Induced nuclear reactions: processes – systems – and elements – Testing – sensing – measuring – or detecting a fission reactor...
Utility Patent
1998-03-18
2001-01-02
Jordan, Charles T. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Testing, sensing, measuring, or detecting a fission reactor...
C250S352000, C250S370150, C376S254000, C062S051100
Utility Patent
active
06169775
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to apparatuses and equipment utilizing vacuum thermal insulation and, more particularly, to apparatuses and equipment for detecting radiation. Apparatuses and equipment for detecting radiation are widely used not only in facilities related to nuclear reactors and facilities related to accelerators but also in the fields of medical equipment, analysis equipment, nuclear physics, astrophysics, industrial instrumentation and the like utilizing radiation.
In conventional radiation detecting apparatuses wherein a radiation detecting element must be cooled, vacuum required for vacuum thermal insulation has been maintained by a physical absorbing material. Further, in order to reduce microphonic noises, a cooling rod has included a part formed by binding thin copper wires together (hereinafter referred to as “copper blade”).
A description will now be made on a physical absorbing material and a chemical absorbing material in the context of the present invention. Rare gases and stable gaseous molecules forming closed shell systems are absorbed by the surface of a solid due to the van der Waal's force. Such absorption is referred to as “physical absorption”. When atoms other than rare gases approach a surface, a chemical bonding force acts between the atoms and the surface to cause absorption. Such absorption is referred to as “chemical absorption”. The physical absorption and chemical absorption normally coexist depending on the type of the solid, the nature of the surface or the types and state of the gaseous molecules. For example, a porous chemical absorbing material can physically absorb a rare gas on its surface by the van der Waal's force, although only a very small amount. Further, even a physical absorbing material sometimes absorbs chemically active gaseous molecules by a chemical bonding force when they approach the surface thereof. A physical absorbing material in the context of the invention is an absorbing material which is intended mainly for physical absorption rather than chemical absorption, which is capable of absorbing various types of gas in a great amount because it is to serve the purpose of performing evacuation by absorbing various types of gases such as water, nitrogen, oxygen, CO
2
, CO, oxides, nitrides, carbides and carbon hydrides that deteriorate vacuum (hereinafter referred to as “absorption evacuation”), which exhibits an increased absorbing speed as a whole when cooled although the speed depends on the types and states of gases, and which discharges the gases it has absorbed as the temperature rises, although there is hysteresis. For example, activated carbon or molecular sieves or zeolite or silica gel or alumina or a mixture including at least one of those types of materials. A chemical absorbing material in the context of the invention is an absorbing material which is intended mainly for chemical absorption rather than physical absorption, which is capable of absorbing various types of gases in a great amount because it is to serve the purpose of evacuating various types of gases which deteriorate vacuum, and which exhibits an increased absorbing speed as a whole when warmed although the speed depends on the types and states of gases. For example, Ti or Zr or Mo or Ta or Nb or V or Al or Mg or Ba or Ca or Sr or Hf or Cr or W or Fe or Re or Ni or Co or Rh or Pd or Pt or Ir or Mn or Cu or K or an alloy including at least one of these types of metals.
Next, a vibration damping material according to the invention will be described. Synthetic resin, synthetic rubber, a porous substance, a special alloy or the like is used as the vibration damping material. Further, vibration damping materials made of special alloys include integral types and multi-layer types. Synthetic resin, synthetic rubber and porous substances have much out gas and low strength. A multi-layer alloy has low weldability and shapability. A radiation detecting apparatus which requires cooling needs to have a vacuum container and components made of materials having less out gas because it employs vacuum thermal insulation. Further, materials having high weldability are preferred. Integral vibration damping alloys have good processability and weldability and have less out gas. Among integral vibration damping alloys, alloys mainly composed of Mn and Cu have a significant effect of vibration damping. Especially, Mn—20Cu—5Ni (atomic percent), Mn—20Cu—5Ni—2Fe, Mn—20Cu—5Ni—2Fe—2Al, Mn—20Cu—5Ni—2Fe—5Al exhibit quite excellent vibration damping characteristics. A vibration damping material in the context of the invention is an alloy including at least Mn and Cu.
In order to achieve a sufficient effect of vacuum thermal insulation, it is normally required to achieve a degree of vacuum of 10
−4
Torr or less. However, even if the vacuum container is evacuated to high vacuum during the baking of the same, the vacuum is deteriorated beyond the degree of vacuum in a short period of time after the vacuum container is closed due to out gas and the like in the vacuum container. Under such circumstances, according to the prior art, when a radiation detecting element is cooled using liquid nitrogen or a refrigerator, a physical absorbing material is also cooled such that the cooled physical absorbing material achieves absorption evacuation below the degree of vacuum to cool the radiation detecting element under sufficient vacuum thermal insulation even if the degree of vacuum in the vacuum container has been deteriorated beyond the degree of vacuum. For example, a conventional radiation detecting apparatus will be described with reference to the drawings.
FIG. 5
shows a radiation detecting apparatus of a type which employs cooling by liquid nitrogen. Vacuum in a cryostat and a radiation detector capsule is separated at a septum
1
to allow each of them to be easily removed.
FIG. 6
shows the use of a refrigerator to separate vacuum in the cryostat and the radiation detector capsule at the septum
1
.
FIG. 7
shows a case wherein a refrigerator is used in the absence of a septum. In the case shown in
FIGS. 5 and 6
, a chamber into which a physical absorbing material is inserted (hereinafter referred to as “physical absorbing material chamber
2
”) is provided in each of the separated sections in thermal contact with a region to be cooled. In the case shown in
FIG. 7
, the cryostat and a radiation detecting element cup share common vacuum, and a physical absorbing material chamber
2
is provided in thermal contact with the region to be cooled. In either case, O-ring
3
made of synthetic rubber such as Viton was used as a vacuum seal, and the surface roughness of major parts in the vacuum container was 0.7 &mgr;mRa.
In the case of cooling using liquid nitrogen shown in
FIG. 5
, bubbles
29
of nitrogen are generated at the cryostat, and vibration occurs when they leave the cryostat. The vibration causes noises when propagated to the radiation detecting element and a fast FET amplifier
31
to deteriorate energy resolution. For this reason, a cooling rod
8
has conventionally included a part formed by binding thin lead wires (hereinafter referred to as “copper blade
30
”). Further, in the case wherein a refrigerator is used as shown in
FIGS. 6 and 7
, vibrations caused by a compressor
27
and cold finger
28
are propagated through the cryostat and the cooling rod
8
to the radiation detecting element and the fast FET amplifier
31
to again cause microphonic noises. In such an electrical cooling system, reduction of microphonic noises is pursued using the copper blade
30
of the cooling rod
8
similarly.
Problems to be Solved by the Invention
However, a physical absorbing material has not been able to provide a sufficient effect of absorption unless cooled to a low temperature and has not been able to cool a radiation detecting element under significant deterioration of vacuum. Further, vibrations caused by the bubbles
29
and refrigerator have been propagated to an outer pipe
32
of the cryostat in addition to the
Morita Mitsukazu
Saito Masaki
Takahashi Koji
Adams & Wilks
Jordan Charles T.
Keith Jack
Seiko Instruments Inc.
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