US 3327491 A
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June 27, 1967 WINDOWLESS VACUUM CHAMBER FOR EXPOSING A COOLED DEVICE TO SUCCESSIVE SAMPLERS Filed June 8, 1966 irw IIIIIH km VACUUM PUMP I k x .1!
INVENT OR Martin 0. Andom'an Wp MM ATTORNEYS United States Patent 3,327,491 WINDGWLESS VACUUM CHAMBER FOR EXPOS- ING A COOLED DEVICE TO SUCCESSIVE SAM- PLERS Martin D. Andonian, Lexington, Mass, assignor to Andonian Associates, Inc, Waltham, Mass, a corporation of Massachusetts Filed June 8, 1966, Ser. No. 556,168 9 Claims. (Cl. 62-45) The present invention relates to cryogenic systems and more particularly to an apparatus for cooling to cryogenic temperatures and supporting in an evacuated chamber an element and for successively and directly exposing said element to various sources of radiations and emissions without disturbing the vacuum.
In recent years, sample analysis and treatment using cryogenic techniques have become increasingly important. In certain operations, it is desirable to expose to one another a pair of elements, such as a cooled detector and sample, or to expose a cooled sample to a source of radiation or particle emission without destroying the thermal and atmospheric environment of the cooled element. This operation is accomplished, according to the present invention, by incorporation of a vacuum lock in combination with the chamber surrounding the cooled element through which successive elements can be mounted, inserted and withdrawn as desired or through which various types of radiation and emission can be directed onto the cooled element. Thus, direct access of the cooled element is achieved without intervening membranes or windows and the cooled element environment is not adversely affected.
The present invention has particular utility in permitting low energy radiation or particle emission to reach a cryogenically cooled element without penetrating a conventional vacuum sealing window. Thus, the present invention is highly suitable for use with, inter alia, solid state radiation detection systems and systems for bombarding and irradiating cooled samples with high and low energy emissions and radiations from various types of sources such as infrared, ultraviolet, particle emissions, gamma ray, and the like.
The present invention is herein disclosed, by way of example, as a solid state radiation detection system using, for example, cryogenically cooled lithium-drifted germanium or silicon detectors.
Solid state detection systems are known wherein the detector is mounted on a heat exchange platform with the cooling medium delivery and return lines leading to and from the platform. The platform and detector are normally arranged in an evacuated chamber or can called a cold finger, and in order to maintain the vacuum therein and enable gamma and other ray peneration into the can, a thin widow is provided at one end thereof adjacent the detector position. However, because of the window, these systems have difficulty detecting low energy radiation such as alpha particle emission, low energy X-rays and the like.
The present invention incorporates a new cold finger design which includes a vacuum lock at the detector end thereof so that the need for a window is eliminated. Without an obstructing window, samples mounted on a movable platform are brought near the detector for analysis. Although this design is primarily intended for alpha particle, X-ray and other low energy radiation detection, it is appareunt that its use is not limited thereto.
One example of the present invention comprises an evacuated cold finger having a solid state detector mounted at the forward end and supported by a heat exchange platform which is cooled by circulating liquefied nitrogen,
helium, or the like. Unlike prior systems, the forward end of the cold finger is open and communicates with a vacuum lock which has a sample holding section at the forward end thereof and a gate section connected between the cold finger and sample holding section. The sample holding section includes a sample support platform mounted on an operating rod. To take a reading, the rod is pushed rearward through a windowless opening so that the sample comes into the immediate vicinity of the detector. After the reading is taken, the rod is withdrawn. Because of the windowless opening, the gate valve in the gate section is closed to preserve the vacuum in the col-d finger. Part of the sample holding section is then disconnected and a new sample mounted on the platform. After reconnecting the sample holding portion, a pump evacuates the interior of the vacuum lock prior to opening the gate valve. When a suitable pressure is reached, the gate valve is opened and another reading is then taken in the manner described.
It is therefore an object of the present invention to provide an apparatus which permits successive exposure of a cryogenically cooled device to various radiations or emissions without affecting the thermal and atmospheric environment of the cooled device.
It is also an object of the present invention to provide a new and improved windowless cold finger using a solid state detector in which samples are successively moved to the immediate vicinity of the detector.
It is another object of the present invention to provide a windowless cold finger in which a solid state detector is in free communication with the sample to be analyzed.
It is still another object of the present invention to provide a cold finger including a vacuum lock for windowless reading, said vacuum lock having a valve portion and a sample holding portion which can be disconnected from the valve portion when the valve is closed to permit changing of samples.
It is yet another object of the present invention to provide a new and improved detecting arrangement in which the sample is mounted on a movable platform which is moved into and out of a windowless cold finger without seriously affecting the vacuum therein.
Other and further objects of the present invention will become apparent with the following detailed description when taken in view of the appended drawings in which the only figure illustrates a longitudinal vertical section of the windowless cold finger and vacuum lock in accordance with the present invention.
With reference to the figure, a windowless cold finger generally indicated as 10 according to the present invention has a thin wall aluminum cylindrical body or can 14 which has a forward flange 12 and a rear flange 16. A closing base plate 1-7 is secured to the back of flange 16 by any suitable means. Can 14 is hollow throughout and is completely open at its forward end. A heat ex change detector mounting platform 18 is supported axially therein by low thermal conducting posts 20 connected from base plate 17 to the rear of platform 18. Platform 18 supports a solid state detector 22 near the forward end of can 14. Detector 22 can be a lithium-drift germanium diode, a lithium-drift silicon diode or the like.
A delivery tube 24 extends through base plate 17 and feeds a cooling fluid into passageways (not shown) within platform 18 in order to cool the same. An exhaust tube 26 also connected to the platform 18 communicates with the passageways therein and provides a return path for the warmed fluid. The cooling medium can be of any suitable type, such as liquefied nitrogen or helium which is normally stored under positive pressure in a conventional dewar (not shown) connected to feed the delivery pipe 24. The warm refrigerant moving through pipe 26 is vented to the atmosphere and the flow rate of the coolant may be varied to obtain the desired cooling rate. Coolant flow rate may be controlled by adjustment of drive pressure in the storage flask or by means of a throttling valve in either the coolant inlet or exhaust lines, although the method found to be most economical is to throttle the exhaust line flow. For further disclosure of one example of a workable cold finger, see United States patent application entitled Flexible Cold Finger for Cooling Samples to Cryogenic Temperatures by Robert C. Wright, Ser. No. 556,135 dated June 8, 1966.
In order to provide alternate isolation and communication with the interior of can through the forward windowless opening thereof, a vacuum lock 28 is mounted to the forward side of flange 12 by any suitable means. Vacuum lock 28 comprises a gate section 30 in the form of a conventional gate valve assembly which defines a pair of enlarged openings 56 coaxially aligned with can 14 and communicating with the interior thereof through the windowless opening. The inner walls of gate section 30 form an elongated chamber 58, said chamber having a portion which extends across the axis of openings 56. Chamber 58 houses an axially movable gate valve 60 which, when seated in a fully closed position, cooperates with the walls of the chamber to block or seal communication through the windowless opening of can 14. Gate valve 60 is provided with a threaded shaft 62, the exposed end of which terminates in a manually operated knob 64. Rotation of shaft 62 causes axial movement of gate valve 60 due to its cooperation with the threaded opening at the upper end of section 30.
Vacuum lock 28 also includes a sample holding section 32 which includes a cylindrical body 34 axially aligned with a windowless opening of can 14 and having a mounting flange 36 releasably connected to gate section 30 by any suitable means. Body 34 includes two separable parts 33 and releasably connected together by quick disconnect coupling 54 which includes an O ring seal 55 to prevent gas leakage. An evacuation port 52 communicates with body 34 through a manually operated valve 50. Port 52 is adapted to cooperate with a vacuum pump (not shown) for reasons outlined below. The sample holding part 33 of body 34 includes an axially aligned threaded cylinder 40 which slidably receives a stainless steel operating body 34 and is directed toward the windowless opening of can 14. To improve the sealing capabilities of cylinder 40, a pair of O ring seals 42 sandwiching a metallic washer-type follower 45 is arranged within a circular groove formed in cylinder 40 and clamped tight by-compression nut 48. A silicon grease lubrication is applied to that portion of rod 44 within cylinder 40 in order to improve the sealing characteristics of the combination. The length of operating rod 44 is sufficient to move the sample holding platform 46 through the windowless opening of can 14 and to position the sample near detector 22.
In operation gate valve 60 is moved to the closed or sealing position to block air passage through openings 56. The spaces then in communication with can 14 are evacuated by means not shown and after detector 22 is cooled to a predetermined low temperature by circulating the cooling medium in tubes 24 and 26, the sample holding part of body 44 is disconnected from part 35 by releasing quick disconnect 54. The sample to be analyzed is then mounted on platform 46 with rod 44 drawn to the right or to its forwardmost position. With the sample in place, part 33 is reassembled to gate part 35 and valve 50 is then opened to enable the vacuum within body 34 to be drawn by a vacuum pump (not shown) connected to evacuation port 52. With the proper pressure in body 34, valve 50 is closed and gate is axially withdrawn to clear openings 56 and expose the windowless opening of can 14.
To take a reading, operating rod 44 is telescoped through cylinder 46 and platform 46 moves through openings 56 to a position immediately adjacent detector 22. After the reading is taken or recorded, operating rod 44 is withdrawn and gate 60 is repositioned to block openings 56 and isolate the windowless opening of can 10. At this time, valve 50' is opened and the sample holding part 33 is again removed from gate part 35. The sample on the platform 46 can then be replaced by another sample and the operation as described above repeated.
Thus, there has been disclosed a radiation detector including a windowless cold finger can in combination with the vacuum lock and movable sample platform which obviates the need for a window between the detector and sample. The present invention can be used with great advantage with the elongated flexible line disclosed in the patent application identified above. It should be understood that various modifications can be made to the herein disclosed example of the present invention without departing from the spirit and scope thereof.
What is claimed is:
1. A cryogenic apparatus comprising an evacuated chamber housing a cryogenically cooled element and having a windowless opening, a vacuum lock comprising an element holding section and a gate section connected to said element holding section and to the windowless end of said chamber, said chamber, gate section and element holding section being in free communication through said windowless opening, said gate section having movable valve means which when closed isolate said chamber from said element holding section, said element holding section including a platform and means releasablycoupling said plat-form to said gate section so that when said sample is isolated said platform can be exposed to permit changing of elements thereon without affecting the conditions within said chamber, and means for posi tioning said platform in such a way that a direct line of sight between the cooled element and any elements on the platform exists at least partially through the windowless opening when said movable valve means is opened.
2. An apparatus as set forth in claim 1 further comprising means connected to the element holding section for evacuating the interior thereof.
3. An apparatus as set forth in claim 2 wherein said means for positioning said platform comprises an elongated rod having one end within said element holding section and its other end exposed and extending outwardly therefrom, said element holding section comprising a body having a quick disconnect coupling removably coupling said body to said gate section and further having means to slidably support said rod and align its direction of movement toward said cooled element.
4. An apparatus as set forth in claim 3 wherein said gate section has at least one opening aligned with the cooled element and said windowless opening and through which said platform can be moved, said gate section having walls defining a second chamber, said valve means including a gate valve movable in said second chamber between a closed position in which said gate valve blocks said opening in the gate section and an open position in which said gate valve unblocks said gate section openmg.
5. An apparatus as set forth in claim 4 wherein said second chamber is elongated and has one portion with its axis crossing the direction of movement of said platform, said gate valve blocking said gate section opening when positioned in said one portion of said chamber.
6. An apparatus as set forth in claim 1 wherein a heat sink platform is supported within said chamber and wherein the cooled element mounted thereon is a solid state detector and wherein the element mounted on said platform is a sample to be analyzed.
7. An apparatus as set forth in claim 3 wherein a heat sink platform is supported Within said chamber and wherein the cooled element mounted thereon is a solid state detector and wherein the element mounted on said platform is a sample to be analyzed.
8. An apparatus as set forth in claim 3 wherein a heat sink platform is supported within said chamber and wherein the cooled element mounted thereon is a solid state detector and wherein the element mounted on said platform is a sample to be analyzed, and wherein the direction of movement of said rod is such that said platform can penetrate said gate section and position the sample in the immediate vicinity of the detector.
9. A windowless radiation detector for enabling the sample to be analyzed to be moved near the detecting element without a window therebetween so that low energy radiation or emission can be detected comprising, a cylindrical hollow cold finger housing having a windowless opening at its forward end, a cold solid state detector supported within the said housing at a position near and just behind said windowless opening and generally coaxially aligned therewith, a vacuum lock comprising a sample holding section and gate section connected between and to said sample holding section and said forward end of said housing, said sample holding section comprising a hollow body generally coaxially aligned with said windowless opening and having a first part connected to the forward side of said gate section and having a second part provided with a quick disconnect coupling which is releasably connected to the forward end of said first part, said second part having a generally coaxially aligned cylinder at its forward end, an elongated operating rod releasably held in said cylinder, a pair of O ring seals sandwiching a washer-type metal follower being retained in said cylinder and contacting said operating rod to provide a sealed support therefor, a sample holding platform mounted at the back end of said rod within said body so that when said operating rod is moved rearward said platform can be positioned near said detector, valve means connected to said body to enable the space within said body to be evacuated, said gate section comprising an opening in each the forward and rear walls thereof, said openings being aligned with said windowless opening and being of such dimension to enable passage of said platform therethrough, the walls of said gate section further defining an elongated chamber, the axis of which crosses the axis of said openings of said gate section, the portion of said chamber in the region of said gate section openings communicating with said gate section openings, a gate valve axially movable in said chamber and being shaped to seat snugly in the last mentioned portion of said chamber to isolate the interior of said housing from the interior of said body, said gate valve provided with means to selectively move said gate valve toward the other portion of said chamber and thus unblock said gate section openings to enable said platform to be moved therethrough toward and away from said detector.
References Cited UNITED STATES PATENTS 2,096,539 10/1937 Gebauer 62-514 3,190,081 6/1965 Pytryga 62514 3,256,712 6/1966 Makowski 62514 LLOYD L. KING, Primary Examiner.