Speaker
Description
Most of the heaviest nuclei synthesized in recent decades were obtained through the use of fusion-evaporation reactions. This mechanism tends to produce mainly neutron-deficient nuclei due to neutron evaporation and the limited available choices of beam-target combinations. Moreover, production cross-sections for the heaviest elements are particularly small, e.g. 0.5 pb at most for the discovery of 294Og [1]. Consequently, Multi-Nucleon Transfer (MNT) reactions are expected to be a complementary mechanism to fusion-evaporation. Indeed, this mechanism is well suited to produce neutron-rich heavy ions with relatively high cross sections at forward angles of the order of µbarns according to the theory [2].
An experiment was performed at Argonne National Laboratory in 2023 to study MNT reactions using a 136Xe beam on a 238U target with detection of the reaction products at forward angles. The setup consisted of the Gammasphere germanium array [3] to perform a prompt γ-ray spectroscopy and the AGFA gas-filled separator 4 to separate the MNT products from the unreacted beam. A decay station for decay spectroscopy studies was also installed at the focal plane, consisting of a DSSD, a MWPC and silicon detectors in a tunnel configuration surrounded by four Clover germanium detectors.
The successful identification and cross-section extraction of few-nucleon transfer channels were achieved for data collected at a beam energy below the calculated barrier. The findings of this analysis and their interpretation as a signature of the dynamical deformation of the colliding nuclei will be presented in this talk.
References:
[1] Yu. Ts. Oganessian et al. Synthesis of the isotopes of elements 118 and 116 in the 249 Cf and 245 Cm + 48 Ca fusion reactions, Phys. Rev. C 74, 044602 (2006).
[2] V.I. Zagrebaev and W. Greiner. Cross sections for the production of superheavy nuclei. Nuclear Physics A, 944:257–307, (2015). Special Issue on Superheavy Elements.
[3 I-Yang Lee. The GAMMASPHERE. Nuclear Physics A, 520:245-258, (1990).
[4] B. B. Back. The AGFA and AIRIS separators at ATLAS. EPJ Web Conf. 163, 00003 (2017)