Detector thermal cycling

Fig. 1 a shows a section of a Laue diffraction pattern of a LSGMO ciystal detected at room-temperature with a ciystal-detector distance of < 58 mm after the 4 thermal cycle. The Laue pattern shows multiplets splitting into 4 reflections, each one generated by Bragg reflections from its corresponding orientation state. The symbols TOl, T02, T03 and T04 (Fig. la) indicate different ferroelastic orientation states and corresponding reflections. 

Fill the Dewar with liquid nitrogen until overflow from the vent tube is observed. The detector itself has a high thermal capacity. It wiU take at least 6h to come to thermal equilibrium. The process of cooling the system from room temperature is discussed in depth in Chapter 12 under thermal cycling . 

Dewar temperature NOTE A cold cryostat is expected during thermal cycling and does not indicate a fault (see Section 12.3) on if this is the case. 3. If the detects has a Be window, tak great care. If the le ng detector is allowed to warm up, high internal pressure could be generated which could cause the Be window to explode. Cover the endc if practical, move the detector to a safe place DO NOT WARM UP contact the m ufacturer immediately... 

It would help if, in times of misery, one had available a printed copy of a test point voltage versus bias curve measured when the detector was working satisfactorily for comparison. This is, perhaps, another item to place in the detector log book when commissioning a new detector (see Chapter 11, Section 11.2). In this particular case, the assumption was made that the enhanced leakage current was due to condensation of gas traces onto the detector within its vacuum enclosure. A thermal cycle was undertaken (see below. Section 12.3) and good resolution was restored. Presumably, the thermal cycle successfully removed the surface contamination from the germanium crystal. 

If the resolution of a detector has degraded with no apparent reason and all the usual checks and adjnstments, such as pole-zero cancellation, fail to cure the problem it may be that a thermal cycle is necessary. ... 

NB The procedure described below is only applicable to modem HPGe detectors. If there are any Uthium-drifted (Ge(Li)) detectors in use at this time, they must not be subjected to thermal cycling. If those detectors are warmed to room temperature, they will be damaged. 

A thermal cycle cannot be rushed. It is essential that the detector is warmed completely to room temperature. Otherwise, if the detector is re-cooled before that, it will have more contamination on its surface than it had before cycling. An improper cycle could make things worse. This is worth remembering. If a detector is inadvertently left to warm partially, it will probably be necessary to complete the warming to room temperature before cooling again. 

Data acquisition systems and/or event detectors (commonly referred to as glitch detectors) are employed to monitor resistance and/or scan for intermittent opens in real time. One of the early techniques for assessing solder joint integrity during thermal cycling was to remove parts periodically from the test chamber and measure resistance manually at room temperature. 

Real time x-ray systems are categorized as 2D and 3D systems. Only 2D x-ray test results for various packages/assemblies ter thermal cycling are presented here. Figure 25 shows features of 2D x-ray systems. The first example (Case 1, shown on the left side of the figure) is an x-ray inspection system with a microfocus source and an image intensifier as the detector, capable of producing offset pseudo 3D features... 

The 256 x 256 HgCdTe detector arrays and silicon multiplexers are fabricated independently. After fabrication is complete, indium columns are deposited onto qualified detector arrays and multiplexer die. These are then mated though the indimn columns to fabricate the hybrid. The hybridization technology is weU developed, and interconnect yields higher than 99.9% have been obtained. The reliability of the hybrids to thermal cycling is good due to the sapphire substrate of the detector arrays. 

Another very important issue is hybrid FPA reliability. Due to the coefficient of thermal expansion mismatch between the detector and multiplexer substrates, there are shear forces and bending of the FPA when thermally cycled between room temperature and 77K. Rockwell is working on novel packaging techniques to make the 1024 x 1024 as reliable as the 256 x 256. 

A 8] The separation layer consists of platinum coated on a silicon substrate. Owing to the low heat capacity, quick temperature cycles can be executed and a resolution down to 7 ppm can be achieved with the integrated thermal conductivity detector. The standard length of the capillary is 860 mm with a channel width of 60 pm. A measurement cycle takes less than 60 s. 

The sample is mounted on a cold finger—preferably cooled by a closed-cycle helium refrig-erator to 10 K—which greatly reduces the thermal smearing of the electron-positron momentum density. The sample is again tilted so that each detector is irrad-iated fairly uniformly, irrespective of gamma emission angle. 

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