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Type Seminar
Date June 17, 2022 - 11:00
Time 11:00
Location Room 105, GANIL, Caen | France
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Spectroscopic studies of the neutron-rich 255-256No with GABRIELA



Kieran Kessaci (Université de Strasbourg, IPHC, Strasbourg, France)

Nuclei around 254No (Z=102) have been widely studied by means of cold fusion reactions using projectile and targets around the doubly magic 48Ca and 208Pb nuclei. Decay-spectroscopy techniques are very powerful to pin down high-K isomers and to study their decay path to the ground state as well as to subsequent states fed by radioactive decay of the nucleus of interest and its daughter. Numerous rotational bands and high-K isomers were observed near 254No giving valuable information on the single particle orbitals ordering around both Z=100 and N=152 deformed gaps (see [1-2] and references therein). 
The experiments were performed with the GABRIELA [3] array, at the focal plane of the SHELS separator [4] at the FLNR in Dubna. The first part of this talk will be dedicated to the presentation of both the experimental setup and the genetic correlation analysis method developed to reveal and to characterize the isomeric states in these Nobelia. 
The 256No was first studied in the sixties by E. D. Donets and his team [5]. Despite several attempts, this “hard-to-reach” nucleus has never been successfully studied in detailed spectroscopy up to the present experiment. The 256No were synthesized through the fusion-evaporation reaction 238U(22Ne, 4n)256No, with a special care for the separation efficiency due to the slowness of the recoils induced by this hot fusion reaction. We performed an alpha-beta-gamma spectroscopic study which allows us to discover a new high-K isomer which gave us a first indication of the possible level scheme of this nucleus. This low-statistic study will be presented in the second part of this talk (see also [6]). The third part of this talk will be focussed on a second experiment performed using a cold fusion-evaporation reaction 48Ca(208Pb, n)255No, with the same setup optimized for a 48Ca beam. Thanks to a higher transmission of the separator, this latter reaction allowed for the discovery of four isomeric states in 255No. The lifetime measurements and excitation energies will be presented and a tentative interpretation in terms of high-K isomers and underlying single particle content will then be discussed.

[1] M. Asai et al., Nucl. Phys. A 944, 308-332 (2015).
[2] Ch. Theisen et al., Nucl. Phys. A 944, 333-375 (2015).
[3] K. Hauschild et al., Nucl. Instr. Methods A 560, 388-394 (2006).
[4] A. G. Popeko et al., NIM. B 376, 140-143 (2016).
[5] E. D. Donets et al., Sov. Journ. of. Nucl. Physics 723, (1966).
[6] K. Kessaci et al., Phys. Rev. C 104, 044609 (2021).