Q. Is there such a thing as a suspended en dash? What would you do in the case of “α and β particle–emitting isotopes,” for example? Does anything go after the alpha symbol, or should it have nothing, even though “particle” applies to that term?
A. There is such a thing as a suspended en dash, but it should be used only to omit a word or phrase that follows the first dash in the full phrase (i.e., before suspension):
pre–Civil War and post–Civil War [two en dashes]
becomes
pre– and post–Civil War [with a suspended en dash]
In your case, here’s what we’d do:
α particle–emitting and β particle–emitting isotopes [two en dashes]
becomes
α particle– and β particle–emitting isotopes [suspended en dash]
but not
α– and β particle–emitting isotopes [suspended en dash]
and not
α- and β-particle-emitting isotopes [suspended hyphen]
That second-to-last example (α– and β particle–emitting isotopes) asks readers to mentally supply the word particle between the alpha symbol and the en dash, which is too much to expect. And in both that example and the last one, the alpha may be misread as alpha minus.
All this assumes you’re referring to two sets of isotopes, those that emit alpha particles and those that emit beta particles. If that’s not the case—or if it is, but the text doesn’t make that clear—consider rewording (e.g., “isotopes that emit both α and β particles” or “isotopes that emit either α or β particles”).
For more on en dashes in compound adjectives, see CMOS 6.86.