A simple method for energy calibration of heavy-ion beams

A method is described for the calibration of analyzing-magnet systems of heavy-ion accelerators. It makes use of resonances in inverse (p, αγ) reactions, i.e. with heavy-ion beams on hydrogen targets. Instead of a gas target we use the very thin hydrogen-containing surface layer on a gold foil, which makes the method very simple and applicable to almost any accelerator. The use of different charge states of the heavy-ion beam for the measurement of the same resonance provides internal consistency checks and makes it possible to cover a large energy range. The various contributions to the observed widths of the resonances used are briefly discussed. The resulting magnet calibration factor shows a linear decrease of about 0.2% over the range of 10-35 MeV equivalent proton energy. This calibration is used to determine an accurate energy, Ep = (429.88 ± 0.14) keV, for the well known narrow resonance in the reaction 15N(p, αγ)12C. (orig.)