  Gas load and pumping determine the quality of vacuum systems. In particle
accelerators, once leaks are excluded, outgassing of materials is an important
source of gas together with degassing induced by particle beams. Understanding,
predicting, and measuring gas release from materials in vacuum are among the
fundamental tasks of ultrahigh-vacuum experts. The knowledge of outgassing
phenomena is essential for the choice of materials and their treatments so that
the required gas density is achieved in such demanding and expensive scientific
instruments. This note provides the background to understand outgassing in
vacuum and gives references for further study.
