Image:Cosser Crookes xray tube.jpg

Drawing of a Crookes type x-ray tube made by Alfred Cossor, from the late 1800s. The caption text: 'A Cossor bulb with automatic softening device and fin radiator for cooling anticathode.' Alterations to image: cropped out caption.

The electrode on the right is the aluminum cathode, which focuses a beam of electrons on a small (~1 mm) spot on the angled platinum anode target, called the 'anticathode', in the center of the bulb, creating x-rays which are radiated downwards. The electrode at the 10 o'clock position is called the auxiliary anode. The device at the top is an 'automatic softener' to control the pressure in the tube. Crookes type tubes had a low vacuum, but with time the residual gas was resorbed and the vacuum in the tube increased, requiring a higher potential to operate, generating 'harder' x-rays, until eventually the tube stops operating. The 'softener' prevents this. When the voltage across the tube increases, the anode potential arcs across the spark gap to the softener electrode, and the current heats a sleeve in the softener, which releases gas, raising the pressure in the tube. Alfred Charles Cossor's workshop in Clerkenwill, London was at that time the only British manufacturer of Crookes x-ray tubes. These cold cathode x-ray tubes were used until the 1920s.

Downloaded from George William Clarkson Kaye (1914) X-rays: An Introduction to the Study of Röntgen Rays, Longmans Green & Co., London, p.42, fig.22 on Google Books

1914

George William Clarkson Kaye

Public domain - author died more than 70 years ago.