Dr. Robert Haring-Kaye (Department of Physics and Astronomy)

Atomic nuclei with approximately 70 constituent particles (protons and neutrons) are in a region of the nuclear landscape that has been termed the “Wild West” [1] since the structural properties of these nuclei are not as well behaved as those of the heavier deformed ones. Rapid structural changes are common with only slight changes in the number of protons and/or neutrons, and with changes in the angular momentum of the system. For example, rapid shape changes have been inferred throughout this region of nuclei, and in some cases different shapes have been deduced within the same nucleus depending on the configuration of the constituent protons and neutrons. Recently, this mass region has also served as a testing ground for a variety of exotic shape and structure properties, such as static asymmetric shapes at low energy [2], shapes with tetrahedral symmetry [3], and unusual intrinsic configurations of protons and neutrons that drive the nucleus toward deformation [4].

During the summer of 2014, my team of summer research students (including an REU participant) and I traveled to Florida State University (FSU) to perform an experiment at the John D. Fox Superconducting Accelerator (funded by NSF) to produce nuclei that may be candidates for the exotic structures mentioned above. These nuclei were populated at relatively high energy and angular momentum, and released sequences of gamma rays as they relaxed to their lowest-energy (ground) state. The gamma rays were recorded by an array of high-resolution detectors and serve as a “fingerprint” of the parent nucleus from which they are emitted, revealing several aspects of the underlying structure.

Future REU students are now poised to analyze the data from this experiment using the techniques of gamma-ray spectroscopy. The results of the analysis will be compared to the predictions of various theoretical calculations and simulations that use a variety of computational methods. In particular, students will have the opportunity to perform and interpret large-scale shell-model calculations that predict the excitation energy spectrum for the nuclei they are studying, as well as the transition rates between these states (which can be used to infer the underlying shape and structure properties). Since the data analysis requires a basic understanding of the techniques of gamma-ray spectroscopy, students will be trained on the relevant experimental techniques using a simplified setup in my on-campus research laboratory, which utilizes the same gamma-ray detection technology that was used in the actual experiment at FSU. Additionally, students will travel to either FSU or the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (also funded by NSF) during each research period so they can become more familiar with the operational procedures and technology present at a large-scale particle-accelerator facility, make meaningful contributions to the preparations for future experiments, and assist with the execution of new experiments.

 

References

[1] W. Nazarewicz, in High Spin Physics and Gamma-Soft Nuclei, edited by J. X. Saladin, R. A. Sorensen, and C. M. Vincent (World Scientific, Singapore, 1991), p. 406.

[2] Y. Toh et al., Phys. Rev. C 87, 041304(R) (2013).

[3] J. Dudek et al., Phys. Rev. Lett. 88, 252502 (2002).

[4] R.A. Kaye et al., Phys. Rev. C 83, 044316 (2011).