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| EEPROM array using 2-bit non-volatile memory cells with serial read operations |
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| Semiconductor blocking layer for preventing UV radiation damage to MOS gate oxides |
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| UV-blocking layer for reducing UV-induced charging of SONOS dual-bit flash memory devices in BEOL |
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Closed cycle gas cryogenically cooled radiation detector
| Details |
Inventors: Gallagher, Brian William; Blionas, Costas; Nicolosi, Joseph Anthony; Barbara, Richard;
Assignee: U.S. Philips Corporation (New York, NY)
Primary Examiner: Nguyen; Kiet T.
Assistant Examiner:
Attorney, Agent or Firm: Barschall; Anne E.
A radiation detector having an evacuated envelope, a radiation detector on a cold finger support in the evacuated space, a closed cycle gas cooling system to cool the cold finger to provide cryogenic operation of the radiation detector, and a getter in the evacuated space to maintain an evacuated condition. The evacuated envelope includes a radiation window. The radiation detector is preferably an X-ray detector employed in an energy dispersive spectrometry system. The evacuated space is preferably held at a pressure of less than about 1 mTorr to achieve molecular flow of remaining gas molecules, minimizing parasitic heat input. The closed cycle gas cooling system employs compressed refrigerant, which is precooled in a counterflow heat exchanger and allowed to expand in proximity to the cold finger, thus absorbing heat and maintaining cryogenic temperatures. A getter material, preferably activated carbon, is provided to absorb gasses and maintain the low pressure during operation. A vibration effect attenuation system is provided to reduce effect of cooler induced reduction in detector resolution. |
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DETAILED DESCRIPTION The present invention relates to a cryogenic radiation detection system having a radiation detector in an evacuated chamber in which the cryogenic condition is maintained by a closed cycle gas cryogenic cooling system.
The detection system preferably includes an X-ray detector or other radiation detector, mounted on a cold finger in a vacuum.
The cryogenic radiation detection system may be employed in energy dispersive radiation spectroscopy, e.
g.
, X-ray spectrometry, elemental analysis in electron microscopy, X-ray fluorescence analysis and nuclear spectroscopic analysis.
In order to achieve the necessary cryogenic operating temperatures for the detecting unit, while employing an efficient cooling system, it is necessary to maintain a vacuum level of at most 1.
sub.
-- 10.
sup.
-3 Torr inside the detecting unit.
This vacuum level reduces the parasitic heat input to the system by substantially eliminating conduction through any gas in the detecting system cryostat.
Available cryocoolers without this type of insulation will not reach operational temperatures at the detector cryostat necessary for low noise operation.
The closed cycle gas cryogenic system does not require a source of expendable liquid nitrogen, and allows use of a remotely located compressor/condenser unit.
The compressor is preferably air-cooled and electrically operated, and supplies high pressure refrigerant to the detecting unit.
The compressor/condenser is linked to the detecting unit by refrigerant supply and return lines.
The compressed refrigerant from the supply line is at approximately room temperature.
The compressed refrigerant is fed to a cryocooler in the detecting unit, where it is precooled by counterflow heat exchange from returning expanded refrigerant.
An expansion chamber is provided in the cryocooler where the precooled compressed refrigerant is allowed to expand, where it absorbs heat and cools the surrounding mass, which is in thermal communication with the cold finger of the detector, which in turn cools the detector
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