A setup for Offline Deposit Irradiation of thin layers

Thin films of radionuclides are a key element in many nuclear physics applications. These include applications as nuclear targets in accelerator-based experiments, e.g., in the production of superheavy elements in heavy-ion fusion reactions. With ever increasing beam intensities of new and more powerful accelerators, the targets have to withstand ever more intense heavy-ion bombardments over long time periods [1]. Freshly produced MP targets usually have to pass a so-called “baking-in” procedure in the accelerator beam, which removes organic impurities and transforms the target layer into a long-term stable form. Previous investigations revealed that this process is not solely heat induced, because heating up the targets does not result in the same transformations as the heavy-ion bombardment [2].

In order to get a better understanding of what exactly is going on during this backing-in procedure and to find a way to reproduce the necessary conditions in the lab, so that targets can be prepared for a beam-time beforehand, independent of accelerator schedule, a small-scale device called “ODIn” was constructed. ODIn consists of a central vacuum chamber, where an electron gun (Kimball Physics EFG-7 with EGPS-1017 power supply) and an ion gun (Tectra IonEtch Sputter Gun GenII) are attached [1].

Overview picture of ODIn, showing the main parts of the setup.
Photo/©: D. Renisch / Univ. Mainz

Samples mounted inside the vacuum chamber can be bombarded with electrons (up to 1.5 keV) or ions (up to 5 keV). The ion gun can be operated with ambient air or supplied from an external gas bottle, e.g. Ar. In order to find proper parameters of the particle beams (focus, deflection, etc.), the sample holder can be equipped with a phosphor screen, which can be monitored by a CCD camera [1].

ODIn sample holder. The left frame contains a phosphor screen for beam monitoring, the right frame contains a 36 kBq Pu-239 target. Photo/©: D. Renisch / Univ. Mainz

First investigations on the influence of those particle beams onto target layers have been done. The conversion of lead(II) carbonate to lead(II) oxide (massicot) could be observed this way [3]. But a lot more research on this topic is still to do, in order to get a better understanding of the chemical and physical changes of different target layers under these conditions. We offer topics related to ODIn for research modules, B.Sc. and M.Sc. theses.


[1] R. Haas et al., NIM A 957 (2020) 163366

[2] S. Hofmann et al., Eur. Phys. J A 48 (2012) 62

[3] C.-C. Meyer et al., NIM A 1028 (2022) 16636