A comparison of thin and thick targets for energy calibration of heavy ion beams with resonances

The signal-to-noise (S/N) ratio near the resonance energy is compared for thick and thin hydrogen containing targets. This is done with a view to assessing the precision of energy calibration methods for heavy ion beams based on resonances in nuclear reactions such as 1H(19F, αγ)16O and 1H(15N, αγ)12C. In a previous work a thick ammonium chloride target was found to have some very attractive features for energy and yield calibration purposes although it was thought that the S/N ratio would be inferior to that of a thin target. Here the S/N ratio for a thick ammonium chloride target is compared with that for a thin target in the form of a hydrocarbon contamination layer which is known to contain a high concentration of hydrogen. It is found that the thick ammonium chloride target can be expected to give a superior S/N ratio in most cases. General expressions are obtained and the accuracies and the precisions of the energy calibration methods are discussed. (orig.)