WO2012046953A2

WO2012046953A2 - Pyroelectric crystal x-ray generating device using radiant heat

Info

Publication number: WO2012046953A2
Application number: PCT/KR2011/006438
Authority: WO
Inventors: 최재호
Original assignee: 단국대학교 산학협력단
Priority date: 2010-10-05
Filing date: 2011-08-31
Publication date: 2012-04-12
Also published as: KR101094128B1; WO2012046953A3

Abstract

The present invention relates to a device for generating X-rays by means of an accelerated electron beam created by the potential difference between an X-ray target and surface charges induced on both end surfaces of a pyroelectric crystal by irradiating radiant heat onto the crystal. A high-energy electron beam is generated by inducing a temperature change in a pyroelectric crystal through the irradiation of radiant heat, thereby minimising temperature deviation in the diametral direction and the length direction of both end surfaces of the pyroelectric crystals, thereby overcoming the size limitations and the structural limitations of pyroelectric crystals used in the prior art and increasing the potential difference which results from increasing the number of induced surface charges. The performance of X-ray generator devices is improved by using the electron beam.

Description

Pyroelectric Crystal X-ray Generator by Radiant Heat

The present invention relates to a pyroelectric crystal X-ray generator by radiant heat, and in particular, radiant heat is irradiated to the pyroelectric crystal to minimize the temperature variation in the length and axial direction of the pyroelectric crystal and increase the temperature of the pyroelectric crystal. It is known that the surface charge induction does not increase or decrease in proportion to the temperature rise in the pyroelectric crystals of a certain size or more because the temperature difference between the heat source contact section and the opposite cross section of the pyroelectric crystal with low heat capacity and low thermal conductivity is large. Provides an X-ray generator that overcomes the limitations.

In the heating method by radiant heat irradiation, radiant heat penetrates into the inside of the pyroelectric crystal during radiant heat irradiation and simultaneously heats the inside and the outside of the pyroelectric crystal, thereby minimizing the temperature deviation in the longitudinal direction and the axial direction of the pyroelectric crystal. Surface charge induction can be maximized.

Pyroelectric phenomenon is a phenomenon in which spontaneous crystals are cut in a direction perpendicular to the polarization direction, and a certain heat is applied to the crystals to induce spontaneous polarization by inducing surface charges having different polarities on both sides of the crystal. Charges induced on the surface form a potential difference large enough to generate X-rays.

Pyroelectric crystals, which are anisotropic crystals, are polarized at equilibrium and have a total dipole moment even in the absence of an external electric field. When the pyroelectric crystal is cut in a direction perpendicular to the polarization direction, surface charges having different polarities are induced at both ends of the cut surface, and thus spontaneous polarization (P _s ) exists in the absence of an external electric field or temperature change. When heat is applied to such a pyroelectric crystal, a change in spontaneous polarization (ΔP _S ) occurs, which is called a pyroelectric effect. The pyroelectric effect forms an electric field (greater than 100 keV) that is large enough to emit electrons or generate effective radiation. The electric field is proportional to the surface charge induced. The magnitude of the surface charge per unit area is given by ΔP _S = γΔT when the pyroelectric crystal is heated. Where γ is the pyroelectric constant and ΔT is the temperature change of the pyroelectric crystal. It can be seen that the amount of surface charge induced with the pyroelectric crystal increases in proportion to the temperature change. Since the surface charge of the pyroelectric is multiplied by the cross-sectional area, the total charge of the cross-section of the pyroelectric crystal is Q = γΔTA, where A is the cross-sectional area. The potential difference due to the surface charge thus induced is V = Q / C.

The magnitude of the electric field in a device composed of pyroelectric crystals and targets

Equation 1

Given by

Also, in a device where two pyroelectric crystals are arranged to induce different charges, the magnitude of the electric field

Equation 2

Is given by

The electric field formed by the pyroelectric crystal has the distance between the pyroelectric crystal and the target as shown in Equation (1). (d_gapThe shorter the), the higher the electric field and the distance d between the two crystals, as shown in equation (2)._gapThe closer to), the longer the length (L) of the pyroelectric crystal, and the greater the temperature change, the greater the induced electric field.

In order to induce charge on the cross-section of the pyroelectric crystal, the heat conductivity of the pyroelectric crystal during heating or cooling must be large to facilitate heat transfer. However, the typical thermal conductivity of pyroelectric crystals is ^45mJ / cm- ^sec for LiTaO ₃ , which is comparable to the glass fiber used for building insulation. In general, other than the second electric crystal LiTaO ₃ also has a thermal property similar to the LiTaO _3. Due to the thermal characteristics of the above-mentioned superelectric crystals, the heat source contact end surface and the opposite surface when heated by a resistance heating or a thermal conduction method using a thermoelectric cooling device (TEC), which is a method of heating a pyroelectric crystal used in the prior art. Temperature difference between the two.

The temperature rise-drop due to the thermal conduction is determined according to the thermal conductivity of the crystal, and when the crystals are connected in the longitudinal direction, the temperature deviation between the two cross-sections becomes larger, and as a result, the surface charge does not increase even if the length of the pyroelectric crystal becomes longer.

The prior art increases the potential difference by causing the polarity of the charge induced in the cross-sections of the two pyroelectric crystals to face the other side in order to increase the potential difference. This concept has a limit that can only increase the potential difference by twice. The reason why this limitation is difficult to overcome is that when a long pyroelectric crystal is used or two crystals are connected in series in the longitudinal direction of the crystal, the conventional method of heating by contact resistance heating method shows that the temperature variation of the crystal in the longitudinal direction is not sufficient. Increased and temperature deviations across the pyroelectric crystals result in slowing or decreasing the potential difference.

In the prior art, a method of arranging two pyroelectric crystals, one of the methods for doubling the induction electric field, facing each other in the cross section of the crystal having the opposite polarity of the surface charge, in which case the electric field induced by the pyroelectric crystal As shown in Equation (2), the closer the distance (d _gap ) of the two crystals facing each other, the wider the cross-sectional area (A) of the pyroelectric crystal, the longer the length (L), and the larger the temperature change, the induced electric field is induced. Becomes large.

In order to induce the temperature change of the crystal, the heat conductivity of the crystal must be large when it is heated to facilitate heat transfer, thereby reducing the temperature deviation of both ends of the crystal. However, if the thermal conductivity of the material is small, if it is heated from one side of the material, the heat transfer has a low thermal conductivity and thus has a temperature deviation from the opposite side. In this case, the longer the length of the sample, the greater the temperature deviation.

The thermal conductivity of a typical pyroelectric crystal is 45 mJ / cm ^-sec for LiTaO ₃ , which is comparable to that of glass fiber optic insulation used for building insulation. Experimentally, a thermoelectric crystal with a low thermal conductivity of 30 ° C when the temperature of the heating surface between the two ends of the crystal having a diameter of 5 mm and a length of 20 mm is 110 ° C is obtained. When connected in series in the direction, it is limited to increase the temperature of the crystal while maintaining a small temperature difference in the longitudinal or axial direction of the pyroelectric crystal.

Conventional pyroelectric crystal heating method is a contact method by resistance heating. Since heat transfer depends on heat conduction, the longer the temperature deviation between the heat source contact surface of the pyroelectric crystal having low thermal conductivity and the opposite surface, the larger the pyroelectric crystal length is. Brings a deviation. This increase in temperature has a problem that results in a significant slowdown of the potential difference increase or decrease over a certain length.

In order to increase the potential difference of the pyroelectric crystal device due to heat conduction and to improve the performance of the X-ray generator, in order to increase the size of the pyroelectric crystal or to facilitate the construction of the device, the pyroelectric method used in the conventional art is a pyroelectric device. It is difficult to reduce the temperature deviation of the crystal cross section.

In the present invention, in order to overcome the limitations of the prior art as described above, the potential difference using a pyroelectric crystal longer than 10 mm, which is known as the limitation of the present technology, is minimized by minimizing the temperature deviation of the length and the axial direction of the pyroelectric crystal by the radiation heat irradiation method. It is an object of the present invention to provide a device for generating high energy X-rays by increasing.

The present invention is a vacuum container; A pyroelectric crystal installed in the vacuum vessel; An X-ray target provided in a direction in which the induced charge generated in the pyroelectric crystal is generated in the vacuum vessel; It provides an X-ray generating apparatus including a radiant heat irradiation apparatus for heating the pyroelectric crystal to generate surface induced charges to impact the X-ray target to generate X-rays.

The radiant heat irradiation apparatus is a radiant heat source that converts electrical energy into radiant energy, or collects infrared lamps or solar radiant energy, or is disposed spirally around the pyroelectric crystal.

The radiant heat irradiation apparatus is mounted inside or outside the vacuum vessel.

The pyroelectric crystals include one or more pyroelectric crystals connected in a longitudinal direction, and two or more of the pyroelectric crystals are in a longitudinally aligned form, or two or more crystals are connected to each other by a predetermined distance on a side of different charge polarities. It characterized in that it has one of the forms facing each other.

The X-ray generator according to the present invention further includes a cooling device for heat dissipation around the pyroelectric crystal.

According to the present invention configured as described above, when the pyroelectric crystal is irradiated with radiant heat to increase the temperature of the pyroelectric crystal, the radiant heat penetrates into the pyroelectric crystal during radiant heat irradiation, thereby simultaneously heating the inside and the outside of the pyroelectric crystal. Even in the pyroelectric crystals with long lengths and large cross-sectional areas, the induced surface charges are increased by increasing the length and cross-sectional area by minimizing the temperature variation in the longitudinal and axial directions, thereby increasing the electric field by maximizing the surface conversion. You get The increase in the electric field will improve the electron and ion acceleration performance, greatly improving the X-ray generation performance using this device.

When the pyroelectric crystal is irradiated with an infrared lamp or a solar radiation-concentrated radiation source as described above, a pyroelectric crystal longer than the length (20 mm or more) than the conventional technique using the contact method is used, or candles connected in series in the longitudinal direction are used. Even with the use of electric crystals, the limitation of the prior art is overcome by heating with a minimum temperature deviation in the longitudinal axis direction of.

Increasing the temperature of the pyroelectric crystal by radiating heat to the pyroelectric crystal increases the temperature of the pyroelectric crystal and minimizes the temperature variation in the longitudinal and axial directions even in the pyroelectric crystal with a long cross-sectional area. Is increased, resulting in an increase in the electric field. The increase of the electric field will improve the electron and ion acceleration performance, greatly improving the X-ray generation performance using this device.

1 is a view schematically showing an X-ray generator according to an embodiment of the present invention,

2 is a view schematically showing an X-ray generator according to the prior art,

3 is a view schematically showing an X-ray generator according to an embodiment of the present invention;

4 is a view schematically showing a pyroelectric X-ray generator to which a reflective target according to an embodiment of the present invention is applied, and

5 is a view schematically showing an X-ray generator according to an embodiment of the present invention.

The conventional method of heating a pyroelectric crystal is a contact method by resistance heating and a thermoelectric effect device (TEC). Since heat transfer is dependent on heat conduction, the gap between the heat source contact surface of the pyroelectric crystal having small heat capacity and thermal conductivity and the opposite side thereof is different. The longer the temperature deviation is, the longer the pyroelectric crystal is. Such a temperature deviation is a limitation of the prior art that results in a significant slowdown of the potential difference increase (or the length of the pyroelectric crystal) is reduced above a certain length (10 mm).

In order to overcome this problem, the heat transfer in the pyroelectric crystal should be carried out by heat transfer rather than heat conduction. Non-contact method of irradiating a pyroelectric crystal with a radiant heat source focused on an infrared lamp or solar light, which is longer than the length used in the prior art (20 mm or more), in the longitudinal axis direction of pyroelectric crystals connected in series in the longitudinal direction or in the longitudinal direction. By minimizing the temperature deviation of the heating to overcome the limitations of the prior art.

A pyroelectric crystal is an anisotropic crystal and has a constant value of a dipole moment that has been polarized even without an external electric field applied in a constant equilibrium state.

When this pyroelectric crystal is cut perpendicular to the polarization axis, the surface positive charge is charged on one surface of the cut surface and the surface negative charge on the other surface. Thus, the polarization value of a crystal is called spontaneous polarization without external electric field and temperature change. When the pyroelectric crystal is heated by changing the temperature of the pyroelectric crystal, the spontaneous polarization value changes. This phenomenon is called the pyroelectrie effect. The surface charges charged by the pyroelectric phenomenon form a large electromagnetic field, and the electric potential difference caused by the electric field emits electrons, and in the case of LiTaO ₃ , a typical pyroelectric crystal, it is formed by a pyroelectric crystal having a diameter of 10 mm and a length of 10 mm. The potential difference is about 100 keV.

In order to improve the performance to the application level, it is necessary to increase the induced surface charge for the practical use of the high energy generator by the pyroelectric crystal. In order to increase the surface charge, there is a method of increasing the temperature change of the pyroelectric crystal or increasing the cross-sectional area and length.

The method of enlarging the temperature change is determined by the nature of the crystal and has its limit value. That is, when the temperature of the crystal is heated above the Curie temperature, the pyroelectricity of the pyroelectric crystal is permanently dissipated. The Curie temperature of BaTiO ₃ , a typical pyroelectric crystal, is 393 K (absolute temperature), LiTaO ₃ is 813 to 970K, and LiNbO ₃ is 1488K. That is, LiTaO ₃ crystals lose their superelectricity when heated to 540 ° C or higher. However, the heat capacity of most pyroelectric crystals is 470J / ^kgK and the thermal conductivity is 45 mJ / cm ^-sec , which ^limits the temperature of the pyroelectric crystals up to Curie temperature without temperature variation in both cross-sections and axial directions.

Figure 2 shows an example of the X-ray generator by the resistance heating method of the prior art. As shown, the heat source 60 is in contact with one side of the pyroelectric crystal 10 to heat the pyroelectric crystal 10 by conduction. The X-ray generator configured as described above can increase the induction of surface charge by increasing the length and cross-sectional area of the pyroelectric crystal 10. However, when the length is increased, the pyroelectric crystal 10 is a heat source due to temperature characteristics. The temperature difference between the surface in contact with (60) and the surface not in contact with (60) becomes large. This temperature deviation causes the number of surface charges to increase no more than a certain length. As a result of the current study, it is reported that the surface charge does not increase over a length of 10 mm. In addition, when the cross-sectional area is increased, a temperature difference between the surface of the pyroelectric crystal and the center of the pyroelectric crystal is generated, and as a result, the increase in the surface charge is slowed down so that the generated energy does not increase even if the length of the pyroelectric crystal is longer than 10 mm. Therefore, the X-ray energy also does not increase.

In order to overcome the above-mentioned slowdown or decrease in the rate of increase of the potential difference, a method of using a long pyroelectric crystal is a method of heating a temperature distribution at a high temperature in the longitudinal direction of the crystal by radiative heat irradiation or by heating two or more pyroelectric crystals. There is a method of increasing the potential difference by connecting pyroelectric crystals in series with non-contact heating.

In the heating method by radiant heat irradiation, the radiant heat applied is transmitted to the pyroelectric crystal, so that the pyroelectric crystal with low thermal conductivity can be uniformly heated in the longitudinal direction and the axial direction by simultaneously heating the inside and the outside of the pyroelectric crystal. Overcoming the size limitations of the crystals leads to increased surface charge induction and thus high potential differences. In addition, the method of arranging the pyroelectric crystals can be freely configured, which is convenient for constructing a structure capable of focusing electrons and ions in the future, and the potential difference derived from each pyroelectric crystal increases in proportion to the number of pyroelectric crystals. The result is high energy X-rays.

Hereinafter, with reference to the drawings will be described in more detail the configuration of the present invention. Figure 1 (a) is a longitudinal cross-sectional view showing an embodiment of the X-ray generating apparatus according to the present invention having a linear radiation heat irradiation device 20, Figure 1 (b) is a cross-sectional view of Figure 1 (a), FIG. 3 (a) is a longitudinal sectional view showing an embodiment of an X-ray generator with a spiral radiant heat irradiation apparatus 21, FIG. 3 (b) is a cross sectional view of FIG. 3 (a), and FIG. 4, and 5 is a cross-sectional view showing another embodiment of the X-ray generator according to the present invention.

As shown, the X-ray generator according to the present invention is a vacuum vessel 30, pyroelectric crystals (10, 11, 14), radiation heat irradiation device 20, spiral radiation heat irradiation device 21, beryllium transmission window 70 and an X-ray target 75. Reference numeral 80 is an X-ray, 50 is a negative charge.

Pyroelectric crystal 11 is installed inside the vacuum vessel 30, and maintains a degree of vacuum of about 10 ^-4 ~ 10 ^-3 Torr.

Meanwhile, the beryllium transmission window 70 is installed in the vacuum container 30 to transmit and radiate X-rays.

The X-ray target 75 is installed in the advancing direction of the vessel by generating an X-ray by collision of electric charges generated in the

pyroelectric crystals

10, 11 and 14. The X-ray target 75 is installed as shown in FIGS. 1, 3, and 5 in the case of a transmissive type, and is mounted at a position having a predetermined angle with the charge propagation direction as shown in FIG. 4 in the case of a reflective type, and generates the generated X-ray 80. ) Is emitted through the beryllium transmission window 70. In addition, the X-ray target 75 may have a thickness of a few micrometers, the thickness of the target having a different value depending on the induced potential difference and the target material.

The pyroelectric crystal 11 is installed inside the vacuum vessel 30, and examples of representative pyroelectric crystals include LiTaO _3, BaTiO _3, LiNbO _3, and the like. The pyroelectric crystal 11 is heated from room temperature to 110 ° C by the radiant heat irradiation apparatus 21, and the charges induced in the cross section are concentrated on the surface to form a high potential difference. Only one pyroelectric crystal 10 may be installed as shown in FIG. 1, a single long pyroelectric crystal 11 as shown in FIG. 5 (a) may be used, and in the longitudinal direction as shown in FIG. 5 (b). It may include two or more pyroelectric crystals 14 to be connected. Two or more of the pyroelectric crystals 14 may be aligned in the longitudinal direction, or two or more crystals may be connected to face each other at a predetermined distance with respect to a surface having different polarities.

The radiant heat radiating apparatus 21 may be a device for converting electrical energy into radiant energy, such as an infrared lamp, or a device for focusing solar radiant energy. The radiant heat irradiation apparatus 21 is preferably arranged spirally around the pyroelectric crystal as shown in Figs. 3, 4 and 5, because it can exert thermal efficiency. It is also apparent that it may have other shapes, such as straight, cylindrical, single looped, or the like. Such a radiant heat irradiation apparatus 31 may be mounted inside or outside of the container 30.

The operation of the X-ray generator according to the present invention configured as described above will be described in more detail.

1 is a cross-sectional view showing an X-ray generator for heating the pyroelectric crystal 10 by the radiant heat irradiation apparatus 20, wherein the radiant heat irradiation apparatus 20 heats the pyroelectric crystal 10 with radiant heat, Charges induced in the cross section of the electrical crystal 10 aggregate on the surface to form a high potential difference, and these charges are radiated toward the X-ray target 75 to collide with the X-ray target 75 to cause the X-ray 80 to break. Will occur. In this case, the thickness of the X-ray target 75 is preferably several micrometers. The thickness of the target 75 has a different value depending on the induced potential difference and the target material.

The pyroelectric crystal 10 is installed inside the vacuum vessel 30 and the superelectric crystal is applied by applying electrical energy to the radiant heat irradiation apparatus 20 while maintaining the vacuum degree of the vacuum vessel 30 at 10 ^-4 to 10 ^-3 Torr. The temperature of (10) is raised. The temperature of the pyroelectric crystal 10 increases from room temperature to 110 degrees Celsius. At this time, the temperature difference between the two end faces of the pyroelectric crystal 10 is much smaller than the temperature difference between the two end faces of the crystal when heated by the contact heating source 60 applied in the prior art as shown in FIG. The minimization of the temperature deviation of both ends of the pyroelectric crystal leads to surface charge more effectively when the crystal length is increased. As a result, the heating method by the radiant heat increases the electric field formed by the pyroelectric crystal in proportion to the increase in the length of the crystal, increases the acceleration voltage and greatly improves the performance of the X-ray generator using the same, thereby enabling commercialization. . Although the method of cooling the pyroelectric crystal 20 is not shown in the drawing, a heat sink or a heat sink fin is attached to the outside of the vacuum apparatus to perform a natural cooling method or a forced cooling method by heat conduction. Fig. 1 (b) is a cross sectional view of the X-ray generator shown in Fig. 1 (a).

FIG. 3 (a) is a cross-sectional view showing an embodiment in which a spiral infrared lamp is configured as a radiant heat irradiation apparatus 21 in the X-ray generator of FIG. 1, and FIG. 3 (b) is an X-ray generation in FIG. 3 (a). Cross section view of the device. The spiral radiant heat irradiation apparatus 21 has a structure in which the spiral radiant heat radiator 21 wraps around the vacuum vessel 30 in the same configuration as the X-ray generator shown in FIG. 1 and the pyroelectric crystal 10. . The spiral heat source 21 has a better temperature uniformity in the longitudinal direction and the axial direction of the pyroelectric crystal than the linear heat source 20 structure. The implementation conditions for heating the pyroelectric crystal by the spiral heat source are shown in FIG. It is the same as the implementation conditions of 1. Degree. 3 (b) is a plan view of the pyroelectric crystal 10 X-ray generator (Fig. 3 (a)) using the helical heat source 21.

4 is an embodiment of a pyroelectric X-ray generator to which a reflective target is applied. The X-ray target 75 is mounted at a position at an angle with the pyroelectric surface, and the generated X-rays are radiated by the X-ray 80 through the beryllium transmission window 70.

FIG. 5 (a) shows an embodiment of X-ray generation by a high energy generator which induces surface charge by heating radiation of a long pyroelectric crystal 11 by radiant heat. An example of inducing surface charge by mounting a pyroelectric crystal 11 of 20 mm or more, the length of which is more than the limit of the prior art, in a vacuum vessel and heating by radiant heat proposed in the present invention, the number of induced surface charges is proportional to the length of the crystal. To increase and overcome the limitations of the prior art. 5 (b) shows another example of increasing surface charge induction, in which two or more pyroelectric crystals are longitudinally aligned to induce a high potential difference between the crystal 14 and the X-ray target and generate X-rays. It is a way to increase the efficiency.

Claims

In the X-ray generator,

A vacuum vessel;

A pyroelectric crystal installed in the vacuum vessel;

An X-ray target provided in a direction in which the induced charge generated in the pyroelectric crystal is generated in the vacuum vessel;

And a radiant heat irradiation device for heating the pyroelectric crystal to generate X-rays.
The method of claim 1,

The radiant heat irradiation apparatus is an X-ray generating apparatus for converting electrical energy into radiant energy.
The method of claim 1,

The radiant heat irradiation apparatus is an X-ray generator that is a radiant heat source focusing on infrared lamps or solar radiation energy.
The method of claim 1

And the radiant heat irradiation apparatus is disposed spirally around the pyroelectric crystal.
The method of claim 1,

And the radiant heat irradiation device is mounted inside or outside the container.
The method of claim 1,

And the pyroelectric crystal comprises one or more pyroelectric crystals connected in the longitudinal direction.
The method of claim 6,

Two or more of the pyroelectric crystals have a form aligned in the longitudinal direction, or two or more crystals connected to each other having a form in which the opposite sides of the polarity of the charge is aligned at a distance.
The method of claim 1,

And a cooling device for heat dissipation around the pyroelectric crystal.
The method of claim 1,

And the X-ray target is a transmissive or reflective type.
The method of claim 1,

The vacuum vessel further comprises a transmission window through which the generated X-rays are transmitted.