TG-37

This tube contains Cesium.  The cesium was used to ionize the air to make the spark jump across the gap more consistently.  Contained approximately 2 microcuries of Cs-137 when new; the half life of Cs-137 is 30.17 years.

Dear John,

no wonder for this warning! Any tube and even many radio collectors live everyday side by side with a lot of harmful materials.

Radioactive materials, as radium bromide or radium chloride, were usually added since WWII inside spark gaps with trigger voltage under 5kV to give a background ionization and help the spark startup. But radioactive materials were also used in many other devices, as TR switches, trigger tubes and even voltage stabilizers, to stabilize their characteristics over an extended temperature range. In the early days radioctive materials were often added with no visible notice outside the envelope. Later in very few cases manufacturers specified type and quantities of radioactive materials added to their tubes, just adding a more or less visible radiation symbol somewhere on the glass. I remember of ads around the early fifties from the University of Berkley offering a variety of radioactive byproducts for the vacuum tube industry. Ionizing radiation can also be found in used vacuum tubes operated at high-voltage, transmitting and radar tubes, CRTs, X-ray tubes.

Anyway tube collectors must be aware of other hazards when handling their babies or disposing broken units. Many tubes contain mercury and it can be easily identified by the droplets usually visible inside the bulb. Several power tubes, either inside or outside to protect wires going from press to the base, make use of asbestos. But other materials cannot be readily identified and their risk or environmental impact is difficult to know. I am referring to the many solid or gaseous compounds used as cathode coatings or getters or other purpose inside the bulb. Who knows how harmful could be the titanium hydride reservoir of some hydrogen thyratrons? Even handling some microwave tubes can be harmful, due to use of poisonous metals, as beryllium.

Regards, Emilio

In the site of Jeremy Harmer this page contains a very intersting partial list of known radioactive tubes and of radioctive materials used by tube industry. Only few manufacturers gave information on these data.

Regards, Emilio