Speaker
Description
The origin of heavy elements such as gold and uranium is one of the most important questions in nuclear astrophysics. Approximately half of the abundances of elements heavier than iron are considered to originate from the rapid neutron-capture process (r-process) in astrophysical environments [1]. To understand the r-process path and the resulting elemental abundances, precise experimental mass data for neutron-rich nuclei along the path are essential. In particular, neutron-rich lanthanoid isotopes are expected to play a crucial role in the formation of the rare-earth peak, although experimental data in this region remain extremely scarce.
We plan to perform precise mass measurements of neutron-rich lanthanoid nuclei produced via the $^{136}$Xe+$^{176}$Yb multinucleon transfer (MNT) reaction at the KEK Isotope Separation System (KISS) [2] using a multi-reflection time-of-flight mass spectrograph (MRTOF-MS) [3]. To obtain sufficient production yields in MNT reactions, a high-intensity heavy-ion beam and a thick target of approximately 10 mg/cm$^2$ are required. However, metallic ytterbium has a relatively low melting point of 824$^\circ$C and is therefore susceptible to thermal damage under high-intensity beam irradiation. Furthermore, fabricating such a thick target layer is difficult using conventional methods such as vacuum evaporation. Thus, the development of a thick ytterbium-based target that can withstand intense beam irradiation is a key technical challenge for MNT experiments.
To address this issue, we focus on ytterbium oxide (Yb$_2$O$_3$), which has a high melting point (approximately 2400$^\circ$C). Using this material, we are developing thick targets using the spray coating method [4]. By suspending Yb$_2$O$_3$ powder in a solvent and spraying the suspension onto a metal backing, we aim to form a thick target layer. In this presentation, we will report on the preparation of thick Yb$_2$O$_3$ targets by the spray coating method and discuss the results of their performance evaluation.
[1] E. M. Burbidge et al., Rev. Mod. Phys. 29, 547 (1957).
[2] Y. Hirayama et al., Nucl. Instrum. and Methods B 353, 4 (2015).
[3] J. Y. Moon et al., RIKEN Accel. Prog. Rep. 52, 138, (2018).
[4] J. P. Greene & C. J. Lister, Nucl. Instrum. Methods A 482, 79 (2002).