Lost sources are a worldwide problem since; on the one hand, a large number of
radioactive sources are being used in developed countries. Thus even if there is a small
probability of failure of regulatory control or of management procedures, the total number of sources that may be mislaid becomes large. On the other hand, in countries having a small number of sources but with inadequate regulatory control and lack of a proper management system, there is a high probability of loss or mistreatment and consequently the number of sources that may cause an accident also becomes large.