Recent experimental studies of high-j single-particle states outside the stable Z = 50 isotopes [1] and N = 82 isotones [2] have shown that the centroids of single-particle strength display systematic changes with neutron or proton number. For the case of the Z = 50 isotopes, the separation of the h11/2 and g9/2 single-proton orbitals was found to increase by ~2 MeV across the seven stable even isotopes. Similarly for the N = 82 isotones, the separation of the i13/2 and h9/2 single-neutron orbitals is seen to increase by ~0.5 MeV with proton number. These centroid shifts are in agreement with those calculated Otsuka et al. [3] with the monopole term in the tensor component of the residual interaction between nucleons. The experiments performed to extract these data rely on the use of single-particle transfer reactions, in particular those well matched for high-l transfer. Over the last few years our collaboration has made use of the facilities at Wright Nuclear Structure Laboratory at Yale University that are particularly well suited for these types of measurements. However, they are limited to the stable beam / target domain, which brings our attention to the capabilities of CARIBU [4] and HELIOS [5] at the ATLAS facility. I will review the experimental data and present information on upcoming experiments at ATLAS that will help us probe further the evolution of single-particle strength.
This research was supported by the DOE Office of Nuclear Physics under Contract Nos. DE-FG02-91ER-40609 and DE-AC02-06CH11357, and the UK Science and Technology Facilities Council.

[1] J. P. Schiffer et al., Phys. Rev. Lett. 92, 162501 (2004).
[2] B. P. Kay et al., Phys. Lett. B658, 216 (2008).
[3] T. Otsuka et al., Phys. Rev. Lett. 95, 232502 (2005).
[4] https://www.phy.anl.gov/atlas/caribu/index.html
[5] A. H. Wuosmaa et al., Nucl. Instr. Meth. Phys. Res. A580, 1290 (2007).

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