Snook (Hydrogen) Tube (1915-1925)


The Snook tube, developed by Homer Snook, is a very unique type of cold cathode x-ray tube because it employs two regulators. The regulator closest to the tube center (towards the left in the photo and diagram) was open to the air. When the gas pressure inside the x-ray tube got too high, current would jump from an electrode to a thin palladium tube in the regulator. This heated the palladium.  When heated, the palladium became permeable and allowed some of the hydrogen inside the x-ray tube to escape. This reduced the gas pressure. The other regulator (towards the right in the photo and diagram), employed a sealed reservoir of hydrogen. When the x-ray tube became too hard, current would jump from an electrode to a thin platinum tube. This heated the platinum and allowed some hydrogen to diffuse from the regulator's reservoir into the x-ray tube and thus increase the gas pressure (i.e., soften the tube).
snook 1000
Notice the absence of a separate anode and anticathode in this tube. 

The focusing (aka Penetration) ring, located towards the center of the tube, helped ensure that the electrons from the cathode were directed to a small area (a few square millimeters) in the center of the target. A buildup of static charge on the glass of the tube could cause the focal point to wander and the ring helped combat this phenomenon. 

Two other possible functions: it helped "overcome the initial resistance in tubes of high vacuum" and helped "decrease uneven heating at the cathode" (Raper 1922).

penetrator Tubes that employed these rings were often referred to as "penetrator tubes" because the resulting x-rays were presumably more penetrating than would be the case without the ring. The image to the left of an early penetrator is from Pusey (1903). Quoting Pusey: "It is based on the principle that with a given vacuum the penetration will be higher the closer the electrodes are together . . . Such tubes are preferred by some operators for fluoroscopic work in which a very high penetration is desired."


This example of a Snook tube was possibly built by the Victor X-ray company  -  Snook served as Vice-President of the Victor Company for a short period of time.

Size: approximately 20" long with 6.5" bulb diameter


The following images were kindly provided by Alastair Wright.

Snook also pioneered the use of transformers, which operated off alternating current, to provide the high voltage for x-ray tubes. At the time, most tubes were powered by induction coils which utilized direct current and required the use of interrupters.


GWC Kaye. X-Rays. Longmans, Gree and Co. London. 1929.

Pusey, W.A. and Caldwell, E.W. The Practical Application of the Rontgen Rays in Therapeutics and Diagnosis. 1903.

Raper, H.R. Elementary and dental Radiography. 1922.

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Last updated: 11/07/07
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