Reducing the influence of static charge on ultra-low alpha particle emissivity measurements
Publication Date: 2015-Jan-22
The IP.com Prior Art Database
Disclosed is a method to reduce the influence of static charge on ultra-low alpha particle emissivity measurements using a grounded metal grid placed on top of the insulating sample.
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Reducing the influence of static charge on ultra - measurements
Electrically insulating samples can have static charge on the surface , which can distort the electric field in an ionization detector because the samples reside within the counter volume. This has the effect of reducing the apparent alpha particle emissivity of the sample.
Past solutions required discharging the buildup of static charge through trial and error and could vary from sample to sample. The confirmation process used a radioactive source near the sample which is time consuming.
The novel contribution is a method to use a grounded metal grid placed on top of the insulating sample. Alternatively, a grounded thin flashed metal layer on top of the non-conducting sample can be used, or the application of a conductive polymer spread onto the sample. In any case, the metal grid acts as a Faraday shield, and shields the counter from the influence of the surface charge on the top of the non -conducting layer.
In practice, reducing the use of the metal grid requires that the metal grid have high transmissivity and low alpha emissivity. It is possible to measure the alpha emissivity of the metal mesh or the metal coating and then subtract its contribution from the emissivity of the combined system.
Figure 1: A glass wafer that has been metalized on the top surface and is grounded to the detector's cathode surface by the clips
Figure 2: A grounded high transmission mesh placed over a square piece of...