where the shelf comprises a channel that is operative to hold a molten material and deliver the molten material to the crucible through a porous wall; heating the shelf and the crucible via resistance heating; melting the scintillation material precursor causing it to flow to the crucible; contacting a melt in the crucible with a pull rod fitted with a seed crystal; and removing the pull rod from the melt at a rate effective to manufacture the scintillator crystal boule.

12. The method of Claim 11, where the scintillation material precursor is sodium iodide, cesium iodide, lanthanum bromide, lanthanum chloride, strontium iodide, or a combination thereof.

13. The method of Claim 11, where the dopant precursor is halide of thallium, cerium, lithium, potassium, europium, calcium, or a combination thereof.

14. The method of Claim 11, further comprising rotating the pull rod and the crucible in opposite directions from one another or in the same direction at controlled rates.

15. The method of Claim 11, further comprising charging a portion of the dopant precursor via the first delivery arrangement with a remainder being charged to the crucible via the second delivery arrangement.

16. The method of Claim 15, where the portion of the dopant precursor charged via the first delivery arrangement is smaller than a remainder portion of the dopant precursor charged via the second delivery arrangement.

17. A scintillator crystal comprising: a scintillator material and a dopant; where the dopant has a standard deviation of less than 0.04 in dopant concentration along the crystal draw direction; where the crystal draw direction is a direction in which a crystal is pulled or drawn from a melt during a crystal growth process.

18. The scintillator crystal of Claim 17, where the dopant has a standard deviation of less than or equal to 0.034 in dopant concentration along the crystal draw direction.

19. The scintillator crystal of Claim 17, where the scintillator material is sodium iodide, cesium iodide, lanthanum bromide, lanthanum chloride, strontium iodide, or a combination thereof.

20. The scintillator crystal of Claim 17, where the dopant is thallium, cerium, lithium, potassium, europium, calcium, or a combination thereof.

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