50 years of elastic recoil detection: How it started

The year 2025 celebrates the 50 years of the development of a technique now mainstream in Ion Beam Analysis: Elastic Recoil Detection (ERD). It was born from the need to detect He in a heavy matrix but turned out to be a handy way to depth-profile H at the same time as Rutherford Backscattering Spectroscopy was carried out to measure heavier elements. Soon after, a time-of-flight version ERD was developed, allowing to obtain separate spectra of each element in a target. This paper gives an account about the context of how it happened, by some of those involved at the time.