Speaker
Description
In recent years, a new research project has been started for cross-section measurement of residues produced in proton- and deuteron-induced spallation reactions on long-lived fission products (LLFPs) (e.g., $^{79}$Se, $^{93}$Zr[1], $^{107}$Pd[2], $^{126}$Sn, $^{135}$Cs) using the inverse kinematics technique at RIKEN RI Beam Factory (RIBF) in order to provide basic data necessary for nuclear waste transmutation. In the measured isotopic-production cross sections for $^{93}$Zr, remarkable jumps originating from the neutron magic number N = 50 were observed in Zr and Y isotopes[1]. In the present work, we have derived isotopic-production cross sections for five nuclei adjacent to $^{93}$Zr (i.e., $^{91,92}$Y, $^{92}$Zr, and $^{93,94}$Nb) from further data analysis of the $^{93}$Zr experiment. Based on the systematic data, the behavior of isotopic production was investigated with particular attention to the effect of neutron shell closure with N=50.
The experiment was performed at RIBF. The detail of the experimental procedure is described in Refs. [1,2]. The cocktail beam containing $^{91,92}$Y, $^{92,93}$Zr, and $^{93,94}$Nb at kinetic energies around 100 MeV/nucleon was produced by in-flight fission of $^{238}$U at 345 MeV/nucleon. Next, the cocktail beam was separated and identified by using the BigRIPS in-flight separator. Particle was separated by using energy degraders and slits placed at focal planes. Particle identification was performed by the TOF-$\Delta$E-B$\rho$ method. Then, the beam particles irradiated secondary targets (CH$_2$, CD$_2$, and C) placed at the entrance of ZeroDegree Spectrometer (ZDS). The residual nuclei produced by nuclear reactions in the second targets were identified event-by-event using ZDS.
As in the case of $^{93}$Zr, characteristic jump structure near N=50 was observed in the isotopic distribution for the elements corresponding to charge-unchanging ($\Delta$Z = 0) and/or one-proton-removal ($\Delta$Z = -1) for $^{91,92}$Y, $^{92}$Zr, and $^{93,94}$Nb. The measured isotopic production cross sections were compared to PHITS calculation with INCL 4.6 for intra-nuclear cascade process and GEM for evaporation process. The overall behavior of isotopic-production cross sections was generally well reproduced by the calculation; however there were some differences: e.g., overestimation of the measured production yields corresponding to few-nucleon-removal reactions. The details of the experimental result and model analysis will be discussed in the presentation.
This work was funded by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan).
References
[1] S. Kawase, K. Nakano, Y. Watanabe, et al., Prog. Theor. Exp. Phys. 2017, 093D03 (2017).
[2] H. Wang, H. Otsu, H. Sakurai, et al, Prog. Theor. Exp. Phys. 2017, 021D01 (2017).
