I've been puzzled a lot on when to use a hyphen in compounds words such as cross-section, time-of-flight, state-of-the-art etc. I am writing scientific documents and I haven't found a definite rule on the use of a hyphen.
However, I came across a general rule according to which such words have to be hyphenated when they come before a noun, otherwise the hyphen is not necessary (or perhaps it's even wrong?). A few examples follow
Cross-section measurements of nuclear reactions.
Measuring nuclear reaction cross sections.
The time-of-flight technique
The particle has a small time-of-flight.
Is there a rule that can be applied in such case or the use of a hyphen is interchangeable?