1. http://www.oxforddictionaries.com/definition/english/vacuum. Oxford University Press 2016 (accessed 30 May 2019).
2. http://dictionary.cambridge.org/dictionary/british/vacuum. Cambridge University Press 2016 (accessed 30 May 2019).
3. ISO3529‐1:1981(en) Vacuum technology ‐ Vocabulary ‐ Part 1: General terms.https://www.iso.org/obp/ui/#iso:std:iso:3529:‐1:ed‐1:v1:en(accessed 30 May 2019).
4. Vacuum for particle accelerators and storage rings
5. Large accelerator vacuum system engineering