KR20120020255A - Methods and apparatuses of neutron generation driven by pyroelectric crystals using the radiation heat source - Google Patents

Abstract

PURPOSE: A method and an apparatus for generating a pyroelectric crystal neutron are provided to improve the generation and performance of an X-ray by enhancing electron and ion acceleration performance. CONSTITUTION: An induced charge is collected on the surface of a cross section of a pyroelectric crystal(11). The collected charge forms a high potential. The charge forms ionized gas by ionizing deuterium gas. The ionized gas is transmitted to a neutron target(75) doped with deuterium. D_D nuclear fusion is formed by colliding the ionized gas with the neutron target. The pyroelectric crystal is installed in a container(30). A temperature of the pyroelectric crystal rises by applying electric energy into a radiation heat source(21).

Description

Method and apparatus for generating neutrons by radiant heat {Methods and Apparatuses of Neutron Generation Driven by Pyroelectric Crystals using The Radiation Heat Source}

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 ionize the injected gas and accelerate the ionizing gas.

The present invention is a method and apparatus for minimizing the temperature variation in the length and axial direction of a pyroelectric crystal by radiating radiant heat to the pyroelectric crystal and increasing the temperature of the pyroelectric crystal, and the heat source contact of the pyroelectric crystal with low heat capacity and low thermal conductivity. The large temperature deviation between the cross section and the opposite cross section overcomes the limitations of the state of the art in that surface charge induction does not increase or decrease in proportion to temperature rise in pyroelectric crystals of a certain size or more. In the heating method by radiant heat irradiation, radiant heat penetrates into the inside of the pyroelectric crystal when radiant heat is irradiated, thereby simultaneously heating 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. Induction of surface charge can be maximized. Increasing the surface charge results in an increase in the number of neutrons generated.

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 when a temperature change is induced, 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 the temperature change of the ΔT pyroelectric crystal. It can be seen that the surface charge induced in 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

(1)

(One)

Given by

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

(2)

(2)

.

The relationship between nuclear fusion by deuterium bonding and neutron generation is as follows.

D + D → ³ He + n (3)

The electric field formed by the pyroelectric crystal increases as the distance between the pyroelectric crystal and the target (d _gap ) decreases as shown in Eq. (1), and the distance d between the two crystals as shown in Eq. _The closer the _gap ), the longer the length (L) of the pyroelectric crystal, and the larger the temperature change, the greater the induced electric field. The neutrons generated as a result of DD fusion using pyroelectric crystals also increase in number of neutrons as the length of the pyroelectric crystal (L) increases.

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 thermal conductivity of a typical pyroelectric crystal is 45 mJ / cm-sec for LiTaO ₃ , which is comparable to that of 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 properties 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 heat 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 both cross sections becomes larger, resulting in no increase in the surface charge even when the length of the pyroelectric crystal becomes longer. That is, the number of neutron generation no longer increases in pyroelectric crystals of a certain length or more. In other words, the number of neutron generation does not increase in pyroelectric crystals having a certain length or more.

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 in both cross-sections of the pyroelectric crystals result in slowing or decreasing the potential difference.

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 applied radiant heat penetrates the pyroelectric crystal and simultaneously heats the inside and the outside of the pyroelectric crystal so that the pyroelectric crystal with small thermal conductivity can be uniformly heated in the longitudinal direction and the axial direction. Overcoming the size limitations of the crystals leads to increased surface charge induction and thus high potential differences. In addition, the arrangement method of pyroelectric crystals can be freely configured, which makes it convenient to construct a structure that can focus electrons and ions in the future, and the potential difference derived from each pyroelectric crystal increases in proportion to the number of pyroelectric crystals. As a result, the number of neutrons increases due to the activation of DD fusion.

In the prior art, a method of arranging two pyroelectric crystals, which is one of the methods used as a method for inducing a high potential difference that can excite DD fusion, is disposed opposite the crystal cross-section of the opposite polarity of the surface charge. In this case, the electric field induced by the pyroelectric crystal has a length L as the cross-sectional area A of the pyroelectric crystal increases as the distance between the two crystals facing each other ( d _gap ) is close, as shown in Equation (2). The longer it is, the higher the temperature change is, the higher the induced potential difference is.

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 , comparable to that of glass fiber optic insulation used for building insulation. Experimentally diameter 5 mm, length 20 mm of the temperature of both ends the heating surface of the crystal 110 ^o C when the temperature difference is 30 ^o C so the low heat conductivity second electric determine if the length of the second electric crystal long and a large cross-sectional area also several crystals In the case of connecting in series in the longitudinal direction, there is a limit in increasing 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, and since the heat transfer depends on the thermal conductivity, the temperature deviation between the heat source contact surface and the opposite surface of the pyroelectric crystal with low thermal conductivity becomes larger as the length of the pyroelectric crystal becomes larger. Brings a deviation. This increase in temperature results in a significant slowdown of the increase in potential difference or a decrease over a certain length.

In order to increase the size of the pyroelectric crystal or to facilitate the construction of the device for the purpose of increasing the potential difference of the pyroelectric crystal device due to heat induction and improving the performance of the X-ray generator, the thermal conductivity method used in the prior art is a superconducting method. It is difficult to reduce the temperature deviation of both sections of the electric crystal. In the present invention, the potential difference is increased by using a pyroelectric crystal longer than 10 mm, which is known as a limitation of the state of the art, by minimizing the temperature deviation of the length and the axial direction of the pyroelectric crystal in a radiant heat irradiation method that can overcome the limitations of the prior art. To form a potential difference sufficient to achieve DD fusion and increase the number of neutrons generated thereby.

The conventional method of heating a pyroelectric crystal is a contact method by resistance heating and a thermoelectric effect device (TEC). Since the heat transfer depends on the heat conduction, the temperature between the heat source contact surface of the pyroelectric crystal having small heat capacity and thermal conductivity and the opposite side thereof is reduced. The longer the deviation, the longer the pyroelectric crystal, the larger the deviation. This temperature deviation is a limitation of the current technology, which results in a significant slowdown of the potential difference increase or a decrease in the length of the pyroelectric crystal 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 overheating with minimal temperature variation, it overcomes the limitations of the prior art and increases the number of neutron generation by DD fusion.

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 will greatly improve the X-ray generation, performance using this device.

Fig. : Conceptual Diagram of Pyroelectric Crystal Neutron Generator by Radiant Heat Irradiation
Fig. : Conceptual Diagram of Pyroelectric Crystal Neutron Generator by Conventional Resistance Heating Method
Figure 3. : Concept diagram of neutron generator connecting two pyroelectric crystals

A pyroelectric crystal is an anisotropic crystal having 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 potential difference caused by the electric field emits electrons, and in the case of LiTaO ₃ , which is 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.

The number of neutrons generated by the nuclear fusion of the prior art is 10 ² -10 ³ per ^{second, which} is one half of the small neutron generators currently developed, and the neutrons for use as portable baggage scanners in airports and ports, which are applications of portable neutrons. That's half the number. On the other hand, the advantage of the neutron generator developed using the pyroelectric crystal is that the size of the neutron generator based on the pyroelectric crystal is about one third of the current portable neutron generator compared to the small neutron generator developed at present. There is no need for a supply, and the price is around 1/30. In addition, when compared with the radioisotope, there is an advantage that the operator is not exposed to radiation and waste is safe when carrying or carrying it.

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 disappears permanently. The Curie temperature of BaTiO ₃ , a typical pyroelectric crystal, is 393 K (absolute temperature), LiTaO ₃ is 813-970 K, and LiNbO ₃ is 1488K. That is, LiTaO ₃ crystals lose their superelectricity when heated to 540 ° C or higher. However, most of the pyroelectric crystals have a heat capacity of 470J / kg? K and their thermal conductivity is 45 mJ / cm-sec, which limits the temperature of the pyroelectric crystals up to the Curie temperature without temperature variations in both cross-sections and axial directions.

Degree. 2 shows an example of a neutron generator by the conventional resistance heating method. In the related art, when the length and cross-sectional area of the pyroelectric crystal 10 are increased, the induction of surface charge can be increased. However, when the length of the pyroelectric crystal 10 is increased, the pyroelectric crystal 10 is in contact with the heat source 60 due to the temperature characteristic. The difference in temperature between the face and the face that is not will increase. 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 number of neutrons generated by DD fusion does not increase.

Degree. Numeral 1 is a neutron generation using the pyroelectric crystals 11 by the radiant heat irradiation 21 As an example, charges induced in the cross section of the pyroelectric crystals 11 aggregate on the surface to form a high potential difference, and these positive charges ionize the deuterium gas. The ionization gas is radiated toward the neutron target 75 doped with deuterium to collide with the neutron target to generate DD fusion, thereby generating neutrons. The pyroelectric crystals 11 are placed inside the vessel 30, and after degassing the gas in the 10 ^-6 Torr container, the deuterium gas is injected to maintain a vacuum degree of about 1 mTorr. Electrical energy is applied to the radiant heat source 21 to raise the temperature of the pyroelectric crystal 11. The temperature of the pyroelectric crystal increases from room temperature to 110 degrees Celsius. At this time, the temperature difference between the two end surfaces of the pyroelectric crystal 11 is shown in FIG. The temperature deviation of both crystal cross-sections is much smaller than in the case of heating by the contact heating source 60 applied in the prior art such as 2. Minimizing 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 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 neutron generating device using the same. Although the method of cooling the pyroelectric crystal 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.

Degree. 3 is an example of neutron generation by two or multiple pyroelectric crystals. Degree. In Fig. 3, two pyroelectric crystals 14 are stacked in series. An embodiment of a neutron generator comprising a spiral spiral infrared lamp as a radiant heat source. Degree. Neutrons are generated by D-D fusion using the same method and working environment as in 1.

11: long pyroelectric crystal
14: Determination of pyroelectrics connected in the longitudinal direction
21: spiral radiant heat generation-irradiation device
30: vacuum container
50: ionization gas
60: heating device by heat conduction
70 deuterium gas
75: deuterium target (neutron target)
80: neutron

Claims (3)

Method and apparatus for generating neutrons by D-D fusion by inducing charges on the cross section of pyroelectric crystal by radiation heat irradiation The method of claim 1, wherein the radiant heat includes radiant heat obtained by converting electrical energy into radiant energy, light energy amplified induced emission light, and solar radiant heat. The pyroelectric crystal of claim 1, wherein the pyroelectric crystal has a form in which a single crystal or two or more crystals are aligned in the longitudinal direction, or two or more crystals are connected to face each other at a predetermined distance on a surface having different polarities of charges.

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