Anton Pancake GM With Double Window (ca. 1950s)
This is the most unusual pancake GM I have ever run across. Manufactured by Anton Electronics Laboratories, Inc. of Brooklyn, New York, it has two identical windows, one on each side! By holding the tube up to the light (photo to the left), you can see right through it! The fine dark circle seen in the middle of the photo is the anode. The metal caps used to protect the windows (not shown) are stamped with the Anton logo: a shield with "ANTON" running diagonally across it.
I have a couple of guesses as to how a pancake probe with two windows might have been used. First, it might have been used in an experimental setup where it was positioned in a beam of charged particles. It would respond to these particles but still allow them to pass through so that they could also be detected by another instrument. A second possibility is that it might have been used to maximize the detection of low energy beta emitters in a gas stream.
As best as I can determine, Anton was the first company to manufacture pancake GMs—the earliest reference I have found is an advertisement in the November 1950 issue of Nucleonics. The first reference I've located where the design is actually described as a "pancake tube" is an Anton advertisement in the August 1956 issue of Nucleonics. In late 1961, Anton Electronic Laboratories, Inc. became Lionel Electronic Laboratories.
Size: 1 5/8" in diameter and 3/4" high
Windows: Metal coated mica, 1.4-2.0 mg/cm² thick