Hollow Cathode Lamps
The most common source for atomic absorption measurements is the hollow cathode lamp,such as the oneshown in Figure 9-11.10 This type of lamp consists of a
tungsten anode and a cylindrical cathode sealed in aglass tube that is filled with neOIil or argon at a pressUl of 1 to 5 torr. The cathode is constructed of the metal
whose spectrum is desired or serves to support a layerof that metaLIonization of the inert gas occurs when a potentialon the order, of 300 V is applied across theelectrodes,which genetates a current of about 5 to 15 rnA as ionsand electrons migrate to the electrodes. If the potentialis sufficiently large, the gaseous cations acquire enoughkinetic energy to dislodge some of the metal atoms from the cathode surface and produce an atomic cloud in a process called sputtering. A portion of the sputtered
metal atoms are in excited states and thus emit their
characteristic radiation as they return to the ground
state. Eventually, the metal atoms diffuse back to the
cathode surface or to the glass walls of the tube and are
redeposited.