JP3130500B2 - Radiation detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to equipment utilizing vacuum insulation, and more particularly to equipment for detecting radiation. Equipment for detecting radiation is widely used not only in facilities related to nuclear reactors and accelerators, but also in fields such as medical equipment using radiation, analytical equipment, nuclear physics, astrophysics, and industrial measurement. .

[0002]

2. Description of the Related Art Conventionally, in a radiation detecting apparatus which requires cooling of a radiation detecting element, a vacuum for vacuum insulation is maintained by a physical adsorbent. Here, the physical adsorbent and the chemical adsorbent in the present invention will be described. Rare gas and stable gas molecules forming a closed shell system are adsorbed on the solid surface by van der Waals force. Such adsorption is called physical adsorption. When atoms other than the rare gas approach the surface, a chemical bonding force acts between the surface and the surface to cause adsorption. Such adsorption is called chemisorption. Depending on the type of solid and surface properties, and the type and state of gas molecules,
Physisorption and chemisorption are usually mixed. For example, a porous chemical adsorbent is capable of physically adsorbing a rare gas to the surface, albeit in a trace amount, by Van der Waals force. Further, even with a physical adsorbent, a chemically active gas molecule may be adsorbed by a chemical bonding force when approaching the surface.

[0003] The physical adsorbent in the present invention is mainly composed of physical adsorption rather than chemical adsorption, and is used for various substances such as water, nitrogen, oxygen, CO ₂ , CO, oxides, nitrides, carbides, hydrocarbons, etc. which are degraded in vacuum. It is an adsorbent that can adsorb a large amount of various gases in order to adsorb various gases and evacuate it (hereinafter referred to as adsorption exhaust). It differs depending on the type and state of the gas, but overall An adsorbent that releases an adsorbed gas when the temperature increases, although the adsorption speed increases by cooling and there is hysteresis. For example, it refers to activated carbon, molecular sieve, zeolite, silica gel, alumina, or a mixture containing at least one or more of these materials. The chemical adsorbent in the present invention is mainly a chemical adsorption rather than a physical adsorption, and is intended to adsorb and exhaust various kinds of gases that have been degraded in a vacuum. It means a material whose adsorption speed increases by heating as a whole, depending on the type and state of the gas. For example, Ti or Zr or Mo or Ta or Nb or V or Al or Mg or Ba or an alloy containing at least one or more of these metals.

[0004] In order to obtain a sufficient vacuum insulation effect, it is usually necessary to set the degree of vacuum to about 10 ^-4 Torr or less.
However, even if the vacuum container is evacuated to a high vacuum during baking, after the vacuum container is sealed, the vacuum deteriorates to a degree higher than the vacuum in a short period due to outgas or the like in the vacuum container. Therefore, when cooling the radiation detecting element using liquid nitrogen or a refrigerator, the physical adsorbent is also cooled, and even if the degree of vacuum inside the vacuum vessel is degraded to a vacuum higher than the vacuum degree, the cooled physical adsorption is performed. It is a conventional technique that the material is sucked and evacuated to the degree of vacuum or less to cool the radiation detecting element under sufficient vacuum insulation. For example, a conventional radiation detection apparatus will be described with reference to the drawings. FIG. 5 shows a radiation detector of the type cooled by liquid nitrogen. The cryostat and the vacuum of the radiation detector capsule are separated by a partition wall 1 so that each can be easily removed.

FIG. 6 shows a case where a cryostat is used and a vacuum between a cryostat and a radiation detector capsule is separated by a partition wall 1. FIG. 7 shows a case where a refrigerator is used and there is no partition wall. 5 and 6, the room into which the physical adsorbent is inserted (hereinafter, referred to as the physical adsorbent chamber 2) is placed in each of the separated portions so as to be in thermal contact with the low-temperature portion. I have. In the case of FIG. 7, the cryostat and the radiation detection element cup have a common vacuum, and the physical adsorbent chamber 2 is placed in thermal contact with a portion where the temperature becomes low.
In each case, an O-ring 3 made of synthetic rubber such as Viton was used for the vacuum seal, and the surface roughness of the main part inside the vacuum vessel was 0.7 μm Ra.

[0006]

However, if the physical adsorbent is not cooled to a low temperature, a sufficient adsorption effect cannot be obtained, and if the vacuum deterioration is large, the radiation detecting element cannot be cooled. The relation of heat energy in cooling is considered by the following equation.

Q = Q−q1 [P {Gp (Tp), Ps, Gi (t)}, Tc, Ts] −q2 (εi, Tc, Ts) −q3 Equation 1 q: cooling rod, physical adsorbent, Endothermic amount for cooling a cooled part such as a radiation detecting element Q: Heat absorbed by liquid nitrogen or a refrigerator q1: Inflow of heat into a cooled part by heat conduction of gas in vacuum q2: Heat radiation Q3: In addition, heat flow into the cooled part due to heat conduction of solid such as electric wiring to the radiation detecting element, Joule heat, etc. P ｛Gp (Tp), Ps, Gi (t)｝: degree of vacuum εi: infrared emissivity of vacuum inner wall and parts in vacuum Gp (Tp): amount of gas adsorbed by physical adsorbent Tp: temperature of physical adsorbent Tc: temperature of part to be cooled Tc = Tp Ps: Degree of vacuum when vacuum is sealed Ts: Environment Degrees Gi (t): Assume that the elapsed time Q from when sealed the vacuum is the value of the cooling capacity with liquid nitrogen or refrigerator, it is almost constant: the total amount of gas that is vacuum degradation t. q1 is the amount of heat flowing into a portion cooled by heat conduction caused by a gas such as a gas permeating the O-ring or outgas from the inner surface of the vacuum vessel, and the degree of vacuum P ｛Gp (Tp), Ps, Gi (T)｝,
It depends on the temperature Tc of the part to be cooled, the environmental temperature Ts, and the like. Also, q1 is the degree of vacuum P ｛Gp (Tp), Ps, Gi
(T)｝ decreases as the vacuum becomes higher, and increases as the difference between the temperature Tc of the portion to be cooled and the environmental temperature Ts increases. Degree of vacuum P {Gp (Tp), Ps, Gi (t)}
Depends on the amount Gp (Tp) of gas adsorbed by the physical adsorbent, the degree of vacuum Ps when the vacuum is completely sealed, the total amount Gi (t) of gas degraded in vacuum, and the like. Degree of vacuum P ｛Gp (T
p), Ps, Gi (t)} are the total amount of gas Gi (t) that is further degraded in vacuum as the amount of adsorption Gp (Tp) is larger and the degree of vacuum Ps when the vacuum is completely sealed is higher. t)
The lower the number, the higher the vacuum. The gas adsorption amount Gp (Tp) of the physical adsorbent increases as the temperature Tp of the physical adsorbent decreases. Total amount Gi of gas degraded in vacuum
(T) increases as the elapsed time t from when the vacuum is completely sealed is increased. q2 is the amount of heat flowing into the portion cooled by the thermal radiation, and depends on the infrared emissivity εi, the temperature Tc of the cooled portion, the environmental temperature Ts, and the like. Further, q2 decreases as the emissivity εi decreases, and increases as the difference between the temperature Tc of the portion to be cooled and the environmental temperature Ts increases.
q3 is the amount of heat flowing into a portion to be cooled due to heat conduction of a solid, Joule heat, or the like, such as electric wiring to the radiation detection element, and may be ignored because it is a small amount.

[0008] From the cooling capacity of Q, q is the above q1, q
This is the amount of heat absorbed after cooling the portion to be cooled, which is obtained by subtracting the inflow of thermal energy of 2, q3.
Therefore, when q is positive (q> 0), the part to be cooled is cooled. When q = 0, the temperature of the part to be cooled becomes constant (thermal equilibrium). If q is negative (q <0),
The temperature of the part to be cooled rises.

Hereinafter, description will be made with reference to the drawings to clarify the problem. Ge detection elements for detecting γ-rays are about 120
Unless cooled below K, sufficient performance cannot be obtained. In the case of a Si (Li) detecting element for detecting X-rays, the same cooling temperature is required. FIG. 8 is a diagram simulating a temperature change (hereinafter, referred to as a cooling curve) of a portion to be cooled after starting the cooling. The vertical axis represents the temperature of the portion to be cooled, and the horizontal axis represents the elapsed time from the start of cooling. Each curve is
This is the case where the degree of vacuum at the start of cooling differs due to vacuum deterioration.
From the smaller value of the degree of vacuum, curve H <curve I <
Curve J. Curve H draws a uniform curve and is approximately 100
While K reaches thermal equilibrium and maintains the cooling temperature (hereinafter referred to as cooling temperature maintenance), curve I has a portion where the angle decreases during cooling. This is because, in the case of the curve H, q is always sufficiently larger than 0 from the initial cooling to the time when the cooling temperature is maintained, whereas in the case of the curve I, q is sufficiently larger than 0 in the initial cooling, but the degree of vacuum is low. P ｛Gp (T
Since p), Ps, and Gi (t)} are bad, q1 and q2 increase as the temperature difference between the temperature Tc of the portion to be cooled and the environmental temperature Ts increases, and the angle decreases during cooling. Nevertheless, since q was slightly larger than 0, the physical adsorbent could be cooled down slowly but the adsorption amount Gp (T
Due to the increase in p), it was possible to adsorb to a high vacuum and cool down completely. In the case of the curve J, as in the case of the curve I, q is sufficiently larger than 0, so that the cooling proceeds to some extent. However, as the temperature difference between the temperature Tc of the portion to be cooled and the environmental temperature Ts increases, q1 increases. And the degree of vacuum P {Gp (Tp), Ps, Gi (t)} is the curve I
Therefore, q1 was larger than the curve I, and the temperature Tp of the physical adsorbent could not be further cooled, and reached thermal equilibrium (q = 0) during cooling.

[0010] If the physical adsorbent is cooled to a temperature close to the temperature of liquid nitrogen (77 K), the adsorption capacity is extremely large. That is, if cooling is performed immediately before the vacuum deterioration after baking and the temperature is reduced to around the temperature of liquid nitrogen, the gas Gi (t) resulting from the subsequent vacuum deterioration is sufficiently absorbed, and the cooling temperature is maintained for a long time. Can be held. However, if the baking is left for several months or more without cooling, and then cooling is performed, as described above, before the temperature of the physical adsorbent reaches the cooling temperature at which the gas Gi (t) caused by vacuum deterioration is sufficiently absorbed. It becomes thermal equilibrium and cannot be cooled.

The conventional radiation detecting apparatus requiring cooling has a cooling curve such as the curve I or the curve J in a short period of time because the vacuum deterioration is fast and only the physical adsorbent is used. I ended up with poor reliability. An object of the present invention is to improve a period in which cooling can be stably performed, which is an important factor relating to the reliability of a radiation detection apparatus requiring cooling.

[0012]

In order to achieve the above object, a radiation detecting apparatus according to the present invention has a main part in a vacuum vessel having a surface roughness of 0.1 μm Ra or less, and a metal seal on a vacuum seal part. used, also was between portions and the inner wall of the vacuum vessel to be cooled is interposed super insulation rate Shio down <br/>. Furthermore, a physical adsorbent and a chemical adsorbent are installed in a vacuum system, and are adsorbed and evacuated.

First, it will be described that q1 is reduced by reducing G (t) in the equation (1), thereby extending the period of stable cooling. In the present invention, the surface roughness of the main part in the vacuum vessel is reduced. This reduces the surface area and reduces microcracks and striations due to processing. Therefore, the amount of gas molecules adsorbed on the surface decreases. Further, since the surface is smooth, gas molecules are easily released during baking.
For these reasons, outgassing from the surface decreases and G
(T) becomes smaller. The smaller the surface roughness, the better, but from the viewpoint of reducing the thermal emissivity εi, it is desirable that the surface roughness be at least up to the mirror surface, that is, 0.1 μmRa or less.

Further, by using a metal seal that does not require vacuum grease in the vacuum seal portion, it is possible to prevent vacuum deterioration due to gas permeating the conventional synthetic rubber O-ring or outgas from vacuum grease, G (t) can be reduced. Secondly, it will be described that the period during which stable cooling can be performed is lengthened by reducing q2 in Equation (1). In the present invention, a super insulation is interposed between the portion to be cooled and the inner wall of the vacuum vessel. The super insulation is a film for shielding infrared rays of heat radiation, and it is desirable that the infrared radiation rate of both sides is small. Although one sheet is effective, it is more effective to arrange them without contact. In this case, there is a difference between the temperature of the film and the temperature of the adjacent film, and the effect is weakened when the films come into thermal contact with each other. Therefore, a mesh such as glass wool or polyester was used as a spacer for preventing the contact. In order to obtain a sufficient heat radiation shielding effect, it is desirable to stack several tens of layers with a set of a film for shielding infrared rays and a spacer. By using such a super insulation, it is possible to reduce the invasion of heat due to heat radiation and to reduce q2.

Third, the vacuum in the vacuum vessel was improved by installing a physical adsorbent and a chemical adsorbent in the vacuum system and performing adsorption and exhaust. The types of chemical adsorbents are those that are heated and evaporated (hereinafter referred to as evaporative chemical adsorbents), those that are not evaporated by heating only (hereinafter referred to as heated non-evaporable chemical adsorbents), and those that are used near room temperature. (Hereinafter referred to as a non-evaporable chemical adsorbent). If the surface of the chemical adsorbent is contaminated by gas adsorption, the adsorbing ability is lost. However, when heated, the chemical adsorbent can diffuse surface dirt due to adsorption into the interior, thereby restoring the adsorption ability. When using an evaporative chemical adsorbent, place the chemical adsorbent in a place where the radiation detection element, etc. cannot be seen, or place the radiation detection element, etc., so that the radiation detection element, electric circuit, insulator, etc. are not contaminated by evaporation. It is necessary to provide a wall or the like between the and the chemical adsorbent. On the other hand, the heated non-evaporable chemical adsorbent and the non-evaporable chemical adsorbent do not stain the radiation detecting element and the like. If the heating non-evaporation type chemical adsorbent or evaporative type chemical adsorbent is always heated, it is possible to always obtain a somewhat high adsorption speed, but infrared rays due to heat radiation from the adsorbent are absorbed by the part to be cooled. This may cause the cooling unit to warm up or cause noise when measuring radiation. In addition, the cooling unit may be warmed by heat conduction by a gas in a vacuum. Therefore, it is less preferable to constantly heat the chemical adsorbent. In this case, similarly to the method for dealing with contamination of the detection element and the like due to vapor deposition, a chemical adsorbent is placed in a place where the radiation detection element and the like cannot be seen, or a wall is provided between the radiation detection element and the chemical adsorbent. If provided, it can be dealt with.

Hereinafter, the results of investigating the effect of installing a chemical adsorbent on the radiation detector of FIG. 7 using a refrigerator will be described. The size of the vacuum vessel of the device is about 2 liters. The vacuum vessel is provided with a terminal for introducing a current from the outside into the vessel (hereinafter referred to as a current introduction terminal). Work in the vacuum vessel can be performed by removing the end cap. The surface roughness of the inner wall of the end cap was reduced to 0.02 μmRa by electrolytic composite mirror finishing. Further, 20 layers were provided on the inner wall of the end cap with a set of a 9 μm-thick infrared shielding film formed by aluminum evaporation on both sides of a polyester film and a 200 μm-thick polyester mesh spacer. The space between the cold finger tip and the radiation detecting element was thermally contacted by a cooling rod having good thermal conductivity. Further, the physical adsorbent chamber is configured to be in thermal contact with the cooling rod. A temperature sensor for measuring the cooling temperature was installed on the outer wall of the physical adsorbent room.

A heating non-evaporation type adsorbent component (hereinafter referred to as a heating non-evaporation type chemisorption component) in which a small heater for energization heating is wrapped with about 1 g of a chemical adsorption material containing Zr, V and Fe as main components. , And two electric wires for electricity supply are provided. This electric wire was fixed by being connected to two copper wires having a diameter of 0.8 mm which were connected to two current introduction terminals on the vacuum side, and was set in a vacuum vessel. Next, a room made of a glossy stainless steel sheet having a thickness of 0.1 mm is used as a wall, and the heated non-evaporable type chemisorption component is not visible from a cooled portion. Call). Next, the physical adsorbent from which the gas physically adsorbed by vacuum heating was removed was inserted into the physical adsorbent chamber. The end cap was placed on the body and baking was started.

Before use, a protective film is formed on the surface of the heated non-evaporable type chemical adsorption component in order to prevent the adsorption performance from being deteriorated due to the adsorption of the atmosphere. Therefore, after completion of baking, the protective film was removed by heating the non-evaporating type chemisorption part at 600 ° C. for 5 minutes.
Activation). First, to simulate vacuum degradation,
Dry nitrogen was introduced into the vacuum in the above state, the refrigerator was driven from various degrees of vacuum to perform cooling, and the result of evaluating the degree of vacuum at which stable cooling was possible is shown in FIG. Curve O is 2 × 10 ^-2 T
orr, curve P from 1 × 10 ⁻¹ Torr, curve Q
Is a case where cooling is started from 3 × 10 ⁻¹ Torr, and a curve P is a case where cooling is started from ¹ Torr. Curves O and P are uniformly cooled, and the cooling temperature is maintained at about 100K. Curve Q
Although the angle became small during the cooling, it was cooled to 100K, and the cooling temperature was maintained. Curve R became thermal equilibrium during cooling, and could only be cooled to about 230K.
In other words, to perform stable cooling with the detector of this configuration,
It is estimated that a degree of vacuum of about 1 × 10 ⁻¹ Torr or less (hereinafter, this degree of vacuum is called a cooling limit vacuum degree) is required.

Next, it can be cooled only to about 230K.
In the curve R, after the measurement, without stopping the refrigerator,
Reheat the molded chemisorption parts at about 600 ° C for 10 minutes (active
After heating, it is heated at about 500 ℃ or more to adsorb chemical adsorbent.
Reactivate the following to diffuse the surface dirt inside
), And measure the degree of vacuum and the change in cooling temperature.
The results are shown in FIG. The degree of vacuum before reactivation is
Since the adsorbent was cooled to about 230K, 1 Torr
2 × 10 from r^-1It was adsorbed and exhausted by Torr. this
After reactivation in vacuum, the degree of vacuum was 10^-FourT
It rapidly decreased to the orr level. For this reason, vacuum insulation is good
The cooling temperature begins to drop and is cooled down to about 100K
Was. At this time, the degree of vacuum for maintaining the cooling temperature depends on the physical adsorbent.
Than 10 ^-FiveIt has been adsorbed and exhausted to the Torr level
I understand.

Next, in the radiation detecting apparatus having the above-mentioned structure, the physical adsorbent and the heat non-evaporative type chemisorption part were exchanged, activated at an early stage of the baking, and the vacuum deterioration was measured for 5 days after the completion of the baking. FIG. 11 shows a comparison of vacuum deterioration between the present invention and a conventional radiation detection apparatus. It can be seen that the vacuum deterioration of the present invention is slower. By removing the data of vacuum deterioration for 5 days, the degree of vacuum after 10 years can be estimated. Even in the case of the present invention, it is estimated that vacuum deterioration of several Torr will occur after 10 years. It can be seen that the cooling limit vacuum degree is reached in about one month.

After the measurement for 5 days, reactivation was performed at about 600 ° C. for 5 minutes, and the change in the degree of vacuum was measured.
Shown in The horizontal axis represents the time from the start of reactivation, and the vertical axis represents the degree of vacuum. By this reactivation, the degree of vacuum is about 3 × 10
It can be seen that the gas is adsorbed and evacuated from ^-2 Torr to about 1 × 10 ^-3 Torr, and this degree of vacuum is maintained for tens of thousands of seconds. Thereafter, the surface of the suction component was soiled, the suction effect was almost lost, and the speed of vacuum deterioration returned to normal. From this, it is understood that the effect of adsorption and exhaustion accompanying the reactivation of the heated non-evaporative type chemical adsorption component used this time lasts only tens of thousands of seconds. 10 ^-4 Torr required for vacuum insulation
It can be seen that many chemisorbing components are needed to maintain the following vacuum with the chemisorbent alone for several years.

Next, FIG. 13 shows the results of measuring the change in the degree of vacuum in the radiation detecting apparatus having the above-mentioned configuration by changing the vacuum to 7 Torr with dry nitrogen and reactivating a new heated non-evaporable type chemical adsorption part. First, reactivation was performed at about 600 ° C. for 5 minutes. As a result, adsorption and exhaustion were performed from a vacuum of 7 Torr to 2 Torr. Next, at about 600 ° C, 1
After performing the reactivation for 5 minutes, the vacuum was sucked and evacuated to about 3 × 10 ⁻³ Torr, which was smaller than the cooling limit vacuum. FIG. 11 shows the result of the measurement and the above-described vacuum deterioration measurement.
It is estimated that stable cooling is possible for about ten years by using the heating non-evaporation type chemisorption component.

After this measurement, a cooling test was performed. As a result, a uniform cooling curve was drawn and the temperature was reduced to about 100 K because the gas was adsorbed and evacuated to a degree of vacuum smaller than the cooling limit vacuum. The chemical adsorbent can be heated and exhausted when exhaust is required. For example, if the degree of vacuum is set to be equal to or lower than the cooling limit vacuum before or at the beginning of cooling, stable cooling can be achieved. Therefore, it is desirable to have a means for automatically heating the chemical adsorbent before cooling or at the beginning of cooling, and to perform adsorption and exhaust to a degree of vacuum lower than the cooling limit vacuum.
In this case, the chemical adsorbent may be sufficiently adsorbed and evacuated, and may be automatically adsorbed and evacuated by using a means for automatically heating the chemical adsorbent for a certain period of time, or a means for measuring the degree of vacuum in the vacuum vessel and a means in the vacuum vessel. Using a means for automatically heating the chemical adsorbent from the measured value of the degree of vacuum, the chemical adsorbent may be heated and adsorbed and exhausted until the degree of vacuum becomes equal to or lower than the cooling limit vacuum degree. Further, using a means for manually heating the chemical adsorbent and a means for displaying the measured value of the degree of vacuum in the empty container, the chemical adsorbent is heated and adsorbed and evacuated until the degree of vacuum becomes equal to or lower than the cooling limit vacuum degree. Alternatively, the chemical adsorbent may be manually heated for a certain period of time.

When it is found that the cooling rate is slow or the target cooling temperature cannot be cooled due to poor vacuum when cooling from room temperature, the measured value of the temperature of the radiation detecting element or the vacuum container is used. The chemical adsorbent may be heated using a means for displaying the measured value of the degree of vacuum inside and a means for manually heating the chemical adsorbent, and may be adsorbed and evacuated to a normal cooling rate. Alternatively, the gas may be adsorbed and exhausted by using a means for heating the chemical adsorbent.

If it is found that the temperature of the radiation detecting element has risen due to the deterioration of the vacuum in maintaining the cooling temperature, the measured value of the temperature of the radiation detecting element or the measured value of the degree of vacuum in the vacuum vessel is obtained. Means for heating the chemical adsorbent, and means for manually heating the chemical adsorbent, and allowing the chemical adsorbent to be adsorbed and exhausted until the normal cooling temperature is maintained. Alternatively, the gas may be adsorbed and exhausted by using a means for performing the above.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the electrical connection of the radiation detection apparatus of the present invention. A temperature sensor and a vacuum sensor are connected to the measurement and control circuit, and these measured values can be displayed on a display device. Each sensor can be connected to two or more sensors. When the manual mode switch is turned on, the power supply for heating the chemical adsorbent is activated, and the chemical adsorbent heater heats the chemical adsorbent and can adsorb and exhaust the same. The automatic mode changeover switch can select a plurality of automatic modes. In each of the automatic modes, the power supply for heating the chemical adsorbent and the refrigerator can be operated by a program stored in the control circuit in advance. For example, when the cooling control start switch is turned on, before or at the same time as driving the compressor of the refrigerator, at the same time, a command to operate the heating adsorbent heating power supply until the indication of the vacuum sensor reaches the set vacuum degree, or a set period of time. If an instruction to operate the heating adsorbent heating power supply is stored, the apparatus can be operated in the set automatic mode. When cooling with liquid nitrogen, there is no refrigerator power supply and refrigerator. When the heating non-evaporation type chemical adsorption component is used as the chemical adsorbent, the chemical adsorbent heater is a heater by energization, but in the case of induction heating or heating by laser, the device is a chemical adsorbent heater. Becomes The following example is an example in which the heating non-evaporation type chemical adsorption component is used as a chemical adsorption material. FIG. 2 shows a radiation detection apparatus for cooling with the liquid nitrogen 25 of the present invention. The vacuum between the cryostat and the radiation detector capsule was separated by the partition 1 so that each could be easily removed. The surface roughness of the inner wall of the end cap 5 was reduced to 0.02 μmRa by electrolytic composite mirror finishing. Also, on this inner wall, 20 layers of superinsulation 6 were installed with a set of a 9 μm-thick infrared shielding film deposited on both surfaces of a polyester film with aluminum and a 200 μm-thick polyester mesh spacer. For the O-ring, a hollow metal O-ring 13 made of Al was used. Since the vacuum is separated by the partition 1, the stainless steel wall 1
1, a chemical adsorbent chamber 12, a heated non-evaporative type chemical adsorption part 10, a vacuum sensor 14, and a temperature sensor 9 were installed. Wiring such as signals from each sensor and power supply to the heating non-evaporating type chemical adsorption component 10 is output to the outside by the current introduction terminal 4 and is measured and controlled by the electric cord 15 by the electric cord 15 and the heating power supply for the chemical adsorption material. 17 was connected. After connecting the radiation detector capsule and the cryostat, the inside of each vacuum vessel was evacuated from the vacuum port and baked. Next, by inserting this cryostat into the dewar, the cooling rod 8 in the cryostat and
The physical adsorbent in the physical adsorbent chamber 2 that is in thermal contact with the cooling rod in the radiation detector capsule and the radiation detection element in the radiation detection element cup 19 are cooled. At the start of this cooling, by setting the cooling control start switch,
As described above, the heated non-evaporable type chemisorption component can be heated when necessary. FIG. 3 shows a case in which the cryostat and the vacuum of the radiation detector capsule are separated by the partition 1 using a refrigerator. Each vacuum vessel has a port for drawing a vacuum. In each vacuum vessel, a chemical adsorbent chamber 12 partitioned by a wall 11, a heated non-evaporable type chemical adsorption component 1
0, vacuum sensor 14 and temperature sensor 9 were installed as shown in FIG. On the rear panel 20, a display device 21, a cooling control start switch 22, a manual mode switch 23, and an automatic mode changeover switch 24 are installed. By setting the cooling control start switch 22, the refrigerator is driven, and the non-evaporable chemical adsorption component 10 can be heated when necessary. By driving the refrigerator, the cold finger tip 7 is cooled, and then the cooling rod 8, the physical adsorbent, and the radiation detecting element are cooled. FIG. 4 uses a refrigerator,
This is a case where the cryostat and the vacuum of the radiation detecting element are not separated by a partition wall. Therefore, the chemical adsorbent chamber 12,
One heating non-evaporation type chemical adsorption component 10, one vacuum sensor 14, and one temperature sensor 9 were installed.

[0027]

As described above, the surface roughness of the main part in the vacuum vessel of the radiation detector is set to 0.1 μm Ra or less, the metal seal is used for the vacuum seal part, the vacuum deterioration is slowed, and the cooling is performed. A super insulation is interposed between the part to be heated and the inner wall of the vacuum vessel to prevent the inflow of heat due to heat radiation, and a physical adsorbent and a chemical adsorbent are installed in the vacuum system. The period during which cooling can be performed stably can be improved by acting.

[Brief description of the drawings]

FIG. 1 is a diagram showing an electrical connection of a radiation detection device according to the present invention.

FIG. 2 is a radiation detection apparatus for cooling with liquid nitrogen according to the present invention.

FIG. 3 shows a radiation detecting apparatus in which the cryostat and the vacuum of the radiation detector capsule are separated by a partition using the refrigerator of the present invention.

FIG. 4 shows a radiation detecting apparatus in which the cryostat and the vacuum of the radiation detecting element are not separated by a partition using the refrigerator of the present invention.

FIG. 5 is a conventional radiation detection apparatus for cooling with liquid nitrogen.

FIG. 6 shows a radiation detection apparatus in which a cryostat and a radiation detector capsule vacuum are separated by a partition using a conventional refrigerator.

FIG. 7 shows a radiation detecting apparatus in which a conventional refrigerator is used and the vacuum of the cryostat and the radiation detecting element is not separated by a partition.

FIG. 8 is a diagram simulating a cooling curve when cooling from a different degree of vacuum in order to clarify a conventional problem.

FIG. 9 is a diagram showing a cooling curve when simulating vacuum deterioration and cooling from a different degree of vacuum in order to clarify the operation of the present invention.

FIG. 10 is a diagram showing an example in which, when thermal equilibrium is reached during cooling, cooling proceeds by applying a chemical adsorbent to maintain the cooling temperature in order to clarify the operation of the present invention. .

FIG. 11 is a diagram comparing vacuum deterioration of the present invention with conventional vacuum deterioration to clarify the operation of the present invention.

FIG. 12 is a diagram showing the degree of vacuum after reactivation and the time during which adsorption takes place in order to clarify the operation of the present invention.

FIG. 13 shows a graph showing the effect of the present invention.
After simulating the vacuum after years, by reactivating
FIG. 4 is a view showing that the gas is adsorbed and exhausted below a cooling limit vacuum degree.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Partition wall 2 Physical adsorbent room 3 O-ring made of synthetic rubber 4 Current introduction terminal 5 End cap 6 Super insulation 7 Cold finger 8 Cooling rod 9 Temperature sensor 10 Heating non-evaporation type chemical adsorption parts 11 Stainless steel wall 12 Chemistry Adsorbent chamber 13 Metal O-ring 14 Vacuum sensor 15 Electric cord 16 Measurement and control circuit 17 Power supply for heating chemical adsorbent 18 Dewar 19 Radiation detection element cup 20 Rear panel 21 Display device 22 Cooling control start switch 23 Manual mode switch 24 Automatic Mode switch 25 Liquid nitrogen 26 Power supply for refrigerator 27 Compressor 28 Cold finger

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01T 7/00 F25B 9/00 G01J 5/02

Claims (10)

(57) [Claims] An apparatus for detecting radiation by cooling a radiation detecting element to a low temperature by vacuum insulation, wherein the vacuum system includes
Adsorbent composed mainly of physical adsorption (hereinafter, referred to as a physical adsorbent)
When adsorbent composed mainly of chemical adsorption (hereinafter, referred to as chemical adsorption material) radiation detecting apparatus characterized by having a. 2. The method according to claim 1, wherein the physical adsorbent is mainly composed of carbon.
Porous material (hereinafter referred to as activated carbon) or molecular
-Sieve or zeolite or silica gel or aluminum
Mina or at least one of these materials
A mixture, wherein the chemical adsorbent is Ti or Zr.
Or Mo or Ta or Nb or V or A1 or
Is Mg or Ba, or at least one of these metals
2. An alloy containing at least one kind of metal.
The radiation detection apparatus according to claim 1. 3. A method for heating said chemical adsorbent.
The radiation detection apparatus according to claim 1, wherein: 4. Before or after cooling the radiation detecting element.
Has means to automatically heat the chemical adsorbent at the beginning of
The radiation detection apparatus according to claim 3, wherein 5. A method for manually heating the chemical adsorbent.
The radiation detection apparatus according to claim 3, further comprising a step . 6. A means for measuring a temperature of a portion to be cooled.
Or a means for measuring the degree of vacuum in the vacuum vessel.
The radiation detection device according to claim 1 or 2, wherein 7. A measured or true value of the temperature of the part to be cooled.
The chemical adsorbent is automatically detected from the measured value of the vacuum in the empty container.
The radiation detecting apparatus according to claim 6, further comprising heating means . 8. A method for heating said chemical adsorbent, comprising :
For measuring the temperature of the part to be removed or the degree of vacuum in the vacuum vessel
3. The method according to claim 1, further comprising:
Radiation detection device. 9. The heat-absorbing non-evaporable chemical adsorbent.
Claim 1, 2, 3, 4, 5,
The radiation detection device according to 6, 7, or 8 . 10. The radiation detecting element is kept at a low temperature by vacuum insulation.
In the vacuum system
Is a porous material mainly composed of carbon (hereinafter called activated carbon).
Or molecular sieve or zeolite or
Silica gel or alumina or at least these materials
Mainly physical adsorption consisting of a mixture containing at least one type
Adsorbent (hereinafter referred to as physical adsorbent)
Therefore, metals that increase the adsorption rate, or reduce these metals
Mainly chemisorption consisting of alloys containing at least one kind
Adsorbent (hereinafter referred to as chemical adsorbent)
A radiation detection device characterized by the above-mentioned .