Since the 1950’s, the nuclear science community has largely accepted the work of A. Bohr and B. Mottelson, for which they received the Nobel Prize in 1975, that the lowest excitations that occur in the nucleus arise from collective behaviour. One can explain the principle of collective nuclear excitations in analogy to the motions of fans in a football stadium; each of them may stand up and run around – like individual protons and neutrons that can be promoted from one orbital to the next – but they can also participate in a “wave” that propagates around the stadium, which is a collective phenomenon. In the atomic nucleus, the collective excitations may be rotations or vibrations that involve multiple particles in the nucleus, or even the majority of them.

For over 40 years, cadmium isotopes have played a key role in the study of the collective behaviour in atomic nuclei. Initially, it was believed that their structures could be described within a collective vibrational model, in which the surface of the nucleus oscillates (vibrates) around a spherical equilibrium shape. Subsequent experimental results inspired new calculations using advanced theoretical models of atomic nuclear structure, which predict that the individual excited states in ¹¹⁰Cd and ¹¹²Cd nuclei adopt various ellipsoidal shapes (for example, elongated like a rugby ball or zucchini, or flattened like a Frisbee or a pumpkin). In parallel, alternative theoretical approaches were developed, that are able to reconcile the existing experimental data on these nuclei with their quasi-spherical shapes.

Recent experiments conducted at the Heavy Ion Laboratory UW made it possible to discriminate between these two fundamentally different interpretations of the structure of cadmium nuclei by determining the shapes of two key states in the ¹¹⁰Cd nucleus. Both the ground state and the excited 0⁺ state deviate from a spherical shape, with the former, in particular, resembling a kiwifruit (or an ellipsoid with all axes having different lengths). Furthermore, the measured quadrupole moments (i.e., charge distribution parameters) of the lowest two spin-2 states are significantly different from zero, ruling out the hypothesis that the structure of these nuclei could result from their vibrations around a spherical shape. These findings were recently published in the prestigious journal Physics Letters B.

The new results on ¹¹⁰Cd  are part of a broad international research programme aimed at determining the shapes of the low-excited 0⁺ states in even-even cadmium nuclei, using a variety of complementary experimental techniques and the most advanced detection systems. Within this programme, Iwona Piętka is preparing a PhD thesis based on experimental data collected with the state-of-the-art gamma-ray spectrometer AGATA. The work is carried out at the Heavy Ion Laboratory UW, within the Doctoral School of Exact and Natural Sciences at the University of Warsaw, under supervision of dr Katarzyna Wrzosek-Lipska i dr hab. Leszek Próchniak.

K. Wrzosek-Lipska, I.Z. Piętka, L. Próchniak, P.E. Garrett, M. Zielińska, T. Abraham, J.M. Allmond, F.L. Bello Garrote, H. Bidaman, V. Bildstein, S. Buck, C. Burbadge, M. Chiari, R. Coleman, G. Colombi, G. Colucci, A. Diaz Varela, D.T. Doherty, S. Dutt, B. Greaves, K. Hadyńska-Klęk, J. Heery, M. Hlebowicz, D. Hymers, J. Iwanicki, G. Jaworski, B. Jigmeddorj, D. Kalaydjieva, M. Kisieliński, M. Komorowska, N. Kopeć, M. Kowalczyk, J. Kowalska, K. Krutul-Bitowska, R. Kumar, A. Mai Quynh, N. Marchini, T. Marchlewski, K.R. Mashtakov, M. Matejska-Minda, C. Michelagnoli, A. Nannini, P.J. Napiorkowski, B. Olaizola, F. Oleszczuk, M. Palacz, E. Pasquali, E.E. Peters, M. Rocchini, E. Sahin, J. Samorajczyk-Pyśk, M. Saxena, A. Stolarz, J. Srebrny, A. Tucholski, A. Trzcińska, M. Venhart, J.L. Wood, S.W. Yates, T. Lidar

Deformation of the 0⁺_1,2 states in ¹¹⁰Cd from low-energy Coulomb excitation,
Physics Letters B, Volume 875, 2026, 140315, ISSN 0370-2693,
https://doi.org/10.1016/j.physletb.2026.140315.

The experimental team during measurements at the HIL.

The excess of the energy of the excited atomic nucleus above the neutron biding energy could be given to giant resonances. These excitations are described macroscopically as nucleon vibrations in the nucleus. By measuring their decay, can be obtained the information about the properties of the atomic nuclei, in which giant resonances are excited. The well-known are giant dipole resonance (GDR), studied in the process of their g decay, in many experiments carried out in the last decades. In contrast to the GDR, the properties of giant quadrupole resonance (GQR) have not been extensively investigated. The g decay of GQR has been measured so far only in the experiment carried out in the 1980s, using inelastic scattering of ¹⁷O on ²⁰⁸Pb. The outcome of this experiment are the only published results of the GQR g decay studies.

Thanks to the construction of the experimental setup for nuclear physics research at the Bronowice Cyclotron Center (CCB) of the Institute of Nuclear Physics, Polish Academy of Sciences, a newly established center for hadron therapy, it has been started the research on GQR g decay using a high-energy proton beam. The article published in Phys. Rev. C shows the results of the measurement of GQR g decay for the ²⁰⁸Pb nucleus performed as one of the first nuclear physics experiments at the CCB. To excite giant resonances the inelastic scattering of protons with an energy of 85 MeV on a ²⁰⁸Pb target was used. During the experiment, the energy of scattered protons, carrying information about the excitation energy of ²⁰⁸Pb nuclei, and the energy of grays emitted as a result of the decay of excited states, were measured simultaneously. The data corresponding to the decay to the ground state, for which the excitation energy was equal to the energy of the emitted g rays, were analyzed. Taking into account the observed g decay of GDR, the spectrum of g rays emitted from the GQR decay was obtained. As the result of the analysis, the probability of GQR decay by the g ray emission was determined to be 3 × 10^-4. This value confirms the previous result obtained for the inelastic scattering of ¹⁷O ions.

Wasilewska, M. Kmiecik, M. Ciemała, A. Maj, F.C.L. Crespi, A. Bracco, M.N. Harakeh, P. Bednarczyk, S. Bottoni, S. Brambilla, F. Camera, I. Ciepał, N. Cieplicka-Oryńczak, M. Csatlos, B. Fornal, V. Gaudilla, J. Grębosz, J. Isaak, Ł.W. Iskra, M. Jeżabek, A.J. Krasznahorkay, S. Kihel, M. Krzysiek, P. Lasko, S. Leoni, M. Lewitowicz, J. Łukasik, M. Matejska-Minda, K. Mazurek, P.J. Napiorkowski, W. Parol, P. Pawłowski, L.Q. Qi, M. Saxena, Ch. Schmitt, Y. Sobolev, B. Sowicki, M. Stanoiu, A. Tamii, O. Wieland, M. Ziębliński

γ decay to the ground state from the excitations above the neutron threshold in the ²⁰⁸Pb(p,p′γ) reaction at 85 MeV

Phys. Rev. C 105, 014310 (2022)

DOI:10.1103/PhysRevC.105.014310

The Josephson effect is a quantum phenomenon appearing in superconductors.
It consists in the spontaneous flow of electric current, due to tunneling, between the two
superconductors separated by a thin insulator layer. The current flow is induced by
phase difference of wave functions describing superconducting electrons on both
sides of the insulator. This is called the Josephson junction.
The phenomenon occurs in metals as well as in ultracold atomic gases.
Search for the Josephson effect in nuclear systems
have been going on for almost half a century.
Theoretical analysis of recent experiments involving collisions of Nickel-60 and Tin-116
provided strong arguments for creation of the Josephson junction.
Contrary to the previous measurements where
the pair transfer cross section has been investigated, this time the gamma radiation spectrum
was analyzed. It turned out that the spectrum of emitted gamma rays agrees with the theoretical
predictions assuming the formation of the so-called AC Josephson junction.

Piotr Magierski

The Tiniest Superfluid Circuit in Nature

Physics 14, 27 (2021)

DOI:10.1103/Physics.14.27