Íàóêîâà êîíôåðåíö³ÿ ²íñòèòóòó ÿäåðíèõ äîñë³äæåíü ÍÀÍÓ
8-12 êâ³òíÿ 2019 ð.
Òåçè äîïîâ³äåé
Ñåêö³ÿ: Åêñïåðèìåíòàëüíà ÿäåðíà ô³çèêà
9 êâ³òíÿ 2019 ð., â³âòîðîê, 10:00
Ðåãëàìåíò: 15+5 õâ.
HIGH-ENERGY EXCITED 0+ STATES IN 158Gd
A. I. Levon1, D. Bucurescu2, T. Faestermann3, R. Hertenberger3,
A. G. Magner1, S. Pascu3, K.P. Shevchenko1, A. A. Shevchuk1, and H.-F. Wirth3
1 Institute for Nuclear Research, Academy of Science, Kiev, Ukraine
2 H. Hulubei National Institute of Physics and Nuclear Engineering, Bucharest, Romania
3Fakultät für Physik, Ludwig-Maximilians-Universität München, Garching, Germany
Excited 0+ states in nuclei are the specific modes of nuclear excitations which were intensively studied in a few last decades. They have a different structure associated, e.g., with pair vibrations, beta vibrations, vibrations caused by spin-quadrupole forces, one- and two-phonon excitations, and so on. The 0+ states occupy a special place in nuclear physics. Many difficulties of the nuclear theory describing the collective dynamics are concentrated just on these states. Theories met difficulties already for consideration of the properties of the first excited states. The multiple 0+ states in deformed nuclei are so far a new challenge for improving the theoretical collective dynamics models. Such models describe the properties of energy spectra of the 0+ states and their excitation cross sections. Comprehensive theoretical efforts were spent to understand the important nature of these 0+ excitations, and to extract information on the evolution of the abundance of 0+ states in the entire region of deformed nuclei, as well on the dependence of their abundance in the excitation energy spectrum. The excited 0+ states can be identified via (p,t) reactions even in the complicate and dense excitation spectra. So far, almost all studies of the 0+ states have been performed for an excitation energy below 3 MeV. We present the results of the 160Gd(p,t)158Gd experiment aiming for the first time the observations of 0+ excitations in the region up to 4.2 MeV [1].
The experiment has been performed at the Tandem accelerator of the Maier-Leibnitz-Laboratory of Munich Universities using a 22 MeV proton beam on a 110 μg/cm2 target of isotopically enriched 160Gd (98.10%) with a 14 μg/cm2 carbon backing. A long (1.4 m) focal plane detector provides the particle identification of masses 1 - 4 in the high-precision Q3D spectrometer. The resulting triton spectra have a resolution of 4 - 7 keV (FWHM) and are background-free. The angular distributions of the cross sections were obtained from the triton spectra at eight laboratory angles from 5o to 40o with step of 5o.
The thirty two new excited 0+ states and four tentative ones have been assigned up to the 4.3 MeV excitation energy with high precision. The total number of 36 excited 0+ states (besides the ground state) in a deformed nucleus, close to a complete level scheme, offers a new opportunity to test nuclear models and obtain more information on the structure of these states. Such abundance of 0+ states have not previously been observed in any nucleus investigated so far. The new information can be interesting, especially among theoreticians, because several models were applied in an attempt to understand the nature of these states. The obtained experimental results are compared with calculations in the framework of the spdf-version of the phenomenological interacting boson model and of a simple version of the semi-microscopic quasiparticle phonon model. Much richer new information should attract the attention of both theoreticians and experimentalists since the observation of thirty six excited 0+ states in one nucleus is the strongest challenge to our understanding of these excitations.
As perspectives, other designations of the experimental results are a statistical analysis of the discovered long sequences of the 0+, 2 +, 4+ collective states, and of the symmetry breaking by fixing the projection K of the nuclear angular momentum in deformed nuclei.