Maker's Name: 
31 × 13 × 13 cm

This item is an X-ray tube. Its maker and place of origin are unknown but it was probably made around 1900. Unlike later X-ray tubes,this tube has no heated filament. Instead, an electrical discharge was started in a small amount of gas in the tube. Ions striking the cathode cause electrons to be emitted, maintaining the discharge. When these electrons strike the anode they can excite the electrons in the plate to a higher energy level. When the electrons fell back to their lower energy levels they would release X-rays. These X-rays would pass through the glass. As you can see this tube has a distinct purple tinge in its glass, indicating it has experienced extensive use.

This X-ray Tube is called a 'focus' tube because the electric field at the cup-shaped cathode 'focuses' the electrons to a small spot on the anode, giving a sharper shadow for imaging applications. A similar tube was used by Max Laue's assistants in their confirmation of his prediction that the layers of atoms in a crystal would diffract x-rays in specific directions.

When these devices were first invented, people had not realised the potential dangers of excessive exposure to X-rays. X-ray tubes were often used as novelties and toys. X-rays can easily penetrate skin and muscle but are stopped by denser substances such as bone. People would position their hand between the tubes and a screen or special viewing apparatus so that they could see their bones. Today, we are aware of the potential for excessive exposure to X-rays to cause cancer and so people who work around X-rays carefully monitor their exposure to ensure it remains at safe levels.

This item is part of the UQ Physics Museum Crystallography Tour
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