Caesium-137 is not widely used for industrial radiography because it is hard to obtain a very high specific activity material with a well defined (and small shape) as caesium from used nuclear fuel contains stable caesium and also long lived Cs-135. Also the higher specific activity caesium sources tend to be made from very soluble caesium chloride (CsCl), as a result if a radiography source was damaged it would increase the spread of the contamination. It is possible to make water insoluble caesium sources (with various ferrocyanide compounds such as , and ammonium ferric hexacyano ferrate (AFCF), Giese salt, ferric ammonium ferrocyanide) but their specific activity will be much lower. A large emitting volume will harm the image quality in radiography. Iridium-192 and cobalt-60, , are preferred for radiography, since these are chemically non-reactive metals and can be obtained with much higher specific activities by the activation of stable cobalt or iridium in high flux reactors.