Original Degradation of thin carbon-backed lithium fluoride targets bombarded by 68 MeV 17O beams

To analyze the cause of the destruction of thin, carbon-backed lithium fluoride targets during a mea-surement of the fusion of 7Li and 17O, we estimate theoretically the lifetimes of carbon and LiF films due to sputtering, thermal evaporation, and lattice damage and compare them with the lifetime observed in the experiment. Sputtering yields and thermal evaporation rates in carbon and LiF films are too low to play significant roles in the destruction of the targets. We estimate the lifetime of the target due to lattice damage of the carbon backing and the LiF film using a previously reported model. In the experiment, elastically scattered target and beam ions were detected by surface silicon barrier (SSB) detectors so that the product of the beam flux and the target density could be monitored during the experiment. The areas of the targets exposed to different beam intensities and fluences were degraded and then perforated, forming holes with a diameter around the beam spot size. Overall, the target thickness tends to decrease linearly as a function of the beam fluence. However, the thickness also exhibits an increasing interval after SSB counts per beam ion decreases linearly, extending the target lifetime. The lifetime of thin LiF film as determined by lattice damage is calculated for the first time using a lattice damage model, and the calculated lifetime agrees well with the observed target lifetime during the experiment. In experiments using a thin LiF target to induce nuclear reactions, this study suggests methods to predict the lifetime of the LiF film and arrange the experimental plan for maximum efficiency.(c) 2022 Korean Nuclear Society, Published by Elsevier Korea LLC. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study analyzes the cause of destruction of thin, carbon-backed lithium fluoride targets during the fusion measurement of 7Li and 17O. The lifetimes of carbon and LiF films due to sputtering, thermal evaporation, and lattice damage are estimated theoretically and compared with the experimental results. The results show that sputtering and thermal evaporation do not significantly contribute to the destruction of the targets, and the target lifetime is mainly affected by lattice damage. The study provides methods to predict the lifetime of the LiF film and optimize the experimental plan for maximum efficiency in nuclear reaction experiments using thin LiF targets.