Hugo, you have already received some very good sources from several people.

By coincidence, I just ran across my folder with:

Gary  M. Anderson, David M. Levy, and Robert D. Tollison. "The 
half-life of dead economists,"  CANADIAN JOURNAL OF ECONOMICS, vol. 
22, no. 1(February 1989), 174-183.

This may not be what you are interested in but it may enlarge your 
interest:  the notion of half-life does, after all, extend into the future.

The specific approach to examining certain questions of interest to 
the authors and the questions themselves my be reconstructed by you 
according to your interests.

One difficult-to-work-out question might concern whether the 
citations are to an expanding field or a moribund field, etc.

Good luck.

Warren J. Samuels