Project Info

Yber is a research project aiming at understanding the nuclear structure of Yb and Er isotopes near the N=104 midshell region and the neutron dripline by investing effort on experimental and theoretical studies.

Experimental aspects

Key observables for the structural classification of nuclei and the study of their deformation are the energies and parities of the levels - the level scheme structure - and the transition strengths, i.e. the transition matrix elements and the involved nuclear wave functions. These quantities can be measured with state-of-the-art nuclear structure techniques. Such as: the angular-correlation method for the spin and parity assignment in excited states and delayed coincidence techniques for lifetime measurements, like the slope method [1] and the generalized centroid difference method [2].

[1] P. C. Simms et al. “New Application of Delayed Coincidence Techniques for Measuring Lifetimes of Excited Nuclear States - Ca42 and Sc47 ”. Phys. Rev. 121 (1961), pp. 1169–1174. DOI: 10.1103/PhysRev.121.1169.
[2] J.-M. Régis et al. “The generalized centroid difference method for picosecond sensitive determination of lifetimes of nuclear excited states using large fast-timing arrays”. NIM A 726 (2013), pp. 191 –202. DOI: 10.1016/j.nima.2013.05.126.

Theoretical aspects

In the nuclear structure field several state-of-the-art theoretical models are used for the interpretation of the experimental results. At the same time the results are used to validate the theoretical models.

For the isotopes in the region of interest within this project, the N = 104 mid-shell region, calculations with both microscopic and macroscopic models can be performed. The microscopic model proxy-SU(3), a symmetry scheme based on the SU(3) symmetry [3], can be used for precise, parameter–free calculations. The analysis with the Interacting Boson Model, a collective model which describes collective excitations of nuclei in terms of bosons formed as pairs of valence fermions [4], and the placement of the isotopic/isotonic chains into the symmetry triangle [5] can reveal the shape-changes along them. More, several macroscopic models, like the geometrical model “confined β-soft” rotor model, which can describe the evolution of the deformation in an isotopic chain for nuclei between the critical point of the spherical to deformed shape transition and the fully axially symmetric deformed shape [6], can be used to classify structurally the isotopes under investigation.

[3] D. Bonatsos et al. “Analytic predictions for nuclear shapes, prolate dominance, and the prolate-oblate shape transition in the proxy-SU(3) model”. Phys. Rev. C 95 (2017), p. 064326. DOI: 10.1103/PhysRevC.95.064326.
[4] A. Arima et al. “Collective Nuclear States as Representations of a SU(6) Group”. Phys. Rev. Lett. 35 (1975), p. 1069. DOI: 10.1103/PhysRevLett.35.1069.
[5] P. Koseoglou et al. “Low-Z boundary of the N = 88–90 shape phase transition: 148 Ce near the critical point”. Phys. Rev. C 101 (2020), p. 014303. DOI: 10.1103/PhysRevC.101.014303.
[6] N. Pietralla et al. “Evolution of the “β excitation” in axially symmetric transitional nuclei”. Phys. Rev. C 70 (2004), p. 011304. DOI: 10.1103/PhysRevC.70.011304.