Closed cycle gas cryogenically cooled radiation detector

• US 5,811,816 A
• Filed: 08/07/1996
• Issued: 09/22/1998
• Est. Priority Date: 06/26/1995
• Status: Expired due to Fees

• Current Assignee: EDAX Incorporated (Ametek Incorporated)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Nicolosi, Joseph Anthony, Barbara, Richard, Blionas, Costas, Gallagher, Brian William
• Primary Examiner(s): NGUYEN, KIET TUAN
• Application Number:
  US08/692,965
• Time in Patent Office: 776 Days
• Field of Search: 250/370.15, 250/352, 250/310, 250/397, 62/51.1, 62/51.2, 62/50.7
• US Class Current: 250/370.15
• CPC Class Codes: F17C 2203/0337 Granular
• CPC Class Codes: F17C 2203/0345 Fibres
• CPC Class Codes: F17C 2203/0395 Getter
• CPC Class Codes: F17C 2205/0332 Safety valves or pressure relief valves
• CPC Class Codes: F17C 2205/0341 Filters
• CPC Class Codes: F17C 2221/014 Nitrogen
• CPC Class Codes: F17C 2223/0153 Liquefied gas, e.g. LPG, GPL
• CPC Class Codes: F17C 2223/033 Small pressure, e.g. for liquefied gas
• CPC Class Codes: F17C 2227/0353 using cryocooler
• CPC Class Codes: F17C 2227/0355 in a closed loop
• CPC Class Codes: F17C 2227/036 "Joule-Thompson" effect
• CPC Class Codes: F17C 2270/0509 "Dewar" vessels
• CPC Class Codes: F17C 2270/0518 Semiconductors
• CPC Class Codes: F17C 3/085 Cryostats
• CPC Class Codes: F25B 9/02 using Joule-Thompson effect; using vortex effect
• CPC Class Codes: F25D 19/006 Thermal coupling structure or interface
• CPC Class Codes: G01J 5/061 by controlling the temperature of the apparatus or parts thereof, e.g. using cooling means or thermostats
• CPC Class Codes: H01J 2237/002 Cooling arrangements
• CPC Class Codes: H01J 2237/2442 Energy-dispersive (Si-Li type) spectrometer
• CPC Class Codes: H01J 2237/2555 Microprobes, i.e. particle-induced X-ray spectrometry
• CPC Class Codes: H01J 37/244 : Detectors; Associated components or circuits therefor

Abstract

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.

Claims

1. An x-ray spectrometer comprising:

an electromechanical cryogenic cooler having a vibration of operation of at least a first level;

an x-ray detector that is cooled by the cooler, the detector having a desired energy resolution of at worst about 140 eV at 5.9 keV from ⁵⁵ Fe at 1000 cps with a 40 μ

S time constant, the detector requiring a vibration of at most a second level in order to achieve the desired energy resolution, the second level being lower than the first level; and

a vibration compensator, coupled between the cooler and the detector, the compensator insuring that the detector receives no more than the second level of vibration.

2. The x-ray spectrometer of claim 1 further comprising

an evacuated housing creating an evacuated space disposed about the x-ray detector, said space being susceptible to gradual vacuum degradation, said degradation causing deterioration of the energy resolution of the detector cumulative to any deterioration caused by said vibration;

and

a getter, disposed within the evacuated housing, said getter being in sufficient amount to maintain a vacuum level at which the compensator will cause the detector to achieve the desired energy resolution.